14

Chapter 2

REVIEW OF LITERATURE

Maize (Zea mays L) is one of the most versatile emerging crops having wider

adaptability under varied agro-climatic conditions. Globally, maize is known as queen

of cereals because it has the highest genetic yield potential among the cereals. It is

cultivated on nearly 150 m ha in about 160 countries having wider diversity of soil,

climate, biodiversity and management practices that contributes 36 % (782 m t) in the

global grain production. The United States of America (USA) is the largest producer

of maize contributes nearly 35 % of the total production in the world and maize is the

driver of the US economy. The USA has the highest productivity (> 9.6 t ha-1) which

is double than the global average (4.92 t ha-1). Whereas, the average productivity in

India is 2.43 t ha-1.

In India, maize is the third most important food crops after rice and wheat.

According to advance estimate it is cultivated in 8.7 m ha (2010-11) mainly during

Kharif season which covers 80% area. Maize in India, contributes nearly 9 % in the

national food basket and more than Rs. 100 billion to the agricultural GDP at current

prices apart from the generating employment to over 100 million man-days at the

farm and downstream agricultural and industrial sectors. In addition to staple food for

human being and quality feed for animals, maize serves as a basic raw material as an

ingredient to thousands of industrial products that includes starch, oil, protein,

alcoholic beverages, food sweeteners, pharmaceutical, cosmetic, film, textile, gum,

package and paper industries etc.

Recent trends (2003-04 to 2008-09) in growth rate of area (2.6 %), production

(6.4 %) and productivity (3.6 %) of maize in India has been of high order and

15

experienced highest growth rate among the food crops. Since 1950-51, the area,

production and productivity of maize have increased by more than 3.4, 12 and 4.5

times from 3.2 m ha, 1.7 m t and 547 kg ha-1 to current level of 8.17 m ha, 19.33 m t

and 2414 kg ha-1, respectively due to increasing maize demand for diversified uses.

In India, the maize is used as human food (23%), poultry feed (51 %), animal feed

(12 %), industrial (starch) products (12%), beverages and seed (1 % each). With the

increasing trends of maize production, the projected demand of maize (22.73 m t) by

the end of XI th five year plan (2011-12) will be achieved through improved maize

production technologies focused on ‘Single Cross Hybrids’.

Maize is one of the oldest human-cultivated crops. The center of origin is

believed to be the Mesoamerica region, at least 7000 years ago when it was grown as

a wild grass called teosinte in the Mexican highlands (FAO, 2006).

Maize spread around the globe after European discovery of the Americas in

the 15th century (OGTR, 2008). Maize has tremendous variability in kernel color,

texture, composition and appearance. Botanically, maize belongs to the grass family

gramineae (Poaceae); it is an annual plant with an extensive fibrous root system. It is

a diploid species, with a chromosome number of 2n = 2x = 20 (Cai, 2006).

The importance of cereal grains in human nutrition is widely recognized, as

they provide substantial amounts of energy and protein to millions people, especially

in developing countries (FAO, 2011).

According to Walcott, (2003) Seed-borne pathogens are a serious threat to

seedling establishment. Amongst many assays used for detection of seed-borne

pathogens visual examination based on characteristic symptoms including

discoloration, shriveled and reduced seed size is the most common, for separating

16

healthy and diseased seeds. Two different most common methods, blotter paper and

agar plate method were used to detect seed borne mycoflora.

Deena and Basuchaudhary, (1984) detected seed-borne mycoflora of chilli

both on agar and blotter method and 25 fungal isolates were recorded. The mycoflora

associated with cocoa beans, ectophytically (Blotter method) and endophytically (agar

plate method).

(Khati and Pandey, 2002). Standard blotter, agar plate method and deep

freezing blotter method were employed to detect the seed-borne Cladosporium

oxysporum on five seed samples of sesame.

Sharfun–Nahar et al., 2005. studied seed-borne mycoflora of 35 samples of

sunflower using standard blotter and deep-freezing techniques.

Tzortzakis and Economakis (2007) investigated the antifungal activity of

lemongrass (Cymbopogon citrates) oil against Colletotrichum coccodes, Botrytis

cinerea, Cladosporium herbarum, Rhizopus stolonifer and Aspergillus niger. The

results showed that fungal spore production was inhibited up to 70 to 100% at 25 to

500 ppm of lemongrass oil concentration. However, lemongrass oil (up to 100 ppm)

accelerated spore germination for A. niger.

Ranasinghe et al., (2002) reported that essential oils of Cinnamomum

zeylanicum and Syzygium aromaticum at concentration of 0.03 to 0.11% (v Ú v)

exhibited strong antifungal activity against F. proliferatum, Lasiodiplodia

theobromae and Colletotrichum musae, the causal agents responsible for crown rot

and anthracnose of banana.

17

Chang et al., ( 2008) investigated the antifungal activity of essential oil and its

constituents from Calocedrus macrolepis var. formosana on the growth of plant

pathogenic fungi. Their experiments showed that sesquiterpenoid components were

more effective than monoterpenoid components of the leaf oil. These results

revealed that T - muurolol and a - cadinol possess antifungal activities against a

broad spectrum of tested plant pathogenic fungi. These two compounds strongly

inhibited the growth of Rhizoctonia solani and Fusarium oxysporum, with the IC50

values < 50 g / ml. These compounds also efficiently inhibited the mycelial growths

of Colletotrichum gloeosporioides, Pestalotiopsis funerea, Ganoderma australe and

F. solani.

The inhibitory effect of essential oil from Satureja hortensis against

Aspergillus parasiticus as an aflatoxins producer was investigated by Razzaghi -

Abyaneh et al., (2008). They found that both carvacrol and thymol compounds were

able to significantly inhibit fungal growth and AFB1 and AFG1 production at

concentrations from 0.041 to 1.32 mM. The IC50 values for growth inhibition were

0.79 and 0.86 mM in methanol for carvacrol and thymol, while for AFB1 and AFG1,

it was 0.50 and 0.06 mM for carvacrol and 0.69 and 0.55 mM for thymol (Razzaghi -

Abyaneh et al., 2008).

In experiment reported by Dikbas et al., ( 2008), antifungal activity of

essential oil from Satureja hortensis were also tested against Aspergillus flavus. The

results of in vitro assay indicated that the oil of S. hortensis at 6.25 l/mL had

fungicidal effect against A. flavus.

The results of in vivo assay on lemon fruits under storage conditions

showed, the concentrations of 6.25 l/mL applied before 8 days of pathogen

18

inoculation had significant antifungal activity even at the end of the 20th days

(Dikbas et al., 2008).

The antifungal activity of Aloe vera (syn: A. barbadensis) leaf pulp (gel) and

its liquid fraction were evaluated for the effect on mycellium growth of Rhizoctonia

solani, Fusarium oxysporum, and C. coccodes (Ro driguez et al., 2005). The results

showed an inhibitory effect of both pulp and liquid fraction of A. vera on

F. oxysporum at 104 g/l. Further the liquid fraction reduced the rate of colony

growth at a concentration of 105 g/ l in R. solani, F. oxysporum, and C. coccodes.

In another investigation performed by Sidhu et al., (2009), individual and

combined methanolic plant extracts were evaluated for their efficacy against growth

and aflatoxin produced by A. flavus. The experiments revealed that combined

extracts of various plant species have synergistic antifungal and antitoxin activity as

compared to their individual extracts. Combined methanolic extract of Azadiracha

indica and Pongamia pinnata oils inhibited 57.32% of fungal growth. However, the

combination of Cymbopogon nardus (Citronella) essential oil and methanolic extract

of Citrullus colocynthis roots inhibited 85.67% of fungal growth and more than 90%

of aflatoxin produced as compared to that of control.

Extracts from 345 fresh plants were evaluated for their antifungal activity

against B. cinerea (Wilson et al., 1997). Of the plants tested, 10% dilution of

Allium and Capsicum species showed the greatest antifungal activity and

completely inhibited spore germination of B. cinerea after 24 and 48 h.

Methanolic extracts of Pimpinella anisum and Illicium verum were studied

for their potential antifungal activities against some filamentous fungi (Yazdani et al.,

2009). The results indicated that methanolic extract of P. anisum seeds did not have

19

any inhibitory effect on A. flavus mycellial growth, while extracts of I. verum fruits

at 16 mg/ml concentration was found to be the most active extract against growth of

A. flavus.

Wang et al., (2005a) reported a chitinase with antifungal activity isolated

from Phaseolus mungo seeds. This protein exerted antifungal action towards

Fusarium solani, Fusarium oxysporum, Mycosphaerella arachidicola, Pythium

aphanidermatum and Sclerotium rolfsii.

Methanol and aqueous extract of Ocimum gratissimum and Aframomum

melegueta on spore germination and mycelial growth of A. niger and Fusarium

oxsporium was studied by Okigbo and Ogbonnaya (2006). The results showed that

ethanol extraction was more effective than water extraction. The antifungal activity

of O. gratissimum leaf extracts was more effective than A. melegueta against spore

germination and mycellial growth of A. niger and F. oxysporum.

Mutungi et al., 2008 investigated the fate of aflatoxins during processing of

maize into muthokoi – A traditional Kenyan food. The effect of processing muthokoi,

(a traditional dehulled maize dish in Kenya) on aflatoxin content of naturally

contaminated maize was investigated. Dehulling decreased aflatoxin levels by 46.6%

(5.5–70%) in maize samples containing 10.7–270 ng/g aflatoxin levels. Soaking

muthokoi in 0.2%, 0.5% and 1.0% solutions iati, sodium hypochlorite or ammonium

persulphate for 6 or 14 h further decreased aflatoxin contents by 28–72% in maize

samples containing 107–363 ng/g a.atoxin levels, and boiling muthokoi at 98o C

for 150 min in 0.2–1.0% w/v iati decreased aflatoxin contents by 80–93%

in samples having 101 ng/g aflatoxin contamination. Findings imply that

exposure to acute aflatoxin levels in maize was minimized during processing

20

and preparation of muthokoi.

Giray et al., 2007 studied aflatoxins level in wheat samples consumed in some

regions of Turkey. Aflatoxins (AFs), the secondary metabolites produced by species

of Aspergilli, specifically Aspergillus flavus and Aspergillus parasiticus, have

harmful effects on humans, animals, and crops that result in illnesses and economic

losses. Wheat that is susceptible to these fungi infections through its growth, harvest,

transport, and storage, is the most important staple food in Turkey. Therefore, this

study has been undertaken to determine the AFB 1, AFB 2, AFG 1, AFG 2 levels by

HPLC in forty-one wheat samples grown and consumed in some regions of Turkey.

The concentrations of total AFs in the wheat samples were determined to be ranging

from 10.4 to 643.5 ng/kg. Fifty nine percent of the samples were found to be positive

for total AFs. The percentage of positive samples for AFB 1, AFB 2, AFG 1, and

AFG 2 were 42, 12, 37, and 12%, respectively. Although the detected levels are

under the permitted levels for AFs in cereals, these amounts should be considered in

regard to overall daily exposure to mycotoxins.

Maqbool et al., 2004 described the sensitivity of ELISA method for the

estimation of aflatoxins. A microtitration plate method was optimized using anti-

aflatoxin B1 antibody and peroxidase – aflatoxin B1 conjugate, based on competitive

enzyme immunosorbent assay principle. Standards of concentrations of 5, 10, 20, 50,

100, 500 ng/L aflatoxin B1, prepared in phosphate-buffered saline, were used.

Standard curves showed that as the concentration of antigen decreased, absorbance

values increased. Fifty percent inhibition was observed at 37 ng/L. Regression

analysis showed that log concentration was inversely related to %B/B0, with a highly

significant negative correlation (-0.980). The lowest detection limit for aflatoxin B1

21

was 5 ng/L. Using this standardized ELISA, aflatoxin B1 was detected in most of the

commercially available poultry samples and their components. The data suggested

that the test is suitable for the accurate determination of aflatoxin B1 concentrations

in poultry feed and its components.

Fu et al., 2008 determined aflatoxins in corn and peanuts collected from

China. A rapid and simple method using ultra-high-pressure liquid chromatography

with UV detection for the determination of aflatoxins B1, B2, G1 and G2 in corn and

peanuts has been developed. In this method, aflatoxins were extracted with a mixture

of acetonitrile and water (86:14) and then purified by solid-phase clean- up with a

MycoSep # 226 AflaZon + column. The toxins were determined by UHPLC–UV

without derivatizing aflatoxins in real samples, which had not been used in other

studies. The mean recoveries of aflatoxins from non-infected peanut and corn

samples spiked with aflatoxins B 1, B 2, G1 and G2 at concentrations from 0.22 to 5

g/kg were between 83.4% and 94.7%. The detection limits (S/N = 3) for B 1, B 2,

G1 and G2 were 0.32, 0.19, 0.32 and 0.19 g/kg, and the corresponding

quantification limits (S/N = 10) were 1.07, 0.63, 1.07 and 0.63 g/kg, respectively.

We also applied this method on real samples. Among 16 peanut samples, 2 (12.5%

incidence) were contaminated with aflatoxin; among 18 corn samples, 4 (22%

incidence) were contaminated. The proposed method is rapid, simple and accurate for

monitoring aflatoxins in corn and peanuts.

Zinedine et al., 2006 studied on Natural occurrence of mycotoxins in cereals

and spices commercialized in Morocco. Sixty samples of cereals (20 of corn, 20 of

barley, and 20 of wheat) and 55 samples of sp ices (14 of paprika, 12 of ginger, 14 of

cumin, and 15 of pepper) purchased from popular markets of Rabat and Sale ! in

22

Morocco were analyzed for mycotoxins. Cereals samples were all analyzed for

ochratoxin A (OTA). The average levels of contamination were 1.08, 0.42, and 0.17

g/kg for corn, wheat, and barley, respectively. Samples of corn were also analyzed

for zearalenone (ZEA) and fumonisin B1 (FB 1 ) the average contaminations were 14

and 1930 g/kg, respectively. Co-occurrence of OTA, FB1, and ZEA was also

checked. Spices samples were analyzed only for aflatoxins (AFs) and the average

contaminations found for aflatoxin B1 (AFB1 ) were 0.09, 0.63, 2.88 and 0.03 g/kg

for black pepper, ginger, red paprika and cumin, respectively. The higher level of

contamination was found in red paprika (9.68 g/kg). The presented result was first

time ever drafted on the natural co- occurrence of OTA, FB1 and ZEA in cereals and

on the occurrence of AFs in spices in Morocco history.

Liu et al., 2006 started work on the determination of aflatoxins in stored

maize and rice grains grown at Liaoning Province of China. Aflatoxin contamination

and its relationship to storage length in stored maize and rice in Liaoning Province,

northeastern China, was investigated. Aflatoxins in 110 samples collected from an

area of 14.68 million km 2 covering storage length from 1 year to over 10 years were

determined by high-performance liquid chromatography with fluorescence detection.

The results showed that almost all samples collected contained aflatoxins. The

average contents in maize, whole grain rice and brown rice were found to be 0.99,

3.87 and 0.88 mgkg -1, respectively. Three-fourths of the total aflatoxins in whole

grain rice (3.87 mgkg -1 ) could be removed by dehusking to as low as 0.88 mgkg -1

in brown rice. No significant aflatoxin increase was observed in whole grain rice and

brown rice over a 10 years storage period. In maize, the amount of aflatoxins was

significantly higher in 2 years than 1year sample. Aflatoxin G 1 was detected as the

major type of aflatoxin in over 40% of all stored grain samples tested and over 92%

23

of rice samples examined. The aflatoxin content in maize and rice is much lower than

the regulated maximum amount allowed in foodstuffs in China and other countries.

We concluded that these grains are safe for human and livestock consumption and for

trading.

Mendez-Albores et al., 2004 used a technique for the detoxification of

contaminated maize flour for the preparation Mexican dish Pozol and then

determined aflatoxins in it using AOAC method. The samples were analyzed for the

presence of aflatoxins. Nineteen out of one hundred and eleven samples were

contaminated with aflatoxin B2 (AFB2 ) and traces of aflatoxin B1 (AFB1 ). The

percentage of samples contaminated with AFB2 in pozol prepared with white maize

was 5.4%. Pozol mixed with toasted cacao paste had a contamination rate of 41.5%.

No aflatoxins were detected in pozol prepared with yellow maize. It was found that

only 1 of 19 contaminated samples had aflatoxin concentrations above 20 ppb.

Abbas et al., 2006 evaluated corn hybrid for aflatoxins. A severe infestation

by aflatoxin-producing fungi diminished food quality of southern United States corn

(maize) in 1998. Corn hybrids (65) naturally infected with Fusarium spp. and

Aspergillus spp. were evaluated from 1998 to 2001 for resistance to mycotoxin

contamination. Kernel corn samples were assayed at harvest for aflatoxins and

fumonisins.

Khan et al., (2002) conducted an experiment to find the suitable packaging

material, easy to handle and which increases the shelf life of wheat flour without

destroying its nutritional value. The wheat flour stored in conventional packaging

materials, i.e. jute, cloth, and woven polyethylene bags, in contact with air

deteriorated more quickly than the wheat flour stored in airtight polyethylene- acetate

24

bags containing free oxygen absorber (FOA). The color, taste, texture, flavor, acidity,

organoleptic evaluation, insect and bacterial count remained acceptable for 2 months

due to anaerobic fermentation of starch in wheat flour in polyethylene-acetate coated

impermeable bags containing FOA, and insect infestation was zero. These changes

were due to anaerobic fermentation of starch in wheat flour.

Carneiro et al., (2005) studied the effect of initial moisture content, drying

parameters and storage duration on grain quality of common wheat and hard wheat.

Wheat grains with different moisture content ranging from 11.7 to13 35 percent were

harvested and stored in polyethylene packets for a storage duration of 0, 2, 4, 6 and 8

months at 20 ± 2ºC. The result showed that harvest expectation and drying process

had no effect on grain quality, whereas storage duration improved the technology of

wheat flour.

Pinto et al., (2002) studied the effect of the population density of Sitophilus

zeamaize in wheat grain on the baking quality of flour. The infested wheat grain

stored for over 60 days had low quality as indicated by the results of protein content,

moisture, sedimentation index and test of flour on extensograph which prevented the

use of this wheat flour for baking.

Milosevic et al., (2005), studied the effect of stored pests on the quality of

commercial wheat and flour. Pests reduced the quality of wheat by reducing water

content and hectoliter mass. The lower quality of flour obtained by milling of

infected wheat was shown in terms of the theological properties as dough stability,

water absorption, and time to break down.

Iconomou et al., (2006) observed a drop in germination of corn seeds with 16

percent and wheat grains with 8 percent moisture content during storage, which varied

25

from 77 to 35 percent in corn and 85 to 42 percent in wheat under ambient conditions

up to 365 and 180 days respectively.

According to Samuel et al., 2011, even after drying, maize grain harvested in

tropical countries retained a certain amount of moisture, and when exposed to air,

exchanges of moisture between the maize grains and surrounding occur until the

equilibrium is reached.

A two-month trial conducted by Reed et al., (2007), at three different levels of

moisture content (low 15.0 %, medium 16.6 % and high 18.0 %) showed gradual

increases in moisture content of 15.1 ± 0.01 %, 16.6 ± 0.04 %, and 18.2 ± 0.03 %, for

low, medium, and high moisture content maize, respectively. Results also showed

great reduction of the mean oxygen concentration and increases in carbon dioxide

level; as expected maize with high moisture contents had a higher rate of oxygen

consumption.

Ahmadi and Mollazade (2009) determined the physical and mechanical

properties of funnel seed as a function of moisture content. They found that there was

a parabolic mathematical equation for sphericity, true density, and deformation on

both seed length and width sections with changes of moisture content.

Juglal et al. (2002) studied the effectiveness of nine essential oils in

controlling the growth of mycotoxin-producing moulds and noted that clove,

cinnamon and oregano were able to prevent the growth of A. parasiticus while clove

(ground and essential oil) markedly reduced the aflatoxin synthesis in infected grains.

Information on physical and aerodynamic properties of agricultural products is

needed in design and adjustment of machines used during harvesting, separating,

26

cleaning, handling and storing of agricultural materials and convert them into food,

feed and fodder. The properties which are useful during design must be known and

these properties must be determined at laboratory conditions. The geometric

properties such as size and shape are one of most important physical properties

considered during the separation and cleaning of agricultural grains. In theoretical

calculations, agricultural seeds are assumed to be spheres or ellipse because of their

irregular shapes (Mohsenin, 1980; Nalbandi et al., 2010).

Maize is an important crop that is used worldwide as human food, as a raw

material for starch and ethanol production, and as animal feed. Because of its

relatively high moisture and starch contents maize is very susceptible to molding. To

prevent molding and rotting in tropical and subtropical regions, grains should be dried

immediately after harvest, and cooled or treated with antifungal chemicals such as

propionic acid. However, humid conditions and economic constraints prevent rapid

drying to safe moisture levels (14% and below). On the other hand, it is easier to

process the maize grains at higher moisture contents (m.c.). Therefore, a technology

that enables safe maize storage at intermediate m.c. (around 18%) is desirable. For

animal feeding purposes, it is possible to ensile high-moisture maize at 25–28% m.c.

with and without microbial and chemical additives.

During the ensiling fermentation of high-moisture maize, lactic acid bacteria

produce organic acids—mainly lactic and acetic acids— which decrease the pH to

4.0–4.5. However, if not treated against molds with suitable antifungal agents, such

silages spoil quickly upon aerobic exposure (Wardinski et al., 1993; Dawson et al.,

1998; Taylor and Kung, 2002). Under tropical conditions grains can be sun-dried to

intermediate moisture levels of about 18% relatively easily. A feasible technology to

27

store such intermediate moisture grains, including maize, is known as self-regulated

modified atmosphere (Richard-Molard et al., 1980, 1987).

In this technology, storage of various grains at intermediate moisture levels

(15–18%) in sealed containers results in depletion of oxygen and enrichment in CO2,

as a result of respiration of the grains, insects and microorganisms (Navarro and

Donahaye, 2005; Navarro et al., 1990, 1993, 1999). In addition, the limited

microbiological activity may result in production of volatile fatty acids (VFAs). Both

the anaerobic conditions and the VFA inhibit fungal development (Moon, 1983;

Weinberg et al., 1993). This technology is environmentally friendly and does not

involve the use of antifungal chemicals. The ecosystem that forms in the sealed

containers with the self regulated atmosphere, and the inter-relationship between grain

respiration and microbial activity has not yet been fully explored.

According to Williams and McDonald (1983), when storage molds invade

maize grain they cause rot, kernel discoloration, loss of viability, vivipary, mycotoxin

contamination, and subsequent seedling blights.

It was revealed by Sone (2001), that broken maize and foreign materials

promote development of storage molds, because fungi more easily penetrate broken

kernels than intact kernels. Similarly, Dharmaputra et al., (1994) reported that

mechanical damage during or after harvesting on maize grains can provide entry

points to fungal spores. Likewise, Fandohan et al., (2006) reported that increases in

grain damage and cracking create an opportunity for fungi to grow and penetrate the

maize grain.

Moisture content and temperature are the two key environmental factors that

influence growth of molds and fungi (Alborch et al., 2011). Maize grain is generally

28

harvested with moisture content of around 18 % to 20 % and then dried. If

inadequately dried the conditions are favorable for molds and fungi to grow, which

can result in a significant decreases in grain quality and quantity.

(Marín et al., 1998). Barney et al., (1995) and Rees (2004), report that fungal

growth in stored grain in the tropical countries is mainly associated with increases in

grain moisture contents, and fluctuation in temperatures, resulting in unsafe storage of

high-moisture grain and moisture migration and condensation.

Study conducted by Reed et al., (2007) on the effect of moisture contents and

temperature on storage molds, found that the higher the initial moisture contents the

greater the infection of maize kernels. According to Miller (1995), the growth and

development of storage fungi in grain are governed by three main factors, crop

(nutrients), physical (temperature, moisture) and biotic (insects, interference

competition) factors.

According to Miller (1995), aflatoxin is predominantly a problem in cereal

grains, particularly in maize; it is produced by three main species of fungi, Aspergillus

flavus, A. parasiticus, and A. nomius. These fungi tolerate and resist a wide range of

conditions, and can be found everywhere such as in soil, in plant and animal remains,

milk, and in grains and seeds such as peanuts and maize (Pitt, 2000). They generate

four significant aflatoxins: B1, B2, G1, and G2.

Guclu (2012) also found a strong relationship between aflatoxin exposure and

liver cirrhosis. Because of the carcinogenic properties of aflatoxins, many countries

around the world have set regulatory limits on allowable aflatoxin levels in foods and

feeds.

29

Research conducted Liu et al., (2006) in China showed a significant increase

in aflatoxins with storage length (i.e. 0.84 g/kg in twelve months to 1.17 g/kg in

twenty four months). Aflatoxin contamination and A. flavus infection are often

associated with high temperature and drought conditions.

Alborch, et al., (2011) revealed that temperature and water activity (aw)

influence not only rate of fungal spoilage, but also the production of mycotoxins.

Research conducted by Kimanya et al., (2010) in rural Tanzania, showed that

the exposure of fumonisins to infants negatively affected growth. There are six

common types of fumonisins; A1, A2, B1, B2, B3, and B4.

According to Fandohan et al., (2003), fumonisin B1, B2, and B3 are most

important ones found in naturally-contaminated maize and in maize fungal cultures,

and produce the highest amounts of toxins (up to 17900 g/g)).

A study conducted by Fareid (2011), revealed that temperature and water

contents are key factors for the growth and mycotoxinogenesis of Fusarium species,

the results shows linear relationships between temperature and levels of fumonisin B1

production; maximum production was observed at 25 °C.

Jian and Jayas (2012) report that some storage fungi attract insects and

promote their growth, but other prevent through secretion of toxic metabolites. In

connection to this, Burns (2003) found direct association between insect feeding

activity, fungal growth and mycotoxin production. Likewise, Setamou et al., (1997),

detected low levels of mycotoxin for less damaged maize (2 %) than in higher

damaged maize.

Hayma, (2003) found that favorable conditions for most grain storage insects

30

to develop is between 25 °C to 30 °C, and relative humidity between 70 % and 80 %.

Conversely, research conducted by Yakubu et al., (2011), shows that insects

infestation problems can be controlled under hermetic storage at moisture and

temperature of 6 % and 16 % and 10 °C and 27 °C, respectively.

Global climatic variability has put into foray several important stresses

impeding the production and productivity scenario. Heat stresses due to rising

temperature and drought due to change in rainfall pattern are the prominent ones.

Agriculture systems are extremely vulnerable to climate change, and especially those

relying on rain-fed agriculture, such as major maize production system in tropical

Asia. A recent study estimates the annual costs of adapting to climate change in the

agricultural sector to be over US$ 7 billion (Nelson et al., 2009).

According to a report from the Asian Development Bank, South Asia will be

particularly hard hit by climate change (Asian Development Bank, 2009). The study

warns that if current trends persist, the yields of key crops and food production

capacity will decrease significantly due to the adverse effects of drought and

increased temperatures, maize (-17%), wheat (-12%) and rice (-10%). Abiotic stresses

are already common on a significant percentage of existing farm lands so efforts to

develop agronomic crops with enhanced stress tolerance are of vital concern (Boyer,

1982). These efforts are particularly important in regions of the world, like South

Asia, where current production systems are not sustainable and could be adversely

impacted by climate change in the near future (Niyogi et al., 2010; Rodell et al.,

2009).

A broader summary reported in the popular press highlights that while

droughts may be an important impediment for production, the real issue for climatic

31

vulnerability would be higher temperatures (Stebbins, 2011). It has been predicted

that growing season temperatures in the tropics and subtropics will exceed even the

most extreme seasonal temperatures so far (Battisti and Naylor, 2009). Not only

tropics, this global warming is also going to affect the temperate regions, where the

hottest seasons on record will become the normal temperature in many locations. Heat

waves have already struck Western Europe, France and Italy so far leading to major

crop losses (Ciais et al., 2005). These incidences illustrates the profound damage that

can be caused (in near future) by high seasonal heat on agricultural production.

Several climate modeling studies have suggested future increases in both

dayand night-time temperatures, which could adversely impact maize production in

the tropical regions (Lobell et al., 2011a; Cairns et al., 2012). Lobell et al. (2008)

suggested that wheat and rice in Southeast Asia and maize in Southern Africa will

likely suffer negative impacts by climate change without sufficient adaptation

measures.

Maize being one of the most important cereal crop and staple food to many

people both in temperate and tropical environment is likely to be greatly hit by the

increasing temperatures. A record drop in maize production due to heat waves have

already been reported globally (Ciais et al., 2005; Van der Velde et al., 2010). The US

Environmental Protection Agency (EPA, 1998) predicted decrease in maize yields

under conditions of future climatic change of 4-42 % due to temperatures rising above

the range of tolerance for the maize crops. Heat waves have already been reported in

several maize growing regions of South-Asia in 2010 (Burke, 2010), however their

effect on maize production needs to be assessed. The uncertainty in the temperature

during the growing season of maize indicates that there is a need to either increase

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tolerance to maximum summer temperatures in existing maize varieties or a change in

maize varieties grow.

Heat tolerant accessions from Asia and other regions are being intercrossed to

produce populations that can be used to develop new cultivars with improved heat

tolerance (Zaidi and Cairns, 2011). However, to increase tolerance of maize to high

temperature stress a better understanding of heat stress effect on maize phenology is

necessary. The greatest challenge in understanding the problems associated with heat

stress is to encompass the diversity of hot environments all over the world.

Maize stress responses are very complex. Interactions between plant structure,

function and the environment needs to be investigated at various phases of plant

development at the organismal, cellular as well as molecular levels (Barnabas et al.,

2008).

High temperatures have been reported to cause severe impediment to panicle

emergence, anthesis, pollen viability and germination capacity and overall

photosynthetic efficiency of crop plants, which are often manifested in their final

grain yield potential (Muchow, 1990; Prasad et al., 2006; Zinn et al., 2010).

Zea mays (L.), commonly referred to as maize, belongs to the Poaceae family

(Inglett, 1970; Farnham et al., 2003). It is thought to have originated in Mexico

(Farnham et al., 2003) but other evidence suggests that it may have originated from

Africa or Asia (Inglett, 1970). The plant is referred to as Indian corn in the United

States of America (Inglett, 1970; Farnham et al., 2003). It is cultivated in a wide

range of climatic conditions ranging from warm temperate areas in the humid sub-

tropical regions as well as in the tropics (Berger, 1962).

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Messing and Dooner (2006) revealed that until the past decade, maize was the

most studied plant species having considerable economic value and served as the

main staple food for millions of people in Africa and the Americas. Of the major grain

crops, maize has the largest total annual grain production in the world (590.5 million

metric tons (mmt) followed by wheat (Triticum aestivum L.) (567.7 mmt) and rice

(Oryza sativa L.) (380.3 mmt) and its average yield per hectare (4.3t) represents more

than that of either wheat or rice.

According to Agrios (2005), the use of chemicals is considered as one of the

best options for managing these diseases in the field, in the greenhouse and in storage.

However, there is a need for continuous search for new chemicals, which can provide

good control of the pathogens and lead to the improvement of yield and quality.

Bujold et al. (2001) reported in their studies on wheat and maize residues

(straw/stalk and grain) that the inoculation of the residues with a Microsphaeropsis

sp. isolate (P 130 A) reduced G. zeae ascopores by 73%.

Horii et al. (2007) revealed that maize, pea (Pisum sativum L.) and soybean

(Glycine max (L.) Merr.) treated with the combination of thiamethoxam and fish

protein hydrolysates slightly improved vigour of seedlings during germination.

According to Wu et al. (2006), the use of thiamethoxam as a seed treatment on

Brassica oleracea var. botrytis did not significantly affect seed germination.

Mullin et al. (2005) reported that maize seeds treated with neonicotinoid

insecticides (thiamethoxam, imidacloprid or clothianidin) resulted in direct mortality

of Carabidae species.

According to Bern et al. (2003), the loss or gain in moisture of maize seed is

34

related to the quantity of water vapour pressure that surrounds the seeds.

Taylor (2003) concluded that in the seed, water is subject to passive

movement since it moves from high to low concentrations. However, even if seeds are

dried to appropriately low moisture content for storage following harvest they can be

subject to mechanical damage such as physical damage of the seed coat and internal

tissues, especially during handling and conditioning, which can hamper seed quality.

According to Gooding et al., (2000), certain requirements must be met when

conducting the germination test. These include: a representative sample of the seed

must be provided; during the test, dormancy must be avoided at all costs; the testing

environmental conditions must be optimal in order to enable germination; and during

the evaluation, the abnormal seedlings should be excluded since they are unable to

produce plants which would survive in the field.

It has been established that favourable conditions, which are encountered in

the laboratory when estimating the germination test, are rare in the field. This results

in the overestimation of the planting value of a given seed lot by the germination

results (Copeland & McDonald, 2001). Halmer (2000) attributed this fact to a

phenomenon known as vigour, which reveals that high germination seed lot can

perform poorly in the field. Because good conditions are scarce in the field, attention

is given to vigour tests, which are important parameters to be measured in the

evaluation of seed quality (Byrum & Copeland, 1995). Therefore, seed vigour tests

have been developed for providing the ability of a seed lot to perform under field

conditions (Sako et al., 2001).

According to Gambin et al. (2006) kernel mass is not controlled by the plant

growth rate per kernel during the effective grain filling period but a linear relationship

35

between final kernel mass and plant growth rate per kernel at the pre- and post-

anthesis stages was reported.

Natural products are a source of new chemical diversity and are the choice of

today’s world. The sources of natural product are plants, animals and microorganisms.

Among them plant and its products are more reliable for its renewability and

therefore, considered as catalyst for human welfare. Still, they are the primarily

required materials for health care system in some parts of the world. Therefore, in the

past few decades, there is a growing research interest in plants as a therapeutic agent.

The therapeutic potential of plant products can be traced back to over five

thousand years ago as there is evidence of its use in the treatment of diseases and for

revitalizing body systems in Indian, Egyptian, Chinese, Greek and Roman

civilizations (Mahesh and Satish, 2008). Also India is one of the mega diversity hot

spots with rich heritage of traditional knowledge of folk medicines. Therefore in

India, plants of therapeutic potential are widely used by all sections of people both as

folk medicines in different indigenous systems of medicine like Siddha, Ayurveda and

Unani and also as processed product of pharmaceutical industry (Srinivasan et al.,

2007).

India has about 4.5 million plant species and among them estimated only

250,000 - 500,000 plant species, have been investigated phytochemically for

biological or pharmacological activity. Still a large number of higher plants as a

source for new therapeutics are to be explored. The potential for developing

phytomedicine into various health care products appears rewarding, both from the

perspective of economy and safety.

Friedman et al. (2007) and Serafinao et al., (2008) noted that many plant

36

extracts are quite effective than the synthetic ones with no or insignificant side effects

and very little scientific research on their biological activity has been worked out.

Furthermore, the growth of multidrug resistant microbial strains which are limiting

the effectiveness of synthetic drugs led to an awareness among the common people

against the use of synthetic product (Sundsford 2004; Edith et al., 2005; Hancock

2005; Isturiz 2008). This factor forced the scientists to develop methods of

bioprocesses for the production and extraction of compounds from natural renewable

sources for their potential application in food, cosmetics and pharmaceuticals industry

with antimicrobial, antioxidant, anti-inflammatory and antidiabetic activity (Velioglu

et al. 1998; Oreopoulou and Tzia 2007).

Nayak and Pereira (2006) proposed that the therapeutic properties of plant

extracts have far more to offer in future as a novel discovery Thus, use of

phytochemicals as major bioactive compounds with multidimensional benefits are

gaining momentum.

Aflatoxins (AFs) are toxicsecondary metabolites produced by species of

Aspergilli, especially Aspergillus flavus and Aspergillus parasiticus. These fungi

can grow on certain foods and feeds under favourable conditions of temperature and

humidity and produce AFs before and/or during harvest, handling, shipment and

storage.

In humans the presence of mycotoxins in foods can be cumulative, leading to

cancers and immune- deficiency diseases. Immediate, acute symptoms may also

occur. Either way, the effects are not entirely understood. In animals, mycotoxins can

reduce production efficiency, increase the death rate, and reduce feed conversion

efficiency. When present in feed, some mycotoxins can pass into eggs or milk and

37

subsequently prejudice human health. Aflatoxin contamination of maize is almost

exclusively from infestation by A. flavus, which produces aflatoxin B1 and B2.

Aflatoxigenic strains of A. flavus are capable of growing on maize in the field and in

storage. Infection of host plants in the field is unavoidable since fact ors that promote

fungal infection and aflatoxin production such as inoculum availability, weather

conditions and pest infestation during crop growth, maturation, harvesting and

storage are difficult to control (Lopez-Garcia and Park, 1998).

Contamination of maize and other food commodities with aflatoxins is a

public health concern because of the ability of aflatoxins to cause human and animal

diseases. Aflatoxins have been implicated with acute and chronic aflatoxicosis,

genotoxicity, hepatocellular carcinoma, suppression of the immune system,

aggravation of kwashiorkor and impaired childhood growth (Hall and Wild, 1994).

Corn (Zea mays L.) is a major crop in the southern United States, where it

plays an important role in the economy in rotation with cotton or soybeans, and in

animal feed, alcohol fermentation and direct human consumption. However, corn

kernels are subject to infection by a variety of toxigenic fungi (Cardwell et al.,

2000).

Aflatoxin has long been monitored by the United States Food and Drug

Administration, and a level of 20 ppb has been set as the limit for corn contamination

with aflatoxin (United States Food and Drug Administration, 2000).

Fungal growth and toxin production in corn have been found to depend on

several interacting factors that stress corn plants (Payne, 1992). Stress factors include

low moisture content of the soil, high daytime maximum temperatures, high

nighttime minimum temperatures, and nutrient-deficient soils (Lillehoj et al., 1980;

38

Abbas et al., 2002).

Mycotoxins are toxic compounds that are produced by many species of the

Aspergillus, Fusarium, Penicillium, Claviceps, and Alternaria genera of fungi

(Huwig et al., 2001).

The toxins are secondary metabolites produced by the fungi after infesting

grain and other food crops. Crops may be contaminated by mycotoxins in two ways:

as parasites on living plants and during storage of harvested crops (Huwig et al.,

2001).

Six groups of mycotoxins are produced by the Aspergillus, Penicillium, and

Fusarium genera of fungi (Yiannikouris and Jouany, 2002).

Mycotoxins have a diversity of chemical structures which accounts for

different biological effects. Mycotoxins can be carcinogenic, mutagenic, teratogenic,

oestrogenic, neurotoxic, or immunotoxic. Aflatoxins B1 and M1 have been

demonstrated to be carcinogenic to animals and humans (Yiannikouris and Jouany,

2002). Food contaminated with very small quantities of aflatoxins can render it unfit

for animal or human consumption.