plant resistance to insects in cotton

Plant Resistance to Insects in CottonAuthor(s): William L. ParrottSource: The Florida Entomologist, Vol. 73, No. 3 (Sep., 1990), pp. 392-396Published by: Florida Entomological SocietyStable URL: http://www.jstor.org/stable/3495457 .

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392 Florida Entomologist 73(3) September, 1990

PLANT RESISTANCE TO INSECTS IN COTTON

WILLIAM L. PARROTT

United States Department of Agriculture Agricultural Research Service

Crops Science Research Laboratory Mississippi State, Mississippi 39762-5367

ABSTRACT

Entomologists and plant breeders have noted that glandless lines of cotton generally are susceptible to phytophagous insects. Gossypol, the yellow pigment present in the glands, has been shown to be the most important allelochemical that provides resistance. In field tests, high gossypol lines have repeatedly been correlated with lessened insect damage, probably due to toxicity of gossypol to Heliothis sp. and other cotton insects.

Recent behavioral-histochemical studies of newly hatched larvae of tobacco budworm, Heliothis virescens (F), feeding on cotton showed that first-stage larvae avoided consuming the glands. However, when these molt between 48 and 72 h of age, they nonselectively consume the glands, suggesting a metabolic adaptation.

Young tobacco budworm larvae prefer to feed along the margin area of the calyx crown of the square, an area devoid of gossypol glands. On resistant lines having glands in the calyx crown, the larvae feed sporadically on the tissue thus avoiding the glands. The numbers of gossypol glands on bracts of small squares, calyx crown, bract mid-rib, and the entire calyx differed significantly between the susceptible and resistant lines. First instar larvae placed on squares of cotton genotypes with high gland density in the small square bract and in the calyx crown, were significantly smaller than larvae placed on line with fewer glands. These and related studies suggest that breeding strategies should concentrate on placing gossypol glands in the calyx crown, the primary site of insect attack.

RESUMEN

Entom6logos y fitomejoradorea han notado que variedades de algod6n sin glAndulas son generalmente susceptibles a insectos fit6fagos. Se ha demostrado que gosypol, el pigmento amarillo presente en las glandulas, es el mas importante aleloquimico que provee resistencia. En pruebas de campo, variedades con alto contenido de gosypol, repetidamente han estado correlacionadas con menor dafio por insectos, probablemente debido a la toxicidad del gosypol a Heliothis es. y a otros insectos del algod6n.

Estudios recientes sobre el comportamiento histoquimico de larvas recien nacidas del gusano de la yema del tabaco, Heliothis virescens (F.), alimentandose del tabaco, demostr6 que larvas en la primera etapa evitaban consumir las glandulas. Sin embargo, cuando estas mudan entre 48 y 72 horas de edad, ellas consumen las glandulas sin seleccionar, lo que sugiere una adaptaci6n metab6lica.

Larvas jovenes de la yema del tabaco prefieren comer a lo largo del area del margen de la corona del caliz del cuadrado, que es un area que no tiene glandulas de gosypol. En variedades resistentes que tienen glandulas en la corona del caliz, las larvas se alimentan esporadicamente del tejido y asi evitan las glandulas. El nuimero de glandulas de gosypol en la bractea de pequenios cuadrados, en la corona del caliz, en la nervadura central de la bractea, y en el caliz entero, fueron significativamente distintos entre las variedades susceptibles y resistentes. Larvas en el primer estadio puestas en cuadrados de genotipos de algod6n con una alta densidad de glandulas en la bractea de pequenos cuadrados y en la corona del caliz, fueron significativamente m'as pequeas que larvas puestas en variedades con menos glandulas. Este y otros estudios similares sugieren que estrategias de fitomejoramiento deben de concentrarse en poner glandulas de gosypol en la corona del caliz, que es el lugar principal que los insectos atacan.



Parrott: Symposium-Plant Resistance to Insects 393

Gossypol, the yellow pigment present in enclosed glands of the genus Gossypium, was first reported to confer resistance to the cotton bollworm Heliothis zea Boddie by Bottger et al. (1964). Since then, cotton breeders and entomologists have searched for methods to select and develop plants with high gossypol content for resistance to this insect and others. Most commercial cotton cultivars have a gossypol content of about 0.5% in squares. Lukefahr & Houghtaling (1969) concluded from laboratory tests that the gossypol level in squares must be increased to approximately 1.2% to inhibit growth and development of the cotton bollworm and the closely related species, the tobacco budworm, H. virescens (F). Growth studies show an increase in growth of tobacco budworm larvae on glandless cotton strains when compared with larval growth on their glanded isoline (Lukefahr et al. 1966). Shaver & Lukefahr (1969) incorporated gossypol into diets and demonstrated a reduction in larval growth rate. Bell & Stipanovic (1977) isolated gossypol and related compounds from glanded cotton plants and found that these compounds are toxic to tobacco budworm larvae. In fact, in some parts of the plant, the related compound may occur in higher concentrations than gossypol itself. In this paper the term "gossypol" is used in a general sense to indicate all the related compounds that affect feeding of the tobacco budworm larvae on cotton plants.

BEHAVIORAL STUDY

Although researchers have tested gossypol for antibiosis (retarted growth and development) to larvae, they have paid little attention to the deterrent effect of gossypol on feeding behavior of young larvae.

Although newly hatched tobacco budworm larvae feed on cotton leaves, they seldom feed on gossypol glands. Waiss et al. (1981) showed that first-stage larvae of the cotton bollworm, generally avoided consuming gossypol glands. Lee (1976) observed that both H. zea and H. virescens selected anthers of high-glandulosity cottons for feeding, but avoid contact with the gossypol-rich ovary. If these Heliothis spp. larvae, at their most susceptible age, avoid gossypol-containing plant parts or tissue, then one could question whether antibiosis is the sole manifestation of the resistance of cotton to Heliothis spp. via gossypol.

We placed laboratory-reared, first-stage larvae on terminal leaves (5 to 6 cm in diameter) of 'Stoneville 213' (ST 213) cotton grown in the greenhouse and allowed to feed for 24, 48, and 72 h. For the 72-h feeding period, newly hatched larvae were allowed to feed on leaves for 48 h and were then transferred to fresh leaves of the same size and allowed to feed for an additional 24 h. This procedure assured that larval feeding damage occurred on the third day (or between 48 and 72 h). At the end of each designated time period, leaves damaged by feeding were removed from the plants and fixed in a Formalin-Acetic Acid-Alcohol solution for 4 h.

A stereomicroscope with 10 X power equipped with a 1-cm2 eye piece micrometer grid divided into 1-mm squares was used to observe feeding damage on the leaves. The number of glands present in 1 mm2 of leaf area was determined for both the feeding and nonfeeding sites on the same leaves. Twenty sites per leaf were chosen randomly. Ten replications were counted for each of the three feeding periods (24, 48 and 72 h).

Due to leaf expansion, gland density per 20 cm2 was greater in smaller (24 h) than in older ones (48 h). There were no differences in the number of gossypol glands on the nonfeeding area of the leaf as compared with the feeding area for the 24- and 48-h time intervals. First-stage larvae frequently bit into the glands, but failed to consume them, however, between 48 and 72 h, a difference between the number of glands was apparent. During this time period, larvae consumed entire portions of the leaf, including the glands. Apparently the older larvae were able to metabolize the contents of the glands. This finding is in agreement with previous work by Shaver & Parrott (1970), who found young larvae to be more sensitive to gossypol than older larvae.




HISTOLOGICAL STUDY

Newly hatched tobacco budworm larvae were placed on the terminal leaves of three cotton types, 'ST-213' (normal gossypol glands), 'Stoneville 7AG' (glandless), and 'BW- 76-31-DH' (high gossypol) and allowed to feed for 24 h.

Histological comparisons of leaves with and without feeding damage were made by selecting 20 leaves from each of the three cotton types and subjecting them to identical histological procedures. Comparisons between fed and unfed leaves were made qualita- tively on the basis of examination of similarly treated materials and similar sampling procedures: no quantification was attempted. The extent to which young larvae damaged or consumed glands was determined from the prepared slides. First stage larvae fed on the perimeter of some glands but generally avoided the glands. These larvae fed readily on the lower epidermal, spongy, and palisade cells, leaving the upper epidermis intact. Larvae avoided the gossypol glands in the mesophyll tissue.

The association of anthocyanin with the gossypol glands was demonstrated by drop- ping weak acid (HC1, ca 5%) on the tissue, producing a bright red halo around the gossypol gland (Hedin et al 1967). The halo tissue turned green with the addition of 10% KOH, whereas gossypol, in the central area of the gland, remained red.

Beck (1965) proposed that resistance mechanisms which have a direct effect on insect feeding be classified as nonpreference. Hedin et al (1980) reported anthocyanins and anthocyanidins to be toxic to larvae of tobacco budworm. These data suggest that the anthocyanin present in the envelope which surrounds the gossypol glands may serve as a feeding deterrent, resulting in nonpreference of the young larvae.

The most critical life stage of the tobacco budworm is immediately after egg hatch when the young larvae search for feeding sites. The influence of gossypol, anthocyanins and other plant allelochemics at this early developmental stage should be greater than that of these compounds during later developmental stages of the insect, since more mature larvae may be better adapted to tolerate previously effective resistance mechanisms.

RELATIONSHIP BETWEEN CALYX GLAND DENSITY AND RESISTANCE

During the early 1970's, an extensive breeding program was begun to develop cotton resistant to the Heliothis spp. complex. This breeding effort was primarily the result of widespread insecticide resistance that was developing in H. zea and H. virescens throughout the cotton belt.

Sappenfield et al. (1974) initially used XG-15, a cotton line developed by Lukefahr & Houghtaling (1969) as a primary gossypol source. In the early stages of their work, they were compelled to rely on expensive analytical chemistry to isolate plants with high gossypol content. Little was known about phenotype expression and gossypol content. Then, Sappenfield et al. (1974) showed a relationship between calyx gland size and density and square gossypol content. This finding provided breeders with the first phenotypic marker to identify cotton plants high in gossypol.

Preliminary observations noted that neonate larvae feed on the margin of the calyx (calyx crown) of cotton cultivars which generally have no gossypol glands in this feeding site. Previous studies by Parrott et al. (1983) showed that first instar tobacco budworm larvae avoid feeding on gossypol glands. The feeding sites and behavior of early instars were observed to determine the effect of gland density and distribution as potential mechanisms of resistance, and to measure the growth of tobacco budworm larvae fed squares from lines with high and low gland densities in the calyx crown.



Parrott: Symposium-Plant Resistance to Insects 395

FIELD & LABORATORY TESTS

In 1984, five lines of cotton were planted on the Plant Science Research Farm, Mississippi State, MS. Four of these lines, BW-76-31, DH-126, 83 MHR-1, and 84-MHR- 3 had resistance to the tobacco budworm. The susceptible '(ST-213)', was used as a control. Squares (8 mm diameter) were harvested throughout the summer, and placed individually into 30-ml plastic cups with 2% agar in the botton (6.4 mm) to prevent square desiccation. A neonate tobacco budworm larva was placed on the square and allowed to feed. Fresh squares were introduced every 2 d. Larvae were weighed at 7 or 12 d. Counts were made on the number of gossypol glands present on bracts of small squares, calyx crown, bract mid-rib, and the total glands present on the calyx.

DH-118, 121, and 126 each were crossed with 'ST-213' and 'Stoneville 825' (ST-825) and lines developed with either high or low densities of glands in the calyx crown from each cross. Lines were selected for gland density in the F2 generation and advanced to F5. In 1986, 12 F5 lines plus the five parents were investigated for resistance to tobacco budworm. Fresh squares were offered to larvae and gland counts made as described above.

Neonate larvae preferred to feed on the calyx crown of the square, the same mor- phological area used by Sappenfield et al. (1974) to select for high gossypol content. While Sappenfield et al. (1974) were selecting for lines with high gossypol gland density on the calyx crown, they were selecting also plants that were resistant to the tobacco budworm.

More glands were present on the bract mid-rib and the entire calyx of DH-126, BW-76-31, and 83-MHR-1 than on 'ST-213', and more were present on the calyx crown of DH-126 and BW-76-31 than 'ST-213' (P ? 0.05). Gland density on the calyx crown was correlated with that on the small square bract (r = 0.58). bract mid-rib (r = 0.65), and total calyx (r = 0.68) gossypol. Each high gossypol line produced larvae smaller than larvae on 'ST-213'.

As with most cultivars, 'ST-213' has few glands on the calyx crown, whereas line DH-126 has glands distributed throughout the calyx. When young larvae feed on buds of 'ST-213', a susceptible line, the margin area of the calyx crown, which is devoid of glands, is perferred; however, on lines with glands in the calyx crown, the young larvae avoid those glands.

In the F5 progeny from DH lines X 'ST-213' and 'ST-825', larvae that fed on high gland density lines were similar in size to those fed on the DH parent, whereas larvae fed on the low-density lines were similar to those fed on the cultivars. Thus, the calyx crown gland density is a measure of resistance, and crosses of high gland density lines with commercial cultivars produced progeny resistant to tobacco budworm larvae.

Gossypol glands are controlled genetically: cotton breeders can manipulate gland size and density through appropriate crosses followed by selecting lines with high gland density in the calyx crown, a preferred feeding site for young larvae.

REFERENCES CITED

BECK, S. D. 1965. Resistance of plants to insects. Annu. Rev. Entomol. 10: 207-232. BELL, A. A., AND R. D. STIPANOVIC. 1977. The chemical composition, biological

activity, and genetics of pigment glands in cotton. Proc. Beltwide Cotton Prod. Res. Conf. 1977: 244-258.

BOTTGER, G. T., E. T. SHEEHAN, AND M. J. LUKEFAHR. 1964. Relation of gossypol content of cotton plants to insect resistance. J. Econ. Entomol. 57: 285-288.

HEDIN, P. A., D. H. COLLUM, W. H. WHITE, W. L. PARROTT, H. C. LANE, AND J. N. JENKINS. 1980. Proc. Int. Conf. Reg. Insect Dev. Behav., Wroclaw Tech. Univ. Press. Wroclaw, Poland, p. 1071.




PLANT RESISTANCE TO INSECTS IN VEGETABLES FOR THE SOUTHERN UNITED STATES

JAMES M. SCHALK

US Vegetable Laboratory 2875 Savannah Highway

Charleston, SC 29414

ABSTRACT

Insecticides are the first line of defence in reducing damage to vegetable crops. The removal of persistent insecticides, the development of insect resistance to insecticides, EPA reregistration requirements and the concern of farm chemicals in ground water, have increased interest in other control strategies including biological control, cultural practices and breeding for insect resistant crops. This presentation is to report on the evaluation, mechanism, chemistry and cultivar/clone development in vegetables with resistance to insects for the southeastern United States.

RESUMEN

Insecticidas son la primera linea de defensa en reducir danio a cultivos de vegetales. La eliminaci6n de insecticidas persistentes, el desarrollo de resistencia a los insecticidas por los insectos, los requisitos de re-registrar los insecticidas por el EPA (la Agencia de Protecci6n del Medio Ambiente), y la preocupaci6n por los productos qufmicos ag- rfcolas en el manto de agua, han aumentado el interes en otras estrategias de control

HEDIN, P. A., J. P. MINYARD, A. C. THOMPSON, R. F. STRUCK, AND J. FRYE. 1967. Constituents of the cottonbud. VII. Identification of the anthocyanin as

chrysanthemin. Phytochemistry 6: 1165. LEE, J. A. 1976. Reaction of Heliothis larvae to high-glandulosity cottons of an im-

proved type. Proc. Beltwide Cotton. Prod. Res. Conf. 1076: 90. LUKEFAHR, M. J., AND J. E. HOUGHTALING. 1969. Resistance of cotton strains with

high gossypol content to Heliothis spp. J. Econ. Entomo. 62: 588-591. LUKEFAHR, M. J., L. W. NOBLE, AND J. E. HOUGHTALING. 1966. Growth and

infestation of bollworms and other insects in glanded and glandless strains of cotton. J. Econ. Entomol. 59: 817-820.

PARROTT, W. L., J. N. JENKINS, AND J. C. MCCARTY, JR. 1983. Feeding behavior of first-stage tobacco budworm (Lepidoptera: Noctuidae) on three cotton cultivars. Ann. Entomol. Soc. Am. 76: 167-170.

SAPPENFIELD, W. P., L. G. STOKES, AND K. HARRENDORF. 1974. Selecting cotton plants with high square gossypol. Proc. Beltwide Cotton Prod. Res. Conf. 1974: 87.

SHAVER, T. N., AND M. J. LUKEFAHR. 1969. Effect of flavonoid pigments and gossypol on growth and development of the bollworm, tobacco budworm, and pink bollowrm. J. Econ. Entomol. 62: 643-646.

SHAVER, T. N. AND W. L. PARROTT. 1970. Relationship of larval age to toxicity of gossypol to bollworms, tobacco budworms and pink bollworm. J. Econ. Entomo. 63: 1802-1804.

WAISS, A. C., Jr. B. G. CHAN, C. A. ELLIGE, AND R. G. BINDER. 1981. Biologically active cotton constituents and their significance in HPR. Proc. Beltwide Cotton Prod. Res. Conf., 1981: 61.



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