progress in developing cassava varieties with resistance to cmd and cbsd in eastern africa

International Institute of Tropical Agriculture – Institut international d’agriculture tropicale – www.iita.org

Progress in developing cassava

varieties with resistance to CMD and

CBSD in eastern Africa

Edward Kanju

Contract review seminar, 11th October 2010, Ibadan, Nigeria


Introduction

• Cassava is an important food crop in Tanzania:– Tanzania is the fifth cassava producer in Africa

– Production is estimated at 7 million MT (fresh weight)

– Is the second important staple after maize

• It is produced mainly through subsistence farming

with use of low inputs, rudimentary technology, large

post-harvest losses and minimal processing

• Yields are lower than world’s average of 10.5 MT/ha


Introduction contd.

• Major causes for low yields:

– Pests and diseases

– Poor agronomic practices

– Poor soil fertility

– Use of cultivars with poor genetic potential

– Drought


Introduction contd.

• Major pests:

– Cassava green mites (CGM)

– Termites

– Cassava mealybugs (CM) -

at some pockets

– Variegated grasshoppers –

sporadic

– White cassava scales -

sporadic

• Major diseases:

– Cassava mosaic

disease (CMD)

• EACMV

• ACMV

• EACMV-UG

– Cassava brown

streak disease

(CBSD)

– Cassava bacterial

blight (CBB)


Cassava Mosaic disease (CMD)


0 400 800 km

2005

> 2,700,000 sq. km

2001 1997

Evolution of the CMD Pandemic


CBSV damages

Super-abundant whiteflies transmit

viruses and cause up to 50% loss

through physical damage


EACMV-UG resistant germplasm developed and

released in all affected countries


Severe CMD symptoms at Kibaha, Tanzania where

no ACMV nor EACMV-UG has been detected


Cassava Brown Streak Disease (CBSD)


• Causal agent:

– Genus: Ipomovirus

– Family: Potyviridae

• Vector: Bemisia tabaci

(Maruthi et al., 2005)

• Losses:

– Economic loss (SSA): >USD 75 million/annum from 1.6 million tons (Manyong et al., 2010)

Affected countries: Malawi, Mozambique, Kenya, Uganda, Tanzania, Rwanda

Uganda

Kenya

Tanzania

Mozambique

Zambia

DRC

ROC

Equatorial

Guinea

Malawi

CBSD reportedCBSD damagingCBSD devastating

Source: James Legg


CBSD leaf symptoms


CBSD stem symptoms on young plants


CBSD Stem Symptoms on older plants


The many faces of CBSD root necrosis


Severely affected roots are unmarketable!


• CBSD has

increased the labour

requirement in trial

evaluation


Breeding for resistance: History

– Host plant resistance is the most effective and

realistic approach to reducing losses

– Started at Amani in 1930s (for both CMD and CBSD)

– Very few varieties possessed resistance to CBSD e.g.

Aipin valenca and Aipin Macaxeira

– Interspecific hybrids were developed and

backcrossed to cassava three times:• Manihot melanobasis – Amani 5543/156 (also had M. glaziovii)

• M. glaziovii – Amani 46106/27 was developed; resistant to CBSD;

still grown in Kenya (Kaleso) – resistance has persisted to date.


Resistant/Tolerant Varieties

• Tanzania: Kigoma Mafia, Kiroba, Nanchinyaya, Namikonga,

Kalulu, Kitumbua, Mfaransa, Gezaulole, Muzege, Kikombe,

Kibangameno, Mwari , UKG 91/041, NDL 90/34 and IR 40-6

(from CIAT).

• Kenya: Kaleso, Guzo, Gushe, Kahoteli, Ambari and Kibiriti

Mweusi

• Uganda: MM 96/4271??? Too early to be sure

Some of the present day so-called local cultivars are former

Amani hybrids


Resistance: Definition

• Virus resistance terminology is a contentious issue on which

there is no general agreement (Thresh et al., 1998)

• Any inhibition of virus multiplication or of its pathogenic

effects on the plant (used in the general sense of Fraser,

1986).

• Breeders emphasize the effect on yield and quality in

contrast to pathologists who consider the fate of the virus in

the plant (Lapidot and Friedmann, 2002).

• Most of the CBSD resistant cultivars are better described as

“tolerant” in that they readily show foliar symptoms but root

necrosis is delayed or absent (Hillocks and Jennings, 2003).


Challenges

• Disease assessment:

– Screening for resistance is based on phenotypic

expression of symptom severity in the field relying

upon natural infection

– Grafting is a very severe challenge (unless we are

looking for immunity)


Inheritance of CBSD resistance:

Update

• Both additive and non-additive genetic effects

reported (Munga, 2009; Mtunda, 2010)– Additive effects were more important than non-additive

• The best parents to use for improvement of CBSD

resistance was Kaleso and Namikonga.

– Using >500 SNP markers we have proved that the

two clones are genetically identical.


Progress of a Breeding Program(Lozano, 1980)

– Genetics of the desired trait

– Number of traits that have to be incorporated

• Biotech can help

– Effectiveness of the evaluation techniques

• Revisit?

– Number of progeny evaluated yearly


Promising clones evaluated at ARI Naliendele,

UYT 2010 S/N Accession Pedigree

1. NDL 2003/031NACHINYAYA X KIROBA

2. NDL 2003/111 NAMIKONGA X KALULU

3. NDL 2005/492 NAMIKONGA - HS

4. NDL 2005/201 NDL 90/034 X NAMIKONGA

5. NDL 2005/1472 NACHINYAYA - HS

6. NDL 2005/1471 NACHINYAYA - HS

7. NDL 2006/283 NDL 90/034 - HS

8. NDL 2006/035 84/00353 X 080/0051

9. NDL 2006/241 I 92/0057 X 84/00353

10. NDL 2006/013 I 90/0099 X I 92/0057

11. NDL 2006/349 KIROBA X KIGOMA RED

12. NDL 2006/034 NAMIKONGA X KIROBA

13. NDL 2006/155 I 90/0099 X I 92/0057

14. NDL 2006/018 NACHINYAYA X KIROBA


Promising clones evaluated on-farm, Eastern Zone,

2010

S/N Accession Pedigree

1. KBH 02/66 96/1613 HS (IITA Ibadan)

2. KBH 02/120

3. KBH 02/135 TME 130 HS (IITA Ibadan)

4. KBH 02/363 I 96/1632 (IITA Ibadan)

5. I 92B/00073 ? (IITA Ibadan)

6. KBH 06/26 LML 2000/2174 HS

7. KBH 06/74 LML 91/0119 HS

8. KBH 06/18

9. NDL 06/74 Nachinyaya x Kitumbua

10. ZNZ 05/31 TMS 4(2)1425 HS

11. ZNZ 06/30 Kitumbua HS

12. ZNZ 06/06 Kigoma Red HS

13. ZNZ 06/63 TMS 30001 HS

14.


Performance of 14 clones selected from the AYT at Mukono,

2008/09

Clone Pedigree Fresh Root Yield

(T/ha)

DMC (%)

MM 2006/0013 Kitumbua-OP 11.2 47.7

MM 2006/0090 Kibaha-OP 18.0 47.4

MM 2006/0130 Kitumbua-OP 8.3 46.0

MM 2006/0143 Kibaha-OP 5.7 43.2

MM 2006/0139 Kibaha-OP 20.1 43.1

MM 2006/0082** Kibaha-OP 9.8 43.1

MM 2006/0128** Kigoma Red-OP 6.9 41.5

MM 2006/0123** Kibaha-OP 13.8 37.9

MM 2006/0083 Kibaha-OP 3.8 37.9

MM 2006/0046 Kigoma Red-OP 5.0 37.6

MM 2006/0112 Kibaha-OP 25.2 34.7

MM 2006/0074 Kigoma Red-OP 5.2 34.5

MM 2006/0005 SS4-OP 17.3 29.4

MM 2006/0138 Kibaha-OP 22.5 40.7

TME 204 (Check) 4.8

Trial Mean 10.2

Lsd (0.05%) 10.7


MM 06/0013 was

one of the eight

clones that had

no visible CBSD

symptoms up to

August 2009. It

has succumbed

to CBSD at all

the three

evaluation sites

in Uganda


MM 06/0090: very low incidence (class 3) at Serere (left

photo); high incidence (class 4) at Mukono (right photo).

Mukono had the highest incidence of severe root necrosis; Serere the

lowest


TME 204


GLCI Participatory Variety Selection (PVS) Trials


Participatory Variety Selection (PVS)

• Enables farmers to test and select improved varieties that

best meet their diverse needs within their socio-economic

and agro-ecological context

• Is a key to providing a steady stream of new material which

is essential to address changing farmer requirements and

to create a suitable multiplication system

• Is an effective means of achieving rapid adoption of newly

developed varieties.

– Directly through farmers using material from on-farm trials

– Indirectly because the participatory approach ensures that the

varieties are more suited to farmers’ diverse needs and the on-farm

trials serve as demonstrations (awareness/promotion) of the best

variteies


The three promising clones clones (MM 96/3567,

MM 96/3972 and MM 96/2335) have succumbed

to CBSD in 2010


Way Forward

• Work very closely with virologists to elucidate mechanism of

resistance and genotype x virus x environment

• Inter-se mating of elite clones to generate new source

population to capitalize on the additive gene variation (identify

parents with high GCA values)

• Development of inbred/semi-inbred lines to exploit hybrid

vigour (identify heterotic groups)

• Incorporate new sources of CMD (CIAT and IITA-Ibadan) and

CBSD (from IITA-Ibadan) to broaden genetic base of the local

germplasm

• Deploy CBSD tolerant germplasm (TC and true seeds) to

recently affected and threatened regions

• Interspecific crosses


Acknowledgements

• All the other Scientists and Technical staff

supporting our work

• All the farmers who actively participate in

germplasm evaluation

• All the donors who fund our activities


Thank you for the attention! Asanteni

sana!

progress in developing cassava varieties with resistance to cmd and cbsd in eastern africa

Technology

introduction cassava

cbsd devastatingcbsd

cbsd e

cbsd stem symptoms

cassava producer

severe cmd symptoms

kenya kaleso resistance

cmd pandemic