Progress in developing cassava varieties with resistance to CMD and CBSD in eastern Africa

Progress in developing cassava
varieties with resistance to CMD and
CBSD in eastern Africa

Edward Kanju

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

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

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: • Major diseases:
– Cassava green mites (CGM) – Cassava mosaic
– Termites disease (CMD)
– Cassava mealybugs (CM) - • EACMV
at some pockets • ACMV
– Variegated grasshoppers – • EACMV-UG
sporadic – Cassava brown
– White cassava scales - streak disease
sporadic (CBSD)
– Cassava bacterial
blight (CBB)


Cassava Mosaic disease (CMD)


Evolution of the CMD Pandemic

2005 2001 1997

> 2,700,000 sq. km

0 400 800 km

Super-abundant whiteflies transmit
viruses and cause up to 50% loss
through physical damage
CBSV damages


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: Equatorial
Guinea Uganda

– Genus: Ipomovirus ROC
Kenya

– Family: Potyviridae DRC

Tanzania
• Vector: Bemisia tabaci
(Maruthi et al., 2005) Malawi
Zambia

• Losses: Mozambique

– Economic loss (SSA): >USD 75 CBSD devastating
CBSD damaging
million/annum from 1.6 million CBSD reported
tons (Manyong et al., 2010)
Source: James Legg
Affected countries: Malawi,
Mozambique, Kenya, Uganda,
Tanzania, Rwanda

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 2003/031
NACHINYAYA 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 DMC (%)
(T/ha)
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

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