Mycosphaerella leaf spot diseases of bananas - CBS

Mycosphaerella leaf spot diseases of bananas: present status and outlook
A great deal of effort has been made over the past decade by several
institutions that started programmes to breed for resistance to BLSD in dessert
and cooking bananas. The priority of the breeding programmes has been to search
for high levels of partial resistance, which is considered to be more durable in
the presence of diverse and evolving populations of a pathogen. In some breeding
programmes, molecular marker–assisted selection was developed to introduce
resistance. Several partially resistant hybrids were produced and tested in multisite
setups such as INIBAP’s International Musa testing programme. Some hybrids
survived the validation stage and were distributed more widely.
Other breeding approaches were developed using biotechnology, and in
particular the production of transgenic plants using genes coding for antifungal
proteins (AFPs) (see session 4: R. Swennen). However, this approach has the
disadvantage of conferring monogenic resistance and is considered unstable in the
presence of diverse populations of Mycosphaerella species. Nevertheless, the strategy
deserves further study. For example, introducing specific resistance genes in
bananas that possess a high level of partial resistance might be an attractive
approach.
Control strategies
In San José, there was much discussion about the potential of new fungicides, rational
ways of using them, the advantages of forecasting systems, and the management
of resistance to fungicides. It was emphasized that effective and rational control
required a greater knowledge of different aspects of the epidemiology of the
pathogens.
It is generally agreed that this theme is probably the one which received the least
attention and hence could still produce important results. The use of fungicides
remains the strategy by which other strategies are compared. In the past, the selection
pressure by different active ingredients has given rise to the disastrous situation where
fungicide-resistant pathotypes are continuously selected. This strategy is no longer
acceptable in a society increasingly concerned about the environment (Romero, 2000).
In future, the aim will be to propose alternatives to chemical control but without
excluding them completely. Integrated control strategies are needed that combine
several different methods of control, methods which individually are only partially
effective. Integrated control strategies would have to be adapted to the different
farming systems of banana production on a large scale and production of plantains
and cooking bananas on smallholdings where rational chemical control is difficult.
1) Chemical control can still be considered, provided that its use is strictly limited.
Forecasting methods should be improved or adapted to different environmental
conditions.
2) Control measures based on cultural practices are known to affect inoculum
pressure in the field e.g. leaf removal, methods of irrigation, management of
planting density. There is potential for the information to be used more
effectively.
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