Search

Mycosphaerella leaf spot diseases of banana caused by Mycosphaerella musicola (Sigatoka leaf spot, SLS) and M. fijiensis (black leaf streak, BLS) are very destructive. The cultivation of resistant banana clones appears to be the most appropriate means to combat disease because genetic resistance is usually more durable than chemical control. Since pathogen populations maintain a high level of genetic diversity and single gene resistances, such as is suspected in total or hypersensitive resistance situations, are easily overcome, the phenomenon of "partial resistance", which may be multigenic and hence more durable, is used in CIRAD breeding programmes. New hybrids of banana developed by CIRAD are routinely selected for resistance against Mycosphaerella leaf spot diseases. There are four steps in the evaluation process. Firstly, the level of resistance to M. musicola is assessed under field conditions in Guadeloupe. Secondly, the most resistant hybrids are selected for detached-leaf resistance tests to M. musicola and M. fijiensis under controlled conditions. Thirdly, the efficacy of partial resistance of selected hybrids against M. musicola is confirmed in the field in the French West Indies and against M. fijiensis in the field in Mayotte. Finally, the durability of the hybrids' partial resistance is assessed by measuring disease severity in experimental plots for several years. This complete 4-steps process allows, through experimental approaches, to select banana cultivars with durable resistance against Mycosphaerella leaf spot diseases. (Resume d'auteur)

Leaf spot diseases of banana caused by Mycosphaerella musicola or Mycosphaerella fijiensis are the main constraints in commercial plantations in most banana-producing countries. In humid, high-rainfall conditions, plantation production of dessert bananas for export can only be achieved through intensive chemical control. The development of chemical control strategies in Belize, Cameroon and the French West Indies (FWI) over the past 20 years is described. In all of these countries, which are representative of many banana-growing regions, there have been difficulties in terms of the efficacy, cost and environmental impact of chemical control. This is the result of three major factors: (i) the tightening of legislation governing aerial spraying, which is becoming more and more restrictive, especially in the FWI; (ii) the small number of fungicides now approved for leaf spot control; and (iii) the development of resistance to systemic fungicides. In Belize, the intensive use of systemic fungicides over the past 20 years (35-40 applications/year) has led to M. fijiensis developing fungicide resistance. Regular applications (40-45 applications/year) of contact fungicides (mancozeb, chlorothalonil) are now used to control black leaf streak. Although in Cameroon systemic fungicides (12-14 applications/year) were originally used in combination with a forecasting strategy to control black leaf streak, fungicide resistance has developed in commercial plantations, and this has led to regular application of contact fungicides (40-45 applications/year). In Guadeloupe and Martinique, M. musicola has been controlled efficiently through the use of systemic fungicides (5-7 applications/year) in a forecasting strategy for more than 30 years. Recent French legislation limiting aerial spraying and the kind of fungicides that can be used has resulted in the development of fungicide-resistant strains of the pathogen. As a consequence, the number of treatments/year has recently doubled (10-14 applications/year). New alternatives for control are needed. The introduction of fungicides that have less negative environmental effects may be a short-term solution. Organic fungicides or biofungicides applied in mixtures with contact fungicides may allow producers to reduce the amount of active ingredient applied. The possibility of reversing fungicide resistance in order to reintroduce a more sustainable forecasting strategy may be a mid-term solution. The introduction of cultivars bred for resistance is a long-term goal. (Resume d'auteur)

The monoculture of banana can have a serious detrimental impact on the environment as pesticide treatments can lead to surface and groundwater pollution. Different approaches based on IPM (integrated pest management) have been developed in the French West Indies to reduce the use of the pesticides in banana cultivation. These methods have been developed using management techniques that prevent the build-up of banana pathogens and also eliminate them, non-chemical techniques, such as cultural practices and biological control, and resistant cultivars. As a result, new crop management systems have led to a 65% decrease of pesticide use over the last 10 years. Major results of the research already undertaken and future research that is being considered to reduce pesticide use in banana plantations are reviewed. (Resume d'auteur)