New approaches to select cultivars of banana with durable resistance to Mycosphaerella leaf spot diseases

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)