Polymorphism at selected defence gene analogs (DGAs) of Musa accessions in Mauritius
One of the major diseases affecting banana is Sigatoka or leaf spot disease that comprises three species, Mycosphaerella fijiensis, Mycosphaerella musicola and Mycosphaerella eumusae. Plants have a large number of defence related genes which trigger a cascade of defense responses that halt the spread of pathogens. Knowledge of the diversity present in genes related to the defense against Sigatoka disease will be useful in developing disease resistant banana cultivars. The defence genes of all sterile commercial banana cultivars (AAA genomes) are considered to have arisen from a similar gene pool belonging to the Musa acuminata complex. The objectives of this study were, (i) to assess the disease response of twelve banana cultivars to M. eumusae, (ii) to assess the level of polymorphisms in selected genes associated with defence against Sigatoka in banana, and (iii) ascertain if this polymorphism was related to levels of resistance to M. eumusae. Defence genes reported to act in response to M. fijiensis were selected and related to the response of M. eumusae. The genetic diversity of selected defence gene analogs (DGA) was assessed using degenerate primers designed from conserved motifs in the aligned amino acid sequences from known resistance genes. Highly polymorphic amplicon profiles for DGAs were selected for comparison. Cluster analysis was used to differentiate to some extent, cultivars considered as resistant/susceptible to M. eumusae. Specific amplicons from the profiles of phenylalanine ammonia-lyase (PAL), iron superoxide dismutase (FeSOD) and ascorbate peroxidase (APX) were unique to a group of resistant cultivars and could act as markers for resistance to M. eumusae.
Keywords: Banana, defence gene analogs, polymorphism