|Caribbean Division - An approach for screening Musa accessions for resistance to virulent Mycosphaerella fijiensis isolates|
L. GANAN (1), E. Alvarez (1). (1) CIAT, Palmira, Colombia
Certain <i>Musa</i> cultivars and hybrids are resistant to black leaf streak disease (BLSD), caused by the fungus <i>Mycosphaerella fijiensis</i>. Because this pathogen is highly diverse genetically, it can attack newly introduced <i>Musa</i> accessions, including resistant ones. The virulence of six <i>M. fijiensis</i> isolates was evaluated in a susceptible cultivar, plants of which were inoculated by brushing weighed fragmented mycelium onto specific areas of abaxial leaf surfaces. The same assay and the same six <i>M. fijiensis</i> isolates were also used to determine the resistance of six <i>Musa</i> hybrids and 10 cultivars under greenhouse conditions. Disease severity (DS) was measured, using digital image analysis software. A qualitative scale was used to determine severity of infection, allowing calculation of incubation period and time of symptom development. Results demonstrated differences in virulence among the isolates, with two showing mild virulence (<20%). Symptoms of BLSD were observed in all accessions, but with significant differences in DS. Two hybrids, one cultivar, and the resistant control, inoculated with the most virulent isolates, nevertheless had the lowest mean values for DS. Categorical data and correspondence analyses clustered the <i>Musa </i>accession<i> x</i> <i>M. fijiensis</i> isolate interactions into three main groups, according to resistance levels. This method is quick, inexpensive, and easy for screening partially resistant <i>Musa</i> accessions against isolates differing in virulence.