STATISTICAL-ANALYSIS OF ELECTROPHORETIC KARYOTYPE VARIATION AMONG VEGETATIVE COMPATIBILITY GROUPS OF FUSARIUM-OXYSPORUM F SP CUBENSE

This study tests whether variation in electrophoretic karyotype (EK) is correlated with presumptive clonal lineages as defined by vegetative compatibility groups (VCGs) in an asexual fungal plant pathogen. Highly reproducible EKs were generated for 118 isolates of the banana wilt pathogen, Fusarium oxysporum f. sp. cubense, representing 15 VCGs in a worldwide collection. Extensive EK differences were observed among the isolates: the chromosome number (CN) ranged from nine to 14 (median = 11; mode = 12), and the genome size (GS) ranged from 32.1 to 58.9 Mbp (mean +/- standard deviation = 43.3 +/- 5.8 Mbp). EK mean variation among 11 analyzed VCGs, however, was highly associated with VCGs, as determined by analysis of variance (P < 0.0001). Comparison of means for both CN and transformed GS data sets identified two groupings of EK types containing identical VCG constituencies: Type I is characterized by high CN and GS values and includes VCGs 0124, 0124-5, 0125, 1210, and 1214, members of which generally had been isolated from banana cultivars with ABB and AAB genotypes. Type II is characterized by low CN and GS values and includes VCGs 0120, 0121, 0122, 0123, 0129, and 1213, which usually had been isolated from cultivars with AAA genotypes. With the exception of VCG 0123, these two EK types correspond to preexisting groupings based on physiology, host specificity, and other molecular markers.