Background
Fusarium wilt (Panama disease) caused by Fusarium oxysporum f. sp. cubense (Foc) is of economic importance in Kenya. The disease is widespread and currently causing havoc to bananas in the main growing regions of Eastern and Central Kenya. There is no information on the pathotypes associated with the spate of infections observed in these regions. This study was undertaken to identify the races of the pathogen involved and their pathogenicity on banana.
Methods
A total of 41 Foc isolates were collected from symptomatic banana plants in Central Kenya. The Fusarium strains isolated were identified based on morphological characteristics and screened using a PCR-based assay with race-specific primers for Foc races 1, 2, and 4. We further evaluated the pathogenicity of a subset of 24 isolates on the banana variety Gros Mitchel, a universally susceptible variety to Fusarium wilt. Conidia were harvested from 14-days-old Foc cultures grown on Potato Dextrose Agar (PDA) and inoculated onto eight-weeks-old tissue-cultured banana seedlings by dipping the seedlings into the inoculum solution. Disease severity was assessed weekly by the extent of chlorosis and vascular discoloration and at the end of the experiment, 140 days post-inoculation, respectively. Root and shoot dry weights were collected at the end of the experiment. The experiment was undertaken using the randomized complete block design (RCBD) experimental design with four replicates and repeated twice. The collected data were subjected to ANOVA and area under disease progress stairs to determine the virulence of the isolates.
Results
Our results indicate that all the 24 isolates were pathogenic to Gross Mitchel to a varying extent and 29 isolates belonged to race 1 of the pathogen. Twelve isolates tested negative for race 1, race 2 and race 4.
Conclusions
The Fusarium isolates tested in this study belonged mainly to Foc race 1, except 12 isolates which tested negative using Foc specific primers. There is a need to investigate the isolates further, with VCGs and sequencing studies, as well as to characterize their virulence on the differential set of banana varieties.