Correlation between susceptibility of pathogen and crude toxin of Fusarium oxysporum f. sp. cubense race 4 in banana cultivars plantlets.

A study was done to investigate the correlation between susceptibility for Fusarium oxysporum f. sp. cubense (Foc) race 4 and susceptibility for crude toxins of the pathogen in banana cultivars. The susceptibility of 36 banana cultivars to pathogen was studied by inoculating plantlet roots with Foc race 4 conidial suspension. The susceptibility of 5 banana cultivars to crude toxins was studied by treating plantlets roots and leaves with crude toxins of Foc race 4. The results showed that 4 cultivars,namely Tianbaojiaojiao (AAA),Chaijiao (AAA),Guangfen1 (AAB) and Gongjiao (AA) showed resistance to Foc race 4,and 2 cultivars,namely Costarica (AAA) and Kangku 5 (AAA) showed intermediate resistance to Foc race 4. The susceptible cultivars showed also higher susceptibility to the crude toxins than the resistant cultivars. Analysis of the difference of disease index,wilt index and leaves lesion area of banana plantlets showed that there is a positive correlation between the susceptibility for the pathogen and crude toxins of Foc race 4 in banana cultivars,and a significant positive correlation between disease index and leaves lesion area of 60-day-old pseudo-planting plantlets (PPP). Measuring the leaves lesion area in the middle leaves of PPP after treatment with crude toxins for 72 h could thus be used as an effective method to identify the resistance reaction of banana cultivars to Foc race 4.