Infectivity of cashew pseudo-apple by Gilbertella persicaria exposed to ultraviolet-B

Disease development by fungi on plants is result of pathogen colonizing host which depends on the initial ability of spores to germinate on host. The ability of G. persicaria spores exposed to UV-B to infect cashew fruit flesh was tested on media obtained from cashew fruits. Juice extracted from unripe and ripe cashew were tested separately and compared with water. Sporangiospores of G. persicaria were exposed to UV-B and then inoculated into unripe, ripe cashew juice and water. Observation for germ tube emergence after incubation at 28°C showed that all three media allowed spore germination, but it decreased with increase in length of exposure to UV-B, except in water. In unripe juice, the decrease was consistent as length of exposure to ultraviolet light increased. In ripe juice, there were also significant differences between unexposed and exposed spores but there was inconsistent trend of decrease contrary to that observed for unripe. However, the spores exposed longest still had the lowest percentage of germination in ripe juice. UV-B treated spores cultured in water produced a different trend in which longest exposure resulted into significantly highest germination percentage. Unexposed spores failed to germinate in water. These results indicate that spores treated with ultraviolet light could still infect both unripe and ripe pseudo-apples and infectivity decreased consistently with exposure in unripe fruits. It also explains why harvested fruits were still rotted by G. persicaria despite UV-B treatment even though the rotting was decreased by ultraviolet light treatment. UV-B on the other hand enhanced spore germination in water, indicating resistance in the neutral medium of water and susceptibility in the nutrient medium of cashew fruit.