Pathological Observation And Pathogenicity Of Fusarium Oxysporum F.sp. Cubense And Its' Fermented Filtrate On Banana

Banana cultivars (Musa spp.) were injured at root tips, followed by the inoculation of Foc4 spore suspension and treatment with fermented filtrate of Fusarium oxysporum f.sp. cubense race 4 (Foc4). The experiment result indicates the pathogenicity evaluation of the two treatment method upon banana cultivars. The pathogen fermenting liquor was filtered through cheesecloth and a membrane filter. Pure fusaric acid was used to estimate the concentration of fermented filtrate. Observation after 20 days'infection process, banana cultivars treated with fermented filtrate show the more severe symptom compared to the level observed 20 days after Foc4 inoculation. Under Foc4 inoculation, banana cultivars manifest differences in degree of resistance to Fusarium wilt, which is shown in a descending order as follows: Resistance FOC No.5 banana, Malaysia banana and Resistance FOC No.1 banana, Drawf banana, Banana Brazil. While banana cultivars treated with fermented filtrate, which result is given in a descending order as follows: Malaysia banana, Drawf banana and Banana Brazil, Resistance FOC No.1 banana, Resistance FOC No.5 banana. Foc4 fermented filtrate treatment increased the symptom severity, and was shown a speed-up in the appearance of the typical FOC symptoms. It appears that the use of Foc4 fermented filtrate to evaluate banana resistance and screen for banana resistant varieties to Fusarium wilt may be potential.The microscopic observations of staining root-tissue sections from Foc4-inoculated banana plants revealed that successful fungal penetration of the host cell was achieved through localized vascular steles of the injured roots. Hyphae of the pathogen grew and multiplied small conidia or chlamydospore, which occurred mainly in xylem vessels of root-tissue and corm-tissue. At this stage of infection, mycelial growth occurred both intercellularly and intracellularly on brown lesions from the corm tissue.Pathogen ingress toward the host cell was accompanied by severe host cell alterations ranging from the granulation and yellowing of cytoplasm to protoplasm retraction; the deposition of lignin and (or) phellem in both host cell walls and vascular stele cell; a decrease of faecula granule; an increase in oxidase activity in root-tissue and corm-tissue; the occlusion of root-tissue xylem vessels space with brown gel and the formation of tylose in vessel cavities of pseudostem-tissue. The polymorphic brown material frequently established close contact with the invading hyphae. The fungal cells become browning necrotic.