Identification Of Genes Related To Pathogen Of Fusarium Oxysporum Injected Banana

Fusarium wilt is a soil-borne vascular disease which known as Fusarium oxysporum f.sp.cubense disease, Panama disease (commonly known as banana yellow leaf disease). It can be spreaded by diseased seedlings, soil, contaminated tools, irrigating water and other ways. Fusarium wilt was first found in Australia in1874, and then occured in Central and South America, Asia and other countries in the world causing huge losses in banana industry. We studied the infection process caused by pathogen and identified disease-related genes for further study the infection mechanisms of Fusarium wilt. This study is important for cultivating resistant bananas by using genetics engineering.We used Fusarium oxysporum f.sp.cubense race four (FOC4) transformated with GFP gene to infect roots of banana seedlings (Musa acuminate L. AAA group cv. Brazilian), then observed the process visually by fluorescence microscope, such as conidia attachment to root surface, reproduction and invasive process. According to observation, infection process was divided into three periods:early stage, middle stage and later stage. In early stage, microconidia adsorbed on the root surface, then developed into hyphae under proper conditions. Hyphae prior to elongate along the cell gap and there were no hyphae infected into the internal of root. In middle stage, hyphae grew fast in spaces between cells and formed a network structure in root surface.Penetration of hyphae into epidermal cells were also observed. Large number of microconidia even filled the whole cell and only a small amount of hyphae penetrated into root cortex. In later stage, hyphae expanded to a wider range around the root epidermal cells and the network structure has completely encased roots. Most of the hyphae penetrated to inner of root until the vascular. Only little hyphae grew along the vascular of root. At last hyphae transferred to the Pseudostem. Therefore, the infection process was that FOC4 gradually infected from roots up to pseudostem rather than microconidia transported in vascular from root up to pseudostem. Roots of control and three different disease stages were selected to extract total RNAs which were reversed into cDNA first strand used as template. Thirty genes in a Banana cDNA library were chosen to do different expression analysis by using semi-quantitative RT-PCR method. The results showed that twenty-one genes were down-regulated expression, four genes up-regulated expression, three genes didn’t have significant changing rules and two genes did not change significantly compared with control plants without infection.Chitinase gene was found to have a significant effect on anti-fungal. We used promoter and inhibitor to treat the roots of banana seedlings. Chitinase gene’s expression and enzyme activity were measured at different phases. The results indicated that chitinase gene’s expression increased with treatment of salicylic acid and so did the enzyme activity. Symptom of fusarium wilt was delayed. Theophylline inhibited the chitinase gene’s expression and enzyme activity. Symptom of fusarium wilt was in advance.