Researches on the control and disease resistance breeding of Banana Fusarium Wilt Disease

Abstract: Banana (Musa spp.) is one of the most important fruit worldwide and the main crop food in some African countries. It is widely cultivated in south China with production amount approximately accounting for 10% of global banana industry. Cultivated banana plants generally have low disease resistance, and thus often suffer yield losses from bacteria, fungal and virus diseases. Among all the diseases found in banana, the Fusarium wilt disease, also known as Panama disease, has been recognized as the most devastating one and no cure has been found for it today. Banana Fusarium wilt was even reported to be one of the most widely distributed and devastating diseases in the history of world agriculture. The disease is caused by soil-borne fungi Fusarium oxysporum f. sp. cubense (Foc) . The pathogen's chlamydospore can survive in the soil for 30 years without banana host under unsuitable conditions. Banana wilt disease was first discovered in Australia in 1874. The first Fusarium wilt case caused by Foc4 in China was reported in Taiwan in 1967. Since then, the disease spread quickly and the damage caused by it is becoming more and more serious. As a result, many historical banana-producing areas are currently unable to plant bananas and most of the survived banana-producing areas are still threatening by it. According to host range and pathogenicity, molecular markers and vegetative compatibility groups of Foc, the pathogen can be divided into three physiological races, two clades, eight lineages and twenty-four VCGs. Foc race 4 (Foc4) can be further divided into tropical fourth physiological small species (FocTR4) and subtropical fourth physiological species (Foc STR4) according to their pathogenic region and temperature adaptation ability. And Foc TR4 is the most virulent and it can infect almost all of the banana varieties. This disease can be spread in many ways and its spreading speed is very fast. The typicalsymptom of the Foc-infected banana is yellowing and the main characteristic is the withered and vascular discoloration of the diseased plants. Banana can be infected by the pathogen in all growth stages and the latent time in different banana species differs a lot. Typical symptom will be found in most of the banana plants at adult stage after the infection of the pathogen. The infection of Foc will greatly change the biological metabolisms of banana plants. The content and activity of some resistance-related substances, such as phenols, defensive enzymes, and endogenous hormones and so on, would change in different degrees. Besides, the gene expression pattern would be also changed significantly. At present, there are two main pathogenic mechanisms of banana Fusarium wilt pathogens, including plugging theory and toxin theory, and Fusaric acid and Beauvericin are known to be the major pathogenic toxins. The reported pathogenic genes of Foc mainly include signal transduction, transcription factors, effectors and the genes related to the colonization ability of F. oxysporum and so on. Currently, enormous attempts, including chemical control, biological control agents and bio-fertilizer production, crop rotation, comprehensive control, disease resistance breeding and etc, have been tried by scientists for the control of the disease. For chemical control, many chemical agents and fertilization methods were used, and the control effects varied a lot when using different fertilizers, different fertilization frequency and different fertilization methods. From the aspects of biological control, the isolation and screening of antagonistic bacteria against Foc TR4 have been a hotspot and some exciting research results have been obtained.The application of endophytic bacteria in the prevention and control of banana wilt is in line with the development trend of ecological protection. Therefore, it is an important and popular direction for banana Fusarium wilt control to excavate and popularize better antagonistic bacteria. Many studies and facts show that crop rotation can significantly reduce the incidence of banana Fusarium wilt. It is especially important to apply comprehensive prevention and control before resistant banana varieties and effective pharmaceuticals can be generalized widely. Breeding banana cultivars with high Fusarium wilt resistance is the fundamental way to control the spread of wilt disease. At present, the breeding methods adopted on bananas include mutagenesis breeding, bud mutation selection, tissue culture mutant screening and conventional cross breeding. The rapid development of molecular biology provides an important approach to the breeding of banana wilt resistance, screening more resistant varieties using radiation mutagenesis, discovering more genes related to resistance to Fusarium wilt and using biotechnology breeding means to mine resistant resources to wilt disease from wild species. Genetically modified transgenic breeding for banana cultivars will become the mainstream in the future. With the rapid spread of the disease in the world, banana Fusarium wilt has become the focus of banana production and research. Many banana-producing countries and related organizations have invested a lot of human, materials and financial resources to carry out research on banana Fusarium wilt in different aspects. In the past few decades, through the continuous research and exploration of scientists, the pathogen of banana Fusarium wilt, pathogenic mechanism and the effect on host have been partly understood to some extent, and some progress has been made in preventing and curing banana Fusarium wilt and disease-resistant breeding. However, in order to completely prevent and control, breakthroughs in cultivation, plant protection and breeding are still in urgent need. It is believed that the worldwide problem of defeating banana Fusarium wilt will be around the corner with the rapid development of molecular biology and bioinformatics and the continuous exploration of scientific researchers.