Genetic Diversity of Fusariumoxysporum f.sp. cubense Isolates(Foc) of India by Inter Simple Sequence Repeats (ISSR) Analysis.

Fusarium wilt (Panama disease), caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. cubense (E.F. Smith) W·C. Snyd. & H.N. Hans. is one of the most catastrophic plant diseases in the world [1] and widespread in all the banana growing regions of Asia, Africa, Australia, and the tropical Americas, destroying more than 40,000 ha of banana in Central and South America over a period of 50 years. In India, the disease is present in almost all the banana growing states and causes severe yield losses in most of the commercial cultivars grown. Although the disease was recorded only in the suscepts of race 1 and race 2 of Foc, recent survey in Theni district of Tamil Nadu revealed the presence of Fusarium wilt strains which can attack race 4 susceptible cv. Grand Naine (Cavendish-AAA). The characterization of these isolates indicated that this new strain belongs to VCG 0124 of race 1 and an inodoratum group [2]. This finding showed that variability is occurring at faster rate within the Foc strains which is threatening the cultivation of important commercial cultivars of banana, particularly Cavendish group of bananas. Moreover, India is considered as one of the centers of diversity for banana. As the Foc is highly variable and considered to be co-evolved with banana [3, 4], there is a great chance of having great diversity among the Foc isolates [5, 6]. Bentley et al. [3] also stressed the importance of studying the diversity of Foc of Asia, the center of origin and domestication of Musa, for thorough understanding of genetic diversity of Foc worldwide.To find out the genetic diversity of Indian Foc isolates of banana, a total of 107 isolates of Fusarium which includes 98 Foc isolates obtained from different banana growing regions of India and seven Foc isolates belong to all known VCGs obtained from Australia and two non-pathogenic Fusarium oxysporum (npFo) isolates were subjected to ISSR analysis. In the initial screening of ISSR primers, out of 34, 10 primers which generated more polymorphic bands were selected for further analysis. The Phylogenetic analysis carried out based on the fingerprints obtained through ISSR analysis indicated the presence of wide genetic diversity among the Foc isolates of India and also its polyphyletic nature. Totally, seven different clusters were obtained and these clusters differentiated the Foc isolates of India based on the races/VCGs. Besides, the cluster analysis clearly distinguished the freshly emerged Foc strain obtained from cv. Grand Naine (Cavendish-AAA) and Poovan (Mysore-AAB) from the other Foc isolates. The non-pathogenic F. oxysporum isolates which have been included for comparison purpose also clustered separately. All these above said findings indicates for the first time the discriminatory power of ISSR to clearly distinguish and separate the Foc isolates according to its race/VCGs and also its virulence. This study would be useful not only to design and develop effective management strategies but also useful for quarantine purposes