Molecular Insights into Fusarium oxysporum f. sp. ciceris- Cicer arietinum L. Pathosystem

Fusarium wilt caused by a soilborne fungus Fusarium oxysporum f. sp. ciceris (Foc) has become a major limiting factor in chickpea production worldwide. Eight physiological races (4 reported from India) are key elements in the development and management of the disease. Clear information on the race scenario and molecular events involved in the developmental stages of the Foc like conidia germination important for establishment of infection is not available.  A thorough understanding of Foc-chickpea interaction at a cellular and molecular level is essential for isolation of potential genes involved in counteracting disease progression. Here we are reporting the recent advances in profiling the race scenario using the latest technology Diversity Array technology (DArT); transcriptome analysis of the early stages of conidial germination and some updates on the Foc genomics. We developed diversity array technology (DArT) Platform for Foc for the first time in any fungal pathogen.  The microarray DArT revealed a total 1813 polymorphic markers with an average genotyping call rate of 91.16% and a scoring reproducibility 100%. DArT cluster analysis, principal coordinate analysis and population structure indicated that the different isolates of Foc were partially classified based on geographical source and race status. A number of race-specific unique and rare alleles were detected. Occurrence of multiple/new races of Foc suggested continuous monitoring of changes in Foc population to check the susceptibility of widely grown resistant cultivars against these races. Transcriptome profiling of predominate race of Foc (race 1) was conducted for conidial germination at 4 developmental stages - 0h (dormant), 2h (pre-germination), 6h (post-germination) and 24h (fully-germinated).  The transcriptome of dormant conidia had shown significant differences from that of germinating conidia and major changes were observed with in the first six hours of germination. Genes associated with metabolism, transport, binding, catalytic activities and transferase activities were found in majority. We detected genes encoding proteins involved in cell wall biosynthesis process (cell wall glucanase, chitin synthase) that plays a diverse role in hyphal growth, conidiogenesis and pathogenesis. Expression of genes involved in cell wall degradation pathway was also found. In some of the recent studies, role of defence related proteins in chickpea during Foc infection have been identified. These studies will serve as an additional resource to augment the existing systems to assist crop improvement efforts and disease management practices for this pathogen.