Defence gene expression profiling to Ascochyta rabiei aggressiveness in chickpea

Significant differences in defence pathway-related gene expression were observed among chickpea cultivars following A. rabiei infection. Differential gene expression is indicative of diverse resistances, a theoretical tool for selective breeding. A high number of Ascochyta rabiei pathotypes infecting chickpea in Australia has severely hampered efforts towards breeding for sustained quantitative resistance in chickpea. Breeding for sustained resistance will be aided by detailed knowledge of defence responses to isolates with different aggressiveness. As an initial step, the conserved and differential expressions of a suit of previously characterised genes known to be involved in fungal defence mechanisms were assessed among resistant and susceptible host genotypes following inoculation with high or low aggressive A. rabiei isolates. Using quantitative Real-Time PCR (qRT-PCR), 15 defence-related genes, normalised with two reference genes, were temporally differentially expressed (P < 0.005) as early as 2 h post inoculation of Genesis090 (resistant) or Kaniva (susceptible). The highly aggressive isolate, 09KAL09, induced vastly different expression profiles of eight key defence-related genes among resistant and susceptible genotypes. Six of these same genes were differentially expressed among ten host genotypes, inclusive of the best resistance sources within the Australian chickpea breeding program, indicating potential use for discrimination and selection of resistance "type" in future breeding pursuits.