| Ascochyta blight caused by a necrotrophic pathogen, Ascochyta rabiei (Pass) Labr., is one of the most devastating fungal diseases of chickpea (Cicer arietinum L.). Elucidation of blight resistance mechanism has been hampered because of a complex quantitative genetic mechanism and the necrotrophic nature of A. rabiei. Molecular breeding and an understanding of the resistance mechanism are thought to be the most promising approach to improve blight resistance in chickpea.; Genetic analysis using the recombinant inbred lines (RILs) generated from the cross of PI 359075(1) (blight susceptible) x FLIP84-92C(2) (blight resistant) showed that blight resistance in chickpea was pathotype-dependent and there was a qualitative genetic effect contributing to quantitative blight resistance. A gene for resistance to pathotype I, designated as Ar19 (or Ar21d) and a quantitative trait locus (QTL) for resistance to pathotype II were mapped to linkage group 2+6 and 4, respectively, and additive interaction between Ar19 (or Ar21d) and a QTL for resistance to pathotype II appeared to determine quantitative blight resistance in chickpea.; Biochemical responses of chickpea to three fungal pathogens, A. rabiei, Fusarium oxysporum f.sp. ciceri, and F. oxysporum f.sp. pisi, were elucidated by examination of expression patterns of fungal response genes after fungal inoculation. Gene expression patterns and signal chemical specificity of the genes revealed that fungal resistance in chickpea was not provided by salicylic acid (SA) or jasmonate (JA)-mediated induced resistance mechanisms.; Transcript profiles in two parental lines, FLIP84-92C(2) and PI 359075(1), and their RILs representing pathotype-dependent resistance patterns were examined using a cDNA-AFLP technique. Differential display of a cDNA-AFLP clone homologous to flavanone 3-hydroxylase (F3H) was identified. The expression pattern of F3H was loosely associated with blight resistance in the RILs and it appeared to be related to resistance to pathotype I of A. rabiei. Therefore, F3H was considered to be a putative gene with a qualitative effect on quantitative blight resistance in chickpea. To verify the genomic and biochemical significance of F3H in blight resistance, further study of the genomic regions linked to F3H is needed.; The results presented here can be applied to other plant species to elucidate genetic mechanisms of quantitative traits or resistance to necrotrophic pathogens. |
