Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2005
Publication Date: October 1, 2005
Citation: Chen, W., Mcphee, K.E., Muehlbauer, F.J. 2005. Use of a mini-dome bioassay and grafting to study resistance of chickpea to ascochyta blight. Journal of Phytopathology 153:579-587. Interpretive Summary: Ascochyta blight is an important disease of chickpea in the Pacific Northwest and many other parts of the world. In order to reliable conduct screening for resistant in chickpea and to test viability of the pathogen, a mini-dome technique was developed for virulence assay of the disease. It was determined that the best condition of assaying virulence of A. rabiei was to use 105 spores/ml as inoculum and to maintain a leaf wetness period of 24 hours under mini-domes at a temperature between 16 and 22 C. This mini-dome technique was used to determine the relative virulence of six chickpea cultivars to isolates of Ascochyta rabiei. Grafting technique in combination with the mini-dome bioassay was used to study the resistance of chickpea to Ascochyta blight. Grafting could allow us to detect any translocated factors reproduced in chickpea plants that mediate disease response, which could help elucidating possible mechanisms of chickpea resistance. Grafting and reciprocal grafting in 36 rootstock and scion genotype combinations showed that Ascochyta blight phenotype was determined by the genotype of the scions, and the rootstock genotypes had no detectable contributions the scion phenotype in response to inoculation with Ascochyta rabiei. The disease phenotype is conditioned locally by the scion genotype.
Technical Abstract: A mini-dome bioassay was developed to study the virulence of Ascochyta rabiei and relative resistance of chickpea. It was determined that the best condition of assaying virulence of A. rabiei was to use 105 spores/ml as inoculum and to maintain a leaf wetness period of 24 hours under mini-domes at a temperature between 16 and 22 C. This mini-dome virulence assay was used to determine relative resistance of six chickpea cultivars to isolates of A. rabiei with known levels of virulence. Grafting was employed to detect any translocated factors produced in the chickpea plant that mediate disease response, which could help elucidate possible resistance mechanisms to Ascochyta blight. The six chickpea cultivars were grafted in all possible scion and rootstock combinations. The grafted plants were then inoculated with isolates of A. rabiei using the mini-dome technique. Results showed that self-grafted plants had similar levels of disease compared with non-grafted intact plants when inoculated with the same isolate, indicating the grafting procedure did not alter host response to infection by A. rabiei. Susceptible scions always exhibited high and similar levels of disease severity regardless of rootstock genotypes, and resistant scions always showed low and similar levels of disease severity when they were grafted onto any of the six rootstock genotyeps. Data indicate that there were no translocated disease-mediating agents that are responsible for susceptibility or resistance in chickpea, or they were translocated at low levels that could not be detected with the virulence assay. Disease phenotypes of chickpea Ascochyta blight were conditioned locally by scion genotypes.