Submitted to: Proceedings for the Canadian Pulse Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: November 1, 2002
Publication Date: December 8, 2002
Citation: CHEN, W., MUEHLBAUER, F.J. A MINI-DOME TECHNIQUE FOR VIRULENCE ASSAY OF ASCOCHYTA RABIEI ON CHICKPEA. PROCEEDINGS FOR THE 4th CANADIAN PULSE RESEARCH WORKSHOP. 2002. pp. 167-171 Interpretive Summary: Chickpea is the third most important legume crop and Ascochyta blight is the most important disease of chickpea worldwide. In order to investigate the pathogen-host interactions, a reliable quantitative bioassay is required. Previous bioassay techniques are inconsistent and not reproducible. We developed an inexpensive and reproducible mini-dome technique to assay virulence of the Ascochyta blight pathogen Ascochyta rabiei. This mini-dome technique provides an important improvement over previous inoculation techniques in that it showed minimum variation among replicates of treatments, which increases the sensitivity in detecting phenotypic (pathogenic) variation among isolates of the pathogen. This technique produced consistent results in repeated trials with isolates collected from a wide geographic area. The development of this technique will allow us to address research questions to understand the mechanisms of the disease. This mini-dome technique will also facilitate resistance breeding in screening breeding materials.
Technical Abstract: Investigations into the genetics of Ascochyta rabiei in general and the genetics of virulence of A. rabiei in particular are hindered by the lack of a reproducible quantitative bioassay for virulence of the pathogen. In order to further our study in genetics of virulence of A. rabiei, a reproducible quantitative bioassay was developed to assess virulence of Ascochyta rabiei isolates on chickpea. The technique mainly consists of inoculating 2-wk old chickpea seedlings by spraying with conidial suspension (1 X 105 spores/ml) and immediately covering the plants in each replicate pot for 24 hours with a transparent or translucent plastic cup to form a mini-dome. The mini-dome produces a uniform high level of relative humidity that is required for infection to occur. The mini-dome was then removed and the plants were grown under regular growth conditions in a growth chamber set at 20 C day and 16 C night temperature regime for 13 more days. The plants were then rated for Ascochyta blight severity using two methods. The first method is the 1 to 9 scale (1 = healthy plant and 9 = dead plant). The second method is based on counting the number of infected leaves divided by the total number of leaves of each plant, and expressed as percentage of infected leaves. The two rating methods provided similar results and were significantly correlated. Initial studies showed that without the mini-dome infections were minimum and sporadic, and that 24 hours under the mini-dome with inoculum concentration of 105 spores per ml induces consistent infection of chickpea by Ascochyta rabiei. This mini-dome technique provides an important improvement over previous inoculation techniques in that it showed minimum variation among replicates of treatments, which increases the sensitivity in detecting phenotypic (pathogenic) variation among isolates of the pathogen. With this technique we were able in repeated trials to show geographic variations among isolates collected from various locations in California, Idaho and Washington. The development of this technique will allow us to address research questions concerning the number of genes that condition pathogenicity in A. rabiei. This mini-dome technique can also be implemented in resistance breeding to screen breeding materials.