Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2004
Publication Date: 11/1/2004
Citation: Chen, W., Coyne, C.J., Peever, T., Muehlbauer, F.J. 2004. Characterization of chickpea differentials for virulence assay of ascochyta blight and identification of chickpea accessions resistant to ascochyta rabiei. Plant Pathology. 53:759-769. Interpretive Summary: Ascochyta blight has been a persistent disease problem of chickpea production in most major chickpea production regions, and is a subject of numerous studies. However, there is no consensus on the best method to describe the virulence variation of the pathogen Ascochyta rabiei. Experiments were carried to out to characterize the interactions between chickpea and Ascochyta rabiei. After examining reactions of a moderately resistant chickpea to inoculations with 34 isolates of Ascochyta rabiei and reactions of 47 chickpea genotypes to infection with 6 isolates, a two-pathotype sytem was proposed for the isolates of Ascochyta rabiei from the western United States. This two-pathotype system will not only simplify the pathotyping procedure while still capturing the major virulence variation, but also will facilitate studying mechanisms of chickpea resistance to Ascochyta blight. In addition, three chickpea germplasm lines were identified to be resistant to Ascochyta rabiei from the western United States.
Technical Abstract: Forty-eight chickpea germplasm lines including 22 differentials that were used in previous studies were characterized for their reactions to inoculation with a set of six isolates of Ascochyta rabiei representing a wide spectrum of virulence, and representative isolates were also directly compared with six previously identified races on eight chickpea genotypes. Many of the chickpea differentials reacted similarly to inoculations with each isolate of A. rabiei, and several of the previously identified races caused similar levels of disease on the differentials. Therefore the number of differentials can be reduced significantly without sacrificing accuracy in describing virulence variation of A. rabiei on chickpea. The major variation in virulence among the US isolates could be described using a two-pathotype system, which was adapted from the three-pathotype system developed at the International Center for Agricultural Research in the Dry Areas located in Syria. The distribution of disease phenotypes of the 48 germplasm lines is bimodal after inoculation with pathotype I isolates, whereas the distribution of the disease phenotypes is continuous after inoculation with pathotype II isolates. Such distinct distribution patterns are indicative that chickpea plants employ different resistance mechanisms to the two pathotypes and that the two pathotypes may have different pathogenic mechanisms. The advantages of using the two-pathotype system in assaying virulence of the pathogen and in studying resistance mechanisms of the host are discussed. Three chickpea accessions (PI 559361, PI 559363 and W6 22589) showed consistent resistance to both pathotypes in repeated trials, and can be employed as resistance sources in chickpea breeding programs for resistance to Ascochyta blight.