ARS | Publication request: Characterization of Ascochyta rabiei for population structure, mating type and pathogenic variability from Pakistan and United States

Submitted to: International Ascochyta Workshop
Publication Type: Abstract Only
Publication Acceptance Date: March 24, 2012
Publication Date: April 20, 2012
Citation: Ali, H., Alam, S.S., Attanayake, R.N., Rahman, M., Chen, W. 2012. Characterization of Ascochyta rabiei for population structure, mating type and pathogenic variability from Pakistan and United States. International Ascochyta Workshop. Page 28.

Technical Abstract: Chickpea production is greatly hampered by blight causing fungal pathogen Ascochyta rabiei (AR) in chickpea growing regions of the world. Genetic variability and mating type frequency of thirty-two AR isolates from six geographical regions of Pakistan were compared with a US-AR population. Pakistani AR (PAR) population had an apparent skewed (3 Mat1-2: 1 Mat1-1) distribution, although Chi-square tests showed non-significant deviation from equal distribution due to small sample sizes, and the US-population showed a 1:1 distribution (1). The results showed that sexual reproduction is rare in PAR due to either unavailability of both mating types or lack of conducive environment but statistical analysis showing panmixia which may be due to past recombinational events. Genetic variation at six microsatellite loci was assessed and each isolate was assigned to a microsatellite haplotype. Population structure using Bayesian analyses differentiated isolates into three distinct clusters, two clusters of PAR and one cluster of the US isolates. However, a few isolates from US shared same genetic background with one cluster of the PAR isolates, providing a potential link of inter-continental migration of the pathogen likely due to seed importation. Additionally, the two clusters of PAR-isolates are not strictly correlated with the geographic locations, suggesting frequent gene flow of AR among different locations in Pakistan. Pathogenic variability of nineteen PAR isolates collected from two different provinces was assessed using chickpea differential lines. The results based on the reactions of isolates with differential lines showed that aggressive and highly aggressive pathotypes II and III are prevalent in Pakistan as compared to previously reported less aggressive pathotype I (3). This study along with a recent report of Imitaz et al (2) documents that highly aggressive pathotypes III and IV have only been reported from Syria and Pakistan (2,3). Future study should focus on the relationship of highly virulent pathotypes within relation to the pathogen population structure, cultural practices and disease selection pressure in these chickpea production regions.