JWSS - Journal of Water and Soil Science

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Four hundred isolates of Ascochyta rabiei (Pass.) Lab. collected from different parts of the country, such as Zarivar Marivan Lake in Kordestan Province Shabestar and Khosroshahr in Eastern Azarbaigan Province Serow, Bokan and Shahindeg in Western Azarbaigan Province Mashhad and Ilam were used in this experiment.

These isolates showed little differences in their cultural and morphological characters and pathogenic behaviors. They were categorized into 17 groups on the basis of collection regions and, based on cultural characteristics, were then reduced to 11 groups. Isolate number 16 from Mashhad showed the highest growth rate while isolate number 1 from Kordestan had the lowest growth rate.

One isolate was chosen as a representative for each group. Pathogenicity of representative isolates from each of the 11 groups were tested. Reaction type of all isolates was studied on differential hosts and one local chickpea line Jam was examined, using Reddy and Nene (1979) method. Races No. 4 and 6 were identified as the two physiologic races.

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This study was carried out on the biochemical aspects of chickpea cultivars and the genomic behavior of A. rabiei pathotypes 4 and 6 in four parts: 1) Determining the number of resistant genes in chickpea native cultivars, 2) Comparing the variation of sodium and potassium electrolytes concentrations in noninfected and infected seedling stems of resistant and susceptible cultivars, 3) Studying the effect of potassium deficiency on five differential cultivars by Hoagland nutrient culture, and 4) Using RAPD-PCR method to detect any genomic differences between the two pathotypes used in this study.

Eighteen native chickpea cultivars were chosen for this study. The result of the experiments showed that cultivar 1-60-144 possesses the highest number of resistant genes, while the others were either relatively tolerant or susceptible. The reduction of electrolytes concentration in infected cultivar ILC-1929 in comparison to resistant cultivar ILC-5928 is an indication of compatibility between the host plant and the pathogen. Increasing the level of resistance in differential cultivars and appearance of induced resistance as the result of potassium deficiency is due to the production of putrecine diamine. Eighty percent similarity of pathotypes genomic bands by using CG marker and primer 171 showed insufficient primer numbers and the necessity for using complementary methods.

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The poor information available on variation of Ascochyta blight fungus is the most important factor limiting chickpea breeding programs for resistance to blight disease. In this study, efforts were made to detect genetic variation of the pathogen in Iran. The RAPD marker was employed to evaluate 26 isolates collected from 16 provinces. Twelve random primers were used to analyze genomic DNA of the isolates. Only ten primers showed polymorphism among isolates. Primer OPK-01 defined the highest number of polymorphism and primer OPK-09 confirmed relatively low degree of polymorphism. On the basis of this molecular marker, the estimated genetic diversity index was 98% and the pair-wise genetic distance of the isolates varied from 0.16 to 0.61. The least genetic distance belonged to isolates 20 and 22 from Qazvin and Golestan while the highest distance belonged to isolates 26 and 12 from Mazandaran and Markazi. The phylogenic tree was constructed by cluster analysis and all the isolates grouped to 22 genetic clusters at the 90% similarity level. The genetic groups were named from A to V and their distribution in Iran was determined. The results revealed that genetic variation among Iranian population of the pathogen is very high, and further that RAPD is a vigorous tool for genomic analysis of Ascochyta rabiei.