Study the Reaction of Some Barley Cultivars to Rhizoctonia solani AG-8, the Causal Agent of Root Rot Disease

Barley is one of the important agricultural products, mostly as livestock feed, and secondly for its important role in human nutrition as bread, soups, baby food and etc. It has the second-largest rank of cultivation area and yield of the national grain production and the Isfahan province, with production 5% of total barley yield, has been ranked eighth in 2010. Because its consumption exceed over the production, barley is one of the major imports to the country. In addition to, agronomy operations, plant diseases are important factors in yield loss. Rhizoctonia root rot (caused by soil-inhabiting fungus Rhizoctonia solani) is one of the important diseases of cereals include barley over the worldwide cultivation area. Apropriate soil fertility, delaying planting dates, crop rotation with insensitive crops such as legumes, planting resistant varieties and fungicide seed dressing are recommended methods to reduce disease damage. Chemical control of this disease is difficult because of its soil-born the pathogen. Therefore, reducing disease level requires application of other methods especially resistance cultivars.
Materials and Methods In this research, the reaction of 8 barley cultivars were examined against root rot disease in greenhouse conditions, in the winter of 2009. Fifteen isolates of the fungus were isolated from infected barley fields in the Isfahan province and their pathogenicity was examined on barley. One isolate with the highest pathogenicity potential was selected and special tests showed that the isolate was Rhizoctonia solani AG-8. The experiment was conducted in a completely randomized design with 4 replications. The test plants were harvested at two times of 4 & 8 weeks after planting. Following parameters were measured: 1- dry weight of plant root and aerial part, 2- disease severity as an index of subcrown internodes infection.
Results and discussion Statistical analysis of recorded data showed that there were significant differences among cultivars with respect to the dry weight of plant parts and disease reactions. Seedling shoot dry weight loss showed significant differences in the level of 5% among the tested cultivars of barley and compared to the healthy controls. The shoot dry weight of Bedonepushine cultivar seedlings treated with pathogen showed the highest loss (75% loss compared to the control) and had a significant difference at level of 1% compared to the healthy controls, thus it has been the most sensitive cultivar with due regard to shoot dry weight. In contrast, the Yoseph, Fajr 3 and Rudasht cultivars, with the shoot dry weight loss of 5%, 7% and 19%, respectively, compared to control, appeared to be more resistance than others. Pathogen effect as reducing root dry weight of seedlings had also significant differences at level of 1% among cultivars and compared to control. The maximum loss of root dry weight among cultivars was found in Bedonepushine cultivar (73% weight reduction compared to the control) while Yoseph, Rudasht and Fajr 3 cultivars, with the root dry weight loss of 6%, 7% and 11% respectively, compared to control, had the lowest weight loss. With a view to roots and crown infection rate, the Fajr 3 cultivar (with an average of 1.6 degree) had the lowest rate of root and crown infection, compared to control, and Bedonepushine cultivar (with an average of 4.6 degree) showed the highest degree of infection. In other cultivars, infection rates were measured between 2 and 4 degrees.
Conclusion In the final data analysis of tested barley cultivars, those with root and crown infection rate less than grade 3 were selected as tolerant cultivars. According to the study, the Yoseph, Fajr 3 and Rudasht cultivars, with comparatively lowest infection index and minimum weight loss, were more tolerant to disease in comparison to others. On the other hand, Bedonepushine, Bahman and Makuy cultivars are causes of highest infection index and maximum weight loss, were introduced as more susceptible cultivars against Rhizoctonia root rot disease. These results provide the possibility of the use of tolerant cultivars to reduce disease damage, and the possibility of transmission of resistance genes to R. solani of tolerant or resistant genotypes to susceptible commercial ones.