چكيده لاتين :
Introduction: Stripe (yellow) rust of barley (Hordeum vulgare L.), caused by Puccinia striiformis f. sp. hordei, is one of the most important diseases of barley in many parts of the world which can cause yield losses due to severe epidemics. Stripe rust of barley is become increasingly important in some parts of Iran due to the cultivation of susceptible cultivars and or appearing new pathotypes. Yield losses of 30 to 70 % occurred in these regions. New, more effective fungicides are available to control yellow rust, but the most efficient, economical, and environmentally friendly approach, is to grow resistant cultivars. It should be noted that the majority of designated Yr-genes are race-specific and therefore become ineffective in combating current pathogen populations due to development of new races. The average lifetime of the genes conferring race-specific resistance is estimated to be five years on the global basis. An alternative procedure for wheat breeders is the use of quantitative resistance. Two types of quantitative resistance, including high-temperature adult-plant (HTAP) resistance and slow rusting resistance, have been intensively investigated. Although several studies have been carried out for assessment of different barley genotypes to yellow rust in Iran, no research has been reported on the screening of barley cultivars for different pathotypes of barley and wheat yellow rusts.
Materials and Methods: In order to, resistance evaluation, seedling and adult plant reactions of 30 barley cultivars were evaluated to yellow rust. The seedling reaction was evaluated in a greenhouse using four barley pathotypes (PSH-51, PSH-84, PSH-85, and PSH-89) and one wheat pathotype (6E150A+, Yr27). The seedling reactions were recorded under greenhouse conditions, based on a 0-to-9 scale. Race population was considered avirulent on the differential set when there were either no symptoms (IT 0) or there were necrotic or chlorotic flecks (IT 1), necrotic or chlorotic blotches without sporulation (IT 2), or necrotic or chlorotic blotches with only a trace to slight sporulation (IT 3 to 4). Race population was considered to be virulent if it caused moderate to abundant sporulation, with or without necrosis or chlorosis (IT 5, 6, 7, 8, or 9).
Adult plant resistance was also evaluated by measuring final rust severity (FRS) and coefficient of infection (CI) under natural infection conditions with two times artificial inoculations. Artificial inoculation, during 2010-2011 cropping years, was carried out by barley and wheat yellow rust inoculum. Percent severity was recorded three times, starting when check reached 50% severity according to the modified Cobb,s scale, and reaction based on Roelfs et al. (1992). The coefficient of infection (CI) was calculated by multiplying disease severity (DS) and constant values of infection type (IT). The constant values for infection types were used based on; resistant (R) =0.1, moderately resistant (MR)=0.25, moderate or moderately resistant to moderately susceptible (M)=0.5, moderately susceptible (MS)=0.75, susceptible (S)=1.
Results and Discussion: Results of evaluations for resistance parameters showed that cultivars Eram, D10, Shori-5, Topper, Afzal, Goharjow and Torsh had susceptible reaction at seedling stage and the high values of FRS and CI, therefore were selected as susceptible cultivars. The cultivars Emir, Asterix and Makouee were resistant both at the seedling and adult plant stages, so they carry race-specific resistance genes against all used-pathotypes. Six cultivars showed resistant at seedling at least against pathotype PSH-85, but moderate or susceptible reactions at adult plant stage in Ardabil. The thirteen cultivars (entries; 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 26), was susceptible at the seedling at least against one pathotype, but had moderate (MR, M or MS) reactions at adult plant stages.
Conclusions: The results of the current study showed that the cultivars had a diversity of reactions, ranging from complete resistance to full susceptibility. Most of the evaluated cultivars exhibited moderate or low performance under high disease pressure shown by the susceptible check. The resistance of all categories (including complete resistance, to partial resistance) to stripe rust was observed. The cultivars having the low level of different parameters supposed to be having gene/s for varying degrees of slow rusting resistance or high-temperature adult-plant (HTAP) resistance. Cluster analysis of barley cultivars based on adult plant resistance parameters and seedling infection types revealed different groups/clusters which indicate considerable diversity for a level of resistance of these barley cultivars.
