Assessment of slow rusting of landraces of bread wheat to Puccinia striiformis f.sp. tritici under artificial field inoculation
Yellow rust caused by Puccinia striiformis f.sp. tritici, is the most devastating fungal disease of wheat, especially in CWANA region. Growing cultivars with durable resistance is the most economical control measure. A field study was conducted to evaluate 500 bread wheat landraces along with the susceptible control ?Morocco? using artificial inoculation under field conditions at Tel Hadia, Syria during 2010-11 and 2011-12 growing seasons. The most prevailing yellow rust virulent race 70E214 was used for artificial inoculation. The disease scoring started when the disease severity was more than 50 % on the leaves of the susceptible check ?Morocco? and continued for four scorings at the intervals of 7 days. Slow rusting resistance was assessed based on the development of disease over time using the Area under Disease Progress Curve (AUDPC), Coefficient of Infection (CI), Final rust Severity (FRS), Infection Rate ?(r)? and Relative Resistance Index (RRI). None of the landraces showed immune reaction and 10% showed lowest values for all parameters, suggesting that resistance in these landraces was controlled by major genes. Approximately 65% of landraces were marked as having different levels of slow rusting and 25% were highly susceptible. Cluster analysis based on partial resistance parameters revealed two major clusters: Susceptible and low level of slow rusting were grouped in the first cluster; Resistant, high level and moderate level of partial resistance were grouped in the second cluster. By comparing the results obtained from RRI and others parameters, we found that landraces with very low values for all parameters exhibited high RRI value of 9, while those that showed high, moderate and low levels of slow rusting, had RRI ranges of 8-9, 7-8 and 5-7, respectively. The landraces with maximum values from each parameter showed very low RRI values of less than 5.