|Douiyssi, A - UNIVERSITY OF MINNESOTA|
|Rassmusson, Donald - UNIVERSITY OF MINNESOTA|
|Roelfs, Alan - FORMER ARS EMPLOYEE|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 1997
Publication Date: N/A
Interpretive Summary: Net blotch caused by the fungus Pyrenophora teres is often a limiting factor in barley production worldwide. Although resistance has been widely reported, few improved varieties with good resistance are available. Barley breeding lines are often evaluated for resistance by inoculating seedlings with a mixture of P. teres cultures in the greenhouse. Our research shows that P. teres isolates differ widely in virulence and that plants of many barley varieties gain or lose resistance with age. Few varieties were resistant at all stages of their development. We also showed that resistance in barley varieties often is effective against some but not all races of P. teres. Our results were not always consistent with results of previous studies; some varieties rated resistant in earlier research were not resistant in our tests, and some varieties previously rated susceptible appeared resistant in our tests. These inconsistencies were caused by differences in the races of P. teres used and by differences in growth stage of the barley plants used in different experiments. Knowledge of these effects will be used by plant pathologists and breeders to develop standardized, more comprehensive tests of resistance in barley to net blotch. This will facilitate progress in reducing the damage of this disease to barley crops throughout the world.
Technical Abstract: Net blotch, caused by Pyrenophora teres, is among the most damaging foliar diseases of barley worldwide. A knowledge of the reaction of local cultivars, putative resistant genotypes, and variability in the net blotch pathogen is necessary to develop a successful resistance breeding program. Disease response of 38 barley genotypes to 15 P. teres isolates were studied at the seedling and adult plant stages in the glasshouse, and fiel responses to net blotch were evaluated at three Moroccan locations. No tested barley was resistant to all isolates and resistance was apparently of the specific type. Pathogenic variability was great, as none of the 15 isolates were identical. For each isolate tested a specific high level of resistance was found in one or more host genotypes. Seedling and adults plants often differed in response to the same isolate. Adult plant resistance was commonly observed in response to isolate I-1, and, seedling resistance was more common to isolate I-14. Adult plant resistance of nin genotypes was undetected in seedling evaluations using isolate I-1. The seedling glasshouse and field responses of the barley genotypes varied considerably limiting the value of seedling testing for resistance. Field reaction of R and MR were consistent across the three locations for the lines Heartland, Minn 7, CI 2333, and CI 2549. The variability observed in P. teres and failure to find genotypes with resistance to all isolates suggests that breeding for resistance should emphasize pyramiding of resistance genes.