TRANSFER TO BREAD WHEAT OF RESISTANCE TO COMMON ROOT-ROT [COCHLIOBOLUS-SATIVUS] IDENTIFIED IN TRITICUM-TIMOPHEEVII AND AEGILOPS-OVATA

Accessions of Triticum and Aegilops species showed a wide range of res istance to common root rot caused by Cochliobolus sativus. The genomes G, M, and U were found to be more resistant than A, B, or D. In cross es between susceptible bread wheat (Triticum aestivum) cultivars and r esistant accessions of Aegilops ovata and Triticum timopheevii, seed s et ranged from 2.7% to 42.6%, depending on the cross. Some reciprocal crosses failed to produce fertile plants. For hybrids derived from cro sses between T. aestivum and T timopheevii, the percentage of chromoso mes forming bivalents increased from 64.6% to 79.7% after selfing and to 88. 1% after backcrossing. In hybrids between Ae. ovata and T. aest ivum, chromosomes formed bivalents at a frequency of 56.6% when the wh eat parent was the Chinese Spring pairing mutant ph1b and 5.1% when th e wheat parent was the bread wheat line H-186. Families derived from t hese crosses were screened for resistance to common root rot in the gr eenhouse and the field. No increase in resistance was found in familie s derived from crosses of common wheat with T timopheevii. However, fi ve families from crosses of hexaploid wheat with Ae. ovata had improve d levels of resistance and yields similar to agronomically adapted whe at cultivars.