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 resistance 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 crosses between susceptible bread wheat (Triticum aestivum) cultivars and resistant accessions of Aegilops ovata and Triticum timopheevii, seed set ranged from 2.7% to 42.6%, depending on the cross. Some reciprocal crosses failed to produce fertile plants. For hybrids derived from crosses between T. aestivum and T timopheevii, the percentage of chromosomes forming bivalents increased from 64.6% to 79.7% after selfing and to 88. 1% after backcrossing. In hybrids between Ae. ovata and T. aestivum, chromosomes formed bivalents at a frequency of 56.6% when the wheat parent was the Chinese Spring pairing mutant ph1b and 5.1% when the wheat parent was the bread wheat line H-186. Families derived from these crosses were screened for resistance to common root rot in the greenhouse and the field. No increase in resistance was found in families derived from crosses of common wheat with T timopheevii. However, five families from crosses of hexaploid wheat with Ae. ovata had improved levels of resistance and yields similar to agronomically adapted wheat cultivars.