VARIATION IN RESISTANCE TO THE GRAIN APHID, SITOBION-AVENAE (STERNORHYNCA, APHIDIDAE), AMONG DIPLOID WHEAT GENOTYPES - MULTIVARIATE-ANALYSIS OF AGRONOMIC DATA

A collection of 87 ancient wheat genotypes, 67 Triticum monococcum, 13 Triticum boeoticum, seven Triticum urartu and one cultivar of the mod ern wheat Triticum aestivum (variety 'Arminda') were evaluated for res istance to the cereal aphid Sitobion avenae, the main damaging aphid p est on winter wheat in Europe. The intrinsic rate of natural increase (r(m)), which is regarded as a good estimate of the fitness of an aphi d population, was used as an indicator for the level of plant resistan ce. Differentiation of the 88 plant genotypes into four distinct group s was achieved with a cluster analysis of the r(m) values. The modern wheat 'Arminda' was more susceptible than any of the ancient wheat gen otypes tested (r(m) = 0.24, i.e. the aphid population doubled every 2. 6 days). A second group of 19 plants ranged from relatively susceptibl e to moderately resistant (0.17 < r(m) < 0.21). Fifty-one plants were allocated to a third group and classified as resistant (0.09 < r(m) < 0.16). The last group contained 17 genotypes with a high level of resi stance where aphid fitness was greatly reduced (0.02 < r(m) < 0.09, i. e. the aphid population doubled every 11.4 days or 7.7 days, respectiv ely). Clustering of the accessions into the different phenetic groups did not follow the geographical origin of the wheat genotypes or the s pecies to which they belong. These results show that ancient diploid w heats, all characterized by the genome A, present considerable interes t for plant breeding for resistance to S. avenae in modern wheat. The potential use of these strong and partial sources of resistance for in troduction of a stable and durable form of resistance to S. avenae in wheat is discussed.