Winter Wheat Cultivars with Temperature-Sensitive Resistance to Wheat streak mosaic virus Do Not Recover from Early-Season Infections.
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Wheat streak mosaic virus (WSMV), Triticum mosaic virus, and Wheat mosaic virus, all vectored by the wheat curl mite Aceria tosichella Keifer, frequently cause devastating losses to winter wheat production throughout the central and western Great Plains. Resistant 'Mace' and 'RonL are commercially available and contain the wsm1 and wsm2 genes, respectively, for resistance to WSMV. However, the resistance in these cultivars is temperature sensitive, ineffective above 27C, and does not protect against the other common wheat viruses. The majority of winter wheat in the Southern Great Plains is planted in early fall as a dual-purpose crop for both grazing and grain production. Early planting exposes wheat plants to warmer temperatures above the threshold for effective resistance. Studies were conducted to determine whether the resistance found in these cultivars would give infected plants the ability to recover as temperatures cooled to a range conducive to effective genetic resistance. RonL, Mace, 'TAM 111', 'TAM 112', and 'Karl 92' wheat were infested with WSMV viruliferous mites at temperatures above the resistance threshold. After the initial 4-week infection period, plants were subjected to progressively cooler temperatures during the winter months, well below the resistance threshold. Throughout the study, plant samples were taken to quantify virus titer and mite populations. Resistant RonL and Mace, which became severely infected during the initial infection period, were not able to recover even when temperatures dropped below the resistance threshold. However, TAM 112 showed resistance to WSMV but, more importantly, it also showed resistance to the wheat curl mite, because the mite population in this cultivar was significantly lower than on all other cultivars. The results of this study are significant in that they represent the first evidence of quantitative resistance to both WSMV and the wheat curl mite in a single wheat cultivar. Resistance to the wheat curl mite has potential to reduce losses to all mite-vectored virus diseases of wheat and not just WSMV.