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Identification and Molecular Mapping of a Wheat Gene for Resistance to an Unadapted Isolate of Colletotrichum cereale

First, second, third, fourth, sixth, and seventh authors: Laboratory of Plant Pathology, Graduate School of Agricultural Sciences, Kobe University, Nada, Kobe 657-8501, Japan; and fifth author: Institute of Plant Science and Resources, Okayama University, Chuo, Kurashiki 710-0046, Japan.

To elucidate genetic mechanisms of host species specificity between graminicolous anthracnose fungi and gramineous plants, infection assays were performed with a Sorghum isolate (Colletotrichum sublineolum), a Digitaria isolate (C. hanaui), a Polypogon isolate (C. cereale), and an Avena isolate (C. cereale). They were specifically virulent on the plants from which they were isolated. When 72 wheat lines were inoculated with an unadapted isolate from Asia Minor bluegrass (Cgp29), however, some exceptional cultivars were recognized. Although most cultivars were resistant to Cgp29, ‘Hope’ was susceptible. In F₂ populations derived from crosses between three resistant cultivars—‘Norin 4’ (N4), ‘Chinese Spring’ (CS), and ‘Shin-chunaga’ (Sch)—and the susceptible Hope, resistant and susceptible seedlings segregated in a 3:1 ratio, suggesting that a major gene is involved in the resistance of each cultivar to Cgp29. In F₂ populations derived from crosses between the three resistant cultivars, all seedlings were resistant, suggesting that these three cultivars carry the same gene. This resistance gene was designated as “resistance to Colletotrichum cereale 1” (Rcc1). Analysis with the CS–Hope chromosome substitution lines and molecular mapping revealed that Rcc1 was located on the long arm of chromosome 5A. Cytologically, Rcc1 was mainly associated with hypersensitive reaction. These results suggest that major genes similar to those controlling cultivar specificity are involved in the resistance of wheat against the unadapted isolate of C. cereale.