Wheat yellow mosaic disease, caused by wheat yellow mosaic virus (WYMV), is transmitted by a soil-borne micro-organism. There have been many outbreaks of WYMV in southwestern Japan since the 1910s. In Hokkaido, the northernmost area of Japan, the first occurrence was reported in 1991. ‘Hokushin’, the leading variety of common wheat in Hokkaido, is susceptible to WYMV, and damage has occurred over a wide area in Hokkaido. We found that the American cultivar ‘Madsen’ was resistant to WYMV in field trials over five years. ELISA tests using an F₂ population indicated that a single dominant gene in ‘Madsen’ contributed to the resistance; however, ‘Madsen’ is a late-maturing cultivar, is not tolerant of pre-harvest sprouting, and is susceptible to snow mold. Therefore, we introduced the resistance gene by repeated backcrossing using ‘Madsen’ as the donor parent and ‘Hokushin’ as the recurrent parent, using field selection. This produced four WYMV-resistant BC₅F₄ generation lines with almost the same agronomic traits as ‘Hokushin’. The resistance gene, YmMD, derived from ‘Madsen’, was mapped on the long arm of chromosome 2D (2DL), between wmc041 and gwm349 using polymorphic SSR markers between ‘Hokushin’ and BCM₅F₄ lines.

View full abstract

Analysis of a set of half-diallel crosses for Aphanomyces root rot (black root) resistance was conducted in sugar beet (Beta vulgaris L.). Five selfed O-type parental lines and ten F₁ lines derived from half-diallel crosses between parental lines were used for analysis. Disease evaluation was carried out in an Aphanomyces-infested field in Ikeda-cho, Hokkaido, Japan for two seasons (2004 and 2005). Diallel analysis related to genetic variances and parameters was conducted using “DIALL” developed by UKAI (1989). In analysis of variance according to Walters and Morton (1978), the additive effect (a) and dominance effect (b) were significant at the 1% level. The (V_r, W_r) graph indicated that the results showed a good fit to the additive-dominance model in the 2004 season, but in 2005, the slope of the regression line of W_r on V_r in the (V_r, W_r) graph was much lower than 1, suggesting the presence of non-allelic interaction. However, the (V_r, W_r) graph of the 4×4 sub-diallel table resulting from exclusion of the array due to a parent “NK195” that greatly deviated from the V_r-W_r regression line showed a regression coefficient close to 1, indicating the absence of epistasis, also in 2005. The estimate of broad sense heritability was 0.95 in both years, and the estimates of narrow sense heritability were 0.66 in 2004 and 0.83 in 2005. Additive variance was larger than dominance variance. The average degree of dominance was 0.776 in 2004 and 0.523 in 2005, indicating incomplete dominance. The average direction of the dominant gene was minus in both years. In conclusion, the results showed that the resistance of sugar beet varieties utilizing the F₁ hybrid could be improved efficiently by the accumulation of resistant genes and by utilizing the dominance effect.

View full abstract