Genetic analysis of a hulless x covered cross of barley using doubled-haploid lines

The effects of the hulless (nud) and rough-awned (Rawl) genes are not fully understood in hulless barley (Hordeum vulgare L.). A study was initiated to (i) determine the potential of hulless lines in a hulless X covered cross, (ii) detect additive X additive epistasis and estimate genetic correlations, and (iii) determine the effects of hulless and rough-awned genes on 11 agronomic traits of barley. Fifty covered lines and 48 hulless lines derived from a 'Kunlun no. 1' X 'CIMMYT no. 6' cross were evaluated for grain yield, test weight, seed weight, height, heading date, and maturity at two locations in Eastern Canada (Charlottetown and Ottawa) in 1998. Plant density, smut resistance, and scald resistance were also recorded at Charlottetown, while spike density was estimated at Ottawa. The 48 hulless lines contained 82 to 100% hulless kernels. At least one hulless line yielded similar to the highest yielding line if it was adjusted by the weight loss of the bull. This suggests that it is possible to breed for high-yielding hulless barley cultivars. Additive X additive epistasis was detected for some of the traits. Yield was significantly correlated with test weight, seed weight, and height. In Eastern Canada, hullessness was associated with 17% lower plant density, 11 to 18% shorter plant height, 15 to 19% lower seed weight, 20 to 21% higher test weight, and 21 to 36% yield reduction. Hullessness, however, was not associated with heading date, maturity, smut resistance, scald resistance, and spike density. Since hulless progeny could have lower emergence rates and shorter plant heights, hulless barley breeding programs should avoid propagating segregating materials from hulless X covered crosses in bulk populations, as many hulless plants may be eliminated by competition. Rough-awned hulless barley had more hulless kernels than smooth-awned. Therefore, selection for rough-awned plants could improve the threshability of hulless barley.