Genetic Analysis of a Hulless × Covered Cross of Barley Using Doubled‐Haploid Lines

Abstract

The effects of the hulless (nud) and rough‐awned (Raw1) 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 × covered cross, (ii) detect additive × 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’ × ‘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 hull. This suggests that it is possible to breed for high‐yielding hulless barley cultivars. Additive × 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 × 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.

Effect of the nud gene on grain yield in barley

“…In Foggia autumn, naked DHs differed from hulled ones also in terms of PH and HD. In this case, the association with a lower PH in the naked DH group is in agreement with the observations of Choo et al (2001) for naked and hulled doubled haploid (DH) lines (like in our case derived from a single hulled × hulless cross), and of Thomason et al (2009) in naked and hulled breeding lines. It could also suggest the existence of either pleiotropic or linked effects of the nud gene.…”

“…In contrast to Choo et al (2001), although in different environments and materials, our results did not confirm that the nud locus had pleiotropic effects either on PH or on STM, on GPS, on HD, or on susceptibility to mildew (ML). This could mean that the associations observed for example by Thomason et al (2009) and Choo et al (2001) with fewer heads/plants per m 2 , and by Thomason et al (2009) with fewer grains per spike were rather due to different, non-isogenic, hulless genotypes used, and/or to environmental factors, or to grain damage conditions that reduced the emergence of hulless barley, than to the direct or even pleiotropic effects of the nud gene.…”

“…This could mean that the associations observed for example by Thomason et al (2009) and Choo et al (2001) with fewer heads/plants per m 2 , and by Thomason et al (2009) with fewer grains per spike were rather due to different, non-isogenic, hulless genotypes used, and/or to environmental factors, or to grain damage conditions that reduced the emergence of hulless barley, than to the direct or even pleiotropic effects of the nud gene.…”

“…For example, McGuire and Hockett (1981) detected genetic interactions of the nud and Lks2/lk2 (long-awned/short-awned) loci with several malting quality traits. Choo et al (2001) hypothesized a pleiotropic effect of the naked gene on plant height, whereas direct effects or linkage with other QTLs have been suggested for other quality-related traits. No associations with either smut or scald resistance, or with heading date, maturity and spike density were found by these authors.…”

“…After the two experiments, the use of such advanced backcross materials strongly suggests that the nud gene per se, when properly introgressed into a hulled background, only leads to irrelevant differences in yield, together with a reduction in grain size, as observed by Choo et al (2001) and Thomason et al (2009). This in turn leads to a HI reduction, exclusively due to the absence of the glume weight.…”