As weeds develop resistance to a broad range of herbicides, wheat
(Triticum aestivum L.) cultivars with superior weed
competitive capacity are needed to complement integrated weed management
strategies. In this study, agronomic and morphological traits that enable
wheat to compete effectively with weeds were identified. Halberd, Cranbrook,
and 161 Cranbrook x Halberd doubled haploid (DH) lines were examined in field
experiments conducted over two growing seasons. The weed species
Lolium rigidum L. (annual ryegrass) was sown in strips
perpendicular to the direction of wheat seeding. Various traits were measured
during each season with competitive ability determined by both percent loss in
wheat grain yield and suppression of ryegrass growth. Width of leaf 2, canopy
height, and light interception at early stem elongation (Z31), and tiller
number, height at maturity, and days to anthesis were important for
competitive ability in 1999. In the previous year, length of leaf 2 and size
of the flag leaf contributed to competitiveness. Seasonal effects appeared to
have some impact on the relative contribution of crop traits to competitive
ability. The morphological traits involved in maintaining grain yield differed
from those that contributed to the suppression of ryegrass growth.
Development of the Cranbrook x Halberd chromosomal linkage map enabled the
putative identification of quantitative trait loci (QTL) associated with
competitive ability in the DH population. Many of the QTL were mapped to
similar positions in both years. Further, several traits, including time to
anthesis, flag leaf size, height at stem elongation, and the size of the first
2 leaves, were mapped to similar positions on chromosomes 2B and 2D.
Narrow-sense heritabilities on an entry-mean basis were typically high within
each year for traits associated with weed competitive ability. However, large
genotype x year interactions reduced these heritabilities, making genetic gain
through phenotypic selection difficult. The identification of QTL repeatable
over seasons indicates the potential for marker-assisted selection in a wheat
breeding program selecting for improved grain yield and weed competitiveness.
Interval mapping of growth quantitative trait loci in Japanese Black beef cattle using microsatellite DNA markers and half-sib regression analysis