Breeding Winter Wheat for Improved Powdery Mildew Resistance and Weed Suppressive Ability against Italian Ryegrass.

摘要

Interest in breeding wheat (Triticum aestivum L.) cultivars adapted to organic production systems is growing in response to rapidly expanding market opportunities in the southeastern United States. Breeding for resistance to biotic stresses is a major focus of the North Carolina State University small grains breeding program. Resistance to these pests and diseases is particularly important in organic systems, where the use of synthetic fungicides and insecticides is prohibited. Resistance to powdery mildew (Blumeria graminis DC f. sp. tritici) and weed suppressive ability against Italian ryegrass ( Lolium perenne L. ssp. multiflorum (Lam.) Husnot) are considered high priority traits for organic wheat producers in North Carolina. Emphasis on breeding for novel sources of powdery mildew resistance is essential because of the rapid evolutionary potential of the pathogen. Italian ryegrass, a major weed in small grain crops, has been identified as a major limitation to organic wheat production in the region. Although Italian ryegrass is controlled with herbicides in conventional production, the efficacies of popular chemical herbicide classes are threatened by the rapid expansion of resistant biotypes. T herefore breeders in the region are increasingly interested in developing weed suppressive wheat cultivars that suppress Italian ryegrass growth and reproduction and complement chemical herbicide options. The wheat germplasm line NC09BGTUM15 (NC-UM15) possesses the first form of powdery mildew resistance introgressed from Aegilops neglecta Req. ex Bertol. Evaluations of F 2:3 families derived from the cross NC-UM15 x 'Saluda' indicated that a single dominant gene, MlUM15, conferred disease resistance. Molecular markers specific to chromosome 7AL segregated with the resistance gene. The multi-allelic Pm1 locus also maps to this distal region of chromosome 7AL. Detached leaf tests revealed that NC-UM15 had a different disease response pattern from lines possessing alleles of the Pm1 complex. Allelism tests with Pm1 will be required to elucidate the relationship between MlUM15 and other Pm loci on 7AL. Research was conducted to identify indirect methods of selection for weed suppressive ability of winter wheat cultivars that correlate well with Italian ryegrass to wheat biomass ratios. Italian ryegrass seed head density and visual estimates of Italian ryegrass biomass during grain fill were highly correlated with Italian ryegrass to wheat biomass ratios and are considered appropriate indirect methods of selection for weed suppressive ability. Fifty-three entries from the North Carolina Official Variety Test (NC OVT) were evaluated for weed suppressive ability against Italian ryegrass in order to identify wheat morphological traits and molecular markers that could facilitate indirect selection for weed suppression. Weed suppressive ability was correlated (P < 0.05) with high early vigor (Zadoks GS 25 and 29), erect growth habit (Zadoks GS 29), high leaf area index (LAI) (Zadoks GS 31), high vigor rating (Zadoks GS 55), and height throughout the growing season in three of four sites. The winter-type short vernalization allele vrn-B1a-in1 was found more commonly than expected by chance among highly weed suppressive lines at both sites in 2012. Research was also conducted to test the relative importance of allelopathy and competitive ability on weed suppression outcomes in the field. Fifty-eight wheat lines from the NC OVT were screened for allelopathic activity against Italian ryegrass in a seedling bioassay. Eight strongly and weakly allelopathic lines with varying final height were then evaluated for weed suppressive ability in the field. Although the allelopathic activity of genotypes differed significantly in the seedling bioassay, no correlations between allelopathy and weed suppression outcomes were found in any of the field sites. Therefore, breeders in the southeastern United States should focus their efforts on improving competitive traits within adapted germplasm in order to achieve maximum gains in weed suppressive ability.