Morphological and Physiological Traits Limiting Grain Production in Goatgrass.

Goatgrass, a wild progenitor of bread wheat, is a source of biotic-resistance genes. It is used to develop synthetic hexaploid wheat to broaden genetic variation for grain yield. This study investigated traits limiting grain yield in Aegilops tauschii. Accession (G3489) with non-brittle rachis, a tetraploid durum wheat and four hexaploid bread wheats: landrace, tall old, semidwarf and dwarf cultivars, were evaluated for pheno-morphologic traits, main stem water-soluble carbohydrate (WSC) content, rate of grain growth, and grain yield under well-watered and droughted field conditions across two years. Goatgrass was later in maturity than bread and durum wheats by 7 days and 50% of tillers produced per plant (14) were non-effective. Number of grains/main spike and grain weight in tauschii was 29 and 11mg, respectively; they ranged from 37 to 58 and from 26 to 60mg in durum and bread wheat. Stem length in tauschii was greater or similar to dwarf bread wheat, but stem weight (377mg) and WSC content (63mg) was less than other species; 1556 and 435mg, respectively. Stem WSC concentration in tauschii was 15.9%; it ranged from 15.0 to 30.4% in other species. Duration of linear grain growth was similar in all species (30 days). Rate of linear grain growth in tauschii (18.5mg/spike/day) was lower than durum and bread wheat: 37.1 to 74.1mg/spike/day. Grain yield/spike in tauschii was 0.54 and 0.34g, in durum was 2.68 and 1.25g, and in bread wheat was 2.18 and 1.27g under well-watered and droughted conditions, respectively. Stem WSC content (84mg) and current assimilates (456mg) contribution to grain yield in tauschii under well-watered conditions was significantly less than other species: 353 to 1174mg and 1506 to 2061mg, respectively. Sterile non-effective tillers and low amount of stored WSC in stem in tauschii, with limited current assimilates, severely constrains grain growth which restricts grain yield in synthetic wheat.