Winter wheat seedling emergence from deep sowing depths

Growers in low-precipitation (<300 mm annual) dryland wheat-fallow areas of the inland Pacific Northwest need winter wheat (Triticum aestivum L.) cultivars that emerge from deep sowing depths in dry soils. Stand establishment is the most important factor affecting winter wheat grain yield in this region. Despite poor resistance to disease, modest grain yield potential, and otter problems, the outdated soft white winter wheat (SWWW) cultivar Moro is widely sown in these dry areas, due to its excellent emergence ability, All other SWWW cultivars are semidwarfs that carry emergence-impeding Rht(1) or Rht(2) reduced-height genes, From 12 solving trials at 2 locations over 4 yr, we compared the emergence capability of Moro to (i) 8 SWWW cultivars and (ii) 16 SWWW advanced experimental Moro-replacement lines. Under both wet and dry soil conditions (soil water content in the seed zone ranged from 11 to 19 mm(2) mm(-3)), seeds were sown deep, with 110 to 160 mm of soil cover. Moro always emerged fastest and achieved the best final stand compared with the semidwarf cultivars, The advanced experimental lines, which contained either no reduced-height gene or a Rht(1), Rht(2), or Rht(8) reduced-height gene, had superior straw strength, disease resistance, and grain quality compared with Moro, The best-emerging advanced experimental lines had coleoptile lengths >100 mm, Coleoptile length was associated with emergence capability among both cultivars (r(2) = 0.71, P < 0.004) and advanced lines (r(2) = 0.62, P < 0.001), From deep sowing depths in this study: (i) cultivars and advanced lines with Rht(1) and Rht(2) reduced-height genes always emerged poorly compared with Moro: (ii) the Rht(8) reduced-height gene did not hamper emergence to the extent that Rht(1) and Rht(2) did; and (iii) several advanced experimental lines with long coleoptiles equaled or exceeded Moro for emergence.