Longer coleoptiles improve emergence through crop residues to increase seedling number and biomass in wheat (Triticum aestivum L.)

Abstract

Crop residues protect soils from erosion, reduce soil water evaporation and increase soil organic matter. Yet management of stubbles for cropping can be difficult. Surface-retained residue can act as a mechanical barrier to slow emergence and reduce seedling biomass. Longer coleoptiles improve seedling emergence with deep sowing and may assist where stubble load is large. In a glasshouse study, six wheat and barley genotypes were sown at 30 and 50 mm depth into pots containing pasteurised soil. Unweathered sorghum, canola and wheat stubble were added at 0, 3 and 6 t/ha equivalents to the soil surface and pots watered above or below the stubble. Stubble species and watering regime had little effect on seedling growth. However, deeper sowing and increased stubble mass adversely affected most seedling characteristics particularly slowing seedling emergence and reducing tiller number to decrease plant biomass (environmental correlations (re) of −0.98** and 0.88**, respectively). Shorter coleoptile Rht-B1b wheats ‘Banks’ and ‘Janz’, and barley ‘Beecher’ emerged slower and abnormally with thicker stubble, and had more sterile tillers to reduce total tiller number and biomass. Deeper crowns for these genotypes also resulted in proportionally less biomass located above the stubble. The converse was true of long coleoptile ‘Vigour 18’, ‘Halberd’, and its Rht8 progeny, ‘HM14bS’ which were less affected by stubble mass and sowing depth. In a corresponding field study, increasing wheat stubble mass from 0 to 3 and 6 t/ha delayed seedling emergence and decreased plant number to reduce biomass. Short coleoptile wheat genotypes ‘Hartog’ and ‘Janz’ emerged slower and produced less biomass at 3 and 6 t/ha of stubble than long coleoptile wheat genotypes ‘Halberd’ and ‘HM14bS’. Emergence of seedlings sown at 50 mm depth with 6 t/ha overlying stubble was similar to that sown at 120 mm with no stubble, reflecting the similar impact of retained residues to deep sowing. Genetic variation for coleoptile length and availability of gibberellin-responsive dwarfing genes such as Rht8 will allow development of long coleoptile wheats for deep sowing or where stubble retention is practiced.