Effects of irrigation on stem lignin and breaking strength of winter wheat with different planting densities

Abstract

Increasing planting density is an important cultivation approach to improve wheat single yield. In field production, over irrigation under densified population conditions can easily cause lodging. Therefore, the lodging resistant wheat cultivar JM22 and the lodging sensitive wheat cultivar SN16 was used as experimental materials. Two irrigation treatments [rain-fed and spring irrigation (at jointing and anthesis stage)] were set with five planting densities (150 × 104 plants ha−1, 225 × 104 plants ha−1, 300 × 104 plants ha−1, 375 × 104 plants ha−1 and 450 × 104 plants ha−1). Lignin accumulation and its monomers (guaiacyl, syringyl and p-hydroxyphenyl) in combination with the apparent and microanatomic characteristics of the basal second stems, were determined to elucidate effects of irrigation on the formation of breaking strength in wheat stems at different planting densities. The results showed that the most important factors affecting the breaking strength of stems were different in different stages and different treatments. Through multiple stepwise regression analysis, it was found that under low density (150 × 104 plants ha−1) conditions, irrigation decreased breaking strength of stem mainly by affecting lignin accumulation and its subunits. However, at medium and high density (225 × 104 plants ha−1-375 × 104 plants ha−1), the decrease of stem breaking strength caused by irrigation was the result of the co-regulation of lignin metabolism, stem microscopic and morphological characteristics. At anthesis stage, when irrigated under the condition of low density (150 × 104 plants ha−1), the content of G subunit increased by 100 μg g−1, the stem breaking strength increased by 0.4 N. At medium density (225 × 104 plants ha−1-300 × 104 plants ha−1), irrigation increased S subunit content by 100 μg g−1, which resulting in high stem breaking strength by 0.5 N. However, at high density (375 × 104 plants ha−1-450 × 104 plants ha−1), along with H subunit content was increased by 10 μg g−1, the stem breaking strength was decreased by 0.14 N. Under irrigated and densified populations conditions, the decreasing range of wall thickness (−13.53%), stem filling degree (−16.65%) and the increasing range of H monomer ratio (15.77%) of high lodging resistance varieties were lower than those of SN16. Therefore, it held better ability to resist adverse environment and maintain lodging resistance. In this experiment, on the basis of irrigation (at jointing and anthesis stage) and 25 × 104 plants ha−1 planting density resulted in the highest yield (10,325.03 kg ha−1) and moderate stem.