The Effects of Planting Density on Lodging Resistance, Related Enzyme Activities, and Grain Yield in Different Genotypes of Oilseed Flax

Knowledge of planting density and lodging resistance is essential to developing effective cropping systems. This study determined (i) the lodging resistance of different genotypes of oilseed flax (Linum usitatissimum L.) under different planting densities, and (ii) the effect of density on lignin content and related enzyme activities in different genotypes in Northwest China. We hypothesized that (i) lignin content and related enzyme activities varied with different planting densities, and (ii) a planting density of 750 x 10(4) grains ha(-1) increased the lignin content and related enzyme activities of stem tissues and improved lodging resistance. The characteristics of oilseed flax from three different cultivars-'Dingya 23' (V1), 'Jinya 10'(V2), and 'Neiya 9'(V3)-were evaluated under different planting densities. Results indicated that increasing plant density increased the phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities but decreased the 4-coumarate:CoA ligase (4CL) activity and lignin content of a high-lodging-resistance cultivar. However, increasing plant density decreased the PAL and TAL activities but increased the 4CL and lignin content of a low-lodging-resistance cultivar. We conclude that plant density affected the plant lignin content by regulating the 4CL activity. Flax seed yield increases with density were mainly due to increased lignin content, bending strength, and regulated PAL, TAL, and 4CL activities. The study concluded that optimizing planting density could play an important role in crop lodging resistance and grain yields in the northwest of China.