Breeding of Italian Ryegrass (Lolium multiflorum Lam.) for a low nitrate concentration by seedling test

In Japan, nitrate poisoning in ruminants caused by the accumulation of nitrate in forage crops is a serious concern. In this study, 3 cycles of phenotypic recurrent selection for nitrate concentration on a dry matter basis were conducted for Italian ryegrass ( Lolium multiflorum Lam. cv. Nioudachi) to develop a breeding method using a seedling test. The seedling test involved the nitrate analysis of a shoot from a plant grown for 6 or 8 weeks in the presence of 50 mM KNO3. The selection intensity was approximately 0.07 for each cycle. The realized heritability of the third generation was calculated to be 0.21 for seedlings and 0.57 for adult plants. In a pot experiment, the nitrate concentration of the adult plants of the third generation was found to be 60% of the value for the original population at an early heading stage. The reduction is related to the increase in dry matter (DM) content as well as the decrease in nitrate concentration on a fresh matter basis. The original and selected populations did not differ in the heading date. The concentrations of K, N and P in the third generation decreased with the increase of DM content, whereas Ca and Mg concentrations remained constant. Variation in the nitrate concentration was found among varieties on the market. In conclusion, the ability to accumulate nitrate is a quantitative genetic trait of Italian ryegrass and large-scale selection for the breeding of low nitrate populations is possible using a seedling test.