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

In Japan, nitrate poisoning in ruminantscaused by the accumulation of nitrate inforage crops is a serious concern. In thisstudy, 3 cycles of phenotypic recurrentselection for nitrate concentration on adry matter basis were conducted for Italianryegrass (Lolium multiflorum Lam. cv.Nioudachi) to develop a breeding methodusing a seedling test. The seedling testinvolved the nitrate analysis of a shootfrom a plant grown for 6 or 8 weeks in thepresence of 50 mM KNO₃. The selectionintensity was approximately 0.07 for eachcycle. The realized heritability of thethird generation was calculated to be 0.21for seedlings and 0.57 for adult plants. Ina pot experiment, the nitrate concentrationof the adult plants of the third generationwas found to be 60% of the value for theoriginal population at an early headingstage. The reduction is related to theincrease in dry matter (DM) content as wellas the decrease in nitrate concentration ona fresh matter basis. The original andselected populations did not differ in theheading date. The concentrations of K, Nand P in the third generation decreasedwith the increase of DM content, whereas Caand Mg concentrations remained constant. Variation in the nitrate concentration wasfound among varieties on the market. Inconclusion, the ability to accumulatenitrate is a quantitative genetic trait ofItalian ryegrass and large-scale selectionfor the breeding of low nitrate populationsis possible using a seedling test.