Tillering responses to the light environment and to defoliation in populations of perennial ryegrass (Lolium perenne L.) selected for contrasting leaf length

Tillering responses to the light environment and to defoliation were studied in two populations of perennial ryegrass (Lolium perenne L.) selected for contrasting leaf lengths. The objective of this study was to determine whether differences in tillering responses between populations, as a result of management practices, affected their competitive ability. Young seedlings were exposed, under controlled conditions, to defoliation, neutral shading (decreased photosynthetic photon flux), low red:far-red ratio and/or decreased blue li!:ht. Selection for longer leaves reduced the tillering rate. After defoliation, this difference between short- and long-leaved populations was magnified. Defoliation decreased both site filling and phyllochron of the long-leaved population but had no effect on the short-leaved population. Lowering the photosynthetic photon flux reduced the phyllochron in both population. Decreasing the red:far-red ratio reduced tillering rate by reducing site filling, whereas decreasing blue light had no significant effects on tillering. Tillering responses to photosynthetic photon flux and to red:far-red ratio were similar in the two populations selected for contrasting leaf length. The implication of these tillering responses in defining the competitive ability of the grass plants is discussed in relation to their management. (C) 1999 Annals of Botany Company.