The inhibitory effect of light on seed and burr development in several species of Trifolium

Abstract

The effect of light on seed and burr development was studied in 20 genotypes from four species of Trifolium. Burrs produced from spaced laterals were enclosed in plastic tubes variously shaded to produce a range of light treatments.

Light inhibited seed development to varying degrees in a range of subterranean clovers, which included strains of T. israeliticum and of all three subspecies of T. subterraneum. In four strains studied intensively the weight of seeds per burr decreased linearly with increases in the logarithm of the light intensity. Light had no effect on seed development in two other geocarpic species, T. batmanicum and T. globosum, which do not actually bury their burrs. The weight of both the pod walls (pericarps) and the sterile calyces was reduced by light in all strains of T. subterraneum. Light also reduced the weight of pod walls in T. israeliticum but had little effect on the production of sterile calyces.

Variation in the pattern of light response between plants of the Seaton Park strain of T. subterraneum was found to be associated with genetically distinct lines.

Four of the subterranean clover strains commonly produced twin-seeded pods in dark and low light treatments. The incidence of twinning in these strains appeared to be greater than that normally encountered in buried burrs.

The ranking of strains of T. subterraneum for susceptibility to light agreed reasonably well with the ranking of the same strains, by others, for seed development above ground. Seaton Park and, to a lesser extent, Dinninup were exceptions in that they were more severely inhibited by light than by lack of burr burial. It is suggested that another factor in addition to light may be involved in the response to burr burial.