Diallel analysis of competition between diploid and tetraploid genotypes of Secale cereale grown at two densities

Abstract

SUMMARYTwo inbred diploid lines of Secale cereale L. and their derived tetraploids were grown together with a commercial diploid and tetraploid in all possible pair combinations in a pot experiment. Comparisons between lines and varieties were made in respect to dry weight measured at 30 weeks.The competitive effects within mixtures were not compensatory, the commercial varieties tending to increase in dry weight more than the homozygous inbred lines decreased. This gave rise to mixture means which tended to exceed their mid-constituent values.The analysis of reciprocal differences in dry weight showed that the effects of competition between any one genotype and its associate in mixtures were constant (alpha competition), the sign and magnitude of the alpha effect being related to the pure stand values of the genotype.The mean effect of competition was to increase the difference in dry weight between genotypes by 2·108 g for each gram by which the genotypes differed when grown alone. In each case the values for genotypes with the higher dry weight increased in mixture whereas the values for those with lower dry weights decreased.Not surprisingly, the commercial varieties were found to be better competitors than the inbred lines, but of more interest was the ineffectiveness of chromosome doubling on competitive ability. Under the conditions of density and fertility reported here, the tetraploid inbred lines could not be distinguished from their diploid progenitors either in their competitive ability or in their reaction to increased density when grown in mixtures. The same is true for the tetraploid and diploid commercial varieties.