Study of intergenotypic competition in Upland cotton, G. hirsutum L

Abstract

Competition was evaluated in four population densities to determine its effect on productivity and yield components, and to assess its importance on breeding for narrow-row culture. A mixture of three genotypes, differing in productivity and growth habit, simulated a segregating early generation, handled as a bulk, where individual plants of a given genotype are randomly surrounded by plants of other genotypes, i.t., competition occurred among distinct genotypes. Pure culture plots of the same three genotypes were grown to provide a basis for estimating intragenotypic competition as it occurs in progeny row or pedigree testing. A tall-vigorous genotype (G) was the strongest competitor in the mixture, averaging 42% more seedcotton yield than in pure culture. A semi-dwarf genotype (N) showed a reduction of 12% when growing in mixture. The most productive genotype (E) in pure stand was the weakest competitor, its yield was reduced an average of 12% in mixed culture. Competition affected the percentage of plants selected in the four population densities. As population decreased, the proportion of N and especially E diminished considerable and consequently a larger proportion of G remained. In contrast, E was selected more frequently when planted in pure culture, especially in high population densities. As population decreased and selection pressure was relaxed, similar proportions of the three genotypes were selected. This study suggests that breeding Upland cotton for high population culture might be most effective in narrow-row nurseries and that bulk breeding, at least under irrigated condition, should be avoided.