Disruptive Selection in Crop Development

Abstract

Cultivated sorghum was developed from a single wild species of the subsection Avundinacea by disruptive selection. It was maintained in the presence of the wild type under disruptive selection in spite of considerable gene flow between the two groups. An intermediate population consisting of early-generation hybrids and homozygous lines was established from the natural wild and cultivated populations. The presence of recently abandoned cultivations and field margins has enabled this intermediate population to become established and persist. The existence of the intermediate population ensures continued intro-gression between the wild and cultivated sorghums and enhances the variability of the cultivated crop whilst the wild type becomes modified in the direction of the cultivated forms. The development of maize can be explained along the same lines except that the crop is of greater antiquity and so divergence has continued further. The pattern Tripsacum-teosinte- maize of maize parallels the wild-intermediate-cultivated pattern of sorghum. The intermediate population could act as a bridge to transfer polyploidy from the wild type to the cultivated crop or polyploidy might arise within the intermediate population. This is shown in Sorghum almum and Zea perennis. [Cf. XXXV, 6435].