Crop mimicry in weeds

Abstract

The selective forces imposed by agricultural practices have resulted in the evolution of agricultural races of weeds or agroecotypes. Some agroecotypes are intimately associated with a specific crop. Such associations can involve a system of mimicry, whereby the weed resembles the crop at specific stages during its life history and, as a result of mistaken identity, evades eradication. Mimetic forms of weeds are most likely to be selected by handweeding of seedlings or by harvesting and seed cleaning procedures. A striking example of morphological and phenological resemblance is found in the cultivated rice mimic, Echinochloa crus-galli var. oryzicola, a native of Asian rice fields but now widely distributed in rice-growing areas of the world. Comparative studies of the growth, devel-opment and patterns of phenotypic variation of cultivated rice, E. crus-galli var. oryzicola and E. crus-galli var. crus-galli demonstrate that the crop mimic is more similar to rice in many attributes than it is to its close relative. It is proposed that intense handweeding practices in Asia constitute the main selective force favoring the evolution of rice mimicry in E. crus-galli var. oryzicola. © 1983 The New York Botanical Garden.