Intergenotypic Competition and Competition with Associated Crops in Cassava 1

Abstract

The competitive ability (defined as root yield in mixture/root yield in monoculture) of Cassava (Manihot esculenta Crantz) genotypes in monoculture, mixed populations and in multiple cropping systems was studied in the field. Strong competitors produced more roots and stems in genotypic mixtures than in monoculture and did so at the expense of weak competitors. Competitive ability was positively correlated with spacing response and stem and leaf-weight at harvest, but negatively correlated with harvest index (proportion of root weight to total plant weight) and root yield in monoculture. Because of the negative correlation of competitive ability with root yield in monoculture, improvement in the productivity of cassava cultivars will likely occur through improvements in plant efficiency and at the expense of competitive ability. It is therefore recommended that in selecting high yielding genotypes potentially adapted to productive environments, strong competitors should be eliminated from segregating populations. Modest yield reductions (9 to 13%) occured when cassava was planted in association with beans (Phaseolus vulgaris L.) or soybeans [Glycine max (L.) Merrill]. Beans, planted in association with cassava, had non-significant reductions in yields whereas yields of soybeans were severely reduced. Yields of beans and soybeans were negatively correlated with vegetative vigor of the associated cassava genotype, but were not correlated with yield or intergenotypic competitive ability of the cassava genotype. Cassava can be planted in association with short-duration crops without sacrificing much in the yields of either crop. High-yielding cassava genotypes with low vegetative vigor would bring about high combined yields of cassava and the associated crop.