Genotype-by-environment interaction and yield performance of two Manihot esculenta Crantz varieties cultivated with legumes in two agro-climatic zones in Congo

Abstract

To assess the adaptive potential of cassava varieties introduced in Congo, the interaction of genotype-by-environment, of two improved varieties, intercropped with tree and herbaceous legumes, in two agroecological zones of Congo (Loudima and Odziba) was studied. Two types of experiments were done, one tested the following treatments: unfertilised Cassava cultivated alone, cassava + pea, cassava + mineral fertiliser and cassava + cowpea, and one also tested cassava + acacia. The assessment of site-by-variety and site-by-treatment interactions was performed using randomised complete block designs. The results revealed highly significant site-by-variety and site-by-treatment interactions for the cassava root mass. The yield of the I93-0029 variety was higher than that of I97-0162 at the two sites. The two types of genotype-by-environment interaction were reflected by the differences between their productivity according to the site. The intercrops with cowpeas (20.6 t/ha) and acacia (19.3 t/ha) gave better cassava yields mean in Loudima for both varieties, while in Odziba, intercrops with all legumes (9.7 t/ha) did not lead to better yields when compared to chemical fertilisation (16.5 t/ha) alone. Varietal selection for intercrops is therefore an important approach to be exploited, especially since the plant material is often selected for monoculture production.