Abstract
Genotype by environment interaction (G x E) of root characters of upland rice namely volume, fresh weight, branching and thickness was conducted with sixteen upland varieties planted in the upland ecology of four tropical environments defined by differences in soil moisture. All the root characters recorded significant genotype (G), environment (E) and G x E interaction. For root volume (RV) and root fresh weight (RFW), the environmental component accounted for over 85% of the total sum of squares (TSS) followed by the interaction component with about 11% in both cases. For root thickness (RT) and root branching (RB), however, the G x E fraction was 63% and 56.3% respectively while genotype effect was responsible for 36.5% and 30.4% respectively. The first interaction principal component (IPC1) captured over 70% of the interaction sum of squares for all the characters with the exception of RB which was 50.6%. Of the total G x E, the Genotype and Genotype by environment interaction (GGE) polygon explained over 93.6% and 93.9% for RV and RFW respectively and also captured over 80% for both root thickness and root branching. The GGE grouped genotypes with different levels of root character expression with different environments. The GGE PC1 for RT had significant negative interaction (p<0.05) with panicle number, PN (-0.506) and grain weight per plant, GWP (-0.552). The GGE PC2 for RT was however positively correlated with PN (0.533) and GWP (0.547). The GGE PC1 for RB was also negatively correlated with PN whilst the GGE PC2 for the same character was positively correlated (p<0.05) with PN (0.595) and GWP (0.574). The implications of these findings for the development of fairly stable genotype are such that different programmes of development must be instituted for different root traits, especially for the traits that showed counteracting relationship with other soil-plant factors.
