The aim of this study was to estimate the genotype by environment interaction of artificially identified cold tolerant rice genotypes in the highland cooler parts of Uganda. The best twenty three cold tolerant genotypes and two susceptible genotypes were evaluated in seven environments, which were characterized by cold weather. Five by five alpha lattice design with three replications was used in each environment. Analysis of variance revealed significant GEI effect in most of the cold tolerance indicator traits. Leaf wilting score was one of the major measures of cold stress observed on evaluated genotypes and it was chosen for demonstration of AMMI ANOVA and GGE-biplot. AMMI analysis showed there were highly significant environments, genotypes and GEI effects on leaf wilting score. The partitioning of total sum of squares (TSS) revealed that the environment effect was a predominant source of variation followed by GEI and genotype. The first two PCA on GGE-biplot explain 72.72% of the total variation of GEI. In general, rice genotypes SCRID091-20-2-2-4-4, MET P9, MET P40, NERICA 1 and GIZA 177 took short duration to mature, had better yield and were cold tolerant in most of test environments.

Rice crop is adversely affected by cold stress which is a common problem in the highland areas of central East Africa (Uganda, Rwanda, north east Tanzania and Kenya) and Madagascar. Cold stress is known to cause 26% to 80% yield loss. Currently, rice production in Uganda is mostly growing to the low altitude areas as there is lack of cold-tolerant varieties that can grow in the higher altitudes of the country. None of the released varieties in Uganda are tolerant cold. The few cold-tolerant lines that have been identified are short-grain types, though Ugandan consumers generally prefer long-grain size. This research aimed at identifying new sources of cold tolerant rice genotypes with preferred traits. A total of 50 lines arranged in a 5x10 alpha lattice design with two replications were used for both stressed and non-stressed experiments. Twenty one (21) days old seedlings were stressed at 10oC in cold air for 10 days and the other remained under normal ambient temperature. IRRI Standard Evaluation System (SES, 2013) was used to score the effect of cold stress on leaf morphology (leaf wilting score) and on leaf color (leaf yellowing score) after 7 day recovery. This study revealed eight highly cold tolerant (SCRID091-20-2-2-4, GIZA 177, NERICA 1, MET P27, MET P23, MET P60, MET P20 and MET P5) in which only GIZA 177 was short grain and fifteen tolerant varieties (MET P32, MET P11, MET P2, MET P17, MET P3, MET P24, MET P16, MET P37, MET P18, MET P9, MET P40, MET P31, MET P39, MET P22, MET P36) were identified.