Phenotypic characterization and genotype by environment interaction of selected rice (Oryza sativa L.) genotypes for cold tolerance in Uganda
Entale, Kidist Tolosa
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Rice is adversely affected by cold stress and which is a common problem in the highland areas of central East Africa (Uganda, Rwanda, northeast Tanzania, and Kenya) and Madagascar. Cold stress is known to cause 26% to 80% rice grain yield loss. Rice production in Uganda is restricted low altitude areas as there is a lack of cold tolerant varieties that can grow in the higher altitudes of the country. This research aimed at identifying new sources of cold tolerant rice genotypes and to estimate the genotype by environment interaction among diverse rice genotypes identified under artificial conditions. 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) day old seedlings were stressed at 10oC in cold air for 10 days and another set remained under normal ambient temperature. IRRI Standard Evaluation System (SES) 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. In addition, survival rate, seedling height, and tiller number were recorded. The results revealed significant variation in genotypic reaction against cold stress indicating high genetic diversity among screened genotypes. Eight highly cold tolerant (SCRID091-20-2-2-4, GIZA 177, NERICA 1, MET P27, MET P23, MET P60, MET P20, and MET P5) and fifteen cold tolerant varieties were identified for further genotype by environment interaction study (GEI). The highly cold tolerant genotypes can be used in rice breeding for cold tolerance. The best twenty-three cold tolerant genotypes and two susceptible genotypes were evaluated in seven environments (E): E1 (Zombo, 2017B), E2 (KAZARDI-Kabale, 2017B); E3 (BZARDI-Mbale, 2017B); E4 (Zombo, 2018A); E5 (KAZARDI-Kabale, 2018A); E6 (Bushenyi, 2018A) and E7 (Bulegeni, 2018A), which were characterized by cold weather for estimating genotype by environment interaction (GEI). Five by five alpha lattice design trials with three replication was used in each environment. Analysis of variance revealed a 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 a short duration to mature, had a better yield, and were cold tolerant in most of the test environments. The genotypes can be recommended as sources of cold tolerance in the development of cold tolerant rice varieties for environments KAZARDI-Kabale and BZARDI-Mbale. They can also be recommended for yield trail for Zombo and Bulegeni. Temperature will not be a problem for rice production in Bushenyi yield can be harvested if the rain is available.