Genetic Studies of Rice (Oryza sativa) For Improvement of Yield And Aroma in Togo

ABSTRACT

In Togo, the quantity of rice produced is very low compared to the needs of the country. Farmers and consumers prefer aromatic rice. The main objective of this research was to increase the local production and supply farmers with aromatic and higher yielding varieties. It was conducted to lay the foundation of a rice breeding programme in Togo. Therefore, the research investigated farmers’ preferences and production constraints, established a germplasm collection and studied its genetic diversity, characterized the germplasm for yield and aroma, developed aromatic and high yielding F1 hybrids and estimated genetic parameters. The methods used to achieve the set goals consisted of focus group discussions and questionnaire survey to record information from farmers, collection of accessions around the country through prospecting survey, genetic diversity studies (notably principal components and cluster analyses), phenotypic and genotypic characterization of the germplasm for aroma and yield, as well as crosses of the parents identified (using the North Carolina Design II) and genetic analysis [notably Genotype by Environment (GxE) interactions, combining ability and genetic variance components] of yield and its component traits at four locations. From the participatory rural appraisal, absence of aroma in the new varieties introduced was the main reason for which farmers failed to adopt them. Their major preferences were presence of aroma, yield and earliness. Birds, insects and iron toxicity were their major production constraints. Collected germplasm comprising of 50 accessions were grouped, after diversity study using 30 agro-morphological traits and 5,736 informative Single Nucleotide Polymorphism (SNP) markers, in four and five clusters respectively, with 13 distinct samples of IR 841, the most widely cultivated aromatic rice variety in the country. Three aromatic (IR 841_Sot, Orylux 5 and Chapeau vert) and six high yielding (Chinoivi, Sipi, Berice 21, Gambiaca_Dan, Londo londo and Wita 4) parents were selected from the characterization, and used respectively as male and female parents to develop 18 F1 progeny iii families. The evaluation of the 18 F1s and their nine parents in the four agro-ecological zones of the country showed large phenotypic variability in the performance of the 27 genotypes for yield and its component traits. The hybrid N3A1 had the highest yield across the sites: 13 t/ha. Significant GxE interactions were detected for the four traits: grain yield, number of panicles per plant, number of grains per panicles, and 100-grain weight. The site Adéta produced more stable yield and number of panicles per plant but had the lowest performance for all the traits. All the traits were highly heritable (> 0.85) except for yield. The parent N5 had a significant general combining ability (GCA) for number of grains per panicle, and the hybrids N1A1 and N6A3 had significant specific combining ability (SCA) for 100-grain weight. No parent nor hybrid had significant GCA nor SCA for yield, showing the challenges to develop F1 hybrid rice varieties for farmers with these nine parents used. However, the progeny families from the parent N5 viz N5A1, N5A2 and N5A3 will be advanced using single seed descent selection method.