Effects of salinity on growth and yield of rice (Oryza sativa L.) and development of tolerant genotypes in Kilosa district, Tanzania

Abstract

Salinity is an ever increasing problem that reduces rice yield in many rice fields around the world. Soil salinity contributes to one of the most serious ecological and environmental problems in most of the irrigation schemes in Tanzania. Developing a salt tolerant rice genotype is one of the solutions to the problem of salinity. Marker assisted selection (MAS) is an indirect selection process where a trait of interest is selected based on a marker (morphological, biochemical or DNA/RNA variation) linked to a trait of interest rather than on the trait itself. Thus, the MAS technique was used in this study because it is very reliable in the selection of several traits associated with salinity and can also accelerate the breeding process and increase selection efficiency. Therefore, the objectives of the study were: i) to evaluate the responses of eight rice genotypes at various levels of salinity for the identification of parents for breeding program. ii) to assess farmer‘s perceptions about salinity problems occurring in their fields in the study area. iii) to estimate heritability of saltol in the new lines, and iv) to assess the marker-trait association and segregation ratio of new rice (Oryza sativa, L) lines.

A study was conducted under a controlled environment in the Department of Crop Sciences and Horticulture of the Sokoine University of Agriculture, to evaluate the responses of eight rice genotypes at three levels of NaCl concentrations (0 mM NaCL, 50 mM NaCl and 100 mM NaCl) and identify parental materials for breeding program. This was followed by a study on farmer‘s perception about the occurrences of salinity problems in their irrigated schemes. The study on farmer‘s perception was conducted in two villages (Ilonga and Chanzuru) in Kilosa District, Morogoro region involving rice farmers. The other study was conducted during April to September 2016 at Chanzuru irrigation scheme in Kilosa District to determine the characteristics of soil, and evaluate segregating populations in selected saline environment at Chanzuru irrigation scheme. The heritability and genetic advance as well as the association of marker with quantative traits were determined during the study.

During the controlled experiment, three salinity indices namely salinity tolerance index, salinity susceptibility index and % relative reduction were used along with the IRRI standard evaluation score for salinity tolerance to rank the rice genotypes in terms of their tolerance and susceptibility. The results of the evaluation of eight rice genotypes showed that SUAKOKO-10 and NERICA-L19 were the most susceptible rice genotypes in comparison with the other genotypes; therefore, they were selected to be used as recurrent parents to improve their salinity tolerance using FL478 as the donor parent.

The study on farmer‘s perception revealed that farmers had a clear understanding of salinity problems occurring and affecting the crop production in Kilosa District. Farmers perceived four major factors contributing to the problem of salinity in their areas, namely, poor quality of irrigation water, poor drainage system, inadequate rainfall and inappropriate use of fertilizers. However, poor quality irrigation water and poor drainage infrastructure were the leading factors perceived to be contributing to the problem of salinity in the areas. As a result of these factors, farmers perceived poor harvest, poor production and poor yield of the rice crops. It was also established that farmers practiced crop diversification and increased farm size in response to the growing effects of salinity on their crop production and livelihoods.

Segregating populations along with the parent materials were evaluated in a saline environment using a randomized complete block design with four replications. Fresh leaf samples from young seedlings were collected for DNA extraction and marker-trait association study as well as inheritance study. High heritability and high genetic advance were established in the new lines for all traits except grain yield per plant and 100-grain weight. Grain yield per plant was positively correlated with number of reproductive tillers and 100-grain weight. When the genotypes were scored for salinity injury, NLF3 population recorded the lowest score indicating that this population was highly tolerant to salinity as compared to other populations. The best performing genotypes among the introgression lines were NLF3 (F3 lines developed by crossing NERICA-L-19 and FL478) and SUF3 (F3 lines developed by crossing SUAKOKO-10 and FL478) for most of the traits studied. For inheritance and marker-trait association studies, the selected markers for the assessment of segregation and goodness of fit fitted well into the expected ratio of 1:2:1. The two markers loci (RM7075 and RM562) used were significantly associated with the number of filled grains per panicle and grain yield per plant in the studied rice materials.