OUMAROU GOITA 

GENETIC IMPROVEMENT OF ALKALINITY TOLERANCE IN RICE IN OFFICE DU NIGER IN MALI 

ABSTRACT

Alkalinity stress is one of the most important abiotic stresses limiting rice production in irrigated systems. Alkalinity stress during seedling stage widely affects irrigated rice production of Office du Niger in Mali. The development of rice cultivars that tolerate alkalinity stress condition has been hindered by the lack of an elaborate breeding program. The objectives of this study were: (i) to evaluate and validate production constraints and varietal preferences of rice farmers in alkalinized zones of Office du Niger; (ii) to identify alkaline tolerant accessions and their association with SSR markers and, (iii) to characterize phenotypically F2 progenies at seedling stage in alkaline hydroponic solution.

Participatory rural appraisal was conducted in three (3) highly alkalinized zones of Office du Niger. Two (2) villages per zone were involved in the study. Fertilizer cost, water management, inadequate agricultural equipments and declining soil fertility were identified as the main constraints of rice production. Overall, alkalinity was the most important abiotic stress affecting rice production. Crop rotation; use of organic matters; ploughing followed by flooding and use of tolerant varieties were the strategies developed by farmers to overcome alkalinity. Taste and swelling for home consumption; grain color and size for marketing were farmers preferred traits. Kogoni 91-1, BG 90-2 and Adny 11 were identified as farmer preferred varieties. Research priorities important to the farmers, included: alkalinity tolerance at seedling and reproductive stages combined; yield and taste and yield alone. Improvement of these characters in new varieties with alkalinity tolerance would enhance productivity with likely positive impact on small scale farmers’ food security, incomes and livelihoods. Farmers had high interest in participatory varietal selection and participatory plant breeding. The morphological and physiological analysis relationships between different rice accessions revealed four accessions (Sahel 210, Damodar India (IRGC 17038), CSR 10 and CSR11) in the same group of the tolerant check (Pokkali).

Genetic diversity and association of Simple Sequence Repeat (SSR) markers with alkalinity tolerance were detected in a set of 26 rice genotypes. Among SSR markers used for morpho-physiological characters, RM208 was significantly (P-value = 0.01) associated with the potassium content in the flag leaves at 37% correlation coefficient. Phenotypic and genotypic association studies identified the accessions Sahel 210, Damodar India (IRGC 17038), CSR 10 and CSR11 in the same clustering as Pokkali (salt tolerant check).

A protocol based on an alkaline hydroponic solution was validated and adopted. The pH 9.0 was superior to separate alkaline tolerant and sensitive rice at early seedling stage. A total of 1,800 individual F2 genotypes were screened and 1,652 were phenotyped in alkaline hydroponic solution. The total number of surviving F2 individuals at twenty five (25) days after transplantation was 34 and varied from one cross combination to another.