GENETIC STUDIES AND IMPROVEMENT OF OFADA RICE LANDRACES (Oryza sativa L.) FOR REPRODUCTIVE STAGE DROUGHT TOLERANCE IN NIGERIA
ABSTRACT
Drought is the most important abiotic factor limiting rain-fed upland rice production in Nigeria. The intermittent and widespread occurrence of drought stress in rain-fed rice fields in sub-Sahara Africa has led to tremendous decreases in yield and food security in this and other developing countries in the sub region. This study was undertaken to: (i) determine farmers‘ perception on the effects of drought on upland rice production (ii) identify upland rice genotypes with high grain yield under severe reproductive stage drought stress (RS) and irrigated control (NS); and (iii) improve Ofada landrace (FUNAABOR-2) for high grain yield under reproductive stage drought stress via a combination of phenotypic and marker assisted backcross selection. Participatory Rural Appraisal (PRA) was conducted among 107 upland rice farmers across two major upland rice growing states (Ogun and Ekiti) in South Western Nigeria employing focus group discussion and semi-structured interviews. Seventy seven upland rice genotypes made up of popular improved and unimproved upland rice varieties in Nigeria were evaluated alongside selected exotic upland rice varieties from across rice growing regions of the world. These genotypes were evaluated under optimal upland growing conditions and ranked using BLUP analysis and base indices to identify lines with best combination of high yield and farmers preferred agronomic traits. Furthermore, 18 genotypes were selected for screening under rainout shelter conditions to identify lines tolerant to reproductive stage drought stress. Breeding populations for identification of promising drought tolerant progenies were developed by crossing FUNAABOR-2, a popular upland rice variety (OFADA RICE) in south western Nigeria with IR84984-83-15-481-B a donor parent for drought tolerance QTLs qDTY12.1 and qDTY2.3. Foreground selections were carried out using peak markers (RM511 and RM250) for drought QTLs qDTY12.1 and qDTY2.3, respectively, whereas flanking markers (RM 28099, RM511,
RM1261, RM28130, and RM28166) were employed for recombinant selections. Introgressed BC1F2 progenies and their recurrent parent, FUNAABOR-2, were evaluated for yield performances and related traits under RS and NS. The PRA revealed that farmers were aware of changes in rainfall patterns during the crop growing seasons and also identified reproductive stage drought stress as one of the major constraints to upland rice production. Wide genotypic differences existed among the genotypes studied based on index ranking. IR 68704-145-1-1-B and IR 63380-16 from IRRI were the best yielding varieties and showed a yield advantage of 45% and close to 200% over the highest and lowest yielding unimproved Nigerian varieties (Ofada 3 and Eboenyi Local), respectively, but only 16% yield advantage over the best improved Nigerian genotype ITA 301. Detailed characterization of 18 upland rice varieties under RS at Ibadan revealed that majority of the Ofada landraces, though susceptible to drought stress, had potential for high grain yield under NS coupled with good recovery ability after resumption of irrigation. Ofada 2 (508.1 g m-2) and Ofada 4 (470.8 g m-2) were the best performers under NS while ITA 117 (152.38 g m-2) and IRAT 109 (133.98 g m-2) gave the highest grain yield under RS. Two introgressed lines with qDTY12.1 and qDTY2.3, BC 103 (417.73 g m-2) and BC 27-1 (398.48 g m-2) were the best performers under NS whereas BC 91-1 (79.38 g m-2) and BC 50 (76.12 g m-2) gave the highest grain yield under RS. BC 103 and BC 27-1 had 58% and 52% yield advantage over the recurrent parent respectively under the NS trial while close to 600% yield advantage over the recurrent parent was recorded for the two best progenies (BC 91-1 and BC 50) under the RS condition. The results obtained from this study demonstrates that farmer-preferred upland rice, FUNAABOR-2, popularly known as Ofada white in south western Nigeria, could be improved for high grain yield under RS and NS conditions through phenotypic and marker assisted selection approaches.