MARKER ASSISTED SELECTION FOR POST-FLOWERING DROUGHT TOLERANCE IN SORGHUM BICOLOR [L.] MOENCH - ABSTRACT
Sorghum is the second most important cereal crop after pearl millet in terms of area planted, production, and per capita consumption in Mali. Production of sorghum is declining due to several reasons including lack of sorghum hybrids and adapted varieties tolerant to drought. Evaluation of sorghum genotypes under different stresses would be useful for identifying genotypes that combine stability with high yield potential for stress-prone areas. The general objective of the study was to improve sorghum grain yield, through the development of high yielding hybrids tolerant to post flowering drought. Among the specific objectives were: (i) to assess sorghum production constraints, importance and farmers’ sorghum variety preference criteria in Mali, (ii) to introgress genes (QTLs) for tolerance to post-flowering drought into elite B-lines of sorghum by backcrossing and (iii) to identify potential parents and hybrids tolerant to post flowering water stress. A Participatory Rural Appraisal consisting of focus group discussions followed by individual interviews was conducted in different communities namely, where sorghum is among the main starchy staple. The focus group discussions were conducted with a total of 74 small-scale farmers whilst 265 households were involved in the interviews. The results indicated that in Mali, the main reasons for cultivating sorghum are for grain, used for human consumption, while the crop residues are used in animal feeding, fencing and compost. The two major sorghum production constraints identified were drought and Striga infestation. Since drought was a major concern for farmers, sorghum hybrids tolerant to post-flowering drought were developed. To accomplish that, the parental stay green lines (B and R) were identified. To generate stay green B-lines populations, three elite lines from the Malian sorghum program, 98-BE-F5P-82B, 03-SB-F5DT-134B and 09PR-3009B (senescent, drought susceptible), were crossed with B35 (stay green donor). Marker-assisted backcrossing method was used to incorporate stay green genes (QTL) into B-lines. Finally, a total of twelve individuals were selected. To identify stay green Rf-lines, the cytoplasmic male sterile line 02-F5DT-12A (12-A) was used as female parent in test crosses and with 120 selected lines from BCNAM’s populations for testing the cytoplasmic male sterility reaction. Ten stay green restorer lines (Rf-lines), useful for developing hybrids for wider adaptation in semi-arid regions were identified. Among them, five lines were used for hybrid seed production. A set of twelve female (B-lines) and five male lines (R-lines) were sown for making crosses in North Carolina Design II mating design in the experimental area of Agriculture Research Centre of Sotuba in Mali. A total of 60 F1 hybrids were obtained. These F1 hybrids were planted along with six sorghum lines used as check. A total of 66 genotypes of sorghum were evaluated in both drought and well-watered conditions. The split-plot design with drought intensity as the main plots were used. To achieve the main goal of study, different methods of analysis were used: combining ability estimation, GGE biplot analysis, and stress tolerance indices using multivariate analysis. The different methods of analyses revealed three hybrids (B35//134B)-F3-44/BCNAM-76-2, (B35//82B)-F3-64/BCNAM-45-1 and (B35//82B)-F3-104/BCNAM-76-2 as the most post-flowering tolerant genotypes with high yield stability in both conditions. Two female B-lines parents (B35//134B)-F3-44 and (B35//82B)-F3-64 and one male R-line parent BCNAM-76-2 had highest grain yield in both environments. The hybrids and parents named above can be introduced as post-flowering drought tolerant genotypes after further evaluation in the semi-arid regions of Mali.
Key words: Drought, Farmers, Hybrid, Lines, Mali, Marker-Assisted Backcrossing, Participatory Rural Appraisal, Sorghum, SSR Markers, Water Stress, Well-Watered.