Population Genetics and Ecological Studies in Wild Sorghum [Sorghum bicolor (L.) Moench] in Ethiopia: Implications for Germplasm Conservation

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Addis Ababa University


An exploration was made from October through November in 2008 to five sorghum growing geographical regions to study the distribution, the range of co-occurrence and diversity in the crop-wild-weed sorghum complex. Data were recorded on in situ quantitative and qualitative phenotypic characters from 30 populations. Moreover, the genetic structure of 19 wild populations from the five regions, eight cultivar populations from three regions, and 10 wild sorghum accessions from ICRISAT was studied using nine SSR loci. The extent of outcrossing was investigated in seven wild/weedy sorghum populations using five polymorphic SSR markers. The study was also aimed at investigating the fitness of wild-crop sorghum hybrids for various juvenile survival, adult and fertility phenological and morphological characters. Further, included in the present study was investigation of ecotypic differences of wild sorghum for dormancy, longevity, and their seed germination requirements as part of a risk assessment of crop-wild gene flow. There was high diversity among the wild/ weedy sorghum populations for phenotypic traits. SSR diversity was greater in the Ethiopian wild sorghum populations than in the sampled cultivars or wild accessions. Analysis of molecular variance (AMOVA) showed that 41% of the genetic variation in the wild plants was partitioned among populations, indicating a high degree of differentiation and the average number of migrants per generation (Nm) was 0.43 indicating limited gene flow within the wild pool. Cluster analyses showed that some wild populations were grouped by geographic region, whereas others were not, presumably due to long-distance seed movement. There was moderate differentiation between the wild and the cultivated sorghum probably because of historical gene flow. Wild sorghums collected from different geographical regionsexhibited variation (range=0.31-0.65) in outcrossing rate. Most wild × crop hybridsdidn’t show any fitness costs with respect to the measured traits and in some cases they showed mid-parent heterosis. The study indicated that crop-to-wild gene flow is possible, and the existence of morphologically intermediate forms between cultivated and wild sorghum indicates that gene flow is likely to have occurred in Ethiopia. Moreover, the high outcrossing rates of wild/weedy sorghum populations in Ethiopia may indicate a high potential for the spread of crop genes into the wild pool. The probable gene flow from the cultivated sorghum to the wild sorghum and introgression may pose risk of lossof genetic diversity in the wild and genes from transgenic sorghum are expected to enterwild populations if transgenic sorghum is deployed in Eastern Africa. Therefore,effective risk management strategies may be needed if the introgression of crop genes(including transgenes) from improved cultivars into wild/ weedy populations is deemed to be undesirable. Key words: Gene flow; genetic diversity; mating systems; population structure; sorghum, transgenic



: Gene flow; genetic diversity; mating systems; population structure; sorghum, transgenic