Population Genetics And Ecological Studies In Wild Sorghum Sorghum Bicolor (l.) Moench In Ethiopia Implications For Germplasm Conservation

An exploration was made from October through November in 2008 to five sorghumrngrowing geographical regions to study the distribution, the range of co-occurrence andrndiversity in the crop-wild-weed sorghum complex. Data were recorded on in siturnquantitative and qualitative phenotypic characters from 30 populations. Moreover, therngenetic structure of 19 wild populations from the five regions, eight cultivar populationsrnfrom three regions, and 10 wild sorghum accessions from ICRISAT was studied usingrnnine SSR loci. The extent of outcrossing was investigated in seven wild/weedy sorghumrnpopulations using five polymorphic SSR markers. The study was also aimed atrninvestigating the fitness of wild-crop sorghum hybrids for various juvenile survival, adultrnand fertility phenological and morphological characters. Further, included in the presentrnstudy was investigation of ecotypic differences of wild sorghum for dormancy, longevity,rnand their seed germination requirements as part of a risk assessment of crop-wild genernflow. There was high diversity among the wild/ weedy sorghum populations forrnphenotypic traits. SSR diversity was greater in the Ethiopian wild sorghum populationsrnthan in the sampled cultivars or wild accessions. Analysis of molecular variancern(AMOVA) showed that 41% of the genetic variation in the wild plants was partitionedrnamong populations, indicating a high degree of differentiation and the average number ofrnmigrants per generation (Nm) was 0.43 indicating limited gene flow within the wild pool.rnCluster analyses showed that some wild populations were grouped by geographic region,rnwhereas others were not, presumably due to long-distance seed movement. There wasrnmoderate differentiation between the wild and the cultivated sorghum probably becausernof 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.rnrnKey words: Gene flow; genetic diversity; mating systems; population structure; sorghum,rntransgenic

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