[Morphological and Molecular Characterization of Introduced Sweet Sorghum and Sequencing of Sucrose synthase gene (SuSy2)]

Sweet sorghum has multipurpose cultivated types and is widely recognized as a potential alternative source of bio-fuel because of its sugar content in the sugar stalk varieties. The objectives of the study were to assess the morphological and molecular variation and relationship among different sorghum varieties. Ten sorghum varieties, nine introduced sweet sorghum varieties from ICRISAT and a control Syrian cultivar 'Razineah', were studied in one season field experiment (2010-2011) under two water regimes, irrigated and pre flowering drought stress, to evaluate the morphological variation and response to pre flowering drought stress. We found large variability and significant differences among the ten genotypes regarding most studied morphological parameters and traits. One genotype (ICSSH30) was superior to all other varieties in terms of maintaining drought-tolerance associated traits and high sugar and bio-ethanol potential yield under the two water regimes, while the cultivar 'Razineah' showed the lowest values among the same varieties. The lowest significant value of stalk height was obtained from the genotype ICSB38, while the genotype ICSV25280 gave the highest significant value of Brix degree among other studied genotypes. Positive correlation was observed between yield component traits, days to 50% flowering, and leaf area under irrigated condition, and significant positive correlation was observed between yield component traits, days to 50% flowering, and leaf area under drought stress condition. On the other hand, a significant negative correlation was found between Brix degree with stalk yield and juice yield under drought stress conditions, suggesting that the late-flowering genotype and the feature of stay-green of leaves improved adaptation to drought stress conditions, and that with increasing the number of days of 50 % flowering to harvest date, there was an improvement in the yield of genotypes due to increased number of days available for dry matter accumulation, with stay green trait enabling carbon assimilation. Inter Simple Sequence Repeat (ISSR) markers were used to assess the genetic diversity of the studied varieties. Out of 20 ISSR primers screened, 9 primers were selected for their polymorphic and repeatable fragments. 110 fragments were polymorphic out of the total 130, while the percentage of polymorphic bands value ranged from 63.6 % of (AC)8 T to 100% of (AG)8 A, with a mean of 84.61%. As a result, poly (AG)-anchored primers were more polymorphic and reproducible than other di-nucleotides and tri-nucleotides motifs. The UPGMA clustering grouped the varieties into two major clusters, clearly separating the Indian varieties from the one Syrian variety. Among the Indian varieties, two sub-clusters were related to the pedigree information, which differentiated the B-line hybrids lines out of other genotypes. Grouping of varieties by UPGMA cluster analysis correlated with the geographical origin, pedigree information, indicating that ISSR markers could be realistically used to evaluate the genetic diversity and differentiation among sorghum varieties. These results were confirmed by the principle component analysis (PCA).