Comparison of two Sorghum genotypes for sugar and fiber production

A comparative analysis of the growth and yield performances of two late maturing and productive sweet and fiber sorghums has been conducted, with the perspective of their introduction in temperate Italian climate areas as competitive multi-product crops. Sweet type sorghum 'Wray' (Sorglum bicolor (L.) Moench ssp. bicolor), and the nonsweet type, 'H173' (hybrid Sorglum bicolor (L.) Moench x Sorghum docna var. technicum), were grown in a field trial under well-watered conditions in northern Italy (latitude 44 degrees 3'N, longitude 11 degrees 2'E). During the crop cycle, growth analysis were performed by collecting data from both non-destructive and destructive samplings. Fundamental growth indexes were calculated as a function of accumulated growing degree days (GDD) from sowing. Yield traits were evaluated at soft dough maturity. Sweet and fiber crops reached soft dough maturity after 1250 GDD and did not statistically differ for total and main stem yields. Mean values of 27 and 20 t ha(-1) dw, respectively, were detected. The sucrose content was more than three times higher and the cellulose and lignin contents 40-50% lower in 'Wray' as compared to 'H173', whereas the level of reducing sugars was similar. Both sorghum types can be considered as interesting new crops which might provide an energy production higher than 10000 kcal m(-2) a potential production of around 6000 l ha(-1) of ethanol (sweet), and up to 15 t ha(-1) of structural polysaccharides (fiber). The rate of leaf formation on the main stem and their final number were similar between the two genotypes. Until the growing differentiation point, one new leaf was visible every 40.5 GDD, thereafter the same growth process required around 123 GDD. During the period of early leaf formation, the fiber type showed a greater tillering ability which positively affected early canopy area and growth parameters. On the other end, the sweet sorghum crop presented enhanced dry matter accumulation capacity after the growing differentiation point as compared to the fiber crop (42.7 and 27.7 g m(-2) d(-1), respectively). This could be the result of higher leaf thickness and leaf area duration. (C) 1998 Elsevier Science B.V.