Combining abilities and heterosis for ethanol related traits in sweet sorghum (sorghum bicolor l.)

Abstract

Sweet sorghum [Sorghum bicolor (L). Moench] is important for production of fodder and ethanol worldwide. Objectives of this study were to determine: (i) the most suitable harvesting stage for sweet sorghum for which ethanol production is a maximum, (ii) the combining abilities for ethanol related traits and (iii) the best sweet sorghum hybrids for production of industrial alcohol. Experiments were conducted in Nakuru (0° 23′S, 35° 35′E), Homa Bay (0.35o13′07′′S, 34o07′44′′), and Kisumu (0o04′06′′S, 34o49′03′′E), counties in Randomized Complete Block Design (RCBD). They involved harvesting of sorghum at various stages for analysis of sugar traits to determine the harvesting stage for sweet sorghum in Western and Rift Valley regions in Kenya for which ethanol production is optimum. Hybrids were made by crosses in a line by tester mating design and the products were evaluated across three locations. Fourteen lines were used as females while four lines were used as testers. Genotype, Genotype × Environment (GGE) biplot and Principal Component Analyses (PCA) were used to select the best performing and most stable hybrids. Results indicated that harvesting sweet sorghum at 104 to 117 days after planting is appropriate for production of kernels and ethanol. Line EUSS10 exhibited the highest ethanol (1062.78 L ha-1) from juice volume of 22976.9 L ha-1 while Line EUSS11 produced 985.26 L ha -1with a brix of 16.21. All the traits such as height, girth, cane yield, brix, juice volume and ethanol yield showed both negative and positive heterosis. Hybrids exhibited positive heterosis ranging from 36.63% to 101.17% and 22.87% to 113.77% for juice and ethanol volume, respectively. Line IS25547 and tester EUSS10 had the highest General Combining Ability (GCA) for ethanol production while BM39 × EUSS10 had the highest Specific Combining Ability (SCA). GCA effects accounted for a larger portion of the treatment sum of squares than SCA effects suggesting that additive gene effects are more pronounced than non additive gene effects in the inheritance of sweet sorghum traits such as ethanol and juice volume. GGE biplot analysis distinguished the best performing hybrids from the rest and PCA revealed that juice volume was one of the most significan components in ethanol production. This study suggests that hybrids IS9203 × EUSS10, GS001 × EUSS10 and NYANGEZI × SS04 can be developed for use by farmers due to their good performance and high stability across the tested environments with long rainy season in the low lands seen to be the best for sweet sorghum production.