The inheritance of fermentable carbohydrates in stems of Sorghum bicolor (L.) Moench

Abstract

Two inheritance studies were conducted at College Station, Texas, to determine the nature and mode of inheritance of fermentable carbohydrates in stems of Sorghum bicolor (L.) Moench. Harvested stems were stripped and topped, and the juice extracted on a cane press mill. Carbohydrate yield was defined as the sum of the glucose, fructose, sucrose and starch concentrations in the juice times the volume of juice extracted. In one study involving 16 F1 hybrids from 2 female and 8 male parents, general combining ability (GCA) values were significant for carbohydrate yield, juice volume and each of the carbohydrate fractions. Specific combining ability (SCA) values were significant only for glucose, fructose and sucrose. The predominance of additive over non-additive genetic variance was confirmed by a GCA/SCA ratio of 13.6 for carbohydrate yield. Correlation and regression analysis indicated that juice volume and sucrose were the most important components of carbohydrate yield. Glucose, fructose and starch contributed only slightly more to the statistical model for predicting carbohydrate yield. Although the average heterosis effect was small and negative, 7 of the hybrids yielded more stem carbohydrate than the better parent. In addition, an average positive heterosis was found for yield of fresh heads, suggesting that higher grain yields of hybrids would offset any loss of stem carbohydrate. Another study consisted of 5 parents and the 10 F1 hybrids of a one-way diallel cross. The parents represented a range of genotypes from dry, non-sweet to juicy and very sweet. In this study dominance effects were greater than additive effects for carbohydrate yield and all components of yield. Heritability values were correspondingly low, with that for sucrose highest at 43.6%. Overall, the inheritance of carbohydrate yield was very complex. Both recessive and dominant alleles were involved, with an excess of recessive alleles. Over-dominance was indicated for juice volume and carbohydrate yield. Partial dominance and epistasis was implicated in the inheritance of glucose and fructose. Other studies evaluated the effect of sterile panicles on stem carbohydrates, and the behavior of stem carbohydrates over time after anthesis. Very little improvement in stem carbohydrate yield was realized with sterile plants...