Performance of Sorghum Hybrid Lines with Tannin Gene from Crosses between Gadam and Tannin Hard Coat Sorghum Varieties

Abstract

Sorghum is a major staple food source in many African countries. In Kenya, it is cultivated by small-scale farmers. Gadam sorghum is the common variety mainly grown for brewing, manufacture of animal feeds and sorghum cakes. However, its yield is about 0.8 t ha- which is low compared to international standards. This is exacerbated by birds' that tend to have a preference for it. The use of birds' resistant sorghum varieties containing higher amounts of tannin than Gadam is a strategy to minimize the damage. However, tannin is an anti-nutritional factor that binds proteins together and inhibits many enzymes in in vitro assays reducing their digestibility and efficiency of utilization. Production of hybrids is one way of improving yield through heterosis. The objective of this study was to evaluate the performance of sorghum through hybridization of Gadam sorghum and hard coat tannin sorghum varieties. The study was conducted at the University of Embu research farm. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replicates. Four (4) sorghum varieties namely, Serena, Gadam, Seredo and Kari/Mtama-1 (used as a control due to its low tannin content) were sourced from the KALRO seed unit at Katumani. Sowing of sorghum varieties was staggered over three weeks to synchronize heading time to enable crossing. Development of F1 hybrid lines was done by reciprocal crossing of Gadam and other varieties, using manual emasculation method. Crosses and their reciprocals were used as plant materials while parents were the controls. Data taken was; compatibility between the parents, changes in levels of expression of the tannin gene, grain nutritional levels, heterosis and yield traits compared to their parents. Collected data was subjected to a one-way analysis of variance (ANOVA) using R statistical software. Mean separation was done using Tukey’s Studentized Range (HSD) at 95% confidence level. The cross Gadam x Serena, Serena x Gadam and the parent Gadam exhibited moderate mean plant height values of 99.5 cm, 120.5 cm and 103.3 cm respectively. The cross Gadam x Serena recorded a desirable negative mid-parent heterosis of -19.89 and -16.16 for plant height and days to maturity respectively. All F1 hybrids recorded positive mid parent heterosis for the weight of full panicle, weight of a thousand seeds, number of tillers per plant, number of reproductive tillers and panicle length indicating possible yield improvement of Gadam sorghum through hybridization. The crosses Gadam x Seredo, Seredo x Gadam, Gadam x Serena and Kari/Mtama-1 x Gadam recorded significantly lower grain filling percentages compared to their parents. Both RNA levels and tannin content were observed to be at the maximum at soft dough stage and declined in subsequent stages indicating synchrony between RNA levels and tannin levels. Parents, crosses and reciprocals also differed significantly (p<0.001) for crude protein, fat, crude fibre, ash, carbohydrates, moisture and tannin content with values ranging from 5.323% to 10.390%, 1.691% to 2.299%, 2.230% to 3.520%, 1.215% to 1.360%, 76.790% to 85.677% , 5.433% to 9.667% and 0.034 mg/g to 1.763 mg/g respectively. In conclusion, all the F1 hybrids have positive mid parent heterosis for number of reproductive tillers, number of tillers per plant, panicle length, weight of full panicle, and a thousand seed weight. There is maternal influence on days to heading, flowering and maturity, and a thousand grain weight. The lower grain filling percentage recorded in the F1 hybrids indicates that the parental lines used have a narrow wide compatibility gene. The decline in Tan1 gene after the soft dough stage shows that Tan1 gene expression in sorghum is determined by the level of seed maturity. The F1s showed marginal improvement in crude protein, crude fibre and carbohydrates but need to be evaluated further to determine the influence of hybridization on total nutrition. Also, heterosis can be utilized to improve the growth and yield of sorghum.