Breeding for Forage Hybrid Sorghum [Sorghum bicolor (L.) Moench] in the Sudan Using Local Stocks as Males and Introduced Genetic Stocks as Females

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Mohammed, Maarouf Ibrahim
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The study was conducted in Khartoum State for two years (2002-2003) and at two locations (Shambat and Islang). The objective was to investigate the possibility of local development of forage hybrid sorghum [Sorghum bicolor (L.) Moench] using 4 local stocks as pollinators and 7 introduced genetic stocks sterilized in A3 cytoplasm as females. The commercial hybrid ‘Panar 888’ was used as standard check. The material was evaluated for agronomic performance and the proximate analysis for some forage quality traits was undertaken. Combining ability study was performed using line x tester analysis and the magnitude of average heterosis, heterobeltiosis and standard heterosis were investigated. Highly significant differences were detected among entries for all characters studied. Partitioning of the entry source of variation revealed significant differences among the various subgroups of entries for all characters. The interaction of entry and its various subgroups with location, unlike that with years, was insignificant for all characters. The second order interactions with hybrids and their parents were insignificant for all characters; however, the comparatively low mean squares of hybrids, pointed to their relative consistency over environments compared to parents. Many hybrids excelled the parental lines in forage yield and some of the yield-related traits. The hybrids : E-35-1 x S. 70, E-35-1 x S. 186, E-35-1 x Garawi and Dale x S.70 significantly out-yielded the commercial hybrid ‘Panar 888’ and the parental lines derived from the local cultivar ‘Abu Sab’in’. The increase in yield attained by these hybrids was attributed to the increase in stem diameter and plant height. The commercial hybrid excelled the experimental hybrids in leaf to stem ratio, tillering and regrowth. The proximate analysis for neutral detergent fiber, crude fiber and Ash indicated that the overall nutritive value of hybrids was better than their parents. Crude protein percentages of hybrids averaged slightly lower compared to their parents. However, this was suggested to be mitigated by the improved intake potential of hybrids. The heterosis study revealed that significant gains in forage yield over mid-parent, better parents and the commercial hybrid ‘Panar 888’ were exhibited by some hybrids indicating that the superiority over the existing maxima in forage yield has been demonstrated. Hybrids with the best heterotic effects for forage yield and at the same time maintaining good performance for this character were those involving the line E-35-1 with the testers : S. 70, S. 186 and Garawi, plus Dale x S.70, Hastings x S. 70 and Sugar Drip x Ankolib. Of these, the hybrids Dale x S.70 and Hastings x S. 70 displayed the best compromise between forage yield, earliness and quality traits. In contrast, the hybrids involving E-35-1 showed undesirable heterosis for earliness and some quality traits. Generally, the means of average heterosis and heterobeltiosis indicated that the general trend for heterotic effects were towards increased forage yield, plant height, stem thickness, tillering, regrowth and reduced leaf to stem ratio. Significant general (GCA) and specific (SCA) combining ability effects in the desirable direction were detected for most agronomic and quality traits. The best general combiners for forage yield were E-35-1 and Dale from lines and S. 70 (selection from Abu Sab’in) from testers. Dale was given the top priority as it maintains desirable GCA effects for many other characters including quality traits. E-35-1, although better than Dale in GCA for forage yield, it turned out to be the poorest general combiner for earliness in flowering, a character highly needed under the prevailing forage production system in the Sudan. It was concluded that economic evaluation may validate the utility of the of E-35-1 hybrids, especially in the highly specialized animal-products sector, where lateness in flowering is not a major problem. Blue Ribbon from lines and Garawi (traditional Sudan grass cultivar) from testers were promising general combiners for earliness. Garawi was also a promising general combiner for leaf to stem ratio, regrowth and tillering, but was the poorest for forage yield. Since Garawi is a highly heterogeneous cultivar, it was suggested that its GCA for forage yield might be improved by selection. Ankolib from testers was also a good general combiner for leaf to stem ratio. For quality traits, Dale from lines and S. 70 from testers were the best general combiners for neutral detergent fiber, followed by the line Hastings and the tester S. 186. The line Hastings was also the best general combiner for crude protein. Blue Ribbon and Sugar Drip from lines and Ankolib from testers were the best general combiners for Ash. The best SCA effects for forage yield were obtained by Sugar Drip x Ankolib followed by Blue Ribbon x Ankolib. Other hybrids with significant SCA effects for forage yield include : E-35-1 x Garawi, Dale x S.70, Hastings x S.70 and E.35-1 x S.186. All these hybrids were among the best yielders, but their yield ranks were not necessarily similar to those of their SCA effects. For earliness in flowering, the best specific effects were shown by E-35-1 x Ankolib, Dale x Ankolib, and Hastings x Garawi. For leaf to stem ratio, the best specific effects were shown by N 100 x Ankolib followed by E-35-1 x Ankolib. The best SCA effects for regrowth were shown by Sugar Drip x S.186, Dale x Garawi and N 100 x S.70. With few exceptions, both general and specific effects were important in the expression of all characters, with general effects being more important than the specific ones. Consequently, both additive and non-additive gene actions were important in the expression of most characters with the preponderance of additive gene actions for days to flower, forage yield, stem diameter, leaf to stem ratio and non-additive actions for plant height and regrowth. The exception being number of tillers per plant which appears to be mainly under the control of additive effects. General effects were more stable over years than specific effects. Interactions of genetic effects with years were more pronounced than those with locations. It was postulated that, testing over years at one location with increased number of replications, might be of value for combining ability evaluation. The contributions of either lines or testers to the total variance were higher than those of line x tester for all characters other than plant height and regrowth. The variability observed among both parental groups was in most cases, not coinciding with their contribution to the total variance. It was suggested that high variability among a parental group did not necessarily imply high contribution of that group to the total variance of the crosses. Selection in early generations might be effective in improving characters predominately controlled by additive genes like number of tillers per plant and days to flower. For characters like forage yield, leaf to stem ratio and regrowth in which both additive and non-additive gene actions were important, it was pointed that the A3 sterility source will preclude the employment of reciprocal recurrent selection in their improvement. Alternatively, heterosis breeding was recommended for forage yield improvement, but for leaf to stem ratio and regrowth, it was suggested that heterosis breeding must be preceded by a selection program based on more genetically diverse material with increased number of lines. Since the exotic material may transfer traits not adapted to the local production system, the choice for local x local hybrids was highly recommended. Male-sterilizing the local stocks in A3 cytoplasm was therefore suggested to benefit from the wide range of variability known to exist in sorghum in the Sudan. Preliminary selection within local stocks was suggested to eliminate undesirable traits or to include some easily inherited desirable traits like juiciness.
October, 2004