Location: Crop Genetics and Breeding ResearchTitle: Yield components in hybrid versus inbred sweet sorghum
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2016
Publication Date: 8/30/2016
Citation: Knoll, J.E., Anderson, W.F. 2016. Yield components in hybrid versus inbred sweet sorghum. Crop Science. 56:2638-2646.
Interpretive Summary: Sweet sorghum accumulates fermentable sugars in its stems, and should be an ideal biofuel crop for the southeastern United States due to its drought and heat tolerance. However, all of the current public cultivars are pure lines, which makes seed production difficult because these plants are tall and often lodging. Producing hybrid seed on short-statured plants should facilitate seed production and may also increase yields due to hybrid vigor. The purpose of this study was to determine if hybrid sweet sorghum actually has any advantage over inbred lines in the Southeast, and to determine the general combining abilities of several sweet sorghum lines. Breeders refer to a parent line’s average performance in hybrid combinations as its ‘general combining ability (GCA).’ Three female lines and 19 male lines were crossed in all possible combinations (known as a Design II mating design), generating 57 hybrids. All 57 hybrids and their parents were planted in the field in a randomized complete block experiment with two replications in 2012 and again in 2014. Each plot consisted of two rows, one of which was used for periodic juice sampling, and the other was used for measuring total biomass at harvest. Also at harvest, three stalks were taken from the sample row, and were divided into leaves, stalks, and panicles to estimate the proportion of each component in the final yield. Juice was extracted from the stalks with a roller mill and the sugar yield was calculated by multiplying (brix – 3) by the mass of the juice. Brix refers to the concentration of dissolved solids in the juice, which are mostly sugars. Later-flowering lines, including Brandes, M 81E, Mer 76-3, and Top76-6, had positive GCA for sugar yields, meaning that they tended to produce hybrids with high sugar yields. Some specific hybrids, mostly with N109A as the female parent, had reduced lodging percentage. Only M 81E had higher juice brix in its hybrids than in the inbred male line. Ten males had higher panicle yields in their hybrids compared to the inbred lines, even though these are sweet sorghums. Overall, sugar yields tended to be similar between inbred male lines and their hybrids, but hybrids usually flowered earlier, thus producing similar yields in less time.
Technical Abstract: Sweet sorghum (Sorghum bicolor (L.) Moench) should be an ideal biofuel crop for the southeastern United States, but the current cultivars are all pure lines, which makes seed production difficult. Hybrid seed can be easily produced on short-statured plants, but less is known about other advantages of hybrid sweet sorghum over inbred cultivars. Heterosis in this crop has not been extensively studied in this region. Three female lines and 19 male lines were crossed in a factorial mating design (Design II) experiment. All hybrids and their parents were planted in the field in a randomized complete block experiment in 2012 and again in 2014. The yields of individual components (leaves, panicles, bagasse, and juice) were calculated based on their proportions of total biomass yields. Sugar yields were estimated from juice soluble solids concentration. Late-flowering lines, including Brandes, M 81E, Mer 76-3, and Top76-6, had good general combining ability for sugar yields, and some hybrids, mostly with N109A as the female parent, had specific combining ability for reduced lodging percentage. Only M 81E had higher juice dissolved solids concentration in its hybrids than in the inbred line. Overall, sugar yields tended to be similar between inbred male lines and their hybrids, but hybrids usually flowered earlier, thus producing similar yields in less time.