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Breeding Sweet Sorghum for Syrup Production
Department of Plant and Soil Sciences
`Food and Wine' magazine included sorghum syrup among four extraordinary mail-order foods which were worth the treasure hunt. Sweet sorghum syrup production is an alternative income source for small farmers. Over 50% of the syrup producers raise five acres or less of sweet sorghum.
Sorghum producers are looking for new varieties which eliminate some of the deficiencies of currently available varieties while maintaining syrup quality. Attributes which could be improved include early maturity, resistance to red stalk rot and maize dwarf mosaic virus, higher sugar concentration in the stalk juice, and standability. Different sweet sorghum genetic types will be crossed to each other, and the progeny of the crosses will be analyzed for a combination of qualities not available in current varieties. Brix, a measure of sugar concentration, will be used to select sweet sorghum genetic types with new levels of sugar concentration. I anticipate identifying sweet sorghum types with higher levels of sugar and releasing a sweet sorghum variety which will reduce production constraints for sorghum syrup producers.
2009 Project Description
Although heterosis is well established in grain and forage sorghum [Sorghum bicolor (L.) Moench], reports of heterosis in sweet sorghum are limited to results from grain sorghum x sweet sorghum hybrids. Recent development of cytoplasmic male sterile sweet sorghum lines allows creation of sweet sorghum hybrids for research and commercial applications. Such male sterility may also affect the allocation of photosynthate to different plant parts creating the potential increase of sugar content in sweet sorghum stems by eliminating seed as a carbohydrate sink. For this application, A3 cytoplasmic male sterility has strong potential for eliminating seed set.
We compared the performance of A3 cytoplasmic male sterile lines and A3 cytoplasmic male sterile hybrids to fertile B3 counterparts and to each other. A3 cytoplasmic male sterile Dale, Wray, and Sugar Drip, and N100 were crossed in all combinations to their male fertile counterparts to generate hybrids, resulting in 20 genotypes including the male fertile lines. The 20 genotypes were grown in a randomized complete block in two years at Lexington, Kentucky. 144 F4 derived lines were tested in two replications at Lexington. Lines were selected with a heading date earlier than (Simon + 7 days), a Brix > 16, lodging score < 2, and weight > Simon. 800 F4 lines from 400 F3 families were evaluated for low incidence of leaf disease, early heading, and low lodging.
Male sterile hybrids and lines had higher brix than male fertile lines. Hybrids produced greater stalk yield due to taller plants with greater stem diameter. Juice fraction and juice composition remained relatively unchanged. Only six hybrids showed positive heterosis for brix. The greater juice yield and higher sugar content of selected hybrids such as A3 N100 x Dale could produce more total syrup or ethanol than current pureline sweet sorghum varieties. Plot weights ranged from 10.2 kg to 25.2 Kg. Brix ranged from 10 to 22. 21 early lines were advanced for further testing. 144 F4 plants were selected for testing in 2010.