Phenotypic and Genetic Diversity in Sweet Sorghum Presents Opportunities for Strengthening Valued Traits Through Cross-Breeding
Sorghum is an important cereal crop due to being highly stress tolerant and efficient photosynthetically and in its water use. It can be grown in areas where little else is able to take hold. Sweet sorghum, varieties of sorghum with high sugar content in their stalks, are of particular use for animal feed, use in syrup, molasses and sugar and in ethanol as part of biofuel. As with other plants, crossing distant lines of sweet sorghum produces a stronger, better producing specimen, known as hybrid vigor. However, such diversity in the genome makes genetic selection of specific traits for improvement difficult. Expanding the knowledge of the genetic diversity in sweet sorghum is of great interest for anyone concerned with crop improvement, including breeders, growers, those in the biofuel industry and scientists.
To assess the phenotypic and genetic variability among sweet sorghum lines researchers at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and Corteva Agriscience in India, the USDA and The Pennsylvania State University selected 75 lines for investigation. The researchers assessed the lines for seasonal phenotypic variance and found significant differences in height, stalk yield, and sugar content (brix %). This indicates that these traits, known to be associated with non-additive genes,could be improved upon by cross breeding heterotic groups. In addition, these quantitative traits had significant genetic differences indicating high genetic variability; genetic variability is of key importance for developing traits of interest in cultivars.
Rapid growth, high biomass and adaptability to adverse conditions are favorable traits that distinguish sweet sorghum from other lines. Sugar content (brix %), biomass, juice yield and fermentation efficiency are important traits for ethanol production and identifying genotypes that optimize these traits is important when breeding sorghum for bioenergy. Identifying contrasting pairs with high biomass but either high sugar yield or low sugar yield may lead to finding lines with different alleles for sugar yield in stem juice and using them as parents in mapping populations aimed at sugar accumulation genes. The researchers used SNP (single-nucleotide polymorphisms) markers generated through genotyping-by-sequencing to group the genotypes into three clusters (I, IIb and III?). Elite lines, like ICSV 25316, ICSV 25311, SSV 74 and ICSV 25300, have traits that are heavily selected for and have high stalk yield and sugar yield, had, as expected, limited genetic variation and were grouped together in cluster I. Genetically distant lines in clusters IIb and III have high biomass yield and present an opportunity for heterotic hybrid combinations with cluster I lines aimed at increasing sugar yield.
Reference:
Pinnamaneni, S.R., Somanna, A.K.G., Ramu, P., Vanamala, J.K.P., and Srivastava, R.K. Assessment of Phenotypic and Genotypic Diversity in Elite Temperate and Tropical Sweet Sorghum Cultivars. Sugar Tech (2022). DOI: 10.1007/s12355-022-01117-3. Read more
Related Project Websites:
ICRISAT – Srivastava: https://www.icrisat.org/team/rakesh-k-srivastava/
