Submitted to: Plant Genetic Resources: Characterization and Utilization
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/20/2004
Publication Date: 7/16/2004
Citation: Pan, Y-B., Burner, D.M., Wei, Q., Cordeiro, G.M., Legendre, B.L., Henry, R.J. 2004. New Saccharum hybrids in S. spontaneum cytoplasm developed through a combination of conventional and molecular breeding approaches. Plant Genetic Resources: Characterization and Utilization. 2(2):131-139. Interpretive Summary: Like other crops, the genes of a sugarcane plant that control the plant's growth and development are found in both the nucleus (nuclear genome) and the cytoplasm (cytoplasmic genome) of the plant's cells. The nuclear genome of the commercial sugarcane varieties (Saccharum hybrids) that are grown around the world today is made up of the nuclear genomes from three ancestral species. The cytoplasmic genome of these varieties, however, is derived from only one ancestral species, S. officinarum (noble canes). The potential value of producing sugarcane hybrids containing cytoplasmic genomes from the other two ancestral species and particularly S. spontaneum has never been explored. This is due primarily to the fact that S. spontaneum is classified as a noxious weed and is therefore regulated by the Animal and Plant Health Inspection Service (APHIS). To produce sugarcane hybrids that have the cytoplasmic genome of S. spontaneum, ARS scientists emerged the flowers of S. spontaneum that were to be used as the female parent in crosses in hot water to render the pollen grains of the individual flowers infertile. Male sterile flowers of S. spontaneum were then pollinated with fertile pollen grains from flowers of two commercial sugarcane varieties. The hybrid nature of the seedlings that were produced from the planned crosses was verified with two types of DNA markers, RAPDs and microsatellites. True hybrids resulting from the crosses were planted to the field and used by breeders in an attempt to further diversify their parental lines. With the application of molecular marker technology breeders are no longer limited to the use of the various species of S. spontaneum as male parents in their varietal development programs. Ultimately, sugarcane breeders should be able to develop new high yielding varieties with greater cold tolerance, ratooning ability, and disease and insect resistance
Technical Abstract: Identification of sugarcane F1 hybrids is difficult when selections are based solely on morphological traits. Our objective was to combine morphological traits and molecular marker analysis to select F1 hybrids from two separate crosses between Djatiroto, a clone of Saccharum spontaneum, and elite sugarcane clones, LCP 85-384 (Cross 97-3144) and CP 62-258 (Cross 97-3146). The maternal inflorescences of Djatiroto were emasculated by submersion in a circulating 45oC hot water tank for 10 minutes to minimize self-fertilization. Cross 97-3144 produced 4.7g of seeds with 338 viable seeds per gram and Cross 97-3146 produced 2.4g of seeds with 166 viable seeds per gram. After greenhouse germination, ninety-six progeny from each cross were transplanted to a field evaluation plot. Evaluations were conducted on the first ratoon crop for stalk diameter (mm), Brix, and a RAPD marker OPA-11-366 that was reproducibly amplified through PCR from the elite clones, but not the maternal S. spontaneum clone. Fifty progeny (52.1%) from Cross 97-3144 and 36 progeny (37.5%) from Cross 97-3146 inherited the RAPD marker. Five putative F1 progeny were selected from each cross, namely, US 99-43, US 99-44, US 99-45, US 99-46, and US 99-47 from Cross 97-3144 and US 99-48, US 99-49, US 99-50, US 99-51, and US 99-52 from Cross 97-3146, based on their relatively larger stalk diameter, higher Brix, and inheritance of the RAPD marker. The hybrid nature of these selected progeny was verified with sugarcane microsatellite markers. This is the first report of the development of Saccharum hybrids with the cytoplasm of S. spontaneum for breeding purpose through a combination of conventional and molecular breeding approaches. Availability of these F1 hybrids could enhance the genetic diversity of Saccharum germplasm and enable sugarcane geneticists and breeders to explore the possible contribution of S. spontaneum cytoplasm in the development of new sugarcane cultivars.