|Schnell Ii, Raymond|
|Richard Jr, Edward|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 20, 2004
Publication Date: November 29, 2004
Citation: Pan, Y.-B., Tew, T.L., Schnell, R.J., Viator, R.P., Veremis, J.C., Richard Jr, E.P., Grisham, M.P., White, W.H. 2004. Microsatellite DNA marker-assisted selection of Saccharum spontaneum cytoplasm-derived germplasm. In: Proceedings of International Symposium on Sustainable Sugarcane and Sugar Production Technology, November 29 - December 2, 2004, Nanning, China. p. 483-489. Interpretive Summary: Sugarcane stores its genes in two cellular compartments, the nucleus (nuclear genome) and the cytoplasm (cytoplasmic genome). The nuclear genomes of all sugarcane cultivars grown around the world today represents mixtures of nuclear genomes from three ancestral species while the nuclear genomes of Louisiana varieties are mixtures of nuclear genomes of two ancestral species, Saccharum officinarum and S. spontaneum. In contrast, the cytoplasmic genomes of all these cultivars are from S. officinarum only. The potential value of the cytoplasmic genomes from S. spontaneum has never been explored. This is due primarily to the fact that S. spontaneum is considered a noxious weed because it has a propensity to reduce sexually by producing abundant seed and vegetatively by producing vigorous rhizomes. In order to develop new sugarcane varieties having their cytoplasmic genomes from S. spontaneum, the ARS scientists emasculated the flowers of ten S. spontaneum lines with hot water and then pollinated these emasculated flowers with fertile pollen from untreated flowers of two commercial sugarcane varieties. The seeds were harvested from these S. spontaneum lines and were allowed to germinate. The seedlings were screened with microsatellite DNA markers. Analyses of DNA marker fingerprints allowed the grouping of all seedlings into four classes. Class H inherited markers from both parents and were hybrids; Classes C and S only inherited markers from either the commercial varieties or S. spontaneum and were considered selfs; and Class X inherited markers from both S. spontaneum and an unknown parent and were considered contaminants. Only the progeny from Class H had a breeding value. From eight to ten Class H progeny were selected from each cross to be included in 2002-2003 crossing program. The availability of these new sugarcane hybrids will enhance the diversity of existing genetic resources and enable sugarcane breeders to explore the utility of cytoplasmic genome of S. spontaneum in the development of superior new varieties.
Technical Abstract: New lines of Saccharum hybrids with an array of S. spontaneum cytoplasm backgrounds are reported. To expand the genetic base of sugarcane, we made eleven bi-parental crosses between ten S. spontaneum (S) and six commercial-type sugarcane (C) clones during the 2001 crossing season. Prior to crossing, all the maternal S. spontaneum inflorescences were emasculated by immersion in a 50oC circulating water bath for 5 minutes. Analysis of microsatellite fingerprints between parents and progeny allowed us to classify 1,952 progeny grown out from these crosses into four genotypic classes. Class H progeny inherited microsatellite alleles from both the S. spontaneum and the commercial-type parents and were, therefore, considered being F1 hybrids. Class S and Class C progeny inherited microsatellite alleles only from one parent and were considered to be either selfs of either parent or F1 hybrids that only inherited allele(s) from one parent. Class X progeny inherited non-parental microsatellite allele(s) in addition to the allele(s) from the maternal S. spontaneum parent and were considered to be contaminants. With the exception of one cross, eight to ten Class H progeny were pre-selected from each cross while still in seedling greenhouse and were backcrossed with commercial-type sugarcane clones. The remaining progeny were transplanted into a breeding nursery for phenotypic evaluation that concurred with the molecular classification. Pearson Correlation Coefficients between molecular and phenotypic classifications were inconsistent that justified the need of molecular markers in the selection process. This study demonstrated that the molecular approach of fingerprinting progeny to confirm parentage prior to field planting even with only one microsatellite marker might substantially increase selection efficiency.