ARS | Publication request: Comparison of biparental and melting pot methods, of crossing sugarcane in Hawaii

Submitted to: International Society of Sugar Cane Technologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 17, 2009
Publication Date: March 7, 2010
Citation: Tew, T.L., Schnell Ii, R.J., Comstock, J.C., Wu, K.K., Nagai, C., Schenck, S., Arcinas, A., Ferreira, S.A. 2010. Comparison of biparental and melting pot methods, of crossing sugarcane in Hawaii. Proc. Int. Soc. Sugar Cane Technol. 27:1-9.

Interpretive Summary: As in other crops, annual yield increases through breeding in sugarcane has been modest. Sugarcane breeders have debated whether greater yield increases would be obtainable by making bi-parental crosses, where flowers of the desired mother and father are isolated, or by making polycrosses (in Hawaii, called melting pot crosses), where flowers from a large number of varieties are fully interspersed. With bi-parental crosses, pedigree information is fully known on the offspring, and specific crosses can be compared so that the best can be repeated. With polycrosses, more viable seed is produced and a vastly greater number of parental combinations occur. In Hawaii, the two methods were used concurrently for 50 years, making it possible to compare which of the two methods contributed the most from the standpoint of commercial varieties produced. The polycross method produced more commercial varieties than the bi-parental crossing method during and following this 50-year period, and all but one variety since 1955. This outcome applies to Hawaii where sugarcane is commercially grown for two years before harvest, and thus, where evaluation and comparison of specific crosses at early selection stages is not very meaningful. The polycross method should continue to be emphasized there, especially since labor is scarce. It does not necessarily apply to other sugarcane growing locations within the U.S., namely Florida and Louisiana, where annual rate of genetic gain has been as great as in Hawaii relying largely on the bi-parental crossing method.

Technical Abstract: Sugarcane (Saccharum spp.) breeders at the Hawaiian Sugar Planters’ Association used bi-parental and melting pot (modified polycross) crossing methods concurrently from 1935 through 1985. While the annual effort expended to make bi-parental crosses was at least as great as the effort to make melting pot crosses over this 50-year period, annual viable seed yield from bi-parental crosses was usually less than 15%, and hence, numbers of seedlings planted to the field from those crosses usually accounted for less than 20% of the total seedling population. In 1985, nine of 10 commercial sugarcane cultivars (>1% of the total sugarcane area in Hawaii) originated from melting pot crosses. In the face of a shrinking sugar industry in Hawaii and a smaller work force in the breeding program, the decision was made in 1985 to rely primarily on melting pot crosses for the production of commercial cultivars. From 1985 through 2005, twelve additional clones that were bred prior to 1985 have since become commercial cultivars. All twelve originated from melting pot crosses. Over the 50-year period that the two crossing methods were used, the melting pot method proved to be more labor efficient and ultimately contributed more than the bi-parental crossing procedure toward the development of new commercial cultivars for the Hawaiian sugar industry. From 1985 forward, the bi-parental crossing method was used more for introgressing desired traits from exotic germplasm through controlled backcrossing than for the development of commercial cultivars.