Hawaii's Half-Century Breeding Tropical Sweet Corn

In 1961, James Gilbert, Chair of the University of Hawaii Dept. Horticulture (UH), welcomed me to his faculty and promptly took me to see fields of sick sweet corn. The culprit proved to be maize mosaic virus (MMV). Within the year we could show that no American sweet or field corns were resistant. A half-century later we can add that no tested commercial temperate sweet corns are resistant to MMV and a host of tropical biotic and abiotic stresses. Among these are many rots (fusarium, aspergillus, bacteria), most tropical viruses and rusts, ear- and army-worms, short daylengths, and tropical strains of most blights and downy mildews. Our data confirm that North America’s sweet corn represents an incredibly narrow germplasm base that offers little more than tenderness to tropical breeders.

Sweet corns bred in the tropics are now grown on ~.5 m acres annually. Thailand is the primary source of improved products including canned, frozen, corn milk and other products. Dominating production are single- and 3-way-crosses with >75% tropical parentage. All appear to have a heritage in Hawaii-based germplasm. Basic foundation sources were ‘Hawaiian Sugar’, an open-pollinated variety bred in the 1940s by A.J. Mangelsdorf, and ‘Hawaiian Supersweet #1” and ‘Hawaiian Supersweet #9’ from our breeding at UH. The first of these carries the historic ‘sweet-corn gene’ sugary-1, the second has gene shrunken-2 and the last has gene brittle-1. The former locus is no longer used. The others often occur in unexpected combinations with endosperm loci such as waxy1 (common in Asia’s ‘sticky’ vegetable maize). Accelerated genetic advance attributes much to Hawaii’s climate, with breeding nurseries in over half the months of the past half-century.

Close collaboration among public breeders in Hawaii, Thailand, and Australia account for the great majority of acceptable modern germplasm. About 2000 open-pedigree inbreds, synthetics, varieties, and germplasm sources are now available from Hawaii’s Foundation Seed (www.ctahr.hawaii.edu/hfs). In general these provide wide adaptability to major diseases, pests, and abiotic stresses common to tropical sweet corn growers. Private industries and international institutions such as CIMMYT and AVRDC made no contributions to this germplasm or provided financial support for its development.

Sweet corn gets to market within ten weeks in most of the tropics. Many regions around the world now can boast monthly or even weekly production of this high value, highly adaptable, and highly respected food crop.