Contributors to this page: CIMMYT, Mexico (Suketoshi Taba, Bonnie J. Furman), with inputs also received from IITA, Nigeria (Dominique Dumet), EMBRAPA (maize and sorghum genebank), Brazil (Flavia Teixeira), USDA(ARS/NC7, ISU), USA (Mark Millard).
When are field banks used
Field banks are usually used when species do not seed propagate, are difficult to establish or have short-lived seeds, and thus where the efforts and costs of constant regeneration of seeds are high, and it becomes more economical, efficient and practical to maintain them permanently in a field genebank.
CIMMYT is currently experimenting the use of field banks for Tripsacum spp., a maize wild relative. There is limited work being done with this wild species, but the most important procedures are mentioned below.
- Clones are maintained planted in fields, at an experimental station mostly used for seed harvesting (the breeding station in Tlaltizapan, Morelos, Mexico). This is complementary to the ex situ seed genebank.
- Clones are cut and cleaned once a year (no special handling is required).
- Tripsacum will not cross breed with maize, so there is no need for isolation.
- Diploid species can produce hybrid caryopsis (seeds) when flower at the same time. Therefore it is necessary to clean seedling volunteers around the clones, to avoid mixing them with the original clones.
- Genotyping the clones should facilitate identification of diploid or apomixic polyploids (endosperm development does require fertilization by a reduced or unreduced sperm cell).
- Currently, viable seeds are harvested and distributed upon request with small amount of seed.
- The major problem has been adaptation to the ex situ sites. Many clones not adapted to the CIMMYT experimental station environment and have been lost.
A low level of sexual reproduction allows for gene flow among diploid and polyploid species, creating the complex pattern of overlapping and highly variable morphology seen in the centers of species diversity in Mexico and Guatemala. In situ monitoring of the species has been carried out in Mexico and Guatemala in the last few years. Contraction of populations at in situ sites of Tripsacum is noted, especially in Guatemala. An ex situ field genebank of Tripsacum can complement in situ conservation. Research on Tripsacum diversity and maize-Tripsacum hybrids can contribute in maize evolution and breeding, and thus the use of Tripsacum in agriculture.
References and further reading
Berthaud J, Savidan Y, Barre M, Leblanc O. 1997. Tripsacum In: Fucillo D, Sears L, Stapleton P, editors. Biodiversity in Trust. Cambridge University Press, Cambridge, U.K.
Duvick SA, Pollak LM, Edwards JW, White PJ. 2006. Altering the fatty acid composition of Corn Belt corn through Tripsacum introgression. Maydica 51:409-416.
Springer TL, Dewald CL. 2004. Eastern gamagrass and other Tripsacum species. In: Moser LE, Burson BL, Sollenberger LE, editors. Warm-Season (C4) Grasses Agronomy Monograph 45. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, Madison, WI. pp. 955-973.
Wilkes G. 2004. Corn, strange and marvelous: but is a definitive origin known? In: Smith CW, Betran J, Runge ECA, editors. Corn: Origin, History, Technology, and Production. John Wiley & Sons, Inc. pp. 3-64.