EMBRYO CULTURE AS A MEANS TO RESCUE DETERIORATED MAIZE SEEDS

Seed germplasm is received and stored at genebanks, such as the Nation al Seed Storage Laboratory, to ensure that genetic diversity is availa ble for future plant breeders. On occasion, low viability seeds are re ceived or seeds may deteriorate unexpectedly between scheduled viabili ty tests, resulting in accessions that cannot be successfully regenera ted with routine procedures. In 1993 and 1994, experiments were conduc ted with the objective of developing procedures to improve the surviva l of low viability maize (Zea mays L.) seeds and thus avoid the loss o f potentially valuable genes. To develop a seed rescue protocol, the e ffects of various antibiotics, C and other nutrient sources, and hormo nes were evaluated on the growth of excised hybrid maize embryos in ti ssue culture. Kanamycin and thiram were effective against bacterial an d fungal contamination and improved the growth of aged embryos. Among the C sources tested, only sucrose stimulated growth of isolated embry os but not whole seeds. Complete nutrient mixtures containing macro- a nd micronutrients and vitamins did not stimulate growth of whole embry os, but they stimulated the growth of isolated axes. Among the hormone s tested, only gibberellic acid stimulated the growth of the primary r oot. The seed rescue protocol developed through these experiments was tested on eight endangered maize landrace populations from Argentina. Six of these eight populations contained sufficient seed numbers to co mpare the embryo culture protocol with whole seed germination. Embryo culture resulted in a twofold increase, an average (range = 0.9-4.0), in plant recovery compared with whole seed germination. This protocol can be used to rescue maize germplasm accessions with a germination pe rcentage below that which results in successful field regeneration.