Attempted "egg transformation" in Zea mays L., using irradiated pollen

Experiments were conducted to determine if "egg transformation" could be achieved in Zea mays L. as described by Pandey in Nicotiana L. Multiple recessive and multiple dominant marker stocks were employed, as well as a tester and a donor line for the "En" transposable element. Recipient tester females were pollinated with dominant donor pollen, which was applied in several treatment combinations. The pollination treatments included: 1) pollen irradiated at 20, 30, 40, 80, and 100 Krad; 2) pollen irradiated with the same doses, mixed with non-irradiated recipient pollen; 3) pollen irradiated at 80 Krad, followed by self pollination delayed 18 h; 4) non-irradiated donor pollen mixed with non-irradiated recipient pollen. Zero seed were produced from 100 pollinations with irradiated pollen. There were 258 pollinations made with irradiated donor plus self pollen mixtures, producing over 21,300 seed. Of these seed, 3 were unexpected. One was clearly from pollen contamination, one was clearly derived from a pre-meiotic mutation, and the third occurred as a mutant sector in the seed's endosperm. There were 56 pollinations with non-irradiated pollen mixtures, producing over 5,000 seed. Among these seed, there were 7 unexpected seed. Three of these were clear-cut cases of heterofertilization. Four progeny were dominant for all seed and seedling markers except one endosperm marker. These cases appear to represent spontaneous recessive endosperm mutations. More than 59,000 potential transformation events were screened producing only 6 apparent mutations. It is concluded that if egg transformation occurs in Zea mays, it is a very rare event, and is not likely to be useful in corn improvement.