The possibility of achieving transfer of one or a few traits from one genotype to another by the use of irradiated pollen was first described by Pandey in Nicotiana (Nature 256:310-313, 1975); however, the subsequent attempts to reproduce the phenomenon in other plants have not been generally successful. In maize, only sublethal doses of radiation can be used for pollen treatment, since no viable seeds are produced at higher doses; in order to study gene transfer in this crop, we utilized a genetic system suitable to distinguish between gene transfer and genetic loss or mutation.
A multiple dominant marker stock was used as pollen source: C Sh Wx Gl15, on chromosome 9; pollen was irradiated with 10, 20, 30, 50 Krad of X-rays and applied to multiple recessive females. The F1 seeds were harvested, scored for endosperm markers, and a sample of each treatment (both normal kernels and with unexpected phenotype) was selfed to observe F2 traits.
The results of pollinations using treated pollen are summarized in Table 1, where, according to each radiation dose, the mean number of kemels per ear, the percentage of sterile or male-sterile plants and the F1 endosperm characters are reported. The F1 generation from irradiated pollen revealed a high proportion of defective endosperm seeds, uncoloured seeds, shrunken seeds and uncoloured shrunken seeds.
The F1 flowering plants were 954, from 1358 seeds sowed; the segregation for endosperm and seedling traits was analyzed in detail on a sample of twenty-one ears showing loss of endosperm markers or large segregation distortions. Single plant progenies showed complete loss of dominant allele C in 21 cases out of 843, of Gl allele in one case and of both Wx and C in one case.
When considering single gene segregation in the whole F2 progeny, plants from irradiated pollen revealed phenotypic ratios different from those of the control plants: a highly significant excess of recessive phenotypes was observed for wx, gl and c alleles.
M. Sari Gorla, M. Villa and E. Ottaviano
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