In recent Newsletters, we reported that immature tassel meristems of both cv. Se60 and Oh43 can be cultured successfully from anther initiation through normal meiosis and microsporogenesis to production of trinucleate, normal pollen (MNL 55:116,1981; MNL 59:72, 1985). The pollen so produced germinates on agar (MNL 59:73, 1985) and on silks and also fertilizes ovules to produce mature kernels (MNL 60:89, 1986). We report here further observations from studies undertaken among the progeny derived from in vitro generated pollen in comparison with those derived from in vivo generated pollen to evaluate variability (tissue culture induced somaclonal variation) by: 1) phenotypic analysis, 2) chromosome analysis and 3) gel electrophoresis.
The kernels produced with in vitro pollen from both cultivars (Se60 and Oh43) were grown in our London nursery during the 1985 and 1986 field seasons and the following observations were taken: 1) plant height; 2) number of leaves/plant; 3) leaf width; 4) tassel length; 5) number of tassel branches; 6) pollen fertility; 7) P% (P = number of kernels per ear/number of ovules per ear) and 8) 100 seed dry weight. The kernels from either cultivar had 100% germinability and yielded mature, healthy, normal and fertile plants. No morphological abnormalities were detected among the progeny (N = 290) either in F1 or F2 generations. Statistical analyses of these characters showed that the plants derived from in vitro pollen (R1) and their selfed progeny (R2) were similar in most respects to in vivo plants for both genotypes. Moreover, the analysis of chromosomes in root tips (N = 45) showed no changes in the chromosome number. The analysis of meiotic chromosomes in these plants is in progress.
Patterns of polypeptide synthesis in plumules and radicles of the seedlings derived from in vitro and in vivo pollen were analysed by 1D and 2D SDS PAGE, according to the procedures used routinely in our laboratory (Can. J. Biochem. 60:569, 1982). Striking differences, both quantitative and qualitative, were observed in the polypeptide patterns 1) between Oh43 and Se60, and 2) between plumules and radicles, no qualitative or quantitative differences were observed in the polypeptide patterns of 1D-gels between in vitro and in vivo seedlings. However, minor quantitative differences between in vitro and in vivo seedlings were detected for a few polypeptides by 2D gel electrophoresis. The significance of these minor differences has yet to be explored.
We conclude that the pollen generated from in vitro cultured tassels produces plants which are similar in most respects to plants produced from in vivo grown pollen with no observable morphological and chromosomal alterations.
D.R. Pareddy, R.I. Greyson and D.B. Walden
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