II.27 Increased barley haploid production following gibberellic acid treatment.
N. C. Subrahmanyam and K. J. Kasha. Crop Science Department, University of Guelph, Guelph, Ontario, Canada.
Haploids can be produced from any line of cultivated barley using the interspecific cross of diploid Hordeum vulgare by diploid H. bulbosum (Kasha and Kao, 1970). The seed set from this cross usually averages about 60% and all seeds are apparently haploids. However, embryos cease to develop about 1O to 12 days after pollination making it necessary to use embryoculture techniques at that stage in order to obtain haploid seedlings.
The success of Kruse (1967) in obtaining intergeneric hybrids led us to experiment with gibberellic acid for the development of haploids. Florets of H. vulgare plants of the cultivars York and OAC-21 were emasculated just prior to anther dehiscence. On the following day, they were pollinated with fresh pollen of diploid H. bulbosum. Starting the day after pollination, gibberellic acid was applied to the pollinated florets by placing one drop (from a #22 hypodermic needle) above the ovary. Depending upon the concentration used these applications were daily from one to 14 days as shown in Table I. The total application ranged from 150 to 225 ppm of gibberellic acid.
The results indicate that both the percent of seed set and the percent of culturable embryos obtained from seeds that were set higher after gibberellic acid treatment. The average of all the gibberellic acid treatments was 80.95% seed set and 91.93% culturable embryos compared to 56.46% seed set and 60.61% culturable embryos on the York control. The results also indicate a higher germination percentage in the treatments. The average of full germination (both root and shoot) in the treatments was 26.09% as compared to 12.44% on the York control. The treatments with the higher concentrations of 100 to 200 ppm were not as effective as lower concentrations applied more often. On the other hand, the treatment with 12.5 ppm had to be stopped at 14 days because seed development had ceased. It would appear that treatments at 75 ppm for 3 days or 50 ppm for 4 days would be the logical ones to follow, although not necessarily more effective than treatments at lower concentration for longer periods of time. It was also observed that some treated embryos continued to develop up to 18 days on the plant. Furthermore, the embryos were usually much larger at the time of culturing if they had been treated.
Gibberellic acid treatments of crosses between diploid H. vulgare and tetraploid H. bulbosum also increased the frequencies of seed set and seedlings. However, in this case the progeny were all triploid interspecific hybrids.
It would appear that gibberellic acid treatment might also be effective in increasing the frequency of twin embryos as 2% of the treated seeds from York contained twin embryos. Both seedlings obtained from such twins were haploid.
A discussion of how gibberellic acid treatment results in a higher seed
set and haploid frequency would be premature at this time. We have observed
an increased development of both the endosperm and the embryo and further
studies on this development are in progress.
References:
Kasha, K. J. and Kao, K. N. 1970. Nature 225:874-876.
Kruse, A. 1967. Royal Vet. & Coll. Yearbook, Copenhagen 1967:82-92.
