| The frequency of twin seedlings in New Zealand wheats
J.M. MCEWAN and K.J.VIZER Crop Research Division, D.S.I.R., Lincoln. New Zealand In the course of a project to obtain heteroploid plants in New Zealand bread wheat varieties, information on the frequency of twin seedlings in these varieties was collected. WILSON and Ross (1) reported recently that in three varieties of winter wheat a twin pair was found per 3,786 seedlings examined. Earlier MUENTZING (2) obtained a large number of wheat twin pairs, but did not give details of their frequency. KIHARA and TSUNEWAKI (3) found one per 1,569 seedlings in normal wheats. In this study five New Zealand commercial varieties and two unnamed hybrid lines were examined, four of them over three consecutive seasons and three for two seasons. The seed lines were obtained each year from autumn-sown field tria's grown near Lincoln, with the exception of the seed of the variety Gabo which came from spring-sown increase blocks in the same district. Weighed or counted samples were germinated on wet paper towels in a germinating cabinet maintained between 75o and 80oF. Seedlings were removed for examination daily and the number of ungerminated grains was deducted from the total after a week of germination. In the three seasons over 500,000 seedlings were examined and 327 twin pairs and two triplets were found; in addition five twins of these varieties were obtained from other sources. The results in Table 1 were examined in several chi-square tests and show that there were substantial varietal differences in the frequency of twin seedlings and highly significant season-to-season variation. The seedlings of a twin pair were generally dissimilar in size, the smaller being displaced to on side of the major seedling. Twin pairs were classified into three groups on the size relations of the component seedlings (Table 2). The number of twin pairs studied was not large enough to determine differences, between varieties in the relative size of the seedlings, except that the difference between Gabo and all the others was very highly significant, (chi-square 13 4 with 1 d.f.). The smaller seedling was displaced to either side of the major embryo with approximately equal frequency (134 and 148). There appeared to be no relationship between seed-size, a determined by 1,000 kernel weight determinations, and frequency of twins (Table 3). The variety Gabo was used to investigate the possibility of recognising ungerminated grain with twin embryos. A sample of 3,000 grains classed as normal yielded four twin pairs, whiel 85 grains apparently with slight morphological abnormalities of the embryo, which had been selected from the same sample, did not produce any twins. It is concluded that the frequency of twin seedlings is a varietal characteristic under the influence of environmental conditions and not related to the average grain size of the variety. Grains with twin embryos could not be recognised by visual examination of ungerminated kernels. References WILSON, J. A. and W. M. Ross 1961. Crop Sci. 1 : 82 MUENTZING, A. 1938. Hereditas 24: 487-91 KIHARA, H. and K. TSUNEWAKI 1964. Seiken Ziho 16: 1-14 |