[Fertilization and the problem of heterosis in tetraploid red clover].

Self-fertility in the tetraploid variety Wielkolistna was studied over a period of nine years. When the flowers were artificially selfed (heads rolled between fingers) seed-setting was on the average 13.61 per head. Weather conditions during the flowering period affected very considerably the degree of self-fertility: favourable conditions promoting better seed-setting. Positive correlation coefficients were found (in 1957, 1963, 1964 and 1965) between self-fertility and seed-setting after free pollination.Inbred lines were established and their performance, seed yield and winterhardiness in I1-I4 were analysed. The degree of loss in green yield was 20-40%. However, several lines showed a higher yield than the controls. Very high uniformity of some features like leaf size and color, type of growth and leafiness could be observed already in the F1.To study the effect of heterosis the following crosses were performed: inbred lines of red clover x inbreds, inbreds x variety Wielkolistna, inbreds x polyploid ecotypes. Crosses were made by hand and without emasculation. In all cases no heterosis effect was observed and the green yield of the putative hybrids was of the same level as that of the inbreds. It could therefore be concluded, that the analysed plants were not of hybrid origin but mostly results of self-pollination.In the second series of experiments the plants were emasculated before crossing. This was done by immersing the flowers in 60% ethyl alcohol for 10 sec., then rinsing the heads in water. Seed-setting after use of this method was very poor: 1.08 seeds per head on the average, due to a damaging effect of the alcohol on female gametes. The green yield of the hybrid progeny was in this case much higher than that of the plants originating from crosses without emasculation (about 22% higher) and from free pollination (13% higher). It could, therefore, be supposed, that by artificial crossing without emasculation, and to some extent by free pollination, a lot of seeds originate from self-pollination.In using hybrid methods it is important to know the degree of self-fertility in a free pollinating variety. To study this problem plants without leaf marking, which were recessive homozygotes, were choosen and freely pollinated by surrounding plants with distinct leaf markings. The number of plant swithout leaf markings in the progeny was a direct measure of spontaneous self-fertility. At the same time some heads on the mother plants were bagged and rolled between fingrs to get data on artificial self-fertility. In 1964 9 progeny and in 1965 25 progeny were tested. In the first year spontaneous self-fertility was on the average 28.73% and in the second 55.20%. This difference was probably due to different weather conditions during the flowering period. They were more suitable in 1963 than in 1964, when a higher percentage of self-fertilization took place.There was great diversity in the degree of self-fertility among the analysed mother plants. Most plants were highly self-fertile (their degree of self-fertility being 40-95%). There is probably no competition between own and foreign pollen grains when they germinate on the stigmas of those plants.The tetraploid variety Wielkolistna can therefore be regarded as a partly autogamous population, its degree of self-fertilization being conditioned by genetical and to some extent external factors.The calculated correlation coefficient between spontaneous and artificial self-fertility was highly significant:r=+0.714 (P=1%).Plants with leaf markings were on the average better in yield than those without them: the green yield of the former was 521 g per plant, whereas that of the latter was 454 g (signif. withP=1%). The inbreeding depression effect is therefore 12.9 percent.In spite of a high degree of self-fertility there exist still some possibilities of applying hybrid methods to tetraploid red clover. These are discussed in the paper.