Mart Jaagus and Ingrid Bender
Jõgeva Plant Breeding Institute, Jõgeva, EE 2350, Estonia
Introduction
Materials and methods
Results
Discussion and conclusions
Breeding of white clover varieties started in Estonia in 1921. All three bred varieties (Jõgeva 1, Jõgeva 4, Tooma) are suitable for grazing. Jõgeva 4 and Tooma are on the Estonian List of Varieties. Initial material for Jõgeva 1 was obtained from a local wild population by mass selection. The variety was introduced in 1928 without comparative variety testing, since there was no white clover variety suited for the local conditions.
A Danish variety, Stryno, was used as original material for breeding of the variety Jõgeva 4. Repeated mass selections for yielding capacity and stability were made from 1933 to 1936. There then followed selections for winterhardiness and disease resistance from the overwintered plants of Stryno, which had naturally crossed with the local wild white clovers. After 1944 selection for persistence and yielding capacity were continued. Jõgeva 4 was included in the List of Varieties in 1960. It belongs to var. typicum.
To get a more persistent variety, breeding with new material was started in 1962. The new variety, Tooma, recommended for sown pastures on peat soils, was included in the List of Varieties in 1990. Tooma (var giganteum × var. typicum) was bred by mass selection from the hybrid progeny obtained by natural crossing of the more winterhardy plants of the Ukrainian variety, Gigant belyi, with local white clover populations.
Two trials were carried out to compare Tooma and Jõgeva 4. They were grown in mixtures with smooth-stalked meadow grass and meadow fescue. The experiment for evaluating of herbage yield was carried out from 1975 to 1980 at Tooma Experimental Station in sown pasture on peat soil. Varieties were grown separately on 10 m2 plots in four replications. Cuts were made five or four times from May to September. The aim was to determine total herbage DM yield, white clover content and crude protein (CP) concentration. The seed yield experiment was carried out from 1980 to 1982 on a sandy loam soil at Jõgeva Plant Breeding Institute. Plot size was 20 m2 and there were five replications. Seeds were harvested in August.
Total herbage DM yields of Tooma and Jõgeva 4 were similar but Tooma had the highest clover yield (Figure 1) and also the greatest clover content (Figure 2). Content of CP of Tooma and Jõgeva 4 was almost equal (Figure 3). In seed production Tooma significantly exceeded Jõgeva 4 only in second year of usage (Figure 4).
Figure 1 Total herbage and clover DM yield of Tooma and Jõgeva 4, 1975-1980
Figure 2. White clover content (%) in total herbage DM, 1975-1980
Figure 3. Content of crude protein, 1975-1980
Figure 4. Seed yield, 1980-1982
Morphologically several organs (petioles, flower heads, pedicles of flower heads, stolons, internodes of stolons) of plants of Tooma are bigger than those of Jõgeva 4, but 1000-seed weight is usually less.
During trials over six years on peat soil Tooma showed better persistence and competitive ability than Jõgeva 4. After the first overwintering and with less precipitation in spring, Tooma had less density in the sward but improved in the humidity of summer and matched the density of Jõgeva 4 for late summer. During the following winters Tooma survived comparatively well and increased its contribution Disadvantages of Tooma are slower growth in spring and weaker rooting ability of stolons. As this rooting is favoured by moisture, it is best suited for peat soils. On mineral soils, irrigation is recommended for better vegetative spreading. To eliminate negative features, use mixture of the both white clover varieties is recommended for pastures.
Because of lower winterhardiness pure-shown swards of Tooma get weedy, thus for seed production it is best grown in mixture with grasses, preferably with turf varieties of smooth-stalked meadow grass e.g. Esto
