1999 * X * 1

J. Leetsar.  
  Eesti piimanduse allakäigu lugu 3
A. Bender.  
  Polüploidiseerimise mõju punase ristiku õite mõõtmetele, tolmeldava entomofauna liigilisele koosseisule ja arvukusele 9
An impact of polyploidization on the dimensions of red clover flowers, species’ composition and number of insect pollinators. In 1993 a field experiment was established in 4 replications the plot size at full bloom stage being of 10 m2, to study the range of morphological and secretory transformations of the flowers of tetraploid red clover varieties ‘Varte’ (early) and ‘Ilte’ (late), both bred at Jõgeva, and the possible effect of these changes to the species’ composition and number of pollinators. The varieties ‘Jõgeva 433’ and ‘Jõgeva 205’, exploited as diploid ancestors in the breeding program of the above-mentioned tetraploid varieties, were included into the trial as cheks.

The florets of the varieties were measured at full bloom stage in 400 replications in the stands of the first, second and third year of use. 30 observations were carried out during the flowering period of each pair of varieties while the pollinator species, the number of individuals visiting the flowers, and the motive of visit were recorded. Tables 3, 4, 6, 7, 8 and 9 present data about pollinators, as an average of three testing years and four replications, calculated as a total of 30 observations’ results.

All the herbage was cut, harvested, dried artificially and threshed by a combine harvester Hege 125 C to determine the seed yields.

The results of measurements indicated that the tetraploid varieties, derived by experimental polyploidization prior to selection, possess ca 10% longer corolla tube, the orifice of which is 30% more spacious. Pre-cutting of the herbage reduced the length of corolla tube of the florets of both early di- and tetraploid red clover varieties and reduced the width of corolla tube orifice as compared with spring growth. The floret’s corolla tube shortened in the following years.

The height of nectar level measured at the spring growth of the early red clover varieties referred to a more intense nectar secretion in the case of tetraploid variety. Although more abundant nectar secretion partly compensates the increase of the corolla tube length, the tetraploid variety ‘Varte’ had significantly longer distance between the orifice of the corolla tube and nectar in the florets than the diploid variety ‘Jõgeva 433’.

In Estonia the early red clover varieties are least insured with pollinators at the spring growth (tables 3, 4 and 5). The number of effective natural long-tongued pollinators (Bombus distinguendus and B. hortorum) is insufficient especially at their flowering season (the second half of June – the first half of July). The flowering period of the late red clover varieties (the second half of July – the first half of August) coincides with the time when the number of bumble-bees is close to the peak and therefore these varieties are considerably better insured with the pollinators (tables 5, 6 and 7). Pre-cutting of the early red clover enables to postpone the flowering season of the varieties into August when the natural pollinators are numerous (tables 5, 8 and 9) and the flowering of crops competing for the same pollinators is over. But due to short growing season in Estonia, the seed does not mature on regrowth every year or the harvest time falls on very late and rainy period causing big losses in harvest. Until the availability of reliable long-term weather forecast this management practice can not be recommended to seed growers.

Summarizing the pollinators recorded at all observations on the varieties’ spring growth and regrowth in the course of three testing years, the following generalizations can be drawn:

  1. The ploidy of a variety affected the pollinators’ visiting frequency of the flowers. Judging on the basis of the total number of pollinators who visited the flowers, the tetraploid varieties appeared to be more attractive for the pollinators.
  2. The ploidy of a variety did not affect the total number of honey-bees who visited the blooming herbage but it did affect the motive of visits (table 10). Honey-bees preferred diploid variety over tetraploid at pollen collection (ratio 63.4% : 39.9%) and tetraploid variety over diploid at nectar collection (ratio 60.1% : 36.6%). Nectar stealing occurred more frequently in the case of tetraploid than that of diploid variety, which is only indirectly caused by the ploidy level of the variety since the honey-bee itself does not bite holes into the corolla tube and is not able to steal the nectar independently. The higher percentage of nectar stealing by honey-bees from the tetraploid varieties results from the preference of B. lucorum to visit the flowers of these varieties more.
  3. Bigger number of pollinator individuals on the tetraploid varieties is due to the preference of bumble-bees to visit more these varieties. At that the ratio of nectar collecting bumble-bees to pollen collective ones was close irrespective of the ploidy level. More intense nectar secretion of the tetraploid varieties attracted more B. lucorum individuals onto their flowers, which all in all altered the ratio of bumble-bees collecting the nectar positively and negatively to a detriment of the tetraploid varieties: 40.7% of the nectar collecting bumble-bees worked negatively on the tetraploid varieties compared with 26.2% on the diploid varieties (table 11).
  4. The ploidy of the red clover variety affected the species’ composition and number of bumble-bees. Of short-tongued bumble-bees B. lapidarius, collecting positively the nectar from the flowers, distinctly preferred the diploid varieties with shorter corolla tubes of the florets in case of option. Another short-tongued species – B. lucorum nearly always steals the nectar both from the florets of di- and tetraploid red clover varieties and almost never collects the pollen. The morphological transformations concurrent with polyploidization have no impact on its preferences, yet the changes in the secretory functions do. Bigger nectar secretion attracted more individuals of B. lucorum onto the flowers of the tetraploid varieties.

Considerably more long-tongued bumble-bee individuals were recorded on the tetraploid varieties’ florets with longer corolla tubes as compared with the diploid varieties.

High seed yields harvested from the trial plots on some years prove a very high potential seed yield capacity of the tetraploid varieties bred at Jõgeva (table 12), the expression of which is, however, dependent not only on the weather conditions during bloom and harvest season, but also on the species’ composition and number of natural pollinators.

Utilization of the polyploid red clover varieties with longer corolla tube of the floret constrains us to search for more possibilities for artificial regulation of the number of natural long-tongued pollinators (B. distinguendus and B. hortorum). Modern entomology is ready to solve that problem.

A. Bender.  
  Polüploidiseerimisega kaasnenud punase ristiku õie morfoloogiliste ja füsioloogiliste muutuste mõju tolmeldajate töökiirusele ja väärtusele risttolmlemise tagajana 24
An impact of morphological and physiological transformations of red clover flowers accompanying polyploidization on the pollinators’ working speed and value as a guarantee for cross pollination. A late tetraploid red clover variety ‘Ilte’ has been bred at the Jõgeva Plant Breeding Institute by experimental polyploidization and following selections. Its floret has a better nectar secretion and 8.9% longer corolla tube, the diameter of which orifice is 33.7% more spacious compared with the diploid parent variety ‘Jõgeva 205’.

To ascertain an impact of the above-mentioned transformations, the work of the pollinators was measured by chronometer at the breeder seed fields of both varieties in 1993…1998. Recorded data served as a basis for the calculations of the working speed of the pollinators and for the specification of their work as a guarantee for cross-pollination.

The slowest pollinator on the flowers of diploid variety ‘Jõgeva 205’ was honey-bee (Apis mellifera L.) who visited 7.1 flowers per minute collecting the nectar through the orifice of the corolla tube, and 13.0 flowers per minute while collecting the pollen (table 3).

An average working speed of positively working bumble-bee species varied relatively little at the nectar and pollen collection, being 22.4 and 22.7 flowers per minute, respectively.

All positively working pollinators worked slower on the flowers of tetraploid variety in comparison with the diploid variety (tables 3 and 4). The most significant difference occurred among the short-tongued pollinators (Apis mellifera L., Bombus lapidarius L.) at the nectar collection (table 4).

A strong positive correlation existed between the working speed of the pollinators at nectar collection on the flowers of both di- and tetraploid varieties and the length of their probosces (r=0.74 and 0.78, respectively, figure 1). Among the species, B. hortorum worked most rapidly at nectar collection and B. distinguendus at pollen collection on the flowers of both variety types (table 3).

B. lucorum, the most numerous bumble-bee species on many years in Estonia, bites a hole to the bottom of the corolla tube of red clover’s floret, takes the nectar without touching the generative organs of the floret taking no part in the reproduction process of the species. The morphological transformations of the floret concurrent with polyploidization have no effect on its working speed, however, the bigger nectar secretion attracts them onto the flowers of tetraploid variety. B. lucorum collects the pollen from the red clover very rarely.

Based on the working speeds and considering the longer working period of the bumble-bees per day (coefficient 1.1), the pollinator-values in honey-bee units (honey-bee at nectar collection = 1.0) were calculated (table 5). A honey-bee collecting the pollen on the seed production field of diploid red clover was equal to 1.8 honey-bee units, the mean pollinator-value of the bumble-bee species was equal to 3.5 honey-bee units.

A honey-bee collecting the pollen on the flowers of tetraploid red clover was equal to 2.1 honey-bee units and the mean value of bumble-bee species accounted for 4.0…4.2 honey-bee units.

As the calculation of honey-bee units was based on a honey-bee who worked a third slower at nectar collection on the flowers of tetraploid variety compared with the diploid variety, it should be considered adequate for guaranteeing the same amount of work if a third more pollinators, converted into honey-bee units, work on a superficial unit of a seed production field of the tetraploid red clover variety.

The value of the pollinators as a guarantee for cross-pollination on the flowers of di- and tetraploid varieties was investigated on the basis of an average number of visited florets in a cluster (table 6) and also by detailed analysis of the work of all examined pollinators (table 7). As a conclusion of this study, it can be stated that the pollinators as a guarantee for cross-pollination did not work less effectively on the flowers of tetraploid red clover variety than on the flowers of diploid variety. A supposition that bigger resource and a longer corolla tube of the floret can alter the character of the work of long-tongued pollinators was not verified. In case of positive working, the short-tongued pollinators (Apis mellifera, B. lapidarius) are the best guarantees for cross-pollination but the character of their work (especially in honey-bee) depends on the number of B. lucorum. By rising multiplicity of the latter, they start to work negatively on the flowers of both di- and tetraploid red clover varieties and do not pollinate the flowers on that occasion.

A fact that B. sylvestris works rapidly on the flowers of both di- and tetraploid red clover was affirmed in the study. The species is unfortunately low in number in Estonia and visits the flowers of red clover relatively seldom.

E. Haak.  
  Õunapuu lehtede põhitoitainete sisalduse sõltuvus väetamisest ja muudest teguritest 38
The content of basic nutritive elements in apple leaves dependening upon fertilizing and other agents. The content of basic nutritive elements in leaves were investi-gated (1991–1997) at the Polli Horticultural Institute in the apple cultivar ‘Talvenauding’ and (1969–1997) in the cultivars ‘Cortland’ and ‘Tellissaare’ on the occasion of fertilizing. Different fertilizer doses and ways were used in (1) pre-planting and (2) yearly fertilizing. The nitrogen and potassium content in leaves varied in great extent between the years even in one fertilizing variant, depending for example upon the yield level. In the case of abundant yield the nitrogen was at high level and potassium at low level. The phosphorus content in leaves was relatively stable and only little dependent upon fertilizing and other agents. It became evident that leaf diagnostic method is not practical in Estonian changeable weather conditions: the content of basic nutritive elements in leaves depends more upon other agents than on the content of nutritive elements in soil and upon fertilizing.
K. Kask.  
  Ploomikasvatus Eestis pärast Teist maailmasõda 46
Plum cultivating in Estonia after the World War II. The domestic plum (Prunus domestica) is the main plum species cultivated in Estonian orchards. The bullace or Damson plum (P.d.subsp. insititia) is becoming much less popular. The cherry plum (P.cerasifera) is relatively new fruit tree and only few cultivars are available. Up to now there is almost only one rootstock – cherry plum seedlings. The plum is the second leading fruit tree. Its produc-tion constitutes 4–9% from the total fruit and berry crop.

However popular fruit tree the plum is, its production has not been stable due to cold winters. Thus, the very severe winters 1939/40 (and the two followings), 1955/56, 1965/66, 1978/79, and 1986/87 killed almost all plum trees of bearing age. The most endangered were North-East region, Jõgeva district, and South-East region (Põlva, Võru and Valga districts), also surroundings of Kuusiku, Türi and Väike-Maarja. Due to winter damages, no crop had given the big plum orchards of the Kullaaru farm (near Rakvere), Raasiku (in Harju district), and the Tõrva farm (Valga district). The worst crop years for the whole Estonia appeared in the periods 1963–1973 and 1977–1983, the greatest crop failure being in 1966 and very bad harvest in 1979 (the crop data were analysed since 1963). The bad harvest appeared also in 1963, 1968, 1969, 1970, 1971, 1975, 1980, 1982, and 1987.

The abundant crops were gathered in 1974, 1976 (record), 1984, 1986, and 1993. The most stable crop yield was in 1990s.

The plum cultivating is concentrated near the bigger towns. Thus, almost one quarter of the trees are planted in home gardens and summer cottages of Tallinn, Harju and Rapla dis-trict. 11% of the trees are growing in Tartu and Tartu district, 9% are growing in Viljandi district. Only a little less of trees is growing in Pärnu district. 7.5% of the trees are growing in East-Virumaa (near big towns Narva and Kohtla-Järve). The smallest number of trees is growing in Hiiumaa district (2%), Järva, Põlva and Valga districts.

The biggest plum producing enterprises with 1–2 ha to 18 ha orchards which gave a good production are situated in Tartu district and in Viljandi district. The productivity of plum trees in good years was 3–15 t/ha, the record 36 t/ha was in 1976 in Sootaga farm near Tartu.

The choice of cultivars have been based mostly on West European ones, for example 'Victoria', 'Edinburgh', 'Emma Leppermann', and on Estonian landraces. In 1990s, the situa-tion is turning to the advantages of local cultivars bred at the Polli Horticultural Institute: 'Ave', 'Julius', 'Kadri', 'Liisu', 'Suhkruploom', 'Vilmitar', and 'Vilnor', which are early or midseason plums of good quality, attractiveness and good size.

According to statistics, plums are imported into Estonia in quantities about one third (1996, 1997) as many they are produced in Estonia. The fresh fruit is available now year around. The yearly export is (to Finland) only 4–8 t. The production plus import makes about 1 kg per capita during the year.

M. Karelson.  
  Eesti Vabariigi agraarpoliitika 1918...1940 60
  Akadeemilise Põllumajanduse Seltsi tegevusest 67
  Akadeemilise Põllumajanduse Seltsi uusi liikmeid 70