Grape

The mode of pollination in the grapevine is not entirely clear. It seems that various types of pollination occur simultaneously. Entemophily has been reported in warm countries, ^{1 - 2} while in cooler climates insect distribution in the vineyard at bloom is very limited. ^{3 , 5} Furthermore, it was reported that in cool climates the nectaries were nonfunctional. In Vitis rotundifolia it was shown that insect pollination is taking place in many cultivars. ² Ane- mophily was shown to be involved in grapevine pollination. ^{4 , 6 , 7} This was based mainly on fruit set of female cultivars in relation to their distance from male or androgynous vines. Improvement in fruit set was achieved by blowing air through the vineyard. ^{8 , 9} On the other hand, Sartorius ⁵ showed that anemophily was effective for a distance of only a few centimeters. Destaminated flowers were pollinated only when the pollen source was no farther than 30 cm away. Thus, many workers suggested that in most cases the major pollination in grapevines is by autogamy. Sartorius ⁵ showed that in many cases aged inflorescences were able to set normal bunches. He also reported that right after flower opening, pollen can already be found on the stigma. Complete pollination, the short life of the stigma, and fruit set in flowers without calyptra drop point to the existence of autogamy. It should be noted, however, that artificial pollination with a mixture of pollen from various cultivars was more efficient in setting fruit than was pollination with pollen from the same or another cultivar. ^{10 - 12} It was also found that, in female cultivars, natural pollination by wind or insects from any distance was less effective than artificial pollination. ¹³ On the other hand, in our work ²⁶² with various cultivars grown under polyethylene cover, pollination was not uniform unless the cover was lifted and wind was allowed to blow through the area. This was true, although the temperature under the polyethylene cover was in the optimal range for pollen germination (between 25 and 30°C). ^{14 - 17} It has been shown that below 10°C and above 35°C, pollen germination is greatly inhibited or does not occur. ^{3 - 18} Rain and dry winds reduce pollination, probably by washing off or drying the stigma, respectively. ^{5 - 17 - 19} Dry winds are usually accompanied by high temperatures, which also have a direct inhibitory effect on pollen germination. ^{3 , 5} The degree of fruit set is both genetically and climatically determined. In some cultivars most of the flowers set fruit, while in others only a small percentage of the flowers will develop. This drop can occur as unfertilized flowers or young fruitlets. In some grapevine cultivars, which do not develop fruit abscission layers, the nonfertilized flowers will develop into seedless small shotberries. Such shotberries might also develop due to early abortion of the embryo. This phenomenon might be enhanced by unfavorable climatic conditions, such as hot dry winds or rain during flowering and shortly thereafter. In some cultivars the calyptra stays as a cap on the fruitlet and drops only at a later stage of fruit development. ²⁰