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The viability of ovules was studied in five plum cultivars under laboratory conditions at four constant temperatures: 5ºC, 10°C, 15ºC and 20ºC and under field conditions over two years. During 10 days from the onset of full bloom, ovule viability in cvs CaCanska Rana,CaCanska Najbolja and CaCanska Lepotica was between 80-100 % at the temperatures of 5ºC, 10ºC and 15ºC, in both years. In the same period, ovule viability in cvs Wangenheims Frühzwetsche and PoegaCa was lower, but never below 50%. At the constant temperature of 20ºC, all plum cultivars showed a decline in longevity of ovule viability, which was pronounced in cv. CaCanska Rana. During the 10 days from the onset of full bloom, ovule viability in all five plum cultivars under field conditions showed a high viability, which approximated to the ovule viability of the cultivars at the constant temperatures of 5ºC, 10ºC and 15ºC, in both years. Determination of the longevity of ovule viability in the mentioned plum cultivars is of great importance due to its effect on the effective pollination period and fertilisation success. This paper deals in detail with the interrelations between the temperature effects on ovule viability, pollen tube growth and fertilisation, as well as on fruit setting.

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