Flowering dynamic and susceptibility of the flowers of black currant (Ribes nigrum L.) and red currant (Ribes rubrum L.) to spring frosts

Period of dormancy in currant cultivars has a short duration and because of that its growing season starts very early. The major reason of yield decrease in currant cultivars is its flowers sensitivity to spring frosts. Because of the short winter dormancy and early entry into the flowering period cultivars are influenced by spring frosts, so the blossom freezing appears. Field trials were conducted in the village Mislodjin (near Belgrade), situated between 44 deg 30 min and 44 deg 45 min north latitude and 20 deg and 20 deg 20 min east longitude. Altitude is between 80 and 90 m. The experiment included cultivars of black (Tsema, Bona, Silmu, Cacak black, Ometa, Malling Juel, Ben Lomond, Öjebyn, Ben Sarek) and red currant (Jonkheer van Tets, london Market, Juniffer, Stanca, Rondom and Rovada). The experiment was conducted during 2007-2009. The dynamic of flowering (from the beginning of flowering time till the fruit set of the first berries) and susceptibility of the flowers to spring frost were determined in this study. Freezing was determined by making a longitudinal section of opened ad unopened flowers immediately after the occurrence of frost, and the degree of freezing was determined from the ratio of the number of frozen flowers and number of total analyzed flowers. The cultivars of black and red currants averagely began flowering in the last decade of March. Among black currants, the earliest in this phenological phase was cultivar Bona (March 25th), and among red currants cultivar Junifer (March 21st). The time span between opening of the first flower to the fruit set of the first berries varied in cultivars of black currant from 16 (Bona) to 21 days (Ometa), and in red currant cultivars from 16 (Junifer and London Market) to 20 days (Rondom). At the time of occurrence of spring frosts, all cultivars were in the process of opening flowers. Regarding all cultivars of black currant, the highest susceptibility to spring frost demonstrated cultivar Bona with 68.42% and Ben Sarek with 41.02% of frozen flowers in the inflorescence. The degree of damage from spring frosts of flowers of black currant depended in a small extent on the date of entry into the flowering period. In red currant, cultivars that started flowering period earlier had much more frozen flowers. In regard to relationship between flower damage and the moment of entering the flowering period phase, red berries cultivars showed a strong, linear correlation coefficient (R = - 0.76, p is less than 0.01). In the red currants, the highest number of frozen flowers in inflorescence had a cultivar Junifer (35.73%) and the smallest cultivar Rovada (8.98%). The highest sensitivity to this factor of environmental stress in black currant cultivars expressed Bona and Ben Sarek, and in red currant cultivars Junifer. At least flower damage by spring frost had cultivars Öjebyn and Rovada.