engleski

Temperature affects reproductive traits in olive tree (Olea europaea L.) – flowering timing and pollen performance

The reproductive phase has proven to be one of the most temperature sensitive stages in plants. Relatively high or low temperatures are often correlated with low fertilization percentages and low fruit setting. The interest in the effect of temperature on reproductive processes is increasing because the global rise in temperature has affected plant populations by inducing a shift in several phenological traits, such as dormancy release and flowering time. In the Mediterranean basin, olive flowers between April and June which is later than most other tree species. This later date allows olive to meet the requirements of an ample accumulation of heat units during the growing season. Six olive cultivars (‘Lastovka’, ‘Leccino’, ‘Levantinka’, ‘Oblica’, ‘Pendolino’ and ‘Itrana’) were employed in field experiment during three years to determine the effect of accumulated temperatures preceding the flowering periods on the beginning of flowering. The flowering periods were assessed by visual examination of eight trees per cultivar. The average flowering date (AFD) was calculated as the number of days from 1 January until the start of the flowering period. The AFD was determined for each experimental year using flowering dates of all tested cultivars. The number of chilling units (CU) was calculated using the daily maximal and minimal air temperatures. The heat accumulation start dates were the first days after the chilling requirement had been met and continued until the start of flowering season. Heat units were expressed in growing degree-days (GDD). The effect of temperature on pollen germination and pollen tube growth was evaluated using in vitro system. Pollen performance has been tested under different temperatures (15, 22±2, 30, 35 and 40 ºC) to evaluate the sensitivity of the microgametophyte to temperature extremes. The olive tree can be used as a sensitive biological indicator of climatic changes since the yearly temperature variations control the timing of the flowering period. High correlations have been found between values of AFD and those of CU and GDD. Moreover, simultaneous flowering of different cultivars is important in achieving a high fruit set after cross-pollination. The flowering periods of most of the studied cultivars overlapped to some degree. Pollen germination in vitro was enhanced when pollen grains were exposed to higher temperatures up to 35 ºC ; however germination failed at 40 ºC. In most of the studied cultivars, the longest pollen tubes were developed at 22±2 ºC and the pollen tube length decreased with higher incubation temperatures. Temperature significantly affected flowering timing and pollen performance in olive cultivars and therefore participates in regulation of final fruit set and yield.

olive; temperature; flowering period; pollen germination; pollen tube growth

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