Influence of pollination treatments and temperature regimes on progamic phase and fruit set in three European plum (Prunus domestica L.) cultivars tollerant/resistant to Sharka virus

Pollination and temperature are predominant factors affecting the progamic phase of sexual plant reproduction. In light of climate change and the emergence of increasing temperatures, new knowledge is necessary to encourage fruit breeding programmes to develop cultivars adapted to these changes, as well as to find the best incompatibility relationships with the aim of achieving high fruit quality and yield. This research was conducted to reveal the effect of pollination treatments and temperature on the progamic phase and fruit set in three European plum (Prunus domestica L.) cultivars ('Jojo', 'Hanita' and 'Katinka') resistant/tolerant to Sharka virus using fluorescent microscopy. Reproductive parameters (flowering overlapping, pollen germination, number of pollen tubes in the upper part of the style and locule of the ovary, dynamics of pollen tubes growth and initial and final fruit set) were investigated in vivo under different pollination treatments (cross, open and self-pollination). The influence of different temperature regimes (20 degrees C, 23 degrees C and 26 degrees C) on the progamic phase was also observed under cross and self-pollination. The pollination treatments significantly influenced the number of pollen tubes in the style and ovary, as well as dynamics of pollen tubes in different regions of pistil. Pollen tubes showed better growth in different crossing combinations compared to open and self-pollination. Higher temperatures accelerated pollen tube growth and reduced the time they need to reach ovules. Generally, 'Jojo' appeared to be the best pollenizer among the examined cultivars, while 'Katinka' exhibited the best response of pollen tube growth to various temperature regimes. The differences observed between growth of the pollen tubes in each genotypetemperature combination revealed that certain crossing combinations were better adapted to higher temperatures so this can be taken into account as one of the adjustments to climate change. The ability of cultivars to respond to high temperatures in the progamic phase can also be helpful for breeding programs in developing new cultivars better adapted to different temperature conditions.