Effect of pollen grain sources on the fruit and seed formation of the Clementine ‎mandarin and the role of genetic similarity of the pollen sources in fertilization ‎

In order to investigate the role of different pollen grains on the qualitative and quantitative characteristics of 'Clementine' mandarin (Citrus clementina), an experiment was carried out based on a randomized complete blocks design with six treatments and four replications. The 'Clementine' mandarin was subjected to the open-, self-, and cross-pollination with the pollen grains of sweet lemon (Citrus limetta), grapefruit (Citrus paradisi), Lisbon lemon (Citrus limon) and sour orange (Citrus aurantium). The compatibility and incompatibility of pollinators were determined using controlled pollination methods and the microscopic analyses of pollen tube growth. The microscopic evaluations revealed that 'Clementine' mandarin is a self-incompatible cultivar but it is compatible with all studied species. The fruit set in the flowers that were pollinated with sweet lemon (73.75%), Lisbon lemon (71.25%), grapefruit (70%) and sour orange (70%) were not significantly different, while the self- and open- pollinated flowers produced a lower leve of fruit set. The highest viable seeds (13.2) were recorded in the fruits that were pollinated with sour orange, while the self-pollinated ones had no seed. In addition, the pollens of sour orange were the most successful for penetration to the basal portion of style and into ovary of ‘Clementine’ mandarin. Evaluation of genetic affinity among Citrus species revealed that sour orange is the most genetically similar species with 'Clementine' mandarin. Results of this investigation showed that the source of pollen grain substantially affect the fruit set as well as qualitative and quantitative attributes of 'Clementine' mandarin. By considering all of the fruit-related factors, the pollens of C. paradisi and C. limon are suggested as the best choice for improving qualitative and quantitative characteristics of 'Clementine' mandarin.