Analysis the effects of pollen grain sources on the fruits set and their characteristics of ‘Clementine’ mandarin using microscopic and molecular approaches

Abstract ‘Clementine’ is one of the most important cultivars of mandarin that always has problems with fertilization and fruit set because of its self-incompatibility. Therefore, for the commercial fruit production, suitable and compatible pollen is required. To determine the best pollen source, ‘Clementine’ flowers were subjected to the different pollen grains including sweet lemon, Lisbon lemon, grapefruit, sour orange, as well as self-pollination and open pollination. Compatibility and incompatibility tests were carried out using controlled pollination method and microscopic study of pollen tube growth. Molecular markers were used to study the genetic relationships of the species and assess the role of genetic similarity on the fruits set and their attributes. The results of the microscopic study indicated that ‘Clementine’ mandarin is a self-incompatible cultivar but it is compatible with all the cultivars used in the experiment. Clementine fruit characteristics significantly influenced by pollen grain sources. The results of controlled pollination showed that the highest percentage of fruit set was obtained from flowers pollinated with sweet lemon pollen (73.75%) followed by Lisbon lemon pollen (69.25%) while the lowest fruit set was obtained from the self-pollinated flowers (11.75%). The highest and the lowest hale seeds were obtained from the flowers pollinated by Lisbon lemon pollen (12.22%) and self-pollinated ones (no viable seed), respectively. High correlation was observed between some of the studied characters that would be useful for selection purposes in the breeding programs. Results of microscopic evaluation of pollen grain tubes revealed that among the studied pollen grains, sour orange pollens were the most successful for penetration to the basal portion of style and into ovary of ‘Clementine’ mandarin. Assessment of genetic relationship among different Citrus species revealed that sour orange was the most similar species with ‘Clementine’ mandarin. High positive correlation was observed between genetic similarities of pollen sources at DNA level with the pollen grain sprouting and penetration to the different parts of style and ovary as well as seed formation percentages. Based on the studied fruit characteristics, grapefruit and Lisbon lemon pollens are suggested as the suitable pollinators for improving the qualitative and quantitative characteristics of ‘Clementine’ mandarin fruit.