Comparison of self- and cross-pollination in pollen tube growth, early ovule development and fruit set of Camellia grijsii
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2019 Friends Science Publishers. Camellia grijsii Hance is one of the most important woody edible oil tree species in Southern China; however, it often has a low fruit set rate. To elucidate the causes of poor fruit set in C. grijsii, self-pollination (SP) with C. grijsii and cross-pollination (CP) of C. grijsii C. villosa tests were conducted. Pollen germination and pollen tube growth into pistils, and early ovule development after SP and CP, were examined using a paraffin section and fluorescence microscopy. The fruit set percentage in SP and CP was also investigated. The results showed that pollen germinated normally on the stigma, and the pollen tubes both reached the style base after SP and CP, but the growth rates of pollen differed significantly between SP and CP, being faster for CP. The pollen tubes arrived at the style base 48 h after SP, but only 24 h after CP. No barriers to SP acted at the stigmatic or stylar level in C. grijsii; however, SP pollen tubes stopped at the upside of the ovary at 72 h due to the presence of ovarian self-incompatibility (OSI). There was also no callose deposition in the ovules at 84 h after SP. The inability of SP pollen tubes to penetrate the ovule and the absence of a mature embryo sac in the ovule were the critical factors that led to ovule abortion. Fruit set following SP (2.1%) was consistently and significantly lower than that obtained from CP (72.9%). Thus, we conclude that the presence of strong OSI gives rise to ovule abortion and is the main cause of the poor fruit set in C. grijsii.
