Self-Sterility in Camellia oleifera May Be Due to the Prezygotic Late-Acting Self-Incompatibility

Abstract

In this report, self-sterility in Camellia oleifera was explored by comparing structural and statistical characteristics following self-pollination (SP) and cross-pollination (CP). Although slightly delayed pollen germination and pollen tube growth in selfed ovaries compared to crossed ovaries was observed, there was no significant difference in the percentages of pollen that germinated and pollen tubes that grew to the base of the style. There was also no difference in morphological structure after the two pollination treatments. However, the proportions of ovule penetration and double fertilization in selfed ovules were significantly lower than in crossed ovules, indicating that a prezygotic late-acting self-incompatible mechanism may exist in C. oleifera. Callose deposition was observed in selfed abortive ovules, but not in normal. Ovules did not show differences in anatomic structure during embryonic development, whereas significant differences were observed in the final fruit and seed set. In addition, aborted ovules in selfed ovaries occurred within 35 days after SP and prior to zygote division. However, this process did not occur continuously throughout the life cycle, and no zygotes were observed in the selfed abortive ovules. These results indicated that the self-sterility in C. oleifera may be caused by prezygotic late-acting self-incompatibility (LSI).

Comparative study on cross-compatibility between Camellia sinensis var. sinensis (China type) and C. sinensis var. assamica (Assam type) tea

“…It was found that the higher elongation rate for cross-pollination and lower rates for self-pollination in some cultivars while there was not a substantial difference in pollen tube elongation rate between cross-and selfpollination in some other cultivars . Liao et al (2014) also supportively depicted that the growth speed of crossed pollen tubes of C. oleifera was slightly faster than selfed pollen tubes as pollen tubes reached style base at 48 h after cross-pollination and 60 h after self-pollination. Comparable remarks were reported by Simura and Oosone (1956) where, in crossed flowers the pollen tubes grew rapidly and reached funiculus base in about 36 to 40 h after pollination, while in selfed flowers they grew uniformly and scarcely reached it by 72 h. Moreover, pollen tubes grew slower in styles of a different species and protruded ovules within 3 to 5 days after pollination (interspecific crosses) whereas that of within the same species (intraspecific crosses) occurs within 1-2 days after pollination (Hwang et al, 1992).…”

“…Tanaka (1988) and Liao et al (2014) reinforced our appraisal by particular studies on self-incompatibility in the genus Camellia. Aside from the normal growth of pollen tubes we observed an unusual zigzag growth at very low frequency in self and remote intraspecific crosses.…”

“…Conspicuously, Hwang et al (1992) has been reported a small frequency of abnormal pollen tubes with a zigzag or branching growth habit in interspecific crosses between C. japonica and C. chrysantha. Apart from that the distorted pollen tubes containing reversal tubes, swelling tube tips with callose deposits, irregular tubes and furcal tubes have been noted in selfing pistils of C. oleifera, an another member of the genus Camellia (Liao et al, 2014). Another report by Rogers (1975) has been documented the presence of self-pollen tubes with swollen and distorted tips in some tea clones.…”

The Floral Biology, Breeding System and Pollination Efficiency of Schima superba Gardn. et Champ. (Theaceae)

“…and Camellia sinensis (L.) O. Ktze. [34]. Furthermore, the pollen tubes did not penetrate the ovule after self-pollination ( Figure 4E).…”

“…Furthermore, the pollen tubes did not penetrate the ovule after self-pollination ( Figure 4E). This may be the result of the generation of resistant materials in the ovule or micropyle (e.g., callose) that prevented the self-pollinated pollen tubes from penetrating the ovule [34]. Fruit and seed set is the standard by which mating success is estimated.…”