Abstract
Pistacia chinensis Bunge is widely acknowledged to be dioecious, but rare monoecious individuals have been found. However, the origin of monoecism and the sex differentiation of different sex types remain intriguing questions. Here, sex expressions were explored by identification of sex-associated DNA markers, determination of the sex stability after grafting, and histological characterization of inflorescence bud development using anatomical analysis. The results showed that (1) although polymorphisms among individuals existed, the banding patterns of Polymerase Chain Reaction (PCR) products for different sex types on the same monoecious tree were consistent; (2) the sex expressions of grafted trees were not consistent with those of scions, indicating that monoecism probably did not originate from a stable bud mutation; and (3) both males and females underwent a bisexual period, then the stamen primordia in female buds degenerated into the second round tepals, while the pistil primordia in male buds gradually disappeared. During the sex differentiation phase, female buds were spindle-shaped, while the male buds were full teardrop-shaped, and male buds were bigger than female buds. Taken together, no sex-associated DNA marker was found, sex expressions were unstable after grafting, and the alternative sex organs appeared in the early stage of sex differentiation, suggesting that sex determination occurred during floral development instead of the early vegetative period. These results indicated that the sex expressions may be affected by environmental factors, increasing the understanding of sex determination mechanisms in P. chinensis and other species.
Highlights
Pistacia chinensis Bunge has been recognized as an important biodiesel tree species in China due to the high oil content of its fruit [1]
Our previous work has shown that pollen and ovaries from monoecious P. chinensis are fertile [12]
DNA samples of every sex type from dioecious and monoecious P. chinensis were amplified by 24 primer pairs (Table 1) which had previously been used for sex identification in the Pistacia genus
Summary
Pistacia chinensis Bunge has been recognized as an important biodiesel tree species in China due to the high oil content of its fruit [1]. It is generally perceived as dioecious [2], and its flowers are unisexual and wind-pollinated, as in other Pistacia species [3]. The non-fruit-bearing (male) trees are indispensable for pollination, which increases the cost, labor, and field space needed for producing fruit. Several cases of monoecious Pistacia species have been reported [4–11]. Our previous work has shown that pollen and ovaries from monoecious P. chinensis are fertile [12]. Monoecious genotypes could produce fruit without male trees, which could
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