Phenology and reproductive biology of Plukenetia corniculata Sm., a traditional wild vegetable of Southeast Asia

Abstract Background Plukenetia corniculata Sm., a member of the family Euphorbiaceae, is a traditional leafy vegetable in Southeast Asia. Its young shoots, leaves, and young fruits are consumed as vegetables, and its mature seeds can be eaten as nuts. Although P. corniculata is not included in the list of threatened species, habitat destruction has affected its survivability in some areas. To enhance the conservation and exploitation of P. corniculata germplasm, more knowledge is necessary to elucidate its flowering characteristics and reproductive biology. Results The results showed that the inflorescence buds of P. corniculata began to appear at approximately 98.72 days after sowing and fruits matured after another approximately 55.33 days. Pistillate flowers always blossomed approximately 5.07 days earlier than that of the first staminate flowers on the same inflorescence. On average, the anthesis of a single staminate flower lasted approximately 9.44 hours, pistillate flower 10.50 days, and the whole inflorescence 26.57 days. The pollen viability reached a maximum of 73.58% at the fourth hour after the staminate flower blooming, and the stigma receptivity usually lasted for approximately 9 days and reached a peak on the sixth day after stigma dehiscence. The pollen-ovule ratio (P/O) and outcrossing index (OCI) values of P. corniculata were 1607.09 and 3, respectively, suggesting its breeding system was classified as facultative xenogamy and self-compatible. Artificial pollination experiments furtherly confirmed that both self- and cross-pollination were compatible in P. corniculata. Additionally, seeds of P. corniculata had 70.67% kernel percentage and the oil content of kernels reached 58.65%. Conclusions This study provided comprehensive data on flowering and fruiting phenology, reproductive characteristics, and breeding system of P. corniculata. The optimal time for emasculation, pollen collection, and artificial pollination were also determined in P. corniculata. High kernel percentage and oil content of P. corniculata seeds are worthy of further study and exploitation. The work lays a foundation for conservation and further breeding strategy of P. corniculata.