Flowering biological characteristics and pollen preservation of Plumbago auriculata

Pollen and stigma morphologies, floral characteristics, and flowering phenologies of introduced and cultivated Plumbago auriculata Lam. in Sichuan were systematically observed, with the collection period and storage temperature of pollen also examined. Results showed:(1) There were obvious differences between pollen and stigma morphology; P (polar axis length) and E (equatorial axis length) values of S-morph pollen were significantly higher than that of L-morph pollen; the stigma of the L-morph pollen was significantly longer than that of the S-morph pollen; and the exine ornamentation and stigma stromae of the two morphs of pollen were significantly different. (2) P. auriculata had a high flowering synchrony index of 0.89, but its relative flowering intensity was at a mid-level. (3) When the two morphs of pollen were harvested during the half-flowering period, viability reached the highest levels. The L-morph pollen viability reached 85.24% ±4.22% and S-morph pollen viability reached 87.74% ±2.95%. (4) L-morph and S-morph pollen maintained better viability when stored at low temperatures after drying at a constant temperature of 25℃ for 0.5 h and 1 h, respectively. (5) Dried pollen was best stored at -86℃, and after 30 d of storage the L-morph pollen viability was 66.51% ±0.85% and S-morph pollen viability was 69.07% ±1.57%. In summary, there were significant differences in the reproductive resource allocation between the two morph plants of P. auriculata, with differences in the size, morphology, and drying time of pollen, and significantly different characteristics in the stigma. Whether these different structures participate in the self-incompatibility reaction of P. auriculata remains to be further studied. In addition, low flowering intensity can cause insect pollination difficulties, which may be an important factor in the extremely low natural seed setting rate.