Analysis of pollen morphology and viability of Choerospondias axillaris from different provenances

To investigate the differences in pollen morphology and viability among different provenances of Choerospondias axillaris, providing a theoretical basis for the selection and utilization of male germplasm resources of C. axillaris.

Pollen from 12 provenances of C. axillaris was used as experimental material. Scanning electron microscopy (SEM) was employed to observe pollen morphological characteristics. In vitro germination assays were conducted using different concentrations of boric acid, sucrose, and calcium chloride. The L₉ (3³) orthogonal experimental design was applied to screen the optimal culture medium for different provenances, Based on the maximum pollen viability of each provenance under different culture media, the pollen viability among different provenances was compared.

The pollen of C. axillaris was medium-sized, predominantly prolate, with some provenances being sub-spherical. The pollen exhibited three germination furrows and existed in a monad symmetric form. The exine ornamentation was uniformly parallel-striate, with equatorial views appearing circular or elliptical and polar views being triangular. The polar/equatorial diameter ratio (P/E) of pollen from the 12 provenances ranged from 1.09 to 1.57, and the pollen grain size ranged from 435.66 to 673.38 μm², There were differences in morphology and grain size among different provenances. Pollen viability varied among different C. axillaris provenances, with the pollen viability of the twelve provenances differing by 30.97% to 88.91% under their respective optimal culture media. The provenances HNTY, AHQM, ZJLS, GXZS, HBXY and ZJQZ, whose pollen germination rates exceeded 60% under the optimal culture media, all had germination furrow lengths lower than the average value. In contrast, HNTY, AHQM and ZJLS, the three provenances with the highest pollen germination rates under the optimal culture media, exhibited both germination furrow lengths and widths below the average value.

According to the NPC classification system, the pollen of the 12 provenances of C.axillaris was classified as the N3P4C5 type. The polar diameter, grain size, and morphology of the pollen can serve as diagnostic criteria for phylogenetic classification. At a genetic distance of 10, the pollen of C.axillaris could be divided into six major categories, Their classification exhibited distinct geographical characteristics. Pollen viability performance of different provenances varied under their respective optimal culture conditions.