Cytogenetic and pollen analysis in Passiflora triloba (Passifloraceae).

Abstract

Passiflora species are prized and grown as ornamental plants due to their stunning blooms. P. triloba has a unique petal count within the genus and remarkable flowers. To obtain cytogenetic and pollen data for this wild species, the following were performed: (i) karyotype and CMA3/DAPI banding; (ii) meiotic and post-meiotic analyses; (iii) pollen viability and in vitro pollen germination; and (iv) in vivo pollination. The species is diploid, with 2n = 2x = 18, and n = 9. The karyotype showed only metacentric chromosomes and CMA+ and DAPI- blocks in all centromeres and in the terminal regions of two chromosome pairs, indicating two pairs of satellites. Meiotic analysis revealed a low percentage of irregularities such as early and lagging chromosomes, asynchrony, and transverse spindle fibers. There was a predominance of interstitial chiasmata with a recombination index of 18.88. In the post-meiotic analysis, few irregularities such as dyads and triads were found, and the meiotic index was 99.08%. Pollen viability was 80.54%, but non-viable pollen grains were also observed with contracted cytoplasm (0.38%), empty (9.9%), pulverized (8.44%), and micrograin (0.64%), while 31.88% of pollen grains emitted pollen tubes after in vitro germination testing. Pollen tube emission and fertilization occurred within 2 hours of in vivo pollination. The cytogenetic and pollen analyses in this study indicate that P. triloba has the chromosome number typical of the Passiflora subgenus, regular meiotic behavior, high pollen viability, and the ability to emit pollen tubes and achieve fertilization, supporting its potential use in interspecific hybridization.