Citogenética de espécies de convolvulaceae juss. da amazônia brasileira: estabilidade numérica, variação heterocromática e divergência populacional

Abstract

Convolvulaceae is a family of flowering plants comprising approximately 2,000 species distributed across 60 genera, including agronomically important crops such as sweet potato (Ipomoea batatas L.). In Brazil, 406 native species have been recorded, with highest diversity in the Cerrado and Caatinga, and a significant representation in the Amazon (122 species in 18 genera). Despite its diversity and importance, cytogenetic knowledge of the family remains limited, with available data largely restricted to the genera Ipomoea and Cuscuta, and concentrated in the Northeast and Southeast regions of the country. Moreover, most studies rely on classical techniques, limiting information to chromosome number and morphology. In this context, this study aimed to cytogenetically characterize Amazonian populations of Convolvulaceae using fluorochrome banding. To obtain meristematic tissue, root tips were pretreated with 2 mM 8-hydroxyquinoline for 24 hours at 10 °C. Slides were prepared after fixation and enzymatic digestion, sequentially stained with CMA and DAPI, and analyzed and photographed after at least three days. Novel chromosome counts were recorded for the species Distimake cissoides and Ipomoea maurandioides with 2n = 30, and Jacquemontia guyanensis with 2n = 20. Chromosome numbers were confirmed for D. dissectus, I. mauritiana, I. triloba and I. asarifolia (2n = 30). One species, Evolvulus nummularius, was found to be a dysploid with 2n = 26, contradicting the previous record of 2n = 24. Heterochromatin bands were also similar to those observed in other populations, with an abundance of terminal and proximal CMA+ regions and few DAPI+ bands. Population-level differences in heterochromatin were observed in D. dissectus, suggesting genetic divergence across the distribution of this species. I. asarifolia also showed variation in chromosome size and band number between an Amazonian and a Caatinga population, suggesting the existence of cryptic species within this taxon. It was concluded that chromosome numbers are stable in the genera Distimake and Ipomoea, even in Amazonian populations, and that heterochromatin patterns are more effective for investigating interespecific-level cytogenetic variability in Convolvulaceae, particularly in Ipomoea and Distimake.