Variabilidade cariotípica em convolvulaceae, com ênfase nos gêneros Jacquemontia Choisy e Ipomoea L.

Abstract

Convolvulaceae is cosmopolitan, with 60 genera and ca. 2,000 species. The family is represented by two main lineages, the subfamilies Dicranostyloideae and Convolvuloideae. In Dicranostyloideae, Jacquemontia presents ca. 120 species distributed in tropical and subtropical regions, and in Brazil there are 50 species, mainly in areas of Caatinga and Cerrado. Only 6% of the genus are cytologically known, showing the series with 2n = 18 and 20. On the other hand, Convolvuloideae is a group of plants formed by genera with n = 15 and high stability of chromosome numbers. Karyologically, the best-known genus is Ipomoea, with ca. 800 species of which 85 have recorded chromosome numbers. This study aimed to characterize in the karyotypes in representatives of the subfamily Dicranostyloideae, with emphasis on Jacquemontia occurring in the semi-arid region, as well as in diploid species of Convolvuloideae with emphasis on Ipomoea, using fluorochrome banding technique and flow cytometry. In Dicranostyloideae, the chromosome numbers for the species analyzed are new: 2n = 18 for Jacquemontia corymbulosa and J. evolvuloides, 2n = 20 for J. chrysanthera, J. nodiflora and J. sphaerostigma, and 2n = 36 for J. mucronifera and J. pentanthos. Dinetus truncatus, the outgroup, has 2n = 28. All analyzed species exibited terminal CMA+ bands. Additionally, J. sphaerostigma has two pericentromeric CMA+ bands, while J. nodiflora and J. pentanthos have terminal DAPI+ bands. The diploid species J. sphaerostigma, J. corymbulosa and J. nodiflora has 1C = 0.93pg, 1.13pg and 1.41pg, respectively, while the polyploids J. pentanthos exibited 1C = 2.25pg and J. mucronifera has 1C = 2 ,32pg. In Convolvuloideae, new counts were recorded for eight species belonging to the genera Camonea, Ipomoea and Operculina. B chromosome was recorded in a population of I. bahiensis. The basic number x = 15 has been suggested for the subfamily Convolvuloidae. The first genome size records are presented for the genera Camonea, Distimake and Stictocardia, as well as for six species of Ipomoea. DNA content ranged from 1C = 0.78pg in I. bahiensis to 1.38pg in Distimake dissectus. Two types of heterochromatin bands were identified in Convolvuloideae, CMA+ band is the predominant type, while DAPI+ band is the uncommon type, with four band patterns occurring in the karyotypes of the subfamily. Among the genera from Dicranostyloideae, the series with n = 9, 10, 12, 13, 14, 15 shows the importance of dysploidy in the diversification of the subfamily. According to the intergeneric relationships in Dicranostyloideae, Jacquemontia probably originated from an ancestor with n = 10, with descendant dysploidy to n = 9 occurring several times during the diversification of the genus. The species J. mucronifera and J. pentanthos possibly are neopolyploids that did not experience drastic reductions in genome size, as observed during the diploidization of older polyploids. Genome size constitutes an efficient cytotaxonomic parameter for the delimitation of Jacquemontia species occurring in the Brazilian semi-arid region, including the species of the J. pentanthos complex. In Convolvuloideae, data show the occurrence of non-parallel evolution between genome size and heterochromatin. This scenario suggests that genome size and chromosome number possibly represent evolutionarily stable strategies associated with adaptation and speciation in the subfamily, while the legacy of variation in heterochromatin remains unknown.