THE EVOLUTION OF CHILI PEPPERS (CAPSICUM - SOLANACEAE): A CYTOGENETIC PERSPECTIVE
Capsicum (chili peppers) is a New World genus with five crop species of great economic importance for food and spices. An up-to-date summary of the karyotypic knowledge is presented, including data on classical staining (chromosome number, size and morphology), silver impregnation (number and position of active nucleolar organizing regions), fluorescent chromosome banding (amount, distribution and type of constitutive heterochromatin), nuclear DNA content measurements (genome size), and fluorescent in situ hybridization (physical mapping of telomeric sequences). Reported chromosome numbers for 23 of the 31 recognized species allow us to distinguish two species groups: one with 2n=2x=24 (13 species) and another with 2n=2x=26 (10 species). The 2n=24 species have comparatively symmetrical karyotypes, mostly with 11 metacentric and 1 subtelocentric (submetacentric) pairs. In contrast, the 2n=26 taxa exhibit more asymmetrical complements, with more submetacentric (subtelocentric) chromosomes and frequently one telocentric chromosome. Active nucleolar organizing regions vary in number from one (several species) to four pairs (C. baccatum). Heterochromatin amounts range from 1.80% (C. annuum) to 38.91% (C. tovarii) of the karyotype length, whilst 1C DNA contents vary from 3.35 pg (C. chacoense) to 5.77 pg (C. parvifolium). GC-rich heterochromatin is universal in the genus; AT-rich heterochromatin appears in C. pubescens, C. pereirae and C. campylopodium. The latter species also exhibits mixed GC- and AT-rich heterochromatin. Lack of telomeric sequences in ectopic localizations in the 2n=24 species supports the hypothesis that x=13 has been derived from x=12. Results of chromosome differentiation are compared with molecular data, and a scheme of possible evolutionary trends in Capsicum with reference to the origin of the cultivated taxa is presented. Postulated derived karyotype traits in peppers are increases in karyotype length and asymmetry, nuclear DNA and heterochromatin content. Capsicum chacoense appears as the most primitive taxon while the Brazilian species with 2n=26 seem to be the most advanced, especially C. campylopodium. The 2n=26 species form two subgroups according to geographical distribution, morphology and karyotypes. This suggests that x=13 arose twice in the genus. Karyological analyses provide valuable diagnostic features for taxonomic identification at species level in the cultivated peppers, particularly in the C. annuum complex (C. annuum, C. chinense and C. frutescens). Results reinforce the hypothesis of three independent lines leading to the domesticated peppers: the C. annuum complex, C. baccatum and C. pubescens.
Moscone, E.A., Scaldaferro, M.A., Grabiele, M., Cecchini, N.M., Sánchez García, Y., Jarret, R., Daviña, J.R., Ducasse, D.A., Barboza, G.E. and Ehrendorfer, F. (2007). THE EVOLUTION OF CHILI PEPPERS (CAPSICUM - SOLANACEAE): A CYTOGENETIC PERSPECTIVE. Acta Hortic. 745, 137-170
chromosome numbers, karyotypes, active nucleolus organizing regions, fluorescent chromosome banding, nuclear DNA amounts, FISH, telomeric sequence