Chromosome numbers in wild and semidomesticated Brazilian Capsicum L. (Solanaceae) species: do x = 12 and x = 13 represent two evolutionary lines?

Abstract

Chromosome numbers were determined in 29 accessions of wild and semidomesticated Capsicum species from the EMBRAPA Hortaliças (Brazil) germplasm collection. 2n = 24 was found in C. baccatum var. praetermissum, C. chinense, C. flexuosum and C. parvifolium, while C. buforum, C. campylopodium, C. cornutum, C. schottianum, C. villosum var. villosum and five other native south-eastern Brazilian species not yet taxonomically named all had 2n = 26 chromosomes. These are the first chromosome number determinations for C. cornutum, C. schottianum, C. villosum var. villosum and the five other Brazilian taxa. Our data confirm published data for C. baccatum var. praetermissum, C. campylopodium, C. chinense, C. flexuosum and C. parvifolium, but not for C. buforum. The prevalence of 2n = 26 chromosomes among Brazilian species, along with the morphological and ecological characteristics presented by the wild and semidomesticated species occurring in Brazil, form a pattern different from that found in Andean wild and semidomesticated species. This supports the hypothesis that there are two different evolutionary lines in the genus and that the native south-eastern Brazilian species belong to the ancestral Capsicum gene pool.

cytogenetics, cytotaxonomy, morphology, peppers

INTRODUCTION

Capsicum L. species, are native to the New World, but are cultivated widely in temperate and tropical regions, where they are used as vegetables, spices, ornamentals and for their medicinal properties. Most Capsicum species contain the alkaloid capsaicin, which determines their pungency, an important factor for the food and pharmaceutical industries.

Despite its importance and the volume of published data on many different aspects, knowledge about the origin and domestication of Capsicum is still controversial. Archaeological evidence indicates that some species were already being cultivated in some parts of South and Central America between 7000 and 5000 bc. Peppers, together with Phaseolus L. and some Cucurbitaceae, are among the oldest cultivated plants in the Americas (Pickersgill, 1969).

The association of aspects such as the antiquity of the genus, its present broad geographical distribution and different ways and areas of cultivation, lead to a wide expression of genetic variability, as seen in the very different morphological types. This situation makes the establishment of taxonomic position and the determination of species relationships rather difficult tasks, and raises many questions that are still unanswered. Even so, there is a general consensus that the genus comprises 20–30 species, mostly classified as wild and semidomesticated, besides the five that are cultivated world-wide: C. annuum L. var. annuum (bell pepper), C. baccatum L. var. pendulum (Willd.) Eshbaugh (ají), C. chinense Jacq. (habanero), C. frutescens L. (tabasco) and C. pubescens Ruiz & Pavon (rocoto) (McLeod, Eshbaugh & Guttman, 1979a, 1979b; McLeod, Guttman & Eshbaugh, 1983a; McLeod, et al., 1983b).

Brazil is considered to be the centre of diversity for the genus and has a richness of germplasm that is reflected in the large numbers of varieties cultivated all over the country, many of which are adapted to specific edapho-climatic microregions and have potential for genetic breeding (Buso et al., 2001). Brazil also has the largest number of wild Capsicum species (Pickersgill, 1984; Bianchetti, 1996), although a comprehensive study of this diversity, especially of the native species, is still lacking.

The most frequent chromosome number in the genus, as well as in the Solanaceae as a whole, is x = 12 (Smith & Heiser, 1951; Lippert, Smith & Bergh, 1966; Pickersgill, 1971, 1977, 1991; Limaye & Patil, 1989; Moscone, 1992) and both the cultivated as well as the wild species with this basic number are ‘true’Capsicum (Pickersgill, 1977, 1991). Until now, x = 13 has been found in C. ciliatum (H., B. & K.) Kuntze, C. lanceolatum (Green.) Morton & Stand. (Pickersgill, 1977, 1991; Tong & Bosland, 1997, 2003), C. mirabile Martius, C. campylopodium Sendtner. (Moscone et al., 1993) and one unidentified south-eastern Brazilian species (Pickersgill, 1977). Natural polyploidy (2n = 48) has been reported so far for just one wild accession of C. annuum (Pickersgill, 1977). The occurrence of the two basic numbers x = 12 and 13 could suggest that there are two different evolutionary lines and that a taxonomic realignment of the genus might be necessary (Pickersgill, 1977; McLeod et al., 1983b). For that, however, more comprehensive studies are needed and in particular a thorough examination of chromosome number distribution among wild Capsicum species, as well as the investigation of a possible relationship between chromosome numbers and morpho-ecological characteristics.

Therefore, in this paper we report chromosome numbers for a range of wild and semidomesticated Capsicum accessions from Brazil and discuss the data in relation to morpho-ecological information.

MATERIAL AND METHODS

All the accessions analysed are part of the Capsicum germplasm collection at EMBRAPA (Empresa Brazileira de Pesquisa em Agropecuária), Embrapa Hortaliças (CNPH), Brasília, DF, Brazil. The collections were made in several locations in the south-eastern region of Brazil, except for one accession from the Amazonian region (Table 1). Vouchers are kept at the CENARGEN (Centro Nacional de Recursos Genéticos e Biotecnologia), EMBRAPA, Brasília, DF, Brazil.

Table 1.

Capsicum species and accessions examined

Species, CNPH1 accession number, collector's2 number	Place of collection3	n	2n
Semi-domesticated
C. baccatum var. praetermissum
3303, LBB 1524	SP, Parque Estadual Jacupiranga	–	24
3325, LBB 1553	MG, Caldas	12	24
3326, LBB 1555	MG, Maria da Fé, Pedrão	–	24
C. chinense
3727, LBB 1720	RR, Vila Apiaú, Roraima	12	–
Wild
C. flexuosum
3324, LBB 1552	MG, Caldas	12	24
C. parvifolium
3331, LBB 1560	MG, University Federal de Viçosa	12	24
C. buforum
3367, LBB 1550	SP, 1 km from Estação Eugene Lefévre	13	–
3368, LBB 1554	MG, Maria da Fé, EPAMIG	13	–
C. campylopodium
3335, LBB 1566	RJ, Santa Maria Madalena	13	26
C. cornutum
3316, LBB 1542	SP, Estação Biológica da Boracéia	13	–
3320, LBB 1546	SP, Paraty-Cunha	13	26
3365, LBB 1527	SP, Parque Estadual Serra do Mar	13	–
C. schottianum
3310, LBB 1535	SP, Estação Biológica da Boracéia	13	26
3311, LBB 1536	SP, Estação Biológica da Boracéia	13	26
3315, LBB 1540	SP, Estação Biológica da Boracéia	13	26
3318, LBB 1544	SP, Natividade da Serra-Bairro Alto SP	13	–
3319, LBB 1545	SP, São Luiz de Paraitinga	13	–
C. villosum var. villosum
3313, LBB 1538	SP, Estação Biológica de Boracéia	13	26
3314, LBB 1539	SP, Estação Biológica da Boracéia	13	–
3317, LBB 1543	SP, Estação Biológica da Boracéia	–	26
3328, LBB 1557	RJ, Parque Nacional do Itatiaia	13	26
Capsicum sp. 14
3301, LBB 1521	SP, Parque Estadual Carlos Botelho	13	–
Capsicum sp. 2 (Oito dentes)4
3302, LBB 1523	SP, Parque Estadual Jacupiranga	13	26
3372, LBB 1525	SP, Estação Ecológica Juréia, Itatins	13	–
Capsicum sp. 6 (Piquete)4
3330, LBB 1559	MG, Lima Duarte	13	–
3337, LBB 1568	MG, Parque Nacional do Caparaó	13	–
3370, LBB 1564	RJ, Parque Nacional Serra dos Órgãos	13	–
Capsicum sp. 7 (Gruta do pião)5
3329, LBB 1558	MG, Parque Estadual do Ibitipoca	13	26
Capsicum sp. 8 (Flor lilás)5
3334, LBB 1565	RJ, Nova Friburgo	13	–

1

CNPH, Embrapa Hortaliças

2

LBB, Luciano de Bem Bianchetti

3

MG, Minas Gerais; SP, São Paulo; RJ, Rio de Janeiro; RR, Roraima

4

Putative new species, numbered and nicknamed followingBianchetti et al. (1999)

5

New species, being proposed as C. pereirae Hunz. and C. friburguense Hunz., Bianchetti & Barboza, respectively.

Somatic chromosome numbers were determined in root-tip cells following the protocol of Pozzobon & Valls (1997) with minor modifications. A detailed karyotypic analysis was not performed, but overall chromosome size and shape, and presence of satellited chromosomes were recorded. Meiotic chromosome numbers were analysed in pollen mother cells from anthers fixed in 3 : 1 ethanol-acetic acid and squashed in 2% propionic carmine.

At least five (generally more than ten) cells with good chromosome spreading and no overlapping were analysed per plant. Semi-permanent slides were examined by light microscopy and the work recorded on photomicrographs and with digital image capturing.

RESULTS AND DISCUSSION

Chromosome number and morphology

The chromosome numbers for 29 accessions of 2 semidomesticated and 12 wild Capsicum species are listed in Table 1. These are the first determinations for C. cornutum (Hern.) A. T. Hunziker, C. schottianum Sendtner, C. villosum Sendtner var. villosum and the five new species. It can be seen that 2n = 26 is the most common number among the wild species. No intraspecific variability for chromosome number was found and no apparent differences in the general size of chromosomes among species were detected. Capsicum chromosomes are about 3 µm in length.

For C. baccatum L. var. praetermissum (Heiser & Smith) A. T. Hunziker, the chromosome number 2n = 24 confirms published data (Pickersgill, 1977; Bertão, 1993; Ferreira, 1998). This species has 11 pairs of metacentric chromosomes and one subterminal satellited pair (Fig. 1). The same result was found by Bertão (1993) and by Pickersgill (1977), who also reported intraspecific variation in the number and position of satellites.

Figures 1–6.

Somatic and meiotic chromosomes of Capsicum spp. Figs 1–4. Capsicum species with 2n = 24 chromosomes. Fig. 1. Mitotic metaphase in C. baccatum var. praetermissum. Arrow points to a satellited subtelocentric. Fig. 2. Late diakinesis with 12 bivalents in C. chinense. Arrow points to the smallest pair of the complement. Fig. 3. Mitotic metaphase in C. flexuosum. Arrow points to a satellited submetacentric. Fig. 4. Mitotic metaphase in C. parvifolium. Arrow points to a satellited submetacentric. Figs 5, 6. Species with 2n = 26 chromosomes. Fig. 5. Diakinesis in Capsicum sp. 1, with 13 bivalents. Fig. 6. Mitotic metaphase in Capsicum sp. 2. Arrow points to the small subtelocentric thirteenth pair. Scale bars = 10 µm.

Capsicum chinense has 2n = 24 chromosomes (n = 12, Fig. 2), the same number as found by several authors (Carluccio & Saccardo, 1977; Pickersgill, 1977; Limaye & Patil, 1989; Bertão, 1993; Moscone et al., 1995, 2003; Moscone, Lambrou & Ehrendorfer, 1996; Ferreira, 1998), who do not concur on several aspects of karyotype morphology. However, as we have not analysed somatic cells, it is not possible to compare results on that aspect. The accession that we analysed is morphologically different from typical C. chinense, presenting characteristics of wild species and it has a twelfth chromosome pair smaller than in other 2n = 24 species.

Among the wild species, only C. flexuosum Sendtner and C. parvifolium Sendtner had 2n = 24, as found by Moscone (1992) and Bertão (1993) for C. flexuosum and by Bertão (1993) and Moscone (1993) for C. parvifolium. In both species we observed 11 metacentric pairs and one submetacentric satellited pair (Figs 3, 4). Bertão (1993) reported the same general chromosome morphology, but one subterminal satellited pair for C. flexuosum, while both Bertão (1993) and Moscone (1993) described 12 metacentric pairs, including the satellited one, for C. parvifolium.

These differences in morphology of the satellited chromosome pair between our results and other published ones, as well as among different authors for C. chinense, could reflect real biological differences or could be the consequence of technical differences such as pretreatment, chromosome condensation or even karyotype representation.

An interesting feature of one of the analysed accessions of C. parvifolium (3331) is that this accession was outstanding among the 363 accessions of the EMBRAPA Hortaliças Capsicum germplasm collection in its resistance to the fungus Phytophthora capsici, one of the most serious diseases of Capsicum in Brazil (Ribeiro et al., 2003).

The eight accessions represented by two new (Capsicum sp. 7 and sp. 8) and three wild Brazilian species also assumed to be new all presented 2n = 26 chromosomes. The thirteenth pair in these is a small one, less than half the size of the other 12 pairs (c. 1.4 µm), with an almost terminal centromere (Figs 5–8). Pickersgill (1977) also reported a small acrocentric thirteenth chromosome pair in one unidentified Brazilian species.

Figures 7–12.

Somatic and meiotic chromosomes of Capsicum species with 2n = 26 chromosomes. Arrows point to the small thirteenth pair. Fig. 7. Diakinesis in Capsicum sp. 2, with 13 bivalents. Fig. 8. Anaphase I in Capsicum sp. 6, with sticky chromosomes. Fig. 9. Pro-metaphase II in C. buforum with a 13 + 13 chromosome distribution. Fig. 10. Diakinesis in C. buforum, with 13 bivalents. Fig. 11. Late diakinesis in C. campylopodium, with 13 bivalents. Fig. 12. Late diakinesis in C. cornutum with 13 bivalents. Scale bars = 10 µm.

Capsicum buforum A. T. Hunziker (Figs 9, 10), C. campylopodium Sendtner (Fig. 11), C. cornutum (Figs 12, 13), C. schottianum(Figs 14–16) and C. villosum var. villosum (Figs 17, 18) also had 2n = 26 chromosomes, the thirteenth being similar in size and shape to that of the new species. Tong & Bosland (2003) reported 2n = 24 chromosomes in one accession of C. buforum. The characteristics that they reported for C. buforum, such as green mature fruits, three to four flowers per node and black seeds have been found so far in all (and only in) the 2n = 26 species studied here. Therefore, a technical problem (e.g. sample misidentification) leading to an erroneous count by the above authors cannot be discounted. Moscone et al. (1993, 1995, 2003) also found 2n = 26 in C. campylopodium, but with two small chromosome pairs. Capsicum villosum var. villosum was the only species analysed in which two satellited chromosome pairs could be identified, in accession 3317 (Fig. 17).

Figures 13–18.

Somatic and meiotic chromosomes of Capsicum species with 2n = 26 chromosomes. Arrows point to the small thirteenth pair, except in Fig. 17. Fig. 13. Metaphase I in C. cornutum with 13 bivalents. Fig. 14. Mitotic metaphase in C. schottianum.Fig. 15. Metaphase I in C. schottianum with 13 bivalents. Fig. 16. Anaphase I in C. schottianum with 13 + 13 chromosome distribution. Fig. 17. Mitotic metaphase in C. villosum var. villosum with two pairs of satellited chromosomes (arrows). Fig. 18. Late diakinesis in C. villosum var. villosum with 13 bivalents. Scale bars = 10 µm.

The origin of the small thirteenth pair in the 2n = 26 species is still to be determined. Some rather speculative suggestions have been presented to date. The constancy in its number and behaviour during mitosis and meiosis supports Pickersgill (1977, 1991), who pointed out that they are not B chromosomes. Moscone et al. (1993) found similarities of C-banding patterns among the small pair and some regions of the other chromosomes in C. campylopodium (as well as in some chromosomes of the 2n = 24 C. pubescens) and suggested that the small pair could have originated through centric fission. In this case, a larger pair of chromosomes in the 2n = 26 species with a reduced or absent short arm would be expected; however, based on published data and our own work, this type of chromosome has not been observed so far in Capsicum and therefore centric fission is an unlikely origin of the 2n = 26 karyotype.

Chromosome numbers, morpho -ecological characteristics and evolutionary considerations

When the present results and published chromosome numbers for Capsicum species (Table 2) are compared, it can be seen that 2n = 24 is the predominant chromosome number among the cultivated, semidomesticated and wild species (most of those from the Andean regions but also in C. flexuosum and C. parvifolium, which are native to Brazil). The four 2n = 24 species that we analysed (the semidomesticated C. baccatum var. praetermissum, C. chinense and the wild C. flexuosum and C. parvifolium) share some morphological and ecological characteristics with most of the Andean wild species (all 2n = 24).

Table 2.

Chromosome numbers reported for Capsicum species

Species	2n	References
Domesticated
C. angulosum Mill.	24	Fedorov (1969); syn. to C. baccatum L.1
C. annuum L.	24	Fedorov (1969); Moore (1973); Pickersgill (1977); Goldblatt (1981, 1984, 1985, 1988); Goldblatt & Johnson (1990, 1991, 1994, 1996, 1998, 2000); Bertão (1993); Ferreira (1998)
	48	Pickersgill (1977)
C. baccatum L.	24	Moore (1973); Pickersgill (1977) Goldblatt (1981); Bertão (1993); Goldblatt & Johnson (1991, 1996); Ferreira (1998)
C. baccatum L. var. pendulum (Willd.) Eshbaugh	24	Goldblatt & Johnson (1990, 1998, 2000); Moscone et al. (1993, 2003)
C. baccatum L. var. umbilicatum (Vellozo) Hunz. & Barboza	24	Moscone (1999); Moscone et al. (2003); syn. to C. baccatum L.1
C. chinense Jacq.	24	Pickersgill (1977); Limaye & Patil (1989) Bertão (1993); Goldblatt & Johnson (1990, 1994); Ferreira (1998); Moscone et al. (1995, 1996, 2003); this work.
C. cordiforme Mill.	24	Fedorov (1969); syn. to C. annuum var. annuum1
C. frutescens L.	24	Fedorov (1969); Moore (1973); Pickersgill (1977); Goldblatt (1981, 1988); Bertão (1993); Goldblatt & Johnson (1991, 1996, 1998, 2000); Moscone et al. (2003)
C. pendulum Willd.	24	Fedorov (1969); Goldblatt & Johnson (1991); syn. to C. baccat um var. pendulum1
C. pubescens Ruiz & Pavon	24	Fedorov (1969); Pickersgill (1977); Goldblatt & Johnson (1991, 1994, 1998, 2000); Moscone et al. (2003)
C. sinense Murr.	24	Fedorov (1969); probably C. chinense Jacq.2
Semi-domesticated
C. baccatum L. var. baccatum Eshbaugh	24	Goldblatt & Johnson (1990); Moscone et al. (2003)
C. baccatum var. praetermissum (Heiser & Smith) Hunz.	24	Fedorov (1969); Pickersgill (1977); Bertão (1993); Ferreira (1998); this work; syn. to C. praetermissum1
C. cardenasii Heiser & Smith	24	Fedorov (1969), Pickersgill (1977)
C. chacoense Hunz.	24	Fedorov (1969); Pickersgill (1977); Bertão (1993); Goldblatt & Johnson (1991, 1994, 1996, 1998); Moscone et al. (2003)
C. eximium Hunz.	24	Fedorov (1969); Pickersgill (1977); Moscone et al. (2003)
C. microcarpum Cav.	24	Fedorov (1969); Goldblatt & Johnson (1991); syn. to C. baccat um1 (probably var. baccatum2)
C. tovarii Eshbaugh, P. G. Sm. & Nickrent Wild	24	Goldblatt (1985)
C. buforum Hunz.	24	Tong & Bosland (2003)
	26	This work
C. campylopodium Sendt.	26	Moscone et al. (1993, 1995, 2003), this work
C. ciliatum (H., B. & K.) Kuntze	26	Pickersgill (1977)
C. cornutum (Hern.) Hunz.	26	This work
C. flexuosum Sendt.	24	Moscone (1992), Bertão (1993), this work
C. galapagense Heiser & Smith	24	Fedorov (1969); Pickersgill (1977)
C. lanceolatum (Green.) Morton & Standl.	26	Tong & Bosland (1997, 2003)
C. macrophyllum Standl.	24	Fedorov (1969); re-classified as Witheringia solanacea L'Her.1
C. maculatum Standl. & Mort.	24	Fedorov (1969); re-classified as Witheringia maculata (Morton & Standl.) Hunz.1
C. mirabile Mart. var. mirabile	26	Moscone et al. (1995)
C. parvifolium Sendt.	24	Bertão (1993); Moscone (1993); Moscone et al. (1993, 1995, 2003); this work
C. schottianum Sendt.	26	This work
C. stenophyllum Mort. & Standl.	24	Fedorov (1969); re-classified as Witheringia meiantha (Don. Sm.) Hunz.1
C. stramoniifolium (H., B. & K.) Standl.	24	Fedorov (1969); re-classified as Witheringia stramonifolia Kunth1
C. testiculatum Vis. ex Dun.	24	Goldblatt & Johnson (1991); not considered as related to Capsicum1
C. tetramerum Stand. & Mort.	24	Fedorov (1969); re-classified as Witheringia solanacea var. solanacea L'Her.1
C. villosum Sendt. var. villosum	26	This work
Capsicum sp. (Brazil)	26	Pickersgill (1977)
Capsicum sp. 13	26	This work
Capsicum sp. 23	26	This work
Capsicum sp. 63	26	This work
Capsicum sp. 73	26	This work
Capsicum sp. 83	26	This work

1

According toBaral & Bosland (2002)

2

L. B. Bianchetti (pers. comm.)

3

Bianchetti et al. (1999)

According to Pickersgill (1969), wild Capsicum species have small, red, erect fruits and seeds are dispersed by birds attracted by the bright fruit colour. During domestication this kind of dispersal was lost, as man probably selected, consciously or not, nondeciduous pendant fruits. The change from erect to pendant fruits could have been due to the increase in fruit size and weight selected for in the domesticated forms. Such fruits, hidden among the leaves, would also be protected against predation by birds.

Capsicum baccatum var. praetermissum is endemic to the south-south-eastern region of Brazil (Bianchetti, 1996). Eventually, some plants might be found in other places, either wild or as escapees from cultivation. The species is found mostly as escapees in disturbed habitats or cultivated in small gardens. The fruits are deciduous, ovoid, rarely globular, bright red, erect and with pale yellow seeds. These morphological and ecological characteristics are shared with the wild Andean taxa.

Capsicum chinense is also found wild or under cultivation and is frequently used by the indigenous inhabitants of the northern Brazilian state of Roraima. Its fruits and seeds are morphologically similar to those of domesticated and wild Andean species (Barbosa et al., 2002).

Capsicum flexuosum is normally distributed in low altitudes in a transition zone between the wild Andean species and those occurring in south-eastern Brazil, Paraguay and Argentina. It presents morphological characteristics from both groups of species: fruits are deciduous, globular, red or orange (characteristic of Andean species adapted to dry climates), opaque and pendant, with blackish seeds (characteristic of Brazilian species adapted to wet climates). Bianchetti (1996) suggested that this mixed morphology could be explained by a recent evolutionary origin of C. flexuosum.

Capsicum parvifolium also presents morphological characteristics of both Andean and Brazilian species. The fruits are red or orange, with pale yellow seeds (characteristic of Andean species adapted to dry climates), globular and pendant (characteristic of Brazilian species adapted to wet climates). This is the only species with a disjunct geographical distribution in dry areas in Venezuela, Colombia and north-eastern Brazil (Bianchetti, 1996). According to Bianchetti (1996), this present distribution could be explained by the following scenarios: a very wide distribution of the species during the late glacial period dwindled, owing to the enlarging Argentinian – Paraguayan – Bolivian arid region, leaving open vegetation areas which were later isolated; or a humid tropical region expanded over South America, including north-eastern Brazil, and a later retreat of the forest and consequent expansion of open vegetation formed refugia in which C. parvifolium is found.

It should be noted that fruit colour in these four species is similar to that of the Andean species, but the pendant fruits of C. flexuosum and C. parvifolium are a characteristic shared by most Brazilian taxa. Both species have undergone environmental changes and some morphological variation, but have maintained the chromosome number of 2n = 24.

The other wild species analysed present a set of morphological and ecological discriminatory characteristics, including: (1) a more coastal (eastern) distribution, usually above 400 m a.s.l.; (2) occurrence in humid forests; (3) fruits that are globular, pendant and greenish-yellowish when ripe with blackish seeds, suggesting that the natural pollinators are probably not birds (Bianchetti, 1996; Bianchetti et al., 1999). We have showed that another distinctive characteristic of these species is the chromosome number of 2n = 26, with the thirteenth pair morphologically different from the other chromosomes of the complement. The joint analysis of these morpho-ecological and cytological aspects strongly suggests the existence of two distinct evolutionary lines. However, how the difference in chromosome numbers is related to phylogenetic relationships is still not clear.

A few other species from the Andean or north-western South American regions, such as C. mirabile and an unidentified species, also have 2n = 26 chromosomes (Pickersgill, 1977, 1991; Moscone et al., 1993; Tong & Bosland, 1997, 2003). Tong & Bosland (2003) attempted interspecific crosses between the 2n = 26 C. lanceolatum from Guatemala and several 2n = 24 species [C. pubescens, C. praetermissum, C. ciliatum (H., B. & K.) Kuntze, C. baccatum, C. frutescens, C. buforum, C. cardenasii Heiser & Smith, C. eximium Hunz. and C. tovarii Eshbaugh] and verified the existence of incompatibility between the 2n = 26 species and the other taxa.

Data in Table 2 show that x = 13 is more common among the wild Brazilian species than in the other Capsicum taxa studied so far. Is the x = 13 a primitive or a derived characteristic? Have the x = 13 species originated from a x = 12 ancestor and acquired one pair of chromosomes (the small pair); have the x = 12 species originated from the x = 13 ones, or have both group of species originated from a common ancestor, having afterwards undergone distinct evolutionary trends? Bianchetti (1996), examining morpho-ecological characteristics of these x = 13 species, suggested that they represent a primitive condition. Moreover, the occurrence of the x = 13 species, C. lanceolatum in Guatemala and C. ciliatum in north-western South America, could represent the remains of an ancient continuous vegetation linking the eastern South American region (where the Brazilian wild x = 13 species are) and the north-western region (Bianchetti, 1996).

Based on his own data and those of Landrum (1981) on Myrceugenia (Myrtaceae), a genus with distribution and phylogenetic problems similar to those of Capsicum, Bianchetti (1996) formulated the hypothesis that the genus Capsicum was distributed in a continuous humid forest vegetation belt extending from the Brazilian south-east to near to Chile. These species, with x = 13, had pendant, greenish-yellowish fruits that were disseminated by forest-inhabiting vectors, probably bats. With the elevation of the Andes, the area located to the east (Argentina) became semiarid and there followed an extreme reduction of the forest, leading to a selection pressure favouring species with the potential to adapt to the new environment. In some of the populations one pair of chromosomes was lost and the surviving x = 12 taxa changed fruit position and colour to erect and reddish and the dispersal vectors changed to open-vegetation inhabitants, probably birds. Afterwards, these species migrated northwards through the Andes to regions of intermediate altitudes and mild climates. In south-eastern Brazil, the vegetation was little altered owing to the region's climatic stability, so the species from that area maintained the primitive characteristics of pendant greenish-yellowish fruits.

CONCLUDING REMARKS

Existing data suggest a clear separation between the wild Brazilian Capsicum species with x = 13 and the others, mostly with x = 12. Morpho-ecological data (Bianchetti, 1996) suggest that Brazilian species are primitive and the others are derived. Cytogenetic information obtained so far cannot confirm whether x = 13 is primitive or derived, but a comparison of our cytological work and the morpho-ecological data suggests that x = 13 is the ancestral basic number and that the two basic chromosome numbers represent two different evolutionary lines. Further studies in a larger number of species and populations, including FISH (Fluorescent in situ Hybridization) analysis, use of DNA markers and crossing experiments, are necessary to elucidate the evolutionary history of Capsicum.

ACKNOWLEDGEMENTS

We thank Dr Andrea del Pilar de Souza Peñaloza, Ms. Sileuza Santos (EMBRAPA-CENARGEN), MSc Sabrina de Carvalho and MSc Claudia Silva (EMBRAP-CNPH) for their help in collecting material for cytogenetic analysis and for maintaining and supplying plants and seeds. EMBRAPA gave financial support and a PhD grant.

Author notes

†

Current address: Departamento de Plantas Forrageiras e Agrometeorologia, Faculdade de Agronomia, UFRGS, Caixa Postal 15100, 91501-970 Porto Alegre, RS, Brazil