Six cultivars of Solanum macrocarpon (Solanaceae) in Ghana

The Solanum macrocarpon complex (the cultivated egg plant) has been studied in Ghana using morphological and experimental methods. Six cultivars belonging to the 5. macrocarpon complex have been recognized and described. The cultivars are S. macrocarpon ‘Gboma’, S. macrocarpon ‘Mankessim’, S. macrocarpon ‘Akwaseho’, S. macrocarpon ‘Kade’, S. macrocarpon ‘Sarpeiman’ and S. macrocarpon ‘Bui’. The very spiny, hairy plant traditionally called S. dasyphyllum is regarded as the wild ancestor from which the cultivars have been derived through a process o f crop evolution. The variation within S. macrocarpon complex is attributable to genotypic differences and environmental factors.


INTRODUCTION
Solanum macrocarpon L. is an important native Afri can vegetable, especially in west Africa where both the leaves and fruits are eaten.In east Africa, particularly Uganda, it is however a minor crop and it is mainly the leaves that are eaten (Bukenya 1984).The crop is also cultivated in South America and Asia.It was introduced to Europe from India, described and illustrated by Miller (1759) and named by Linnaeus (1771).
Despite its importance as a vegetable and its wide spread occurrence, little has been done until now to re cognize and describe any of the cultivars.

METHODS A ND MATERIALS OF MORPHOLOGICAL STUDY
Materials belonging to the 5. macrocarpon complex were collected from different localities throughout southern Ghana, and also (mainly seeds) obtained from elsewhere in Africa (Togo, Nigeria and Uganda).In sou thern Ghana, farms where 5. macrocarpon is grown, were visited.Herbarium specimens were made.Ripe fruits, from which seeds were later extracted, were col lected from farms and in some cases from markets.Occasionally, when mature fruits were not available, transplants were collected and later replanted in an ex perimental garden.Photographs of flowering and fruit ing plants were taken.
Each individual (transplant) or each fruit was given a different accession number.In the laboratory, seeds from different accessions were extracted and spread on paper to dry at room temperature.After drying a mini mum of 20 seeds from each accession (fruit), they were sown in compost soil in seed pots.Pots were housed in a greenhouse at a mean daily maximum temperature of 34,8 °C and mean daily minimum temperature of 22,1 °C.Pots were watered every two to three days.When seedlings were at the three-leaved stage (about two weeks after germination), they were picked out of the seed pots and transferred to seed boxes kept outside in sunshine.When the plants were about a month old they were removed from the seed boxes and planted in the experimental garden.About ten plants of each accession were planted.The plots were constantly weeded and plants watered when necessary.The major pests of the plants (caterpillars) were controlled by spraying with DDT (Five grammes of powder in about four litres of water).
The morphological characteristics of the plants were observed in their developmental process.When plants had fully grown, measurements of the characters of stem, leaves, flowers and fruits were taken.
The following accessions were studied:
The above specimens were deposited in University of Ghana Herbarium.

RESULTS
A summary of morphological measurements is given in Tables 1-4.The results of morphological study show that there is tremendous variation within the S. macrocarpon com plex.Some of the accessions within the complex have big, deeply lobed leaves while others have small and less lobed leaves.Also flowers vary in their size and depth of corolla lobing.Whereas the flower calyx length of many accessions was 10-22 mm, one accession had a calyx length of about 60 mm; whereas the ratio between lamina length and petiole length of many accessions was 8-10, a ratio of 25-46 was obtained in one accession.
Apart from the above morphological variation, con sidered to be due mainly to genotypic differences, en vironmental factors were also seen to play a significant part in the phenotypic variation in the S. macrocarpon complex.One such factor was noted to be cultivation methods.For example, at Avenor near Accra in Ghana, S. macrocarpon was seen to be grown in crowded rows and the leaves were removed constantly for sale when the plants were still young.Figure 1 shows a typical planting of S. macrocarpon on a farm at Avenor.The plants here had a height of less than 0,3 m, and they had small fruits (30-35 mm diam.) and small leaves (170 x 90 mm).When seeds collected from a farm at Avenor were grown in our experimental farm with proper spac ing of plants and no trimming, the plants attained a height of about 0,7 m with a fruit diameter of 40-60 mm and a mean leaf size of 255 x 164 mm.It was Bitter (1923) who first realized the tremendous variation within the S. macrocarpon complex and he described several infraspecific taxa.He also noted that the traditional separation of S. macrocarpon from S. dasyphyllum on the basis of the latter being spiny and hairy and the former unarmed and glabrous, was not satisfactory.He was for example able to describe, 'a spineless variety of S. dasyphyllum and a spiny subspe cies of S. macrocarpon'.
We noted that there was a continuous range of varia tion in hairiness and spininess from very hairy and spiny accessions to glabrous and unarmed accessions.It also appears that spininess is a heterozygous character.This was demonstrated by the fact that when seeds from a single fruit (Katende U G .l -S.macrocarpon) were sown, about 60 % of the plants that grew were spiny and 40 % not spiny.Some plants of accession Hall 47172 (S. macrocarpon) from Medina near Accra, were seen to bear spines, though S. macrocarpon, according to most authors, is non-spiny.
The type specimen of S. macrocarpon is Thonning 117 from Guinea [Ghana].We have studied the IDC microfiche photographs of two duplicates on IDC micro fiche No. 2203-101: III.3-6.The specimen illustrated in HI. 3 is glabrous, leaves oblong and subentire and that in ID. 5 is glabrous, leaves oblong.Some of the leaves on this specimen are subentire while others are more or less deeply double-lobed with major lobes bearing minor lobes.TTie type specimens for S. dasyphyllum, Thonning 144, came from 'Guinea' (i.e.near Accra, Ghana (Hepper 1976).The IDC microfiche photographs (No. 2203-102: I. 1 ^) show that the plants have oblong, deeply double-lobed leaves.They are very hairy and the stem, midribs and primary lateral nerves bear robust spines.Bitter (1923) and recent other workers like Heine (1963) realized that the two species are very close.Bukenya (1980 in unpublished M.Sc.thesis) con cluded that the species traditionally called S. macrocar pon and S. dasyphyllum were one and proposed to sink the latter under S. macrocarpon.
In this paper we have treated the S. macrocarpon com plex as a combination of the former two species, i.e. 5. macrocarpon L. and S. dasyphyllum Schum.& Thonn.
Our study has enabled us to identify seven groups belonging to the S. macrocarpon complex.Since this complex is basically a cultivated crop, it is not satisfac tory to give formal taxonomic ranks to these groups.We have therefore decided to give cultivar names to all these groups, except one which is wild.The wild one matches Bitter's S. dasyphyllum var.dasyphyllum in its dense spines and hairs and double lobing of the leaves.We believe that this wild plant is the ancestor of the cultivars and that the cultivars have arisen after a long process of cultivation and selection for non-spininess and non-hairi ness.The name cultivar is used in this context in the same sense as used in the International Code of Nomen clature for Cultivated Plants of 1969.
The cultivar names are either the Ghanaian native names for the plants or names of localities where the cultivars were collected in Ghana.An attempt was made to compare the present cultivars with the taxa that Bitter (1923) described in Series Macrocarpon.
This cultivar is comparable to Bitter's S. macrocarpon var.macrocarpon (var.culvum).Type: Guinea [Ghana], Thonning 117.This cultivar is comparable to Bitter's S. macrocarpon var.primovestitum except that 'Mankessim' may bear spines which are lacking in var.primovestitum and the former has more and persistent hairs.The locality of Bitter's 5. macrocarpon var.primovestitum is on the coast of Mozambique.
This cultivar is comparable to Bitter's S. macrocarpon var.macrocarpon forma megistocalyx Bitter, in the form of the big calyx.The calyx of our cultivar is even bigger than in forma megistocalyx.The major difference is that 'Akwaseho' has some sessile stellate hairs and spines may be present on leaves while forma megistocalyx lacks hairs and spines.The locality of forma megistocalyx was Congo (Lower Zaire) Region, Kisantu, G illets.n. 4. S. macrocarpon 'Kade' (Figure 5) Leaves very narrow and deeply lobed, middle lobe up to 80 mm long; subsessile with simple, sessile stellate or stalked stellate hairs.Calyx fairly long but narrow, up to 30 x 60 mm.Fruit ovoid or spherical, 30-70 x 40 mm, green or green with patches when young, turning yellow when ripe.
Locality: Ghana, Abodon, 6°26'N, 1°32'W, H all47169.This cultivar does not match any of Bitter's taxa.It is unique in that its leaves are so narrow and deeply lobed and it may have an oblong fruit which is unusual in S. macrocarpon.3. S. macrocarpon 'Akwaseho' (Figure 4) Plants similar to 'Mankessim', spiny or not spiny, but leaves more deeply lobed, middle lobe up to 70 mm long and fruits larger: about 50 x 90 mm.Leaves subsessile with some simple and sessile stellate hairs.Calyx very big, up to 60 x 30 mm.Fruits ivory-coloured when young, turning yellow when ripe.This cultivar is comparable to Bitter's S. dasyphyllum var.semiglabrum (C.W. Wright) Bitter, except that in the former the spine length on the midrib ranges from 0-13 mm whereas in the latter the range is 6-10 mm.The type locality of semiglabrum is Nupe-Benue Pro vince in northern Nigeria.This cultivar is comparable to Bitter's S. dasyphyllum var.dasyphyllum except that the former is less hairy than the latter, probably because the former is occasionally cultivated.Bitter's locality of var.dasyphyllum is Gui nea [Ghana], Thonning 144.
4 .-Sum m ary o f m eans o f characters o f h erm aphrodite flow ers (m m ).Each figure represents a m ean o f no less than a cro ca rp o n 'G b o m a' S. m a cro ca rp o n 'M ankessim ' S. m a cro ca rp o n 'A k w a seh o ' S. m a cro ca rp o n 'K ad e' S. m a cro ca rp o n 'Sarpeim an' S. m a cro ca rp o n 'B u i' S. d a sy p h y llu m var.d a sy p h y llu m (putative w ild ancestor)