1. The eleven wild species of
Vigna studied can be classified into four groups on the basis of their morphological affinities.
i) In the first group comprising of the species viz.
V. parviflora Welw.,
V. wilmsii Burtt Davy.,
V. oblongifolia A. Rich., and
V. gracilis Hook. flowers are small zygomorphic, keel and style are not twisted, the posterior two sepals are fused and seeds are small oblong with caruncle.
ii) The second group consisting of the three species viz.
V. luteola Benth.,
V. marina (Burm) Merr. and
V. schimperi Baker differs from the first group in having larger flowers and reniform seeds without caruncle.
iii) The plants of the third group consisting of the species
V. vexillata (Linn.) Benth. and
V. davyi Bolus. have conspicuously large irregular flowers in which the posterior two sepals are not fused, keel slightly twisted with one sided pouch, style slightly twisted tuberous root and seeds reniform without caruncle.
iv)
V. membranacea A. Rich. is the lone member of the fourth group having several common features of both the second and third groups.
2. The plants of the third group in having slightly twisted keel with one sided pouch also show their affinity to the genus
Phaseolus.
3. The karyotypic study of the
Vigna species has shown the presence of two chromosome numbers 2n=22 and 2n=20.
V. parviflora,
V. wilmsii,
V. oblongifolia,
V. gracilis,
V. sehimperi,
V. luleola,
V. marina,
V. vexillata and
V. davyi and the cultivated species
V. catjang,
V. sinensis and
V. sesquipedalis have 2n=22 chromosomes. Only two species viz.
V. heterophylla and
V. membranacea have 2n=20 chromosomes.
4. The chromosome number 2n=24 reported for
V. catjang,
V. sinensis and
V. sesquipedalis by some workers has not been observed in any of the six varieties, two from each group, studied.
5. The chromosome complements of the fourteen species are more or less similar in the number of long, medium and short chromosomes and in their gross morphology.
6. The chromosmes of all the species are very small, ranging from 1.6 to 3.7μ in length and have submedian primary constriction. Long chromosomes in the different species vary from 3.0 to 3.7μ and the short chromosomes from 1.6 to 2.0μ.
7. Meiotic studies have shown regular pairing of the homologous chromosomes forming bivalents in diakinesis and metaphase, and normal subsequent meiotic stages.
8. The possibility of eleven as the basic chromosome number of
Vigna has been indicated. It has been assumed that the 2n=20 chromosomes type
V. heterophylla has been derived from the first group of species and the
V. membranacea from a 2n=22 chromosome group intermediate between the second and the third groups.
9. The three cultivated types
V. catjang,
V. sinensis and
V. sesquipedalis need not be considered as distinct species but should be regarded as members of a polymorphic species,
V. sinensis with three subspecies viz,
V. sinensis,
V. sinensis subspecies
catjang and
V. sinensis subspecies
sesquipedalis.
10. They resemble the plants of the second group and are likely to have been derived from them.
V. luteola of that group is most closely related to the cultivated species and is the only species that gave a few pods in crosses with them. It seems that
V. catjang and
V. sinensis have been gradually differentiated from a common ancestral stock and
V. sesquipedalis is a later selection from
V. sinensis.
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