Cucurbit Genetics Cooperative Report 3:66-67 (article 36) 1980
Taxonomy of Cucumis callosus (Rottl.) Cogn. - The Wild
Melon of India
V. A. Parthasarathy and C. N. Sambandam
Division of Horticulture, ICAR
Research Complex for NEH Region, Shillong - 793 003, India (first author); Faculty of Agriculture, Annamalai University,
TN-608 101, India (second author)
Cucumis callosus, a feral species of India, has
attracted the attention of muskmelon breeders, as this species
is reported to possess genes for resistance to fruitfly
and leaf-eating caterpillars (9). But this species remains
to be a controversy for taxonomists. The synonym given for
this species is C. trigonus (2). While cytologists
have shown that C. callosus (syn: C. trigonus)
has 14 somatic chromosomes (3, 10), the breeding experiments
of Naudin (6), Vavilov (11), and of Sambandam and Chelliah
(9) have given evidence of free compatibility between C.
callosus and C. melo. Hence, to obviate the
confusion regarding the chromosome number as well as the
relationship with other Cucumis species, the present
study was undertaken.
Seeds of stocks maintained in the Division of Horticulture,
Annamalai University, were used in the study. Counts of
somatic chromosomes were made from the root tip cells following
the procedure of Roy (8) using proppiono-orcein stain. To
ascertain the compatibility with other Cucumis
species, crosses were made (including reciprocals) with
seven Cucumis species, namely, C. metuliferus,
C. anguria, C. longipes (= C. anguria var. longipes), C.
zeyheri, C. myriocarpus, C. dipsaceus, and C. melo.
The success of each cross was determined by the percent
fruit set and the number of well developed seeds. The F1 fertility was determined by pollen fertility and viability
(germination). Meiotic studies were carried our in the PMCs
of F1 plants to study the behavior of chromosomes during
The metaphase plates revealed the somatic chromosome number
of 24 for C. callosus. The crosses with seven
Cucumis species indicated that C. callosus
was crossable with only C. melo. The number of
well developed seeds per fruit in the cross C. callosus
x C. melo was, on an average, 266 seeds and the
seeds showed about 93% germination. The pollen mother cells
showed normal bivalent formation, indicating cross compatibility
between C. melo and C. callosus.
The somatic chromosome number observed from the study (2n=24) is disagreement with that of Singh and Roy (10) who
reported the 2n number to be 14. It is interesting to note
the report of Brown et al. (1) who stated that
C. trigonus from India was mislabeled and in reality
was C. hardwickii. Cucumis trigonus is
the synonym for C. callosus (2). But the confusion
in the taxonomy of Cucumis, especially those found
in India, is due to the fact that names have been given
based on the morphological differences. To substantiate
this, the following statements of Hooker (5) and Gamble
(4) are presented. While Hooker and Gamble described C.
trigonus and C. pubescens as synonyms, chakravarthy
(2) placed C. trigonus under C. callosus
and C. pubescens under C. melo. Watt
(12) made a statement very long ago which still holds good
for Indian Cucumis. He stated much confusion exists
regarding the Indian so called wild and cultivated species
and varieties of Cucumis.
Based on the chromosome number, its free compatibility
with C. melo, and normal behavior of chromosomes
during diakinesis, we conclude that C. callosus
does not warrant a separate species status and is nothing
but a progenitor of C. melo. This confirms the
earlier breeding experiments of certain workers (6, 7, 9,
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of Cucumis species by paper chromatography of
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atlas of flowering plants. Allen and Unwin Ltd.,
- Gamble, J. S. 1923. Flora of the presidency of
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- Hooker, J. D. 1879. Flora of British India.
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- Naudin, C. 1859. Revue des Cucurbitaces cultivees au
Museum en. Ann. Sci. Nat. Ser. 4 Bot. 12: 79-164.
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Cucurbitaceae. USDA PL-480 Res. Project (Final Report).
Patna Univ. 263 pp.
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the evaluation of cantaloupe and muskmelon varieties for
the resistance to the fruit fly (Dacus cucurbitae C.).
USDA PL-480 Res. Project. Annamalai Univ. 67 pp.
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in Cucumis. Caryologia 27: 153-160.
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principal centres of origin of cultivated plants of the
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The senior author thanks the Indian Council of Agricultural Research for the award of Senior Fellowship to him during the study.