B-chromosome Variation in Cucumis melo L.

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Cucurbit Genetics Cooperative Report 8:55-56 (Article 20) 1985

Ramachandran, C., V. S. Seshadri, and R. A. Pai
Indian Agricultural Research Institute, New Delhi-110012, India

The occurrence of B-chromosome (supernumerary chromosomes) in C. melo has been previously reported in the root tip cells in the cultivars ‘Phut’, or snap melon (C. melo var. momordica) and Hales Best Improved (4,5). The present communication deals with the range of variation of B-chromosomes in muskmelon and also reports for the first time its occurrence in pollen mother cells.

The squashing techniques employed for the study of chromosomes at mitosis and meiosis have already been described (3). Of the 41 cultivars and genetic stocks examined (2), four entries were found to carry B-chromosomes in root tip cells and one had in pollen mother cells also.

The variation in the number and size of B-chromosomes are given in Table 1. Among the four cultivars only ‘Bokor’, a bush variety from Hungary was having B-chromosomes in the root tip cells as well as in pollen mother cells. The number of B-chromosomes varied from 0-2 in root tip cells and 0-1 in pollen mother cells. The size ranges from 0.50-0.75. The pollen mother cells of ‘Bokor’ carried B-chromosomes in about 22.5% cases. The absence of B- chromosomes in the pollen mother cells of three cultivars and variation in the number of B-chromosomes in different cells can be attributed to their progressive elimination during cell division and development (1).

B-chromosome in pollen mother cells of the cultivar ‘Bokor’ does not pair with normal chromosomes. It would appear therefore, that the B-chromosome in it had an antique origin and must have undergone irreversible transition in its chromatin phase, resulting in less homology, with the putative chromosome. B-chromosome does not seem to have any effect on plant morphology or meiotic behavior of normal chromosome. Even though the cultivar ‘Bokor’ carrying B-chromosome in somatic and pollen mother cells was a bushy type, other three cultivars having B-chromosomes only in somatic cells were having normal viny growth habit.

Table 1. Number and size of B-chromosomes in muskmelon.

 
Variety Source Root tip cells Pollen mother cells Size of
B-chromosomes
No. of
cells
studied		 Number of
B-chromosomes
0 1 2		 No. of
cells		 B-chromosomes
0 1
Bokor Hungary 16 6 10 – 80 62 18 0.50
Akra Jeet Bangalore, India 12 2 2 8 80 80 – 0.50-0.75
C. melo var.
callosus		 Tamilnadu, India 20 7 8 5 80 80 – 0.50-0.75
Mon-4 New Delhi, India 15 0 4 11 80 80 – 0.50-0.75

Literature Cited

  1. Jones, R. N. 1975. B-chromosome systems in flowering plants and animal
    species. Rev. Cytol. 40:1-100.
  2. Ramachandran, C. 1983. Cytogenetical studies in Cucumis. Ph.D. thesis
    submitted to IARI, New Delhi-110012, India (unpublished).
  3. Ramachandran, C., V. S. Seshadri, and R. A. Pail 1984. Cytogenetical
    studies on dessert and non-dessert forms of muskmelon. Cytologia (In
    Press).
  4. Sen, R. and K. B. Datta. 1978. Cytological studies on some Indian
    cultivated varieties of Cucumis L. J. Cytol. Genet. 13:16-22.
  5. Singh, A. K. and R. S. Yadava. 1978. Cytogenetical investigations in
    Cucumis L. – B-chromosomes in two Cucumis species. Curr. Sci. 47:742-
    43.