Knob distribution in Himalayan strains of maize

The results of the pachytene analysis of 29 maize collections from the North-Eastern Himalayas (N.E.H.) and two American races have been summarized in Table 1. Pachytene chromosomes have been well identified on the basis of their relative lengths and arm ratios. Hence, it was possible to assign exact positions of knobs on particular chromosomes. There was a preponderance of subterminal knobs in the N.E.H. collections, suggesting that Mexican teosinte has played a significant role in the evolution of Himalayan maize.

Except for the Sikkim Primitive types (S.P.), the knob number, in general, among the N.E.H. maize is low. In order to study relationships between knob number and altitude, material collected from different ethnic groups of Sikkim at various altitudes has been studied. Maize collections from Sikkim at altitudes ranging from 1,200 to 1,400 m have an average knob number of 4, while the collections from 1,440 to 1,700 m have an average knob number of 5, and the collections from the highest altitudes (1,740 to 2,440 m) have the mean knob number of 4.5. Thus, the strains collected from Sikkim do not differ in knob number with the change of altitude. These observations may also be interpreted to indicate that maize collections from different parts of Sikkim have a common origin.

However, the status of the Sikkim Primitive types is quite different. Of the seven strains of the S.P. type studied, four (S-18, S-23, T-1. and T-2) have a high mean knob number of 9, while three (M-1, M-15 and M-25), although classified as S.P. types on the basis of morphological similarities (MNL 56:122-123, 1982), appear to be different in lineage with a very low average knob number of 2.5.

Of the two American races studied, Pira has a mean knob number of 13 and Confite Morocho, 4. Both these races have knobs at subterminal positions.

The variation in the knob position, number, shape and size in some of the collections from Sikkim is depicted in the ideograms.

Table 1. Distribution of knobs at pachytene.

Figure.

Suchira Pande, J. K. S. Sachan and K. R. Sarkar


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