--S. K. Katiyar and J. K. S. Sachan
To study the pollen size and surface features of exine, pollen grains of ten distinct collections of Coix, including both Coix aquatica and C. lacryma jobi, three collections of teosinte, including Zea diploperennis, Z. luxurians and Z. mays ssp. parviglumis, four collections of maize (Zea mays L.) and one collection each of Chionachne koenigii and Trilobachne cooki were collected and a stereocan S4-10, scanning electron microscope was used for the observations and photography.
The pollen grains of different species and genera studied were round or slightly oval in shape and uniporate. The pollen of maize was in general larger with a mean pollen grain size of 106.14um, followed by teosinte (85.11um), Coix (55.99um) and Chionachne (34.70um). Pollen grains of Coix aquatica had a mean diameter of 61.49um and were found to be larger than the pollen grains of C. lacryma jobi which had a mean diameter of 50.50um.
Table 1. Mean chromosome length (um), relative length (um) and arm ratio
at pachytene in maize, teosinte and Coix (2n=10).
|Total genomic length||565.58||547.03||838.60|
|Mean chromosome length||56.55||54.70||167.72|
Teosinte: mean of three species of teosinte studied viz., Z. diploperennis, Z. mays ssp. parviglumis, Z. luxurians.
Coix: mean of all 26 collections studied.
The scanning electron micrographs (SEM) of pollen of the different material studied have shown that within the genus (except Coix) exine sculpture was similar, but marked differences were observed at intergeneric levels. However, in Coix enormous variation within the genus was noticed. In maize pollen the spinules were distributed more or less uniformly all over the tectum. They did not follow any linear pattern. The pollen surface of all three species of teosinte studied was similar to maize. The spinules were less densely spaced in teosinte than in maize, however no differences were found in size and shape of the spinules in maize and teosinte and also among teosintes.
In Coix pollen the spinules were thinly distributed over the tectum and appeared to follow curved paths. The differences in terms of size and shape of spinules were noticed among various genotypes in the genus Coix. Unlike other collections, one culture of Coix aquatica was observed to have depressions in the tectum which formed a network over the entire surface. In Chionachne pollen, the spinules, which were sparse in distribution, showed a tendency to form groups of 9 to 12. In conclusion, the results of the SEM studies of the exine pattern suggest that maize is very closely related to teosinte followed by Chionachne and lastly Coix. In sparse distribution of spinules and by following the curved paths Coix and Chionachne showed some degree of closeness.
Table. Mean pollen grain size and range in maize and its relatives.
|Material||Mean (in um)||Range (in um)|
|Coix lacryma jobi||50.50±3.16||38.00-65.00|
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