Peculiarities of chromosomal behaviour in the natural autotetraploid Pennisetum orientale L.C. Rich

Abstract

Detailed meiotic studies have been carried out in three populations of Pennisetum orientale collected from the Mall, Chail and Tara Devi hills in Simla. The cytological investigations revealed the presence of two chromosome numbers i.e. 2 n=36 and 2n=54. With base number x=9 known for the species the two cytotypes exist at tetraploid and hexaploid level. The tetraploid plants were found in all the three populations. However, the hexaploid plant was found growing along with the tetraploid plants in the Mall population. While the two cytotypes could not be distinguished morphologically, cytologically they showed contrasting behaviour of chromosomes. Meiosis in the hexaploid cytotype was normal with regular bivalent formation observed in all the cells studied. Whereas in tetraploids meiosis was highly erratic and followed more or less similar course in all the three populations. It was characterized by the presence of hexavalents and octavalents at diplotene/ diakinesis. However, quadrivalents (upto 9) followed by trivalents were the most common bigger associations observed. Significant variation existed in the type and frequency of multivalents in the cells within and between anthers of similar plant which was associated with a drastic cell-to-cell variation in chiasma frequency. While the presence of upto 9 quadrivalents per cell point towards the autotetraploid nature of the species, being reported for the first time, the presence of hexavalents and octavalents point towards interchanges superimposed on autopolyploidy. Details of the chromosomal behaviour in the two cytotypes is discussed.

Key words:

• chiasma frequency
• meiosis
• Pennisetum
• polyploidy