Meiotic Behavior of Carica papaya L.: Spontaneous Chromosome Instability and Elimination in Important cvs. in North Indian Conditions

Abstract

Cytogenetical analysis was done in tropical species of papaya that is widely cultivated for its fruits and papain production. The proper and orderly chromosome behavior of the species is a perquisite to ensure high fertility and seed set in the crop. A study on pre-meiotic and post-meiotic stages was done on commercially important cultivars of India and few exotic cultivars. The meiosis in the flower buds was highly disturbed and many meiotic irregularities were recorded from the material fixed in summar. These ranged from chromosome stickiness (44%), chromatin bridges (21.1%), laggards (4.8), chromosome diminution/degeneration (5.2), and micronucleus (5.9%) formation, in the commercially important varieties. Pollen stickiness accounting for persistent pollen adherence in groups of 3–10 was observed in all the varieties ranging from 85.95% in cv. CO2 to 11.64% in CO5. Callose deposition on tetrads accounting for adhesion of pollen grains (permanent tetrads) was also observed. These were found to have a profound effect on the pollen fertility of the cultivars, wherein most of the commercial papaya cultivars had less than 50% of fertile pollen. Thus the role of meiotic irregularities in poor seed setting and seed production capacities under northern Indian conditions, specifically during the summer season has been established. Genetic or abiotic stress factors could be responsible for inducing such kind of anomalies, which are manifested in the form of pollen sterility and poor seed setting. Crop regulation strategies need to be evolved, so that the maximum seed set and fruit production occurs after this period to off set the restrictions imposed due to irregular meiosis.