Investigations into Causes of Sterility

II. Tabernaemontana cornaria Willd

Abstract

Tabernaeynontana cornaria Willd., a common cultivated shrub with white flowers, fragrant at night, bears fruits and sets seeds in sub-Himalayan tract. But in the plains of Uttar Pradesh (India), the plants are completely fruitless. The investigations into the causes of fruitlessness has revealed irregularities in the development of male gametophyte.
All the plants scrutinized showed the haploid chromosome number to be n=11. Chromosomes during diakinesis and metaphase I were mostly paired but precocious separation of 1 to 3 bivalents was frequent. Later stages of meiosis showed laggards, unequal distribution, bivalent bridges and polyspory. These anomalies account for pollen variability and to some extent for sterility.
The tapetum of microsporangium failed to show typical cataclysmic mode of development of angiosperms. Instead, tapetum was seen to persist even after the microspores had aborted. This delay in degeneration of tapetum could account for complete sterilization of pollen grains. Difference in the temperature and photoperiod in sub-Himalayan tract and the plains of Uttar pradesh seem to be responsible for pollen sterility and consequently to fruitlessness.