Vernalization and Photoperiodism — 124 — A Symposium 



perature treatment to accelerate flowering is due to the prevailing environ- 

 mental conditions, of which short day-length is an important factor. Ex- 

 posure to short-days in these strains was found to prolong, and long days 

 or continuous illumination to curtail, the vegetative period. An exposure 

 of low temperature treated seeds to long days for a period of only 7 days in- 

 duced a significant earliness in the varieties which all along the rest of their 

 life cycle were grown under short day conditions. B. P. Pal and G. S. 

 MuRTY (1941) have also shown acceleration by long photoperiods and re- 

 tardation by short days. It thus appears that for vernalization of wheat in 

 India a photostage of long days is necessary, and once this is passed the 

 plants complete their developmental phases independent of subsequent day 

 length. Wheat being a winter crop, its low temperature requirement under 

 Indian conditions is met by sowing in winter, but the prevailing short day 

 length delays the completion of the photostage till the natural day length in- 

 creases, when flowering takes place. Comparing the results of simul- 

 taneous sowings of the same varieties at Delhi (Lat. 28.38° N.) and Almora 

 (Lat. 29.37°N.) in October and February, B. Sen (1943-44) considered 

 that after-sowing environmental factors completely mask the effect of chilling 

 of seeds. It would be interesting to find out in these cases the effects of 

 different photoperiods on the strains showing acceleration of flowering by 

 chilling. 



K. K. Nanda and J. J. Chinoy (1945), in an attempt to prove the 

 presence of a developmental phase associated with the formation of normally 

 functioning gametes, have shown that long photoperiods as well as short 

 photoperiods after the completion of the photostage increase pollen sterility, 

 while with natural day length sterility is very much lower. This emphasises 

 the importance of a critical number of long days, beyond which long days 

 have only an adverse effect. According to B. P. Pal and G. S. Murty 

 (1941), varieties of English wheat grown under tropical conditions require 

 chilling followed by long days for inducing earliness ; in the absence of chill- 

 ing long days have no effect. For Indian wheat, on the other hand, chilling 

 is not as important as long days for vernalization. But for yield and normal 

 growth low temperature is an essential feature, as in summer sowings the 

 crop yield becomes poor. They have further shown that the flowering 

 duration of Indian wheat despite the prevailing short day condition is less 

 than the English wheat grown under identical conditions. These differ- 

 ences in the behaviour of the varieties of English and Indian wheat support 

 the thesis of N. I. Vavilov (1941) that by centuries of adaptation in trop- 

 ical climate these strains have become differentiated into a distinct ecological 

 and physiological group. 



Mustard {Brassica spp.) : — Acceleration of flowering by pre-sowing 

 low temperature treatment of sprouted and unsplit seeds of the Indian va- 

 rieties of mustard was noted by B. Sen and S. C. Chakravarty (1938, 

 1942) . Response was more in the case of sprouted seeds than unsplit seeds. 

 Although the degree of vernalization induced is less in the unsplit seeds its 

 advantages are: {1) germination of almost all the seeds, whilst sprouted 

 seeds germinated only 30 to 40 per cent, (2) retaining power of germination 

 without devernalization when dried and stored at room temperature for 

 more than six years (B. Sen and S. C. Chakravarty, 1946). The effects 



