Vernalization and Photoperiodism — 32 — A Symposium 



by "vernalization by short days." This is thought to be the shortest period 

 yet reported within which winter varieties of rice will flower. Alam 

 (1940/41) had already concluded that all varieties require a minimum 

 period of 30 days for vegetative growth and a subsequent period of about 

 30 days of exposure to short days for flowering. This acceleration claimed 

 by Sircar and Parija is applicable to the cultivation of rice in Bengal. 

 A variety of fine rice could be grown in a much shorter time ; by inducing 

 early maturity it could escape flood ; early harvesting would leave sufficient 

 time for preparation of fields for subsequent crops in the rotation. 



Two experiments on vernalization of rice by temperature may be noted. 

 Parthasarathy (1940) vernalized sterilized seeds in darkness or con- 

 tinuous light at 10 to 20°C. for three weeks. Those vernalized in darkness 

 flowered 4 to 5 days earlier than the control. Skripcinskii (1940) ob- 

 tained a distinct response from one variety only, British India 1220, in tests 

 made for 3 years at the Rice Testing Station, Krasnodar. This variety 

 eared 10 days earlier after vernalization at 6 to 8°C. and 8 days earlier after 

 vernalization at 15 to 17°C. than the control plants grown in short day. 



In addition to experiments on the relation between light and tempera- 

 ture and the course of development, Indian workers have also adopted a 

 special pre-sowing treatment for inducing or increasing drought resistance. 

 Chinoy (1942) developed the technique for wheat, and Parija (1943) has 

 applied it to rice ; water requirements for the treated plants were significantly 

 less than for the control plants and the yield of grain significantly greater 

 when the interval of watering is 8 days. Similar experiments have been 

 made with jute, the effects of alternate moistening and drying and after- 

 sowing light conditions being observed on drought resistance and earliness 

 of flowering (Kar, 1944). There was an increased resistance to drought 

 after treatment, but the earliness observed was due to the photoperiods fol- 

 lowing sowing. 



Pal and Murty ( 1941 ) state that, although low temperature at the time 

 of germination may be indispensable for the normal development of English 

 winter wheat, Indian wheats come into ear (without chilling) even at high 

 summer temperatures, indicating that low temperature is not indispensable. 

 A further indication that Indian varieties have little if any requirement of 

 low temperature, but that response to light can be readily obtained is also 

 seen in the experiments of Kar (1940). 



Sen and Chakravarti (1945) have been testing the response of wheats 

 to vernalization since 1938. The non-Indian varieties. Holdfast, Little 

 Joss, Yeoman, Juliana and Yorkwin have been used, and significant re- 

 sponses have been obtained, that is, earlier emergence of the inflorescence 

 in plants from pre-chilled seeds. Results of attempts to vernalize Indian 

 varieties of wheat in different parts of India have led to the general ac- 

 ceptance of the fact that the cultivated strains of Indian wheat will not re- 

 spond to vernalization because of their shorter life cycles. Sen and 

 Chakravarti have, however, found that a very good response was obtain- 

 able in the first, second and third generation hj-brids made by them be- 

 tween T.P. 4 (Indian wheat) and Yeoman (Cambridge winter wheat). 

 Further trials have shown that a response can be obtained in a number 

 of pure strains of cultivated Indian wheats and have now led to a systematic 



