Abstract
Two separate experiments were designed, one in solution and the other in soil culture to determine the most sensitive growth stage of rice to salt stress and relative toxicity of various salts in the growth medium. Four rice varieties i.e. Basmati-370, NIAE-6, BG-402-4 and 1R-1561 were used for these studi!s. Two salinity levels (control and EC 10 dSm ) were developed by adding NaC1 to solution culture; and NaC1 alone,NaCli-CaC12, Na2CO3 & a salt mixture (Na2S0+NaC1A-CaC124-MgSO4 in the ratio of 9:5:5:1) in4soil culture. Silt stress applied at the time of transplanting and at panicle initiation stage caused the maximum reduction in paddy yield while for straw yield seedling (transplanting) stage proved more crucial. With respect to type of salinity, NaC1 alone was more toxic then NsCI+CaC12, Na2CO3 or the salt mixture. Comparative toxicity of Na and Ca2+ is discussed.
INTRODUCTION
Plant growth is affected by salinity at all stages of development, but sensitivity varies from one growth stage to the other (Maas and Hoffman, 1977). Determination of the sensitive stage is necessary for the development of a rapid procedure for mass screening of various genotypes of a crop as the testing could then be confined to the sensitive stage only. In addition, such an information in useful for the utilization of saline water for irrigation which may be applied, if necessary, at the relatively less sensitive stage
