DAMAGE CAUSED BY FROST TO THE YIELD COMPO NENTS OF WHEAT

In the experiments, studies were made on the survival % of four winter wheat varieties with good frost resistance and two with poor frost re sistance, and on the degree of plant damage after freezing at -14-degr ees-C and -16-degrees-C under phytotron conditions. The survival perce ntages of the varieties Mv 4, Mv 9, Mv, 15, and the experimental Mv 21 -85 did not differ significantly at the two freezing temperatures, tho ugh there was a slight reduction in the number of plants which survive d at the lower freezing temperature. A considerable occured in the var ieties Baranjka and Zagrepchanka. The scoring values gave a good refle ction of the variety ranking determined on the basis of survival % and of the different effect of the two freezing temperatures, chiefly for varieties with poorer frost resistance. On the basis of the scores, t he plants were divided into two groups for each treatment and each var iety: plants which suffered frost damage (a score of 2-3), plants whic h suffered no frost damage (a score of 4-5). Twenty plants from each g roup were raised to maturity in pots. The yield parameters of plants d amaged by freezing al -14-degrees-C were reduced to a lesser extent th an those frozen at -16-degrees-C. Of the eight parameters tested, the reduction in the number of ears per plant and consequently in the numb er of grains in the side ears, the grain mass and the total grain yiel d, gave the clearest indication of the extent of plant damage. There w as no change in plant height, while the number of grains and the grain mass in the grain eat decreased only in a few varieties after freezin g at -16-degrees-C. ''Frost damage'' in the economic sense consists of two factors: the ratio of plants destroyed by frost. and the yield lo ss of the surviving plants. This latter is difficult to estimate in pr actice and can only be measured at harvesting.