Plant damage after freezing, and the frost resistance of varieties from the facultative and winter wheat observation nurseries

In the first experiments, studies were made on the survival % of four winte r wheat varieties with good frost resistance and two with poor frost resist ance, and on the degree of plant damage after freezing at - 14 degreesC and -16 degreesC under phytotron conditions. In the second experiment the fros t resistance of the varieties included in the 9(t)h Facultative and Winter Wheat Observation Nurseries (FAWWON) was determined after freezing in the p hytotron at - 15 degreesC. The scores gave a good reflection of the variety ranking determined on the basis of survival % and of the different effects of the two freezing temperatures. On the basis of the scores, the plants w ere divided into two groups for each treatment and each variety: plants whi ch suffered frost damage (a score of 2-3), and plants which suffered no fro st damage (a score of 4-5). Twenty plants from each group were raised to maturity in pots. The yield pa rameters of plants damaged by freezing at - 14 degreesC were reduced to a l esser extent than those frozen at -16 degreesC. Of the eight parameters tes ted, the reduction in the number of ears per plant and consequently in the number of grains in the side ears, the grain mass and the total grain yield , gave the clearest indication of the extent of plant damage. The results o f the second experiment indicated that in some cases the frost resistance o f the varieties could be predicted from the wheat production zone (e.g. var ieties from Eastern Europe and Nebraska have excellent frost resistance), w hile in other zones winter hardiness and frost resistance depended rather o n the country or on the breeding location.