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 fourwinter wheat varieties with good frost resistance and two with poor frostresistance, and on the degree of plant damage after freezing at –14 ^°C and –16 ^°C under phytotron conditions. In the secondexperiment the frost resistance of the varieties included in the 9^thFacultative and Winter Wheat Observation Nurseries (FAWWON) wasdetermined after freezing in the phytotron at – 15 ^°C. The scoresgave a good reflection of the variety ranking determined on the basis ofsurvival % and of the different effects of the two freezing temperatures. Onthe basis of the scores, the plants were divided into two groups for eachtreatment and each variety: plants which suffered frost damage (a score of2–3), and plants which suffered no frost damage (a score of 4–5).Twenty plants from each group were raised to maturity in pots. Theyield parameters of plants damaged by freezing at – 14 ^°C werereduced to a lesser extent than those frozen at –16 ^°C. Of the eightparameters tested, the reduction in the number of ears per plant andconsequently in the number of grains in the side ears, the grain mass andthe total grain yield, gave the clearest indication of the extent of plantdamage. The results of the second experiment indicated that in some casesthe frost resistance of the varieties could be predicted from the wheatproduction zone (e.g. varieties from Eastern Europe and Nebraska haveexcellent frost resistance), while in other zones winter hardiness and frostresistance depended rather on the country or on the breeding location.