FROST-RESISTANCE TESTING ON TRITICUM-DURUM (DESF.) GENOTYPES IN THE MARTONVASAR PHYTOTRON

In the experiments the frost resistance of eight T. durum wheat variet ies of various origins and of sixteen T. durum genotypes bred in Marto nvasar was evaluated in the phytotron after freezing at -13 degrees C and -15 degrees C. In order to determine the degree of frost resistanc e the number of plants surviving freezing was recorded and each plant was scored on a 0-5 scale. For some of the T. durum genotypes tested i n the freezing experiment the grain yield was also determined in field experiments. The bread wheat variety Mv 15, which has excellent frost resistance and was used as the control, exhibited approx. 94% surviva l at both freezing temperatures. When frozen at -15 degrees C the vari eties Odmadur 1, Odmadur 2 and Martondur 1 and many of the T. durum li nes bred in Martonvasar showed survival rates approaching that of Mv 1 5. None of the T. durum genotypes tested was found ro have frost resis tance worse than that of the poorly resistant bread wheat variety NS R ana 2 at either freezing temperature. The grand mean of the survival p ercentages after freezing for all the genotypes tested was 80.96 % at -13 degrees C and 54.45 % at -15 degrees C, while the grand mean of th e individual plant scores was 2.53 at -13 degrees C and 1.58 at -15 de grees C. It can thus be seen that freezing at the lower temperature le d to an increase not only in the killed plant rate, but also in the nu mber of surviving, but severely damaged plants. The degree of correlat ion between the grain yield and the scores obtained after freezing at both temperatures was determined for genotype pairs where was a signif icant difference in the scores, but not in the survival percentages. A close positive significant correlation ( r=0.871) was found between t he scores and the grain yields of the genotype pairs tested. In genera l genotypes with better scores gave higher grain yields, i.e. among th e genotypes with similar killed plans rates, those which suffered a gr eater extent of individual plant damage during freezing also had lower productivity than the more resistant types.