Biochemical Methods for the Characterisation of Walnut Genotypes with Different Levels of Frost Tolerance

In plants, stress induces changes in peroxidase enzymes, which play various physiological roles, including involvement in the development of resistance. Experiments were performed at the Elvira major Experimental Station of the NARIC Research Institute for Fruitgrowing and Ornamentals in Érd, Hungary, on two genotypes selected in Hungary (‘Alsószentiváni 117’ and ‘Milotai 10’), on the Californian-bred cultivar ‘Pedro’, and two genotypes bred in Hungary by crossing ‘Pedro’ with the two Hungarian selections: ‘Milotai intenzív’ and ‘Alsószentiváni kései’. These genotypes were chosen on the basis of frost tolerance. Measurements were made on the peroxidase activity and total polyphenol content in the leaves during sprouting (May 2nd, 12th and 20th 2016) and in the uppermost internode of the shoots (November, December 2016; January 2017). Higher peroxidase enzyme activity and polyphenol content in the uppermost internode were good indicators of the frost tolerance of the genotypes and of the stress level to which they were exposed.