sodininkystė ir daržininkystė 25(4)

SCIENTIFIC WORKS OF THE LITHUANIAN INSTITUTE OF
HORTICULTURE AND LITHUANIAN UNIVERSITY OF AGRICULTURE.
SODININKYSTË IR DARÞININKYSTË. 2006. 25(4).
TECHNIQUES FOR COLD HARDINESS RESEARCH
FOR APPLE ROOTSTOCKS
Jean-Pierre PRIVÉ
Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food
Canada, Bouctouche New Brunswick, E4S 2J2, Canada.
E-mail privej@agr.gc.ca
Abstract. Three reliable methods are explained for estimating different types of
cold hardiness in Malus. They include: 1) a whole plant controlled freezing experiment
for the assessment of low mid-winter injury, 2) electrical impedance spectroscopy
(Z), for the estimation of multiple freeze-thaw cycling injury and 3) a controlled
freezing protocol to facilitate the rapid screening of large populations of Malus
seedlings. The aim of this manuscript is not the results of these three methods but
rather the description of the methods for cold hardiness testing. With the first method,
plant mortality and morbidity (shoot, trunk and root regrowth) proved to be
good indicators for evaluating low mid-winter cold hardiness. Of these, incremental
root growth was the most sensitive to cold temperatures. The results from this
study were validated by the good correlations between the laboratory findings and
the 2004 field survival data from New York, USA following a test winter. The next
method, Z, used root pieces of Ottawa 3 subjected to one, two and three controlled
freeze-thaw cycles at temperatures of -3, -6, -9 and -12°C. Root tissue integrity, as
measured by Z, was severely reduced with multiple events of freeze-thaw cycling
and confirms that freeze-thaw cycling is more detrimental to apple rootstock viability
than periods of constant freezing. Screening for cold hardiness in seedlings of
Malus, 16–20 weeks after radicle emergence, was the third method and holds promise
in segregating large seedling populations and could increase the efficacy of
breeding for cold hardiness.
Key words: cold stress, electrical impedance spectroscopy, Malus, seedling
screening, whole plant freezing and regrowth.
Introduction. The cold hardening process of plants in temperate zones of the
world parallels the march of the seasons. Canada, situated between the arctic and
the 42°N latitude, has many different growing areas, all with their own particular
environments. Recently, studies have begun to examine the relationship between
local climate and apple production (Caprio and Quamme, 1999). In the Okanagan
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