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ARS Home » Northeast Area » Geneva, New York » Plant Genetic Resources Unit (PGRU) » Research » Publications at this Location » Publication #381492
Title: Low temperature tolerance in apple shoots following exposure to warm temperatures in late winter

Author
item MORAN, RENAE - University Of Maine
item PETERSON, BRYAN - University Of Maine
item Fazio, Gennaro
item CLINE, JOHN - University Of Guelph

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2021
Publication Date: 5/11/2021
Citation: Moran, R.E., Peterson, B.J., Fazio, G., Cline, J.A. 2021. Low temperature tolerance in apple shoots following exposure to warm temperatures in late winter. HortScience. https://doi.org/10.21273/HORTSCI15665-20.
DOI: https://doi.org/10.21273/HORTSCI15665-20

Interpretive Summary: Climate events like a short winter warm-up period have a tendency to decrease the cold hardiness potential of some plants and increase the sensitivity to successive cold snaps. We measured tolerance to cold temperature of apple rootstock cultivars and advanced selections after a 2-day exposure to warm temperatures by measuring tissue injury displayed by discoloration (browning). We found that the amount of sensitivity caused by deacclimation varied among shoot tissues and rootstocks. An important finding in this research was that two days of warm temperature was sufficient to cause loss of hardiness in most rootstocks.

Technical Abstract: We measured the cold temperature (0 to -40 °C) tolerance of xylem, phloem and cambium in one- and two-year-old shoot pieces from apple rootstock cultivars and advanced selections ‘Malling 9 T337’ (M.9), ‘Malling 7 EMLA’ (M.7), ‘Budagovsky 9’ (B.9), ‘Geneva® 41’ (G.41), ‘Geneva 30’ (G.30), ‘Geneva 935’ (G.935), ‘Geneva 814’ (G.814), G.4013, G.5257 and Vineland 6 (V.6) after a 2-day exposure to warm, 22 °C, or cold, 2 to 4 °C, temperatures. Injury was measured on a 0 to 10 rating scale based on percentage of discolored cross-sectional xylem and phloem, and cambial length and circumference with brown discoloration, with 0 indicating no browning and 10 indicating browning in the entire tissue. Injury was also measured as intensity of browning on a scale of 0, no browning to 5, dark brown to black. The weighted averages of the two ratings were used to calculate an index of browning. Genotypic variation occurred in the degree of deacclimation, which ranged from none to as much as 15 °C. Two genotypes, ‘G.41’ and ‘M.9’, showed little change in hardiness in both years they were tested. ‘G.935’ and G.5257 showed a small loss of hardiness in the one year they were tested. ‘B.9’ loss of hardiness occurred in the cambium, but not the xylem. V.6 lost hardiness after warm-exposure, but showed almost no injury at temperatures as cold as -35 °C. Two genotypes, G.4013 and ‘G.814’, lost substantial hardiness in both years and may be vulnerable to late winter freeze-thaw events, but were among the hardiest prior to deacclimation. The amount of deacclimation varied among the three shoot tissues. At the time of testing, the cambium showed a high degree of hardiness with the cold exposure, and little injury at temperatures as cold as -35 °C in G.4013, ‘M.9’, ‘B.9’, ‘G.41’ and V.6. Two days of warm temperature was sufficient to cause loss of cambial hardiness in most genotypes, but not of the phloem. Deacclimation in the xylem occurred, but was not as severe as in the cambium in 2014 and 2015.