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ARS Home » Northeast Area » Geneva, New York » Plant Genetic Resources Unit (PGRU) » Research » Publications at this Location » Publication #354269
Title: Genotypic variation in apple rootstock cold temperature tolerance during spring and fall

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

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2018
Publication Date: 9/15/2018
Citation: Moran, R.E., Peterson, B.J., Fazio, G., Cline, J. 2018. Genotypic variation in apple rootstock cold temperature tolerance during spring and fall. Journal of the American Society for Horticultural Science. 143:319-332.

Interpretive Summary: Apple trees growing in northern climates can be susceptible to different types of freeze injury when severely cold temperatures occur before they develop cold hardiness, to a degree that exceeds their midwinter hardiness, or in the spring after they lose cold hardiness. In most regions of apple production, tree loss to cold temperature injury occurs in fall when trees are acclimating (getting ready for cold temperatures) or in spring during the process of de-acclimation and bud burst. This manuscript describes the reaction (freeze damage) of some rootstocks to experimental cold treatments at different time points of acclimation and de-acclimation during the year. This research identifies some rootstocks like CG.3902 to be hardy to Spring freezes and CG.5257 to be somewhat susceptible to the same freezes. Most rootstocks tested were tolerant to mid-winter temperatures as low as -40°C and some exhibited tissue damage at -30°C. It is important to note that these measurements were collected on rootstock tissues and not on whole grafted trees as the graft could influence the cold tolerance of the whole tree.

Technical Abstract: We measured the cold temperature tolerance of xylem, phloem and cambium in two-year-old shoot pieces from apple rootstock genotypes ‘Malling 9’ (M.9), ‘Malling 7’ (M.7), ‘Budagovsky 9’ (B.9), ‘Geneva 41’ (G.41), ‘Geneva 30’ (G.30) and ‘Geneva 935’ (G.935), as well as 8 genotypes in the Geneva (G.) series and three in the Vineland (V.) series. Following exposure to temperatures as low as -35 °C during Oct. 2013 to Apr. 2014, injury was measured as a 0 - 10 rating based on percentage of cross-sectional xylem, phloem and cambium with brown discoloration, with 0 indicating no browning and 10 indicating browning in the entire tissue. During Oct. 2014 to Apr. 2015, a second experiment was conducted in which shoots were exposed to temperatures as low as -40 °C, with injury measured as xylem, phloem and cambium browning using an index of injury that accounted for both the percentage of browned tissues and the intensity of browning. Many genotypes, including M.9, M.7, G.935, G.4011, G.4292, G.5087, and V.5, had only partial xylem injury in the fall, whereas others (G.41, M.7, G.214, and G.4011) had more widespread xylem browning when temperatures dropped below -30 °C. G.30 had moderate to severe browning at temperatures as warm as -15 to -19 °C, indicating potential vulnerability in xylem tissue in October. Most of the Geneva rootstocks were similar to one another in their extent of phloem browning, which generally decreased from October to November. Notably, G.4013 exhibited severe phloem browning at relatively warm temperatures in late October but accrued additional hardiness by the November test date, whereas genotypes M.9, B.9, G.30, and G.41 developed considerable phloem hardiness by late October and did not accrue additional hardiness by November. From October to January, Geneva and Vineland genotypes displayed a level of xylem and phloem hardiness to -35 to -40 °C. Based on the level of hardiness that occurred in this study, it appeared that Geneva and Vineland apple rootstocks have a low degree of susceptibility to injury in January. However, shoot hardiness in April was highly variable between the two years, with severe browning of xylem and cambium at -40 °C in every genotype sampled in Apr. 2014, but not in Apr. 2015. M.9 and G.3902 appeared to be the least vulnerable to injury in April, whereas G.5257 seems most likely to suffer injury following the deacclimation conditions that occurred in this study. Rootstocks G.30, G.41, G.4292 and G.814 could also be vulnerable based on xylem injury at -20 °C. G.30 had tender xylem in both the fall and the spring, but hardy phloem in the fall and hardy cambium in the spring. Rootstock G.4013 had the least hardy cambium and phloem in the fall, and G.5257 the least hardy cambium in the spring, and are likely to be vulnerable to damaging temperatures during fall acclimation and spring deacclimation.