CHARACTERIZATION OF LOW TEMPERATURE DAMAGE AND SUBSEQUENT REGROWTH RESPONSE OF FIELD GROWN ROSES

Abstract

Plants of field grown rose cultivars Blaze, Gold Glow, Queen Elizabeth, Mr. Lincoln, Montezuma, Don Juan, Chicago Peace, and Pink Peace endured two major freezes. Temperatures fell to -13°C on 16 December 1989 and as low as -20°C during an extended period from 17 to 28 December 1989 when the highest temperature reached was 5°. Grade 1 plants of each cultivar were harvested on 5 January 1990. At harvest, discoloration of the pith, xylem ray parenchyma and bud union tissue was assessed. Additional plants were then potted and forced in a glasshouse at 15° night temperalure with venting at 21° during the day. At the end of the initial flush of growth, which was defined as either the opening of the first flower or the determination that all new shoots were blind, new growth was rated and measured. Blaze exhibited minimal damage with only slight pith discoloration. The total number of flowering shoots (TNFS) for Blaze was 5.5 per plant which is an expected number from a grade 1 plant. Of the other cultivars. Gold Glow and Pink Peace exhibited pith, xylem, and bud union damage with up to 50% cane dieback, but produced flowering shoots from the graft union. However, only half the expected TNFS per plant were produced. The remaining cultivars also exhibited higher damage levels than Blaze which resulted in reduced shoot numbers and flowering. Only Blaze plants received an acceptable plant marketability rating.