Dehardening in flower buds of saskatoon-berry, Amelanchier alnifolia, in relation to temperature, moisture content, and spring bud development OLAVI JUNTTILA' AND CECIL STUSHNOFF Department of Horticulture Science, Universio of Saskatchewan, Saskatoon, Sask., Canada S7N 2H0 AND LAWRENCE V. GUSTA Crop Development Center, Universio of Saskatchewan, Saskatoon, Sask., Canada S7N 2H0 Received May 6, 1982 JUNTTILA, O., C. STUSHNOFF, and L. V. GUSTA. 1983. Dehardening in flower buds of saskatoon-berry, Amelanchier alnifolia, in relation to temperature, moisture content, and spring bud development. Can. J. Bot. 61: 164-170. Flower-bud dehardening of saskatoon-berry (Amelanchier alnifolia Nutt. 'Smoky' and 'Pembina') was studied under natural and controlled conditions. Flower buds were hardy to -45OC until the middle of March, after which hardiness gradually declined to - 12'C by the beginning of May. Petal expansion was associated with a loss of hardiness, even though bud moisture content decreased slightly. Hardiness of unopened flower buds was closely correlated with bud moisture content ( r = 0.94) and under outdoor conditions there was a significant positive correlation between cumulative degree days (base 0°C) and bud moisture content. Imbibition in gibberellic acid (GA3) increased water uptake and reduced hardiness of excised flower buds compared with imbibition in water. Treatments with abscisic acid and salicylic acid had no significant effect on hardening. Budbreak, in the postrest period, required only 73 degree day (base 2°C) heat units. Low-temperature exotherms were not detected in intact flower buds but were present in hardy excised florets. JUNTTILA, O., C. STUSHNOFF et L. V. GUSTA. 1983. Dehardening in flower buds of saskatoon-berry, Amelanchier alnifolia, in relation to temperature, moisture content, and spring bud development. Can. J. Bot. 61: 164-170. Le dCsendurcissement des bourgeons floraux de 1'Amelanchier alnifolia Nutt. 'Smoky' et 'Pembina,' a CtC CtudiC dans des conditions naturelles et contr61Ces. Les bourgeons floraux sont rCsistants au froid (jusqu'h -45°C) jusqu'i la mi-mars, puis la resistance diminue jusqu'h - 12°C au dCbut de mai. Le diploiement des pCtales est associC h une perte de resistance, m&me si la teneur en humidit6 du bourgeon diminue 1Cgkrement. La rCsistance des bourgeons floraux fermCs est CtroitementcorrClCe avec la teneur en humidit6 du bourgeon ( r = 0,94). Dans les conditions naturelles, il y a une corrtlation significative entre le nombre cumulatif de degrCs-jours au-dessus de 0°C et la teneur en humidit6 du bourgeon. Comparativement h l'imbibition dans l'eau, l'imbibition dans l'acide gibbkrellique (GA3) augmente l'absorption d'eau et diminue la rCsistance au froid des bourgeons floraux excisCs. Les traitements i l'acide abscisique et i l'acide salicylique n'ont pas d'effet sur l'endurcissement au froid. Le dCbourrement des bourgeons aprks la dormance exige seulement 73 degrCs-jours (au-dessus de 2°C) d'unitCs calorifiques. Des exothermes de basse temperature n'ont pas CtC dCcelCs dans les bourgeons floraux intacts, mais Ctaient presents chez les fleurs rksistantes excisCes. [Traduit par le journal] Introduction The saskatoon, Amelanchier alnifolia Nutt., is pres- ently in the early stages of domestication as a native fruit crop. This berry crop is somewhat unique to the Great Plains region of North America in terms of potential for a new fruit crop. Several cultivars have been developed primarily from selections of superior native genotypes (Harris 1973). A few cultural studies have been conducted, but essentially no information has been published on the physiological behavior of this crop. It is known from natural distribution patterns that the species is well adapted to low temperature extremes and a wide range of soil texture and pH (Miller and Stushnoff 1970); however, no systematic studies have 'permanent address: Institute of Biology and Geology, University of Tromso, Tromso, Norway. been reported on phenological development or physio- logical control of growth processes. The purpose of this study was to determine the level of cold hardiness and the rate of dehardening for saska- toon-berry buds during the postrest period. Studies were set up under natural and controlled environment condi- tions and involved several variables including tempera- ture, water content, and spring bud development stage. The influence of gibberellic acid (GA3), abscisic acid (ABA), and salicyclic acid on bud dehardening was also studied under controlled environment conditions. Materials and methods Plant material All experiments were conducted with flower buds of two Amelanchier alnifolia Nutt. cultivars, 'Smoky' and 'Pem- bina.' Twigs with flower buds were collected 10 times at 7- or 0008-4026/83/010164-07$01.00/0 01983 National Research Council of Canada/Conseil national de recherches du Canada Can. J. Bot. Downloaded from www.nrcresearchpress.com by Hubei university on 06/10/13 For personal use only.