DETERMINATION OF COLD-HARDINESS AND ESTIMATION OF POTENTIAL BREEDING VALUE OF APRICOT GERMPLASM

Controlled laboratory freezing tests were carried out on dormant apric ot (Prunus armeniaca L.) shoots preconditioned to attain maximum cold hardiness. Determinations were made of the temperatures required to ki ll 50% of the flower buds [T-50 (FB)] and 50% of the shoot xylem [T-50 (SX)]. The 27 genotypes in this study differed significantly from eac h other in T-50 (FB) and T-50 (SX). Using 'Goldcot' as the climaticall y adapted hardy standard, 27 genotypes were placed in three hardiness classes; those more hardy than 'Goldcot,' those equally hardy as 'Gold cot' and those less hardy than 'Goldcot'. The mean T-50 (FB) was 28.7C and the mean T-50 (SX) was -35.3C, indicating that shoot xylem hardin ess of apricots was at least several degrees greater than flower bud h ardiness. The range in newer bud hardiness among the 27 genotypes was 2.8C while that for shoot xylem hardiness was 6.7C. Seven genotypes ha d hardier flower buds than 'Goldcot' including two named Harrow cultiv ars ('Harlayne' and 'Haggith'), four numbered Harrow selections (H7814 180, HW-446, H8205044 and HW460) and one other cultivar ('Manchu'). Am ong 16 genotypes equally bud hardy as 'Goldcot,' four were named narro w cultivars ('Harcot,' 'Harglow,' 'Hargrand' and 'Harogem') and eight were numbered Harrow selections. One named Harrow cultivar ('Hag-gith' ) was more wood hardy than 'Goldcot'; while three Harrow cultivars ('H arlayne,' 'Harcot' and 'Hargrand') and seven numbered Harrow selection s were equally wood hardy. The goal of breeding apricot cultivars equa l to or more cold hardy than 'Goldcot' was achieved because bud hardin ess of six of the seven Harrow introductions was equal to or greater t han 'Goldcot.' The potential breeding value of the 14 named cultivars was estimated by using their total long term performance ratings for 1 4 attributes, then applying the bud and wood hardiness classifications made here as additional factors. The ranking of breeding value for th e 14 named cultivars from highest to lowest was as follows: 'Harlayne' > 'Harcot' = 'Hargrand' = 'Harval' > 'Harglow' = 'Harogem' > 'J.L. Bu dd' > 'Manchu' > 'Gibbs' = 'Sunglo' > 'Haggith' = 'Veecot' > 'Stella' > 'Goldcot.' The potential breeding value of the six named Harrow intr oductions for the fresh market exceeded that of the eight other cultiv ars, including 'Veecot' and 'Goldcot,' the two commercial standards. C onsequently, they warrant greater use as parents and wider testing as cultivars.