Determination of Cold Hardiness and Estimation of Potential Breeding Value of Apricot Germplasm

Abstract

Controlled laboratory freezing tests were carried out on dormant apricot ( Prunus armeniacaL.) shoots preconditioned to attain maximum cold hardiness. Determinations were made of the temperatures required to kill 50% of the flower buds [T ₅₀(FB)] and 50% of the shoot xylem [T ₅₀(SX)1. The 27 genotypes in this study differed significantly from each other in T ₅₀(FB) and T ₅₀(SX). Using 'Goldcot' as the climatically adapted hardy standard, 27 genotypes were placed in three hardiness classes; those more hardy than 'Goldcot,' those equally hardy as 'Goldcot' 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 hardiness of apricots was at least several degrees greater than flower bud hardiness. The range in flower bud hardiness among the 27 genotypes was 2.8C while that for shoot xylem hardiness was 6.7C. Seven genotypes had hardier flower buds than 'Goldcot' including two named Harrow cultivars ('Harlayne' and 'Haggith'), four numbered Harrow selections (H7814180, HW-446, H8205044 and HW460) and one other cultivar ('Manchu'). Among 16 genotypes equally bud hardy as 'Goldcot,' four were named Harrow cultivars ('Harcot,' 'Harglow,' 'Hargrand' and 'Harogen') and eignt were numbered Harrow selections. One named Harrow cultivar ('Hag-gith') was more wood hardy than 'Goldcot'; while three Harrow cultivars ('Harlayne' 'Harcot' and 'Hargrand') and seven numbered Harrow selections were equally wood hardy. The goal of breeding apricot cultivars equal to or more cold hardy than 'Goldcot' was achieved because bud hardiness of six of the seven Harrow introductions was equal to or greater than 'Goldcot.' The potential breeding value of the 14 named cultivars was estimated by using their total long term performance ratings for 14 attributes, then applying the bud and wood hardiness classifications made here as additional factors. The ranking of breeding value for the 14 named cultivars from highest to lowest was as follows: 'Harlayne' > 'Harcot' = 'Hargrand' = 'Harval' > 'Harglow' = 'Harogem' > 'J.L. Budd' > 'Manchu' > 'Gibbs' = 'Sunglo > 'Haggith' = 'Veecot' > 'Stella' > 'Goldcot.' The potential breeding value of the six named Harrow introductions for the fresh market exceeded that of the eight other cultivars, including 'Veecot' and 'Goldcot,' the two commercial standards. Consequently, they warrant greater use as parents and wider testing as cultivars.