Root hardiness for the apple (Malus domestica Borkh.) rootstocks M.26, MM.106, MM.111, M.7A, and M.7EMLA at - 8 and - 11C and trunk survival for the tender cultivar Gravenstein and the hardy cultivar Wealthy at -25 and -35C were evaluated both destructively (tissue examination) and nondestructively (regrowth measurement the following season). No differences in root survival were detected at -8C by either method; at - 11C, MM.111 rated better than the others, while regrowth was higher on M.26, MM.111, and M.7A than on MM.106 or M.7EMLA. Root survival did not differ for the scions at either temperature, but regrowth was greater for `Gravenstein' than Wealthy' at both temperatures. Trunk tissue survival at -25C was consistently lowest for scions on M.7EMLA, and regrowth was less than on M.26 and MM.111. At -35C there were no significant rootstock effects. For the scions, lateral wood tissue survival at -25C was highest for Wealthy', but the weight of the new growth did not differ. At -35C bark tissue survival and regrowth was greater for Wealthy' than for `Gravenstein'. Evidence is presented in support of the occurrence of reciprocal effects. Correlation between the two methods was highest for root exposure at - 11C and for the assessment of trunk bark.
C.G. Embree and K.B. McRae
E.N. Estabrooks, C.G. Embree and H.Y. Ju
Apple trees of the tender cultivar Gravenstein were grown on four promising, dwarfing, stembuilders and two known hardy rootstocks to evaluate hardiness. After eight growing seasons and a “test winter” from 1992 to 1993, trees were subjected to a destructive harvest to assess the amount of blackheart. The extent of blackheart was used as an indicator of sublethal winter injury. The amount of blackheart in the stembuilder trunk was significantly different among stembuilders but not between rootstocks. The stembuilder Bud 9 had more blackheart than Dudley, Lobo, KSC 28, and Ungrafted (Dudley). Similarly, the percentage of blackheart in the scion part of the tree showed differences due to cultivars and stembuilders but no difference due to rootstocks.
C.G. Embree, E.N. Estabrooks and H.-Y. Ju
To determine the effects of rootstock and frameworking on hardiness, `Gravenstein' apple, which is not winter hardy, was grafted on trees frameworked with the hardy genotypes `Budagovsky 9' (B. 9), `Lobo', Kentville Stock Clone (KSC 28), or `Dudley', all of which were propagated on either `Beautiful Arcade' (BA) seedlings or on `Alnarp 2' (A. 2) rootstocks. For comparison, `Dudley' was grafted on `Dudley' frames propagated on both rootstocks. Growth after 8 years was greatest at Kentville; `Gravenstein' was larger than `Dudley', although when grafted, it was 40% smaller on the dwarf B. 9 than on the `Lobo' frame. On one night in Feb. 1993, all sites recorded temperatures below –30 °C. Blackheart was therefore measured in the rootstock trunk, framebuilder, and scion to document the resistance to this sublethal winter injury. Trees at the two colder sites, Truro and Centreville, had more blackheart than did those at the milder site. The percentage of blackheart in the trunk and frame was greatest for B. 9 and least for KSC 28. The tender scion, `Gravenstein', exhibited extensive blackheart regardless of site, rootstock, or the hardiness of the frame. The hardy scion, `Dudley', had some blackheart in the colder locations but none at Kentville. Blackheart levels in `Gravenstein' were very high on the framebuilder B. 9, and while generally less with the other hardy framebuilders, they were still high. While the hardy frames may have helped improve the survival of this cultivar, they did not change its hardiness status relative to `Dudley', even when `Dudley' was one of the hardy framebuilders.
C.G. Embree, B.H. Lesser and A.D. Crowe
The 30 apple (Malus domestica Borkh.) rootstock candidates selected for cold hardiness, known as the Kentville Stock Clone (KSC), with `McIntosh' and `Delicious' as scion cultivars, were compared at 11 years of age for tree size, weight, fruit yield, and crop efficiency under field conditions. Trunk cross-section area and tree weight were highly correlated. Tree size was similar for the two cultivars in most cases and ranged in size from semidwarf to very vigorous. Cumulative yield efficiencies varied by nearly two-fold and were not correlated with tree size. The most efficient rootstocks were KSC 28, KSC 7, and KSC 6 in the semidwarf, semivigorous, and vigorous size classifications, respectively.
B.H. Lesser, C.G. Embree and A.D. Crowe
The precocity and productivity of 30 Kentville Stock Clone (KSC) apple (Malus domestica Borkh.) rootstocks, with `McIntosh' and `Delicious' as scion cultivars, were assessed independently of each other using a procedure involving computer-aided fitting of curves to yearly production data. A good fit to the data was obtained after biennial fluctuations in yield were removed by using a weighted, 3-year running average. For all 30 rootstocks combined, `McIntosh' was more precocious and reached a higher level of productivity compared to `Delicious'. There was poor correlation between precocity and productivity.
C.G. Embree, B.H. Lesser and A.D. Crowe
The effects of 30 Kentville Stock Clone (KSC) selections on fruit size and color of `McIntosh' and `Delicious' apples (Malus domestica Borkh.) were monitored over 5 years. Fruit size was influenced by the rootstock and, when averaged over the duration of the study, ranged from 108 to 132 g and 131 to 161 g for `McIntosh' and `Delicious', respectively. Variation in fruit size due to crop load (CL) was greater for `McIntosh' than for `Delicious'. Fruit color was influenced by the rootstock in all years for `McIntosh' and in 3 of 5 years for `Delicious'; it was strongly associated with tree size for `Delicious' only. An overall performance index, which also included price based on quality, was developed, and the best performers in each size group were: semidwarf KSC 18 and 28; semivigorous KSC 7, 11, and 24; and vigorous KSC 3 and 6.
C.G. Embree, K.B. McRae, E.N. Estabrooks and C. Pratt
Vegetative and fruiting characteristics were measured for a spur mutant of `McIntosh' apple (Malus × domestics Borkh.). Nine-year-old `MacSpur' trees in an orchard in New Brunswick, Canada, were grouped according to three degrees of spurriness. Reduced terminal growth, fewer limbs per tree, more flowering spurs per unit length of 2- and 3-year-old wood, less yield, and lower yield efficiency were associated with the highest degree of spurriness. The variability suggests that `MacSpur' may be an unstable periclinal chimera.