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- Author or Editor: P. L. Forsline x
Fruit finish, productivity, and tree size of 5 ‘Golden Delicious’ subclones (Malus domestica Borkh.) were compared during a 4-year period. Russeting damage greater than permitted for U.S. Fancy grade was observed in 20% of ‘Smoothee’ fruits, 55% of ‘Golden Delicious’ and 95% of each of 3 spur-type strains. No differences were observed in cumulative yield, trunk cross-sectional area, tree spread, tree height or efficiency between ‘Smoothee’ and ‘Golden Delicious’. Fruits of spur-type trees matured about 1 week later than nonspur type.
Resistance to apple scab (Venturia inaequalis) in apple cultivar breeding has been derived mainly from the Vf gene from Malus floribunda 821, which introgresses horticulturally unfavorable characters. M. sieversii, now thought to be the primary progenitor of M. × domestica, grows wild in many diverse habitats in Central Asia and can have fruit quality comparable to commercial cultivars. Since 1989, four major collections of M. sieversii have been made in Central Asia, where scab is endemic. Some seed collections have been made from trees with superior fruit, that were not infected with scab. Over a 6-year period, 3000 seedlings from 220 wild M. sieversii trees representing 10 diverse ecosystems in Kazakstan, Uzbekistan, Kyrgyzstan, and Tajikistan have been inoculated with conidia of five races and two wild types of V. inaequalis. Suspensions (270,000 conidia/ml) were applied to 4- to 8-leaved seedlings, which were incubated for 48 h at 19°C with constant leaf wetness. Symptoms for three resistant reactions were assessed 2 to 4 weeks after inoculation: A = chlorosis with crinkling (Vf type reaction); B = stellate necrotic lesions (Vr type reaction), and N = large necrotic areas (uncharacterized resistant reaction). Results indicated that nearly 20% of the seedlings showed one or more of the resistant reactions. The range of resistance within seedling populations from each of the 220 single-tree sources ranged from 0% to 75%. Significant differences existed among seedlings from each of the ecosystems. Most resistance reactions appeared to be similar to those observed for Vr from “Russian seedling.” Resistant selections with superior horticultural traits may constitute a genepool for increased efficiency of breeding scab-resistant cvs. This genepool may also be useful to address the breakdown of resistance to V. inaequalis race 6.
Malus sieversii is one of the primary progenitors of the cultivated apple. Since 1989, several collecting trips have been made to central Asia by personnel of the USDA and Cornell Univ. to collect seeds of wild Malus sieversii from many diverse ecosystems. In 1992, an ex situ plot in Geneva, N.Y., was established with trees grown from seed that was collected in three different habitats in Kazakstan, Tajikistan, and Uzbekistan in 1989. In 1995, trees grown from seed that was collected in five additional habitats in Kazakstan and Kyrgyzstan in 1993 were added to the ex situ plot. In the summers of 1995 and 1996, tips of vigorously growing shoots of 1135 seedlings from 79 different populations were inoculated by hypodermic syringe with 5 × 108 cfu/ml of Erwinia amylovora strain Ea273. Seedlings from the 1989 collection were in the fourth and fifth field-growing seasons, with some beginning to bear fruit. Seedlings from the 1993 collection were in first and second field-growing seasons. Results from both seasons indicated that individuals within each of the 79 populations of M. sieversii are resistant to fire blight (defined as ≤20% shoot length infected). Resistance differed among populations, with some populations having no resistant individuals and others having >80% of the seedlings resistant. The range of resistance is quite similar to that seen among apple cultivars from North America and Europe. In another test, some accessions from 1989 collection had sufficient bloom for inoculation in 1995 and 1996. At full bloom, blossoms on these trees were inoculated with the E. amylovora suspensions (5 × 107 cfu/ml) using a backpack sprayer. These also gave diverse resistant reactions.
Three separate experiments were conducted in a mature Vitis labruscana Bailey ‘Concord’ vineyard in New York to determine the response of grapevines to daily, season-long sulfur dioxide (SO2) exposure, or to intermittent SO2 exposure simulating emissions from a 1700 MW coal-fired power plant. There was little SO2-induced necrosis on grape foliage from daily or power plant SO2. However, both treatments in ambient air increased susceptibility of leaves to oxidant stipple injury due to ambient ozone (O3). Daily SO2 increased leaf chlorosis. Power plant SO2 had no effect on vine growth, yield, or shoot maturation. Daily SO2 reduced soluble solids, growth, yield, and shoot maturation of grapevines. Damage to grapevines from SO2 seemed to be independent of SO2 induced leaf necrosis. SO2 reduced foliage tolerance to O3 injury in grapevines already stressed by ambient O3.
The cold resistances of 14 Malus clones were determined in early March annually from 1974 to 1978. Dormant twigs were cooled at −1.8°C/hr, samples removed at 5° steps from −15 to −45°, and thawed gradually. After thawing, impedance measurements were made and the twigs were held for 16 days under intermittent mist to determine recovery. Rankings of data on growth of twigs held under intermittent mist for 16 days after thawing were similar but not identical to direct impedance values obtained immediately after thawing. Tissue damage had no evident relation to shoot diameters. Surfically discernible root germs, which were present on Mailing 7 (M 7), M 26, M 27, Malling-Merton 106 (MM 106), and Cornell-Geneva 10 (CG.10), were killed at or above −15°. ‘Empire’ and Ottawa 4 were least sensitive and ‘Katherine’ and ‘Jonagold’ most sensitive to low temperatures. The responses of M 26 to low temperatures varied widely from year to year. We could discern no relationship between hardiness in late winter and timing of spring budbreak. The growth response method reported here appears to be closely related to whole plant response under field conditions.
Susceptibility to woolly apple aphids (Eriosoma lanigerum Hausmn.) was evaluated on 391 Malus clones in a mature cultivar test orchard and on 164 clones in the greenhouse and nursery. A spray program based on Mesurol (4-methylthio-3,5-xylylmethyl-carbamate) resulted in increased aphid populations in the orchard and thereby enhanced identification of susceptible clones. Resistant cultivars included ‘Northern Spy’, several derivatives of ‘Northern Spy’, ‘Ivory’s Double Vigour’, ‘Kola’, Malus halliana Koehne, M. hupehensis (Pamp.) Rehd., M. X robusta (Carr.) Rehd. No. 5 (R5), and M. tschonoskii (Maxim.) Schneid. No evidence was seen that a biotype capable of colonizing ‘Northern Spy’ and its derivatives had arisen in New York.