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  • Author or Editor: D. F. Dayton x
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‘Prairifire’ is an attractive new ornamental crab apple with bright red-purple flowers, blooming 5–7 days later than other cultivars with that color, and immune or highly resistant to several destructive diseases of Malus.. Flower production is heavy and annual on both spurs and axillary buds on 1 year shoots. The flower color does not fade seriously nor develop an unattractive “muddy” appearance. Since axillary flowers develop somewhat later than do those on spurs, the flowering period is extended up to a week longer than if spurs were the only flowering sites. The small, dark-red fruits either dry on the tree or are eaten by birds, thus eliminating any clean-up problems from dropped fruits.

Open Access
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Tetraploid chimeral apple sports, the Kimball Mcintosh (3), and the Doud Golden Delicious (1), were crossed with apple scab-immune unnamed seedlings to produce presumably triploid progenies. These sports were used as seed parents. Seedlings lacking normal vigor in the greenhouse were discarded but some lacked vigor in the field even though earlier they had appeared moderately vigorous. In the field the vigorous seedlings were normal in all respects except for their slowness to come into bearing. With other similar triploid progenies attempts to hasten fruiting by girdling had little effect. Furthermore, the cut on girdled limbs often allowed the entry of the causal organism of fireblight, with resultant serious infection.

Open Access
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The technique of disbudding to force development of adventitious buds was used to test for possible genetic heterogeneity in tissues derived from the internal histogenic layers of several apple varieties and strains. Following treatment of 1-year old trees in the greenhouse, adventitious buds were readily produced by 5 strains of ‘Delicious’ and by ‘McIntosh’, but none by ‘Golden Delicious’ in 3 successive years of trial. Fruiting trees developed from adventitious bud growth indicated considerable heterogeneity among the histogenic layers of several of the source varieties. Adventitious trees of ‘Starkrimson’ closely resembled the source variety in fruit characters and in fruiting and growth habits as did most of those of ‘Redspur’. Three adventitious trees of ‘Redspur’ were markedly different in fruiting and growth habits, indicating the existence of internal chimeras. Adventitious trees of ‘Richared’ and ‘Bridgham Red Delicious’ produced fruit with pigmentation closely resembling that of the original ‘Delicious’, indicating that these sports probably resulted from mutations in L I of the growing point. A late-coloring sport of ‘Starking’ produced 3 adventitious trees each representing a different class of pigmentation intensity of the fruit. A striped sport of ‘McIntosh’ produced trees with fruits having an entirely blushed pattern of color development, thus striped-fruited forms of this variety probably resulted from undesirable mutations in L I. The strong tendency to produce adventitious buds probably accounts for an important fraction of the unusually large number of ‘Delicious’ sports.

Open Access
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Abstract

Progenies of ‘Golden Delicious’ apple (Malus domestica Borkh.) crossed with 12 Malus species and hybrids were screened for resistance to powdery mildew incited by Podosphaera leucotricha (Ell. & Ev.) Salm. under greenhouse conditions. Noninfected seedlings were recovered from Morton Arboretum (M.A.) 8 (an unknown interspecific hybrid), M. zumi calocarpa Rend., M. sargenti Rehd. 843 × self, and M. baccata jackii Rehd. Evidence for a single heterozygous dominant gene conferring resistance in M.A.8 and M. sargenti was confirmed by field tests of resistant seedlings.

Open Access
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Abstract

Abscisic acid (ABA) at 1 and 10 μg/ml concn supplied to growing plants of ‘EM XVIa’ (very vigorous) through grafted living conduits of the same tissue and of ‘EM IX’ (very dwarfing) was inhibitory to growth during the first 10-14 days of treatment. The ‘EM IX’ tissues also had an inhibitory effect of their own, which ABA enhanced. The higher concn was more inhibitory but not proportionately so. During the first 10 days, 1 μg/ml ABA markedly reduced solution absorption below that of water. Absorption of all solutions by ‘EM IX’ tissues was in all cases less than by those of ‘EM XVIa’. A drastic decrease in absorption was evident after 10 days.

Open Access

Abstract

A gene conditioning the 3-type resistance reaction to Venturia inaequalis Cke. (Wint.), recovered from M. micromalus Mak., is shown to be carried at the Vf locus, and thus allelic with similar genes recovered from 10 other Malus species and forms. Malus micromalus and M. atrosanguinea (Spaeth) Schneid. 804 are shown to carry allelic genes conditioning the pit-type of resistant reaction. The symbol Vm is assigned to this locus.

Open Access
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Abstract

Roots, shoots, and leaves of 1- and 2-year-old ungrafted plants of EM IX, VII, and I, and roots of EM XVIa, were extracted to detect an inhibitor that appears identical with abscisic acid (ABA). The extracts were coned, partially purified chromatographically, and bioassayed using the wheat coleoptile straight growth and Lepidium seed germination tests. A strongly inhibitory substance was found in both bioassays at or close to the Rf values reported for maximum ABA activity or determined with the synthetic form.

Extracts of EM IX tissue contained the highest levels of this inhibitor, presumed to be ABA. Progressively lower levels were found in extracts of EM VII, I, and XVIa, which is the same as the order of these clones in increasing vigor of grafted scions. This same order was indicated in nearly all bioassays of the 3 types of tissue extracts. Extracts of roots collected in early spring after overwintering either in storage or out-of-doors, in midsummer, and in the fall after cessation of growth all placed the clones in the same order. Levels in root and leaf extracts were generally higher than in those of shoots.

The Lepidium seed bioassay appears to offer a convenient method for identification of strongly or semi-dwarfing individuals or clones. Leaves offer an obvious advantage over shoots or roots.

Open Access

Abstract

Significant differences in mean leaf hair density values were found between strains of ‘Delicious’ apple (Malus domestica Borkh.) within locations (states). There were also location differences among strains common to more than one location (state). Ranking of strains according to the amount of pubescence present appeared relatively consistent between states.

Open Access

Abstract

‘Jonafree’ is an attractive red apple (Malm domestia Borkh) with field immunity to apple scab incited by Venturia inaequalis (Cke) Wint. The fruit is of medium size and matures with ‘Jonathan’. It is released as a potential commercial cultivar with strong resemblance to ‘Jonathan’ in many major horticultural characters in addition to its similar maturity date.

Open Access

Abstract

Apple scab, caused by the fungus Venturia inaequalis (Cke.) Wint. is one of the most economically important apple diseases, because of the annual loss of marketable fruit, tree debilitation as a result of foliage destruction, and the cost of chemicals, equipment, and labor for its control. Infection can occur at any time during the growing season in humid apple-producing areas of the world. Most scab control programs must be based on the application of 5 to 15 or more protective fungicide sprays from the beginning of bud break to harvest. Estimates of direct costs for scab control including fungicides, equipment costs, and labor range from 20 to 30¢ per bushel or some 10% of the annual cost of production. In addition, chemical control must be exacting with application of spray materials most efficacious in rainy spring weather it is oftne difficult to move equipment through the orchard.

Open Access