Apple tree rootstock named ‘G.257’

Abstract

A new and distinct variety of apple tree rootstock Malus domestica x Malus robusta hybrid ‘G.257’ is described. The new variety is a semi-dwarfing rootstock that is resistant to fire blight (Erwinia amylovora) and crown rot (Phytophthora cactorum) and tolerant to the replant disease complex. The ‘G.257’ rootstock is useful in that it can be propagated clonally and used as a rootstock or root system for apple trees as well as for interstems of apple trees.

Claims

1. A new and distinct variety of apple tree rootstock named ‘G.257’ as herein described and illustrated.

Description

DESCRIPTION OF THE FIGURES

(1) New apple tree rootstock ‘G.257’ is illustrated by the accompanying photographs. The colors shown are as true as can be reasonably obtained by conventional photographic procedures.

(2) FIG. 1 shows a dormant one-season growth shoot (including buds and bark).

(3) FIG. 2 shows adaxial (upper) and abaxial (lower) laminae of leaves.

(4) FIG. 3 shows a root system with fine roots.

(5) FIG. 4 shows a fully developed stool bed with leaves and shoots.

(6) FIG. 5 shows graft unions on finished trees.

(7) FIG. 6 shows a bundle of rooted rootstock liners.

(8) FIG. 7 shows 4-year-old trees in organic production.

(9) FIG. 8 shows immature fruit.

DETAILED BOTANICAL DESCRIPTION OF THE INVENTION

(10) The following description of apple tree rootstock ‘G.257’ contains references to color names taken from The Royal Horticultural Society Colour Chart (RHS), 2001 edition. Botanical descriptions follow the Manual of Cultivated Plants (Bailey, 1949). Tree: Habit.—A self-rooted tree of ‘G.257’ is a shrub typically standing about 2-2.5 meters tall by about 2 meters wide when 8 years old. A single dominant trunk may develop with highly branched form. When grafted in the orchard it produces very few suckers (i.e., new shoots emerging from below ground). Liners planted in the nursery stop apical growth mid-season. Productivity.—In an intermediate trial performed at a research farm (Geneva, N.Y.), the ‘G.257’ rootstock received the cultivar ‘New York 1’ (Malus domestica) as the scion and was compared to the Malus domestica check rootstocks ‘Malling 9’ (M.9 EMLA; unpatented), and ‘Malling 26’ (M.26; unpatented). ‘G.257’ displayed the highest cumulative yield and was shown to have statistically similar (p≤0.05) yield efficiency (kg yield/cm.sup.2 trunk cross sectional area) as all the check rootstocks. Precocity.—Scion cultivars budded on ‘G.257’ exhibit the same early bearing/precocity as those budded on ‘M.26’. Fertility (fecundity).—The ‘G.257’ plant produces flowers and fruits regularly. Dormant Shoots (buds and bark): Dormant mature shoots.—Color: Yellow-Green (RHS 146C and 146D) with low exposure to full sunlight grading to Greyed-Orange (RHS 175C and 175D) with full light exposure. Texture: Very light pubescence which gradually disappears in older tissues. Size: 30-60 cm long; can produce sylleptic spines in 10-20% of new shoot depending on sun exposure. Axillary buds.—Size: 3-4 mm long and 3 mm wide with little pubescence. Shape: Obtuse, sessile, somewhat appressed and flattened. Texture: Some pubescence. Bark on three-year-old shoots.—Color: Greyed-Orange (RHS 177C). Lenticels: Color: Greyed-Orange (RHS 164A). Size: 0.3-0.4 mm in diameter. Quantity: 2-3 lenticels per cm.sup.2. Leaves: Mature leaves.—Leaf arrangement: Alternate. Shape: Simple, flat, oblong-ovate. Size: Length: 90 mm. Width: 40 mm at the widest point. Laminae: Somewhat straight. Apex: Acuminate. Base: Nearly symmetrical rounded. Margin: Acutely serrated, with about 6 serrations per cm. Upper surface: Color: Green (RHS 143B). Texture: Glabrous and translucent. Lower surface: Color: Yellow-Green (RHS 144B). Texture: Somewhat pubescent. Venation: Netted. Leaf poise: 15°-25° from the shoot, depending on shoot orientation. Stipules: Length: 9 mm. Width: 2 mm. Petioles: Diameter: 2 mm. Color: Gradation of Greyed-Red (RHS 181A-B) at the base going to Greyed-Red (RHS 179B-C) at the laminae. Flowers: Habit.—Flowers borne on spurs, shoot terminals, and from lateral buds on growth from previous season. Flower diameter.—40 mm. Fragrance.—None. Buds.—Location: Located on spurs and terminals; are mixed, typically producing a truss of 5 to 6 flowers and one bourse shoot. Shape: Lateral buds are obtuse, sessile and somewhat appressed. Size: Length: 4 mm. Width: 3 mm. Habit: Buds near the base of the shoot of the previous season usually produce 3 to 5 flowers and a single short shoot; mid-shoot buds may have 2-4 flowers; and more distal buds are usually vegetative. Petals.—Size: Length: 25 mm. Width: 18 mm. Shape: Spatulate. Apex: Obtuse. Margin: Smooth. Texture: Smooth. Color: Closed petals: Red (RHS 54A). Open petals: White (RHS 155D) with Red (RHS 54A) striations in some of the petals. Reproductive organs.—Pistils: Length: 6 mm. Color: Yellow-white (RHS 145B). Stamens: Length: 4 mm. Color: White (RHS 155D). Anther color: Yellow-Brown (RHS 167D). Fruit: Mature fruit.—Size: Height: 30-35 mm. Diameter: 30-35 mm. Shape: Round. Color: Partial Yellow-Orange skin (RHS 21AB) with Red (RHS 43B) blush overtones depending on the exposure to the sun and other growing conditions. Sepals: Persisting on an inset calyx. Flesh: Taste: Astringent (not meant for consumption). Color: Yellow-Orange (RHS 20C). Seed: Color: Greyed-Red (RHS 179A), translucent. Shape: Tear drop shape. Size: Length: 4-6 mm. Diameter: 2-3 mm at the widest point. Number: Generally five seed per fruit. Disease resistance: As described above, the ‘G.257’ rootstock of the present invention exhibits resistance to fire blight. The percent lesion measured after inoculation of potted liners in the greenhouse using four different strains of E. amylovora was negligible for two of the strains and moderate for the other two, indicating a specific resistance to the bacterium. The ‘G.257’ rootstock, having survived the inoculation with crown and root rot, is also considered resistant to crown and root rots caused by Phytophthora cactorum. ‘G.257’ displays tolerance to the replant disease complex.