Plant Pathology Research at The Kearneysville Tree Fruit Research and Education Center

Disease Susceptibility of New Apple Cultivars

A CSRS regional project -- NE-183, Multidisciplinary Evaluation of New Apple Cultivars -- has been initiated to evaluate new apple cultivars under a wide range of edaphic and environmental conditions. In the spring of 1995, replicated plantings of 26 new apple cultivars (five trees of each cultivar) were planted at 28 sites in 14 states and 2 Canadian Provinces. Plantings were designated as either a "horticultural" or "pest" planting depending on whether the primary objective was to evaluate horticultural qualities or pest and disease susceptibility. One of each type of planting was established at the Appalachian Fruit Research Station, Kearneysville, WV, in April 1995. This page summarizes relative foliar disease susceptibility data for the 1995 through 1997 growing seasons.  Data on susceptibility of fruit to apple scab and rot diseases were collected in 1998. 

Cultivar/Rootstock Combinations

The experimental design was a randomized complete block design with 5 single-tree replicates.  Cultivars included:   Braeburn/M.9; Braeburn/MARK; Golden Delicious/M.9; Golden Delicious/MARK;Yataka/M.9; Yataka/MARK; Arlet/M.9; BC8M15-10/M.9; Cameo/M.9; Enterprise/M.9; Fuji Nagafu/M.9; Gala Supreme/M.9; Ginger Gold/M.9; Golden Supreme/M.9; Goldrush/M.9; Honeycrisp/M.9; Fortune/M.9; NY 75414-1/ M.9; Orin/M.9; Pristine/M.9; Sansa/M.9; Senshu/M.9; Shizuka/M.9; Suncrisp/M.9; Sunrise/M.9; PioneerMac/M.9.  In 1995, only 1 shoot per tree was assessed; whereas 5 shoots per tree were assessed in 1996 and 1997, and 10 shoots were assessed in 1998.  Disease assessment included all leaves on the shoot and data are expressed as percentages of infected leaves/shoot.  All fruit were assessed in 1997 and 1998.

Results

With data compiled from 1995 through 1997, Ginger Gold and Sunrise were the cultivars most susceptible to apple scab; whereas Pristine, NY75414, Goldrush, and Enterprise were highly resistant.  Gala Supreme and Sansa also exhibited low susceptibility to scab (Table 1).  Goldrush was most susceptible to powdery mildew in our tests, although mildew pressure in these test years was only light.  Tests in Virginia, where mildew pressure has been higher, have shown Ginger Gold, also, to be highly susceptible to powdery mildew.  For cedar-apple rust, the most susceptible cultivars included Creston, Shizuka, and Goldrush.  Cultivars resistant to cedar-apple rust included Gala Supreme, PioneerMac, Fortune, Suncrisp, NY75414, Golden Supreme, Sansa, and Enterprise.

In 1998, the most leaf scab was observed on Yataka (Table 2).  Other cultivars with high scab levels (higher than the standard PioneerMac) included Ginger Gold and Orin.  Pristine, NY75414, Goldrush, and Enterprise continued to be highly resistant to leaf scab.  Many cultivars showed a high level of scab similar to that of PioneerMac, and these included Braeburn, Cameo, Fuji, Golden Supreme, Shizuka, and Suncrisp.  For powdery mildew, highest levels were seen on Braeburn, followed by Suncrisp, Creston, Sansa, and Ginger Gold.  As in previous years, the most susceptible cultivars to cedar-apple rust included Goldrush, Shizuka, and Creston.  Fruit scab results generally agree with leaf scab rankings (Table 3).  In 1998, highest fruit scab levels were seen on Sunrise, Arlet, Orin, Golden Delicious, and Ginger Gold.  Cultivars with highest rot levels were Golden Supreme and Braeburn.

Table 1. Cultivar relative susceptibilities (% leaves infected) to apple scab, powdery mildew, and cedar-apple rust from the West Virginia NE-183 pest planting at the Appalachian Fruit Research Station (compiled from 1995 - 1997).

Data from all leaves on 5 terminals/tree, 5 replicate trees, data collected in June of each year, letters denote the significance of differences among means with the Waller-Duncan Bayesian k-ratio t-test (P = 0.05) (Waller option in SAS GLM procedure).  Scab data are from 1996 and 1997 (1995 not included).   All scions on M.9 rootstock unless otherwise noted.

Table 2. Percent leaves with apple scab, powdery mildew, cedar-apple rust, and leaf spot from the NE183 pest planting located at the Appalachian Fruit Research Station, Kearneysville, WV (6/17/98).