Table 2. Pawpaw Regional Variety Trial (PRVT) cooperators and cooperating institutions by location.

2Outside pawpaw native range.

(West Chester, Pa.), and open-pollinated seed from some modern varieties. In 1993, the PPF and KSU embarked on a joint venture to test 10 commercially available pawpaw varieties and 18 of PPFs advanced selections from the Maryland orchards (Table 1). These advanced pawpaw selections were selected based on superior traits including fruit size and taste, high flesh-to-seed ratio, resistance to pests and diseases, and overall productivity on a year-to-year basis. From 1995 to 1999, 12 universities or private cooperators established a PRVT (Pomper et al., 1999; Table 2). The objective of the PRVT plantings was to evaluate commercially available named pawpaw varieties and PPF’s advanced selections within and outside of pawpaw’s native range. In 1995, PRVT plantings were established in Kentucky (Princeton, Ky.), Louisiana, North Carolina, Oregon, and South Carolina. In 1998, a PRVT planting was established in Frankfort, Ky. In 1999, PRVT orchards were planted in Indiana, Iowa, Michigan, Maryland, Nebraska, New York, and Ohio. Here we report on the status of the pawpaw RVT plantings in Frankfort and Princeton, which were established in 1998 and 1995, respectively.

Materials and methods

PLANT MATERIAL. Rootstock was propagated in greenhouses as described by Pomper et al., 2002a, 2002b). Seed for rootstock for both plantings was harvested from open-pollinated half-sibling trees in rows six and seven from the experimental pawpaw orchard at the Western Maryland Research and Education Center in Keedysville, Md. Buds of each of the varieties and advanced selections to be tested were donated by R. Neal Peterson and were chip budded onto actively growing 1-year-old rootstock, 7 to 10 mm (0.3 to 0.4 inch) in diameter. Grafted trees were grown in the greenhouse over the summer. At both Kentucky PRVT sites, 8 replicate trees of each of the 28 grafted scion varieties (Table 2) were placed in a randomized complete block design with 8 complete blocks (block = 4 rows × 7 trees) at an in-row spacing of 2 m (6.6 ft) and between-row spacing of 5.5 m (18.04 ft). Rows were placed in north-south orientation.

actively growing 1-year-old rootstock, 7 to 10 mm (0.3 to 0.4 inch) in diameter. Grafted trees were grown in the greenhouse over the summer. At both Kentucky PRVT sites, 8 replicate trees of each of the 28 grafted scion varieties (Table 2) were placed in a randomized complete block design with 8 complete blocks (block = 4 rows × 7 trees) at an in-row spacing of 2 m (6.6 ft) and between-row spacing of 5.5 m (18.04 ft). Rows were placed in north-south orientation.

FRANKFORT PLANTING. Grafted trees were overwintered in a walk-in cooler until planting in late March 1998. A total of 224 grafted trees (eight trees of each selection), and 75 Kentucky seedlings serving as border row trees, were planted in a Lowell silt loam soil (pH 6.9) at the KSU Research and Demonstration Farm in Frankfort. Trees were fertigated with Peters 20–20–20 (20N–8.7P–16.6K) water-soluble fertilizer (Scotts Co., Marysville, Ohio) once in May, June, July, and August each year for a total of 12.10kg·ha-1 (10.8lb/acre) of nitrogen (N). Additional irrigation was provided as needed. Tree height was recorded early each spring from 1998 until 2001. Trunk diameter was determined in Apr. 2001. The number of fruit on each tree was counted on 4 July 2001 following the normal June drop period.

PRINCETON PLANTING. A total of 224 grafted (eight trees of each selection), and 75 Kentucky seedling trees as border row trees, were planted in October 1995, in a Crider silt loam (pH 6.9) at the University of Kentucky Research and Education Center, Princeton. Trees were fertilized with 28.0 kg·ha-1 (25 lb/acre) of N. For 2001, the number of fruit on each tree was counted on 3 July 2001. Average fruit weight was based on selections where 10 or more fruit were harvested and was determined on 27 and 30 Aug. 2001. The number of fruit produced by each selection was also determined at harvest in 2000. Average fruit weight for each selection was based on the weights of 10 or more fruit harvested on 25, 29, and 30 Aug. 2000, and 1 and 13 Sept. 2000.

3 July 2001. Average fruit weight was based on selections where 10 or more fruit were harvested and was determined on 27 and 30 Aug. 2001. The number of fruit produced by each selection was also determined at harvest in 2000. Average fruit weight for each selection was based on the weights of 10 or more fruit harvested on 25, 29, and 30 Aug. 2000, and 1 and 13 Sept. 2000.

STATISTICAL ANALYSIS. Data on trunk diameter, increase in tree height, and fruit weight by variety or advanced selection were subjected to GLM analysis of variance using the statistical program Costat (CoHort Software, Monterey, Calif.). Treatment means were separated based on the Student-Newman-Keuls separation of means, or independent t tests when appropriate, at a significance level of P < 0.05.

Results

FRANKFORT PLANTING. Of the 224 grafted trees that were planted in March 1998, 95% of trees survived. Most of the trees that died were lost during the first summer after planting. The varieties Wilson and Taylor, and the advanced selection 2-10, had the poorest survival rate (75%). All other varieties and advanced selections had survival rates of 88% or higher (Table 3).

Trunk diameter and tree growth (increase in tree height) varied significantly among varieties (P < 0.001 for both variables). Based on trunk diameter measurements taken in 2001, most selections displayed excellent vigor, although some selections tended to have smaller-diameter trunks (e.g., ‘Middletown’, 11-5, 3-21, and 5-5). Based on height measurements taken from 1998 to 2001, most selections also displayed excellent growth, though some selec-

HorTechnology · July–September 2003 13(3)