Anthony Bratsch,1 Robert Bellm,2 and Don Kniepkamp3

ADDITIONAL INDEX WORDS. Asimina triloba, rootstock, anthesis, native, scaffold, axillary

SUMMARY. Following spring planting in 1998, and for four seasons (1998–2001), early growth and development were characterized for seven grafted [PawPaw Foundation (PPF), Frankfort, Ky.) pawpaw Regional variety trial (PRVT) rootstock] pawpaw (Asimina triloba) varieties, ‘Davis’, ‘Taylor’, ‘Rebecca’s Gold’, ‘Sunflower’, ‘Overleese’, ‘Prolific’, ‘Wells’, and one nongrafted seedling strain. Survival rate after four seasons was 96.5% for grafted trees and 100% for seedling trees. Entries exhibited significant differences in total height, trunk cross-sectional area (TCSA), average shoot length, first winter cold injury and percent bloom. By the end of 2000, seedling tree height and TCSA were greater as compared to the named varieties. Seedling height averaged 134 cm (52.8 inches), with a TCSA of 4.54 cm² (0.704 inch²), while the least vigorous variety (Davis) had an average height of 77 cm (30.3 inches) and a TCSA of 1.54 cm² (0.239 inch²). Average shoot length was significant only in the year of planting, ranging from 39.3 cm (15.47 inches) for ‘Davis’, to 61.3 cm (24.13 inches) for ‘Sunflower’. Tip dieback occurred in the winter following planting on all varieties; this damage ranged from 23.3% (“Taylor”) to 73.4% (“Overleese”). In 1999, lower axillary shoots (LSL) breaking below the damaged tips grew longer [31.1 to 50.6 cm (12.24 to 19.92 inches)] than upper distal axillary shoots (DASL) [15.8 to 44.6 cm (6.22 to 17.56 inches)], indicating a lack of apical dominance and vigor of emerging top buds. All named varieties developed flower buds by the spring of the fourth season, with budding ranging from an average of 0.5 buds/tree (“Rebecca Gold”) to 6.0 buds/tree (“Prolific”). Viability of these buds as determined by successful anthesis ranged from 0.4% (“Davis”) to 63.8% (“Wells”). No fruit were set from these flowers.

Pawpaw is the only temperate member of the tropical custard-apple family (Annonacea) (Bailey, 1960) and is the largest native fruit in North America (Darrow, 1975). It is endemic to the eastern U.S. and it grows in the wild as far north as Ontario, Canada, south to Florida, and west to Nebraska (Kral, 1960). It has received attention in recent years as a potential new crop with multiple uses, including fresh-market sales of the custard-like fruit, and the vegetative parts have medicinal and insecticidal properties (Layne, 1996). A PRVT was established at 12 locations across the United States, coordinated by staff at Kentucky State University, (KSU) Frankfort, Ky. (Pomper et al., 1999).