Early Growth Characteristics of Seven Grafted Varieties and Non-Grafted Seedling Pawpaw

Abstract

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', `Sunfl ower', `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 `Sunfl ower'. 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 fl ower buds by the spring of the fourth season, with budding ranging from an average of 0.5 buds/tree (`Rebeccas 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.