PPF 1-7-1, PPF 8-58 and PPF 11-5. These are now the named varieties 'Shenandoah', 'Rappahannock' and 'Susquehanna' (patents pending).

In addition to the work of Peterson during this period, two contests were held for choosing the best pawpaws in 1990. The first was conducted by Brett Callaway, Horticulturist at KSU (Fig. 3). Callaway patterned his contest on that of 1916 and meant to gather a wide geographic breadth of germplasm with which to initiate a breeding program. His contest generated more than 400 entries from 14 states (B. Callaway, personal communication) and most entries were new selections from the wild. The prize winning entry came from David Wells of Salem, Ind., whose tree is now propagated as the variety ‘Wells’. The second contest was organized by Mark Blossom, of Eureka Springs, Ark., who was strongly interested in pawpaws (Blossom, 1993). Because of the many difficulties he encountered, few specimens from his collected germplasm survive and no varieties were selected (M. Blossom, personal communication).

The Callaway contest marked the beginning of a committed pawpaw research program at KSU, first headed by Callaway (1991–1993), then Desmond Layne (1993–1997), and currently Kirk Pomper (1998–present). A germplasm collection was started in 1991 with the seed collected through the contest. In 1994, KSU was designated the official Asimina satellite repository of the USDA National Clonal Germplasm Repository, Corvallis, Ore. At present this contains over 1700 accessions, including 40 varieties, from 16 states (Layne, 1996; Pomper et al., 2003). KSU is one of the sites of the regional variety trial. KSU researchers have conducted many studies, including germination protocols, seedling cultural requirements, tissue culture, isozyme identification, and DNA fingerprinting, [Finneseth et al., 1998; Huang et al., 1996, 1997, 1998, 2000, 2003; Layne, 1996; Pomper et al., 1999, 2000, 2002a, 2002b, 2002c, 2003].

pository, Corvallis, Ore. At present this contains over 1700 accessions, including 40 varieties, from 16 states (Layne, 1996; Pomper et al., 2003). KSU is one of the sites of the regional variety trial. KSU researchers have conducted many studies, including germination protocols, seedling cultural requirements, tissue culture, isozyme identification, and DNA fingerprinting, [Finneseth et al., 1998; Huang et al., 1996, 1997, 1998, 2000, 2003; Layne, 1996; Pomper et al., 1999, 2000, 2002a, 2002b, 2002c, 2003].

The KSU repository collection also contains over 300 hybrid seedlings arising from a diallele cross that Peterson performed in 1993 between eight of his advanced selections. These seedlings were established at the farm in 1995, with the trees first bearing fruit in 2002. Fruit quality and production will be evaluated in coming years (K. Pomper, personal communication). Progeny in these controlled crosses were used to identify inter-simple sequence repeat markers that segregate in simple Mendelian fashion and these markers have been used to assess genetic diversity in 19 papawp varieties (Pomper et al., 2003).

LESSONS FROM PETERSON’S PAWPAW BREEDING. Peterson’s breeding project was the first pawpaw breeding and evaluation project involving thousands of seedlings, statistical measurements, and the use of selection indices. His project demonstrates the results of one person working for 20 years with limited resources. His design emphasized both quantity and quality, consisting of more than 1000 accessions using seedlings from the best germplasm available. However, two major flaws in his design were the lack of grafted specimens of standard varieties such as ‘Overleese’ for performance comparison, and an insufficient number of accessions of seedlings from named varieties.

resources. His design emphasized both quantity and quality, consisting of more than 1000 accessions using seedlings from the best germplasm available. However, two major flaws in his design were the lack of grafted specimens of standard varieties such as ‘Overleese’ for performance comparison, and an insufficient number of accessions of seedlings from named varieties.

In evaluating his collection, Peterson recorded quantitative measurements of vigor, yield and fruit quality (Peterson, 1991) (Table 1). Each accession in Peterson’s experiment had a score computed based on 3 years of data, as 1 year of data was insufficient because fruit quality and yields varied from year to year. Breeding value was computed as a weighted sum of the variables of importance to the breeding objective. The variables were standardized by the reciprocal of their standard deviations to remove the arbitrary effect of the unit of measure. Weights were applied to reflect the relative importance of traits economically and to adjust for the incommensurability of dissimilar traits, such as taste and yield. Taste was evaluated by means of taste panels consisting of four subjects testing three samples from each tree (early, middle and late fruit) and eight variables (Table 1).

Peterson also used factor analysis, viz., principal components analysis. This analysis adjusted for the correlations between different traits and improved the ability to discriminate the better phenotypes in the collection. Although two

Table 1. Variables included in selection index of R.N. Peterson's pawpaw breeding.

Dimension

Vigor

Yield

Fruit quality

HorTechnology · July–September 2003 13(3)