Scientists at several universities are conducting experiments with pawpaw. James Flore of Michigan State University is investigating cultural requirements. At University of Maryland, Harry Swartz is experimenting with tissue culture, James Marshall is experimenting with food processing, and Carol Karahadian and Marilyn McGrath are analyzing volatiles. The author and Swartz are breeding and selecting pawpaw, in an effort to develop commercial quality cultivars. Since 1981 they have assembled a germplasm collection of roughly 1200 accessions, open-pollinated seedlings from the historic collections of Buckman, Zimmerman, Hershey, Allard, the Blandy Experimental Farm, plus some from modern cultivars (Peterson, 1986). The trees will be evaluated for three fruiting seasons, 1988 through 1990, followed by selection and controlled crosses. Three cycles of evaluation, selection and crossing (about 30 years) are anticipated in order to ensure the discovery of a variety of truly superior genotypes. A few cultivars may be identified in the first or second cycle. The following traits are critical needs in their breeding program, whose relative weights are as yet unassigned:
Moderate to large fruit size, 200-400 gm.
Attractive, clear skin colors with little blotching and streaking.
Thicker, tougher skin, affording greater protection.
Mild and agreeable aroma.
Mild to rich satisfying flavor, with a pleasant aftertaste.
Firm, custardy, melting flesh.
Few seeds of small size, with seed: fruit ratios less than 4 percent.
Good to excellent nutritive value.
Fruit that abscises early, at a firm-ripe stage.
Reduced metabolism, less perishable fruit.
Lower linolenic acid levels (reduced susceptibility to rancidity).
Small tree size for easier harvest, less than 3 m.
Precocious bearing, 4 years or less.
Vigorous growth under low to medium inputs.
Open branching structure with strong crotch angles, self-pruning.
Fruit borne near the base of the branches for strong support.
High flower density, 3 or more flower buds per branch.
High fruit set under natural pollination, greater than 25 percent.
Consistently high yields, over 2 kg per meter of tree height.
Resistance to Talponia plummeriana Busck (pawpaw peduncle borer).
Cold hardiness and drought tolerance.
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