The other 18 clones to be evaluated were selected by R. Neal Peterson from PPF orchards at the University of Maryland Experiment Stations at Queenstown and Keedysville, Md. The PPF advanced 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.

The perimeter of the Corvallis PRVT field was surrounded by a one tree wide border of pawpaw seedlings or guard trees. The planting was removed in October 2002 due to the decline and death of trees from an unknown disease that apparently spread through the orchard.

The initial PRVT planting consisted of 224 grafted trees and 76 seedling guard trees. Two years after planting, 32 grafted trees had either failed to establish or had died after an initial healthy start. Additional trees were observed to decline each succeeding year. Vascular-wilt-like symptoms became apparent each spring after trees leafed out. As transpiration demand increased with warmer and drier weather, severely affected trees collapsed and died. Moderately affected trees became chlorotic with stunted new growth. Blue and black vascular discoloration was observed beneath the bark of declining trees along the lower parts of the main stem, particularly at and above the graft unions. This symptom has been described as blue-stain. A cankerlike bark splitting was also observed near the base of many declining trees (Fig. 1), with smaller cankers on upper scaffold branches. Several species of fungi in the genera Ceratocystis and Leptographium have been associated with blue-stain in conifer timber, and a few species are associated with tree diseases. In most cases, spread of these fungi has been attributed to assorted bark beetles or other insects (Jacobs et al., 2000; Jacobs and Wingfield, 2001; Sohlheim and Safranyik, 1997). Microscopic examination of wood and bark samples from stem cankers on declining pawpaw trees, including blue-stained wood from what appears to be an infection front found no evidence of fungal tissue. Blue discoloration beneath the bark of pawpaw trees seems to be a common response of this host to injury and may be associated with more than one disease or disorder.

chlorotic with stunted new growth. Blue and black vascular discoloration was observed beneath the bark of declining trees along the lower parts of the main stem, particularly at and above the graft unions. This symptom has been described as blue-stain. A cankerlike bark splitting was also observed near the base of many declining trees (Fig. 1), with smaller cankers on upper scaffold branches. Several species of fungi in the genera Ceratocystis and Leptographium have been associated with blue-stain in conifer timber, and a few species are associated with tree diseases. In most cases, spread of these fungi has been attributed to assorted bark beetles or other insects (Jacobs et al., 2000; Jacobs and Wingfield, 2001; Sohlheim and Safranyik, 1997). Microscopic examination of wood and bark samples from stem cankers on declining pawpaw trees, including blue-stained wood from what appears to be an infection front found no evidence of fungal tissue. Blue discoloration beneath the bark of pawpaw trees seems to be a common response of this host to injury and may be associated with more than one disease or disorder.

By July 1999, 25% of grafted trees in the Corvallis PRVT had died, and 2 years later mortality exceeded 50% (Fig. 2). Initial poor establishment of selections 1-68 and 11-13 (three out of eight replicate trees were alive in Spring 1999) and ‘Taytwo’ (four out of eight replicate trees were alive in 1999) suggest that either scions of these selections may have been diseased when they were initially grafted, or these selections are more susceptible to this disease than the other genotypes in the planting. These selections had 100% survival in the Frankfort PRVT (Pomper et al., 2003). Disease symptoms were not restricted to grafted pawpaw trees. Seedling guard row trees in the trial were unaffected until July, 2000 when 6 of 76 guard trees died and 10 more were in decline. By July 2001 14 guard trees were dead. Trees in the PPF orchard at Queenstown have exhibited similar disease symptoms to those in Oregon, but only about 1% die annually (N. Peterson, personal communication).

replicate trees were alive in 1999) suggest that either scions of these selections may have been diseased when they were initially grafted, or these selections are more susceptible to this disease than the other genotypes in the planting. These selections had 100% survival in the Frankfort PRVT (Pomper et al., 2003). Disease symptoms were not restricted to grafted pawpaw trees. Seedling guard row trees in the trial were unaffected until July, 2000 when 6 of 76 guard trees died and 10 more were in decline. By July 2001, 14 guard trees were dead. Trees in the PPF orchard at Queenstown have exhibited similar disease symptoms to those in Oregon, but only about 1% die annually (N. Peterson, personal communication).

In July 2001, after 6 years in the field, mortality at Corvallis was 75% or more for selections 1-7-1, 1-23, 1-68, 3-11, 3-21, 11-13, ‘Overleese’, and ‘Taytwo’ (Table 1). Selections with highest survival included 9-58 (seven surviving trees) and ‘Wilson’ (100% survival). Trees were rated for symptom severity each year since 1999 (data not shown). Selections with the lowest symptom severity include 1-7-2, 2-54, 7-90, 8-58, 9-58, ‘Mitchell’, ‘PA-Golden #1’, ‘Taylor’, and ‘Wilson’.

Efforts to isolate the pathogen as-