FIELD GRAFTING WITH HEALTHY AND NEEDLE-BLIGHTED EASTERN WHITE PINE TREES AND THE EXPRESSION OF DISEASE SYMPTOMS
Healthy and needle-blighted eastern white pine trees (Pinus strobus L.) were intergrafted in the forest using bottle and cleft crown graft techniques. The grafts were made in four combinations of diseased and healthy scions and stock branches and at three different stages of development of the graft components. High percentages of successful grafts were obtained when the partner combinations included healthy scions and when the grafting was done in early May with active top growth just beginning in both scions and stock. Fewer grafts survived when diseased scions were employed and when the field grafting was carried out with dormant-collected scions or with scions and stock both possessing advanced new growth.Each grafted partner retained its original identity. Needle-blight symptoms appeared simultaneously on diseased scions and their mother trees, while the healthy stock trees remained unaffected. Conversely, healthy scions and their mother trees were unaffected while the diseased stock trees displayed the needle-blight symptoms on their foliage. No disease symptoms were transmitted by stem grafting. A search revealed that perennially needle-blighted trees were joined to neighboring healthy trees by natural root grafts, and that there was no visible communication of the disease symptoms. Additional evidence has been presented to show that needle blight is nonparasitic in etiology and that susceptibility to needle breakdown is inherent in the individual.