INTERREGIONAL COOPERATIVE RESEARCH IN FRUIT TREE VIRUSES AND 

 ASPECTS OF CONTROL MEASURES: PRESENT AND FUTURE^ 



R.C. McCrum 

 Department of Botany and Plant Pathology 

 University of Maine 



A few commercial nurseries conduct virus indexing programs in 

 regard to their propagating stocks and also maintain nuclear stock 

 blocks. Individual State Experiment Stations as well have for 

 several years cooperated in certification programs with commercial 

 nurseries in regard to Prunus tree fruit nursery plants. There is, 

 however, at the present no general U.S. recognized certification 

 or regulatory program for distribution of virus-indexed or virus- 

 free apple nursery stocks. In this respect, the U.S. orchardist 

 is not as fortunate as his European counterpart in receiving reli- 

 able virus-free materials. The European distribution of virus-free 

 material, handled through regulated programs, involving both re- 

 search and inspection agencies, results in great volumes of clean 

 budwood from the initial source which is built up and released to 

 the industry by the cooperating nurseries. Part of the problem in 

 the U.S. in not duplicating this accomplishment is the reluctance 

 of the American growers to set up a uniform, regulated approach for 

 handling virus- indexed trees. Also, because of our numerous and 

 separate fruit growing areas, there tends to be a larger diversity 

 in apple cultivars due to the different climatical aspects, grow- 

 ing seasons, temperature limiting factors, other pressing disease 

 pathogens, soil types, processing requirements and changing con- 

 sumer demands, each one a critical factor to specific area growers. 

 In addition to this, there is a rapid development of patented selec- 

 tions being offered to the trade. 



In spite of these handicaps, there has been considerable prog- 

 ress in obtaining and using virus-clean apple trees and we must 

 realize that it is only 5 years since the first introduction and 

 distribution of the IR-2 program's virus-free apple stocks began. 

 We are just beginning to realize that our research findings and 

 dissemination of this knowledge, which has led to increased quar- 

 antine interest in regard to the import of pome fruit tree mater- 

 ial, signifies that the U.S. itself must also establish certifi- 

 cation criteria and procedures in order to export it's own nurs- 

 ery material to meet the expanding world competition. 



There is little or no control on the shipping of virus-infec- 

 ted apple budwood or treesthroughout the United States. This has 

 in the past led to a high incidence and spread of latent viruses, 

 particularly in cases where new cultivars have been desired quickly, 

 in large amounts, and have been put on older, sometimes infected 

 stock trees for a fast buildup of material. Exchange of nursery 

 stocks among regions and nursery suppliers, without detailed inform- 

 ation as to original source and disease status, also helps to in- 

 crease the problem. 



Part I appeared in Nov. -Dec, 1976 issue of Fruit Notes 



