BROWN- LINE DECLINE OF APPLE 



Daniel R. Cooley/ Ted R. Bardinelli,"'" 



2 

 and William J. Manning 



Department of Plant Pathology 



A new disease of young apple trees has become evident in the 

 Northeast in recent years. The disease is called brown-line or 

 graft union necrosis. Isolated trees in young plantings decline 

 suddenly, may appear to be girdled, and can be snapped off at the 

 point of union between scion ana rootstocK. A distinct brown-line 

 IS evident at tne point of graft union. 



Researchers in New York State were able to determine that 

 the problem occurs most often when MM106 is used as a rootstock 

 and that it often originates in the nursery. Tomato ringspot virus 

 (TmRSV) was isolated from diseased trees. The dagger nematode, 

 Xiphenema americanum ,was also associated with the problem. TmRSV 

 and the dagger nematode together appear to cause brown-line decline. 

 TmRSV is found in many plants including raspberry, grape, elder- 

 berry, florist's geranium, and many common weeds such as dandelion, 

 chickweed and plantains. The dagger nematode feeds on the roots 

 of infected plants and carries virus particles to clean non-infected 

 roots, where new virus infections are initiated. , 



Rootstocks and cultivars differ in their sensitivity to TmRSV. 

 Some are tolerant and can carry the virus without showing symptoms 

 or decline. Sensitive plants decline and die over a prolonged 

 period. Hypersensitive plants respond to TmRSV infections by rapid 

 destruction of cells near the point of infection. This prevents 

 the virus from spreading further into the plant. 



Dr. James Cummins (Cornell University) believes that union 

 necrosis results when a tolerant rootstock and a hypersensitive 

 scion become infected with TmRSV. MM. 106 is highly tolerant to 

 TmRSV and is usually symptomless. A number of apple cultivars, 

 particularly Red Delicious, are hypersensitive to TmRSV. When the 

 virus from the rootstock comes in contact with the hypersensitive 

 scion, the scion reacts by killing its cells at the graft union. 

 The result is a brown line at the graft union which prevents water 

 and nutrient translocation into the scion. The scion dies and is 

 easily broken off at the graft union. 



Cummins has rated a number of apple cultivars for brown-line 

 sensitivity and rate of decline when grown on MM. 106. Some show 



1 2 



Extension Technicians, and Associate Professor, respectively. 



Department of Plant Pathology, University of Massachusetts, Amherst 



01003 



