Constriction disease of Stanley plum (Brown line)
Tomato Ringspot Virus (TmRSV)
Brown line disease is due to an incompatibility at the graft union when Stanley plum and some other European or hybrid plum varieties are grafted onto Myrobalan (Prunus cerasifera) rootstock. Asian plums are not affected. Infected trees show a general decline and bear small, pale green leaves. The scion grows quicker than the rootstock, giving the rootstock a constricted appearance just below the graft union (A). A distinct brown, sunken line at the union is apparent underneath the bark (B).
Widespread; the virus is endemic to North America.
Any disease or disorder affecting the root system or rootstock/scion union can produce similar above-ground symptoms. Brown line can be distinguished from similar diseases by cutting away the bark and observing the darkening at the graft union.
The resistant plum rootstock, Marianna 2624, can be substituted for Myrobalan. TmRSV can survive in a number of weed hosts, is seed-transmitted in dandelion, and is vectored by the dagger nematode Xiphinema americanum Cobb and X. rivesi Dalmasso. Thus, good weed control and pre-planting site preparation can help to reduce the incidence of this disease when Myrobalan rootstock must be used.
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