Select Malus clones for rapid detection of apple stem grooving virus

Highly sensitive, rapidly reacting woody plant indicator clones were found when 201 Malus clones were screened for response to apple stem grooving virus (ASGV). A clone of M. micromalus (GMAL 273.a) displayed diagnostic foliage symptoms within 2 to 4 weeks of bud-inoculation in the greenhouse. Clones of M. yunnanensis (GMAL 2342) and M. tschonoskii (GMAL 1834) expressed diagnostic symptoms after 6 to 8 weeks. This is in contrast to the 6 to 8 months frequently required for reliable ASGV reactions to appear on inoculated plants of Virginia Crab (Malus domestica), the currently recommended ASGV indicator, grown under the same conditions. When Virginia Crab and the three Malus selections were screened in two separate years with 19 ASGV isolates from diverse geographic origins, foliar symptoms were produced most consistently on M. micromalus GMAL 273.a and least consistently on Virginia Crab. M. micromalus GMAL 273.a is superior to Virginia Crab as a rapid woody plant indicator for ASGV.