THE NATIONAL AND INTERNATIONAL ROLES OF THE IR-2 VIRUS-FREE FRUIT TREE REPOSITORY

The IR-2 virus-free deciduous fruit tree repository began modestly in 1955 but since has sent virus-free propagating materials to 102 investigators in 34 states of the USA and 107 investigators in 37 other countries. All Prunus, Malus and Pyrus cultivars are indexed across extensive indicator-hosts. Concurrent varietal identifications and trueness-to-type determinations are made. Thermotherapy of diseased cultivars at 37.7 C is done by two methods—direct exposure and tip grafting. Tip grafting for virus elimination from Prunus is possible if alternating temperatures of 34 C and 37.7 C for 12 hours each are used instead of constant 37.7 C.