Rapid/Sudden Apple Decline Syndrome: In recent years, across Central and Northeastern regions of the United States, and in Ontario, Canada, there are more frequent reports of rapid decline of established apple trees. Affected trees show rapid appearance of chlorotic leaves throughout the entire canopy followed by tree collapse within weeks after first visual symptoms. Typical chlorotic symptoms in symptomatic trees can be easily spotted among healthy plants in an orchard, but the actual cause of the decline is likely to have occurred much earlier. Several potential causes have been put forward, including abiotic and biotic stresses, viruses, rootstock and scion compatibility, soil health, and their interactions. The true cause could be one or a combination of several of these, with different causes possible in different orchards. We have started to characterize microbial communities in the soil, and rhizosphere, endophytes in the rootstock and scion of declining and healthy looking apple trees from the affected orchards at sequence levels to narrow down potential causes of sudden and rapid decline.