Phytophthora Shuck and Kernel Rot, a New Disease of Pecan Caused by Phytophthora cactorum

Phytophthora shuck and kernel rot infection usually started at the stem end of the pecan fruit and progressed distally to encompass the entire shuck within 4 to 6 days. A distinct margin developed between dark brown necrotic tissue and healthy green tissue during rotting of the shucks. Phytophthora cactorum was isolated from the rapidly rotting pecan fruit. Two to three weeks after the symptoms appeared, the diseased shucks dried and stuck tightly to the shell. The seed coat of the kernel turned dark brown and the endosperm rotted. The new disease of pecan was first observed during September 1988 on maturing pecan fruit in central Georgia in the vicinity of the town of Byron where growers estimated losses of 50% or greater in some orchards. In south Georgia near the cities of Albany and Cordele, the disease was present but less severe. The causal agent was identified as P. cactorum and deposited with ATCC as isolate B1, ATCC No. 66186. Laboratory and field inoculations of nut clusters using the B1 isolate produced typical symptoms observed in nature. Symptoms of the disease were observed in 13 orchards, and the pathogen was isolated from the soil of 10 of these orchards in south and central Georgia.