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United States Department of Agriculture

Agricultural Research Service

Title: Phytophthora Shuck and Kernel Rot, a New Disease of Pecan Caused by Phytophthora Cactorum

Authors
item Reilly, Charles
item Hotchkiss, Michael
item Hendrix, Floyd - UNIV. OF GEORGIA

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 1997
Publication Date: N/A

Interpretive Summary: A new pecan nut disease was discovered during the 1988 growing season. This disease was caused by the water mold Phytophthora cactorum. The fungus infected nearly mature pecan fruits from early September through harvest causing yield losses up to 50 percent. The disease also reduced the quality of the remaining kernels by darkening the seed coat. Conditions associated with disease development were prolonged periods overcast, high humidity, cool temperature, and frequent rainfall. Disease was observed more frequently in irrigated orchards.

Technical Abstract: 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. Rotted shucks turned dark brown leaving a distinct margin between necrotic and healthy tissue. 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 kernels 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 percent 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 The American Type Culture Collection as isolate B1, ATCC No. 66186. Laboratory and field inoculations using B1 isolate produced typical symptoms on nut clusters. Symptoms of the disease were observed in 13 orchards brought to our attention by state pecan extension specialists, and the pathogen was isolated from the soil of 10 of these orchards in south and central Georgia.

Last Modified: 10/23/2014
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