Root Rot of Kiwi (Actinidia chinensis) Caused by Pythium ultimum. A. J. Latham, Alabama Agricultural Experiment Station, Auburn University, AL 36849. W. A. Dozier, Jr., Alabama Agricultural Experiment Station, Auburn University, AL 36849. Plant Dis. 73:938. Accepted for publication 16 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0938D.
In April 1986, kiwi (Actinidia chinensis Planch.) plantings were made at the Wiregrass Substation (WES) and Gulf Coast Substation (GCS). At WES, 63% of the plants developed root rot by March 1987, and the sites were replanted. During July, 69% of the plants died after an extended wet period. At GCS, rainy hurricane weather during September 1988 caused saturation of kiwi plantings and resulted in asphyxiation and leaf drop from approximately one-third of bearingage plants. Many of the kiwi plants at GCS failed to bud out the following spring, and root rots were found on 28% of 208 plants examined. Pythium ultimum Trow var. ultimum and P. ultimum var. sporangiferum Drechs. were consistently isolated from rotted roots collected from both the WES and GCS sites. Pure cultures of the Pythium spp. were increased on cornmeal-sand mixtures and used to infest soil of potted kiwi plants. Six weeks after inoculation, kiwi exposed to the fungi had developed root rots similar to those observed in the field and had died; kiwi grown in uninfested soil remained healthy. The same species of Pythium were reisolated from potted kiwi plants.