Alvaro Ureña1, Dave Mitchell2, and Dan Legard1.
1University of Florida, Gulf Coast Research and Education Center – Dover. 2Department of Plant Pathology, University of Florida, Gainesville
INTRODUCTION
Colletotrichum spp. cause anthracnose diseases of strawberry. These pathogens cause diseases on many plant parts include crowns, leaves, petioles, runners, fruits and peduncles. Historically, those diseases cause serious losses in strawberry worldwide. The ability of the pathogen to cause latent infections has placed Colletotrichum among the most important pathogen groups internationally. In Florida, Colletotrichum crown rot typically affects 2% to 4% of strawberry plants in production fields, but losses up to 80% have occurred in the 1980’s when warm and humid conditions and infested planting material caused serious outbreaks of crown rot. In Florida, work done at the University of Florida, GCREC-Dover using molecular methods has shown that Colletotrichum crown rot is caused mainly by C. gloeosporioides. The source of the inoculum for epidemics in Florida is unclear. In California, the fruit rot pathogen C. acutatum can survive in soil up to 9 months. The purpose of this study was to evaluate the ability of C. gloeosporioides to oversummer in crown tissue under field conditions in Florida.
METHODS
Field experiments were conducted during 1998 and 1999 at the University of Florida, GCREC-Dover. Crowns were removed from plants that were naturally infected with C. gloeosporioides and placed inside of cloth bags with 2 oz. of soil. Bags were buried at a depth of 5 inches (1998 and 1999) or 2 inches (1999) in replicated plots. On a regular schedule, bags were recovered; the crowns were washed and surface sterilized then sectioned and plated onto semi-selective medium (1998 and 1999). The remaining crown material was ground with 2 oz. of water and dilution plated onto semi-selective medium (1999 only). Data was analyzed as percentage of crowns that C. gloeosporioides was recovered from.
RESULTS
The results of the experiments are presented in Figure 1. During the first year of the study (Summer 1998), C. gloeosporioides was recovered from up to 100% of buried crowns for the first 21 days and then declined rapidly until it was not detected 56 days after burial. During the 1999 experiment C. gloeosporioides was again recovered from up to 100 % of the crowns after 14 days at both depths evaluated (two and five inches). In this current experiment, recovery of C. gloeosporioides has declined to low levels by day 56. Based on the information collected, it is expected that C. gloeosporioides will disappear from crowns before transplanting time for the 1999 to 2000 season.
These results suggest that C. gloeosporioides does not over summer in strawberry tissues in Florida. The time between the end of last season strawberry crop and the planting of the next season (four to six months) should be sufficient to eliminate C. gloeosporioides from strawberry plant debris. This suggests that other sources of inoculum, such as transplants or other plant hosts, may be important for the initiation of Colletotrichum crown rot in Florida. Current research at the GCREC-Dover is being conducted to investigate these possibilities.