Epidemiology and Management of Fusarium Root,Crown, and Stem Progress Report — June 1998
Epidemiology and Management of Fusarium Root, Crown, and Stem of Lisianthus (Eustoma grandiflorum)
Dr. R. J. McGovern, Associate Professor of Plant Pathology, and Dr. B. K. Harbaugh, Professor of Floriculture, University of Florida, Gulf Coast Research and Education Center, Bradenton, FL
Date:
5/29/98
Title of Project:
Epidemiology and Management of Fusarium Root, Crown, and Stem of Lisianthus
Institution where work is being conducted:
University of Florida
Amount of Endowment Grant:
Covering Period:
7/97 to 6/98
Anticipated Date of Project Completion /Final Report:
June 1998
Individual(s) Conducting Project:
(List Project Leader First)
Robert J. McGovern
Telephone Number: 941-751-7636
Industry Needs Addressed and Objectives
A destructive crown and stem rot caused by the fungus Fusarium avenaceum has become widespread in production areas devoted to both cut flower and pot flower production of lisianthus in Florida and California. In 1995-1996 losses of up to 30% occurred among Florida cut flower producers. During 1996-1997 we found that plant mortality varied by cv., planting date and transplant source, and ranged up to 70% in both California and Florida. (We estimated that the three Florida lisianthus growers surveyed sustained combined losses of about $150,000). Our objective was to develop an effective management strategy for Fusarium crown and stem rot based on obtaining data in the following areas:
- Potential of F. avenaceum to survive in soil following the cropping season
- Determination of contamination/infection of lisianthus seed by the pathogen Identification of alternate hosts of F. avenaceum
- Identification of sources of resistance among commercial lisianthus cvs.
- Examination of primary and secondary spread of the pathogen at production sites
- Evaluation of interactions between F. avenaceum, F. solani, and F oxysporum
- Evaluation of the efficacy of chemical and biological control
Progress to Date
Progress on our research objectives has been made as follows:
- Pathogen Survival. The survival of F avenaceum was very low in soil removed from two lisianthus production sites in Florida with high incidences (>50% plant mortality) of crown and stem rot.
- Seed Transmission. Fusarium avenaceum was not detected by plating 1,000 seeds from each of 25 commercial cvs. of lisianthus on a Fusarium-selective medium. We have successfully used the polymerase chain reaction (PCR) to differentiate between cultures of F avenaceum. F oxysporum, and F solani from lisianthus in preparation for use of this procedure in screening additional lisianthus seed for F avenaceum.
- Alternate Hosts. We detected the fungus by isolation and PCR in the symptomless root systems of begonia, Madagascar periwinkle, marigold, petunia, rudbeckia, salvia, and verbena, one month following inoculation with the fungus.
- Pathogen Spread. The fungus was consistently detected in lisianthus transplants from two California production sites, and this appears to be the primary source of F. avenaceum for recent outbreaks of crown and stem rot. We have also detected the fungus in styrofoam transplant trays and have established that it may be transmitted on pruning tools.
- Chemical Control. Fludioxonil (Medallion), azoxystrobin (Heritage), and a combination of thiophanate methyl (Domain) and iprodione (Chipco 26019) were effective in suppressing F. avenaceum and should provide a useful component in integrated management of the disease.
Future Research
- Seed Transmission. We will follow-up with an intensive screen (c. 20,000 seeds) on selective media of a single lisianthus seed lot identified by PCR as potentially infected by or infested with F avenaceum.
- Host Range. The susceptibility of plants commonly produced as cut-flower or pot-flower crops either in rotation with, or in proximity to, lisianthus such as Antirrhinum majus, Aster spp., Chrysanthemum x morifolium, Dianthus caryophyllus, Gypsophilapaniculata. and Helianthus annuus to F avenaceum will also be tested.
- Resistance. Fifty to sixty commercial pot and cut flower cvs. of lisianthus including the Echo. Flamenco, Hallelujah, Heidi, Mermaid, and Lisa series will be compared for susceptibility to
F. avenaceum. - Secondary Spread of F. avenaceum. The distribution of the disease within individual production beds will be mapped and then interpreted by use of several spatial analyses. We will also investigate spread of F. avenaceum by air using spore traps.
- Interactions Between F. avenaceum and other Fusarium Species. Experiments will be conducted using a susceptible lisianthus cultivar infected by isolates of F avenaceum, F oxysporum, and F solani alone and in combination.
- Biocontrols. The effectiveness of commercial biocontrols including Gliocladium virens, Streptomyces lydicus, Pseudomonas aureofasciens, and Trichoderma harzianum will be evaluated.
Anticipated Benefits
This work is justified by the lack of fundamental data on Fusarium crown and stem rots and wilts in lisianthus and the crop's importance of lisianthus to the U.S. and worldwide florists' crop market. The projected research will enable lisianthus growers to implement an integrated approach to managing crown and stem rot which will be both effective and environmentally sound. The management techniques developed in this research should have broad applicability to diseases of other florists' crops induced by Fusarium and other soil borne fungi.
