Identifying Sources and Pathogenicity of Anthracnose Strains Found on Weeds in Strawberry Fields
Restricted (Penn State Only)
- Author:
- Fronk, Leah
- Graduate Program:
- Horticulture
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 27, 2023
- Committee Members:
- Erin Connolly, Program Head/Chair
Richard P Marini, Thesis Advisor/Co-Advisor
Kathleen Demchak, Committee Member
Sara Ruth May, Committee Member
Kari Anne Peter, Committee Member - Keywords:
- Fragaria X ananassa
Colletotrichum acutatum
Colletotrichum gloeosporioides
Fragaria x ananassa
weeds
endophyte - Abstract:
- Anthracnose, caused by fungi in the Colletotrichum acutatum and C. gloeosporioides species complexes, is responsible for significant economic losses in strawberry production worldwide in nursery and farm environments. Symptoms can be seen on fruit, petioles, leaves, and crowns. The presence of diseases caused by Colletotrichum in nursery transplants is of great concern to strawberry growers. The pathogen is often present without symptoms in transplants and may be further spread to soil, equipment, and other plants by water-splashed spores. It is also possible that some spores may be wind-blown into the planting from the surrounding environment. Colletotrichum can remain asymptomatic on strawberry and other plant material for some time until it causes lesions on fruit or other plant parts. Since strawberry is often managed as a perennial crop or in fields with minimal crop rotation, weeds in strawberry fields are suspected to be another source of the disease. In other studies, Colletotrichum of the same species infecting strawberries was found on various weed species in strawberry fields. We hypothesized that common weeds in strawberry fields are hosts to Colletotrichum and thus could serve as reservoirs of disease inoculum either infecting disease-free plants or exacerbating disease problems. Funded by the Pennsylvania Vegetable Growers Association, the objectives of this 2-year study were to survey Pennsylvania strawberry fields to determine if weeds in strawberry fields are infected with Colletotrichum, and compare the species found on weeds to those infecting strawberry. During 2021 and 2022, 144 weed plants were collected from 6 Pennsylvania strawberry production fields with active anthracnose infections. Fourteen of the 20 weed species were endophytically infected with Colletotrichum. From these weeds, 54 single-spore cultures of C. acutatum isolates were recovered. While detection frequency varied, all perennial weed species were infected with Colletotrichum. A total of 46 isolates were also recovered from infected strawberry plants. The predominant fungal species identified on both weeds and strawberries through PCR and phylogenetic analysis was C. nymphaeae, part of the C. acutatum species complex. To further test pathogenicity, detached strawberry fruit were inoculated with isolates from selected weed species. Strawberry fruit developed symptoms in almost every instance. Strawberry growers should be aware that allowing weeds to persist in strawberry fields can allow Colletotrichum to hide. Whether weeds or strawberry plants are infected first is unknown, but the fact that Colletotrichum nymphaeae could persist on weeds means weed control takes on added importance. Much more work is needed, but for now, we have more answers on how clean plants may first become infected in nursery or grower fields.