Detection and management of Colletotrichum acutatum sensu lato on strawberry
Colletotrichum acutatum sensu lato, one of the most economically damaging pathogens of strawberry, is the primary causal agent of anthracnose fruit rot (AFR). A key challenge in managing AFR is detecting the pathogen on asymptomatic plants. To meet this need, a loop-mediated isothermal amplification (LAMP) assay was developed that incorporated two sets of primers: LITSG1 targeted on the ITS region of ribosomal DNA and Ltub2 on the β-tubulin 2 gene. In pure culture assays, Ltub2 was specific for detection of C. acutatum, whereas LITSG1 detected C. acutatum and two additional anthracnose pathogens, C. gloeosporioides and C. fragariae. LITSG1 had 10-fold higher sensitivity (20 pg of mycelial DNA) than Ltub2 (200 pg) in detection of C. acutatum from pure cultures. The LAMP assay was also tested on asymptomatic greenhouse and field plants, and was shown to have strong potential for detection of C. acutatum in planta.
Field experiments were conducted at the ISU Horticulture Research Station near Gilbert, IA, during the 2012, 2013, and 2014 growing seasons to validate an AFR warning system that had been previously developed and tested in Florida. Five treatments included a factorial combination of two spray timing methods (warning system and calendar-based) and two fungicides (captan and pyraclostrobin), plus a non-sprayed control. The day-neutral strawberry cultivar Tristar was spray-inoculated with C. acutatum conidia at the beginning of the bloom period. In each year, the AFR warning system saved one to two fungicide sprays compared to calendar-based treatments. In general, the warning system-based treatments controlled AFR as well as calendar-based sprays. The results provide evidence that the Florida warning system may be valuable for helping Midwest strawberry growers to reduce fungicide use against AFR.
Finally, I developed a case study entitled “Strawberry anthracnose: managing a hidden menace” to challenge students to help an Iowa strawberry grower decide how to manage AFR with fewer fungicide sprays. When students study this case, they learn how plants become infected and how a disease-warning system uses information about the weather to help growers manage diseases with less reliance on fungicides. The case study was tested by Iowa State University horticulture and plant pathology undergraduate students, and feedback from students and instructors has been integrated to improve the case study.