Location: Emerging Pests and Pathogens Research
Project Number: 8062-21000-048-021-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2026
End Date: Jul 31, 2027
Objective:
Black dot and silver scurf, caused by fungal pathogens Colletotrichum coccodes and Helminthosporium solani, respectively, are two surface blemish diseases widely prevalent across all potato production regions in the U.S. The blemishes caused by both diseases reduce tuber quality in terms of aesthetics, cause tuber weight loss, thus negatively impacting marketability of tubers especially fresh pack tubers. The research objective is to develop a direct tuber testing protocol for detection of two blemish pathogens of potatoes: C. coccodes and H. solani. A broader goal with this project is to develop an FTA card-based direct tuber testing workflow for surface blemish pathogens that can be used both as a diagnostic and quality assurance tool by agronomists to make commercial crop management decisions.
Approach:
We will develop a cost- and time- efficient duplex qPCR, which can detect both the fungal pathogens simultaneously. This involves identifying optimum conditions (annealing temperatures, primer and probe concentrations) for duplex amplification of the two pathogens and identifying key parameters such as amplification efficiency, linearity, dynamic range, limit of detection, and limit of quantification. Our current FTA-card based pathogen detection workflow involves collecting four core samples per tuber (stolon scar, apical eye, and two eyes on the tuber). We will follow this current workflow to detect both C. coccodes and H. solani from tubers. We will obtain tubers from different sources and categorize them into symptomatic and asymptomatic tubers, based on visual observations. Tuber samples will be tested for both fungal pathogens by pressing the tuber core samples onto FTA cards. Nucleic acid extractions and qPCR protocols we develop will be used to detect both fungal pathogens. To compare this FTA-card based pathogen detection workflow with traditional methods, pathogen isolations will be conducted from these same tubers (from which tuber core samples were obtained for FTA cards) by incubating tubers in a humid chamber for two to three weeks and subsequently observing pathogen signs (microsclerotia of C. coccodes or conidia and conidiophores of H. solani) using a dissecting microscope. In addition to detecting C. coccodes from tubers, efforts will be directed to detect the pathogen from stems and leaves. Black dot infested tubers of at least two cultivars will be grown in a greenhouse in potting soil. As plants near senescence, stem and leaf sections will be taken from each plant, split in half and one half placed on FTA cards and processed as described above. Another half of stem or leaf sections will be plated onto agar medium, incubated for 28 days, and examined for the presence or absence of C. coccodes.