Infection severity of Colletotrichum coccodes in Russet Burbank potatoes with respect to environmental potassium

Black Dot (Colletotrichum coccodes) is a soil borne fungal disease that ruins potatoes before and after harvest. Infections initiate on plant material below ground, and control is dependent upon systemic delivery of fungicides. Potassium is an essential mineral that has been shown to be important in physiological processes such as plant defense. Our objective was to assess the affect of potassium concentrations in the plant's environment with disease severity. Russet Burbank potatoes were grown hydroponically and artificially infected with spores of C. coccodes in solutions of varying levels of Potassium (0, 10, 80, 160 mg K L-1). Infection was assessed by plating roots on modified potato dextrose agar (mPDA) and through quantitative RT-PCR. Using specific primers, standard curves were generated from fungal and potato DNA dilutions, and these in turn were used to generate infection coefficients (IC) for total tissue DNA. The IC from different treatments were compared. C. coccodes was present in all of the samples. Symptoms were visible on the tips of roots, on root hairs and on the lowest stem portions. Greatest infection occurred in treatments of 0 and 10 mg, pathogen was visibly reduced in the 160 Mg K treatment; although, at this concentration leaves appeared slightly chloritic, suggesting a possible loss of fitness. This study demonstrated that the amount of available soil K can affect plant health through disease susceptibility.