CONICET | Buscador de Institutos y Recursos Humanos

Without fungicides, conventional potato production is not possible in many regions of Argentina. Fungicides increase production costs and those commonly used are considered environmental and human health hazards. Phosphites are low-toxicity compounds derived from phosphorous acid and combined with different cations, such as potassium or calcium. While phosphites are widely used to protect many crops against Phytophthora pathogens, they have not been adequately tested for control of late blight and other potato diseases. Phosphites promote, not only activation of plant defense mechanisms, but also crop development. We have carried out phytopathological, physiological and biochemical studies when used for potato disease control. Our research demonstrated a number of promising properties associated with these compounds. Calcium or potassium phosphites (CaPhi, KPhi, respectively) applied to seed tubers immediately after cutting at 3 litre ha-1 promoted early emergence, increased stem number and stem diameter, produced earlier tuber initiation and increased the number of tubers per plant in cultivars Bannock Russet, Shepody, Spunta and Kennebec. Ground cover and chlorophyll content were also enhanced by CaPhi or KPhi treatment. In addition to these physiological effects, seed tuber treatment with phosphites increased resistance against Phytophthora infestans, Fusarium solani and Rhizoctonia solani. Protection was high against P. infestans, intermediate against F. solani and low against R. solani for all cultivars tested. Foliar application of CaPhi or KPhi provided protection against P. infestans in all cultivars, although the degree was cultivar specific. Protection was significantly higher at early stages of crop development. Expression of β-1,3-glucanases was induced at different times after treatment but no correlation between β-1,3-glucanases expression and foliar protection level was found. Tubers from plants treated with four foliar applications of CaPhi or KPhi had a smaller colony diameter of P .infestans and a reduction of the lesion area caused by F. solani and Erwinia caratovora. KPhi had a larger effect than CaPhi. The same tubers had an increase in the activities of chitinases, peroxidases, serin protease inhibitors and polygalacturonase inhibiting protein, which is consistent with the expected role of these products in stimulating host resistance. However, these responses were also cultivar and compound dependent. Preliminary studies showed that the periderm thickness of potato tubers increased in tubers from treated plants (KPhi), with different pattern of cell wall proteins. On the other hand, pectin extracts, showed that these are modified by KPhi treatment or F. solani infection. Morpho-histological analysis will contribute to determine if these changes in the cell wall architecture are part of the defense responses induced by KPhi. Phosphite applications caused an increase in total yield in all cultivars except Spunta. Based on these results, it is concluded that KPhi and CaPhi play an important role in potato disease management, in enhancing yield and tuber quality. The response to Phi treatment depends on both the type of Phi and the cultivar analyzed. This is of interest to further utilizations of Phi in integrated crop management strategies.