Phosphites in potato disease management and their role in sustainable improvement of yield and quality

LOBATO MC; LASSO M J; OLIVIERI FP; MACHINANDIARENA M; FELDMAN ML; DALEO GR; CALDIZ DO; ANDREU AB

Christchurch. New Zealand.

Congreso; 7th World Potato Congress,Christchurch; 2009

Without fungicides, conventional potato production is not possible in many parts of the Argentina.  Fungicides increases 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 on Phytophthora pathogens of many crops, they have not been adequately tested for control of late blight and others potato diseases. Phosphites promotes, not only activation of plant defense mechanisms plants but also favour 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 this compoust. Calcium or potassium phosphites (CaPhi, KPhi, respectively) at 3 litre ha-1  applied to seed tubers immediately after cutting promoted early emergence, increased stem number and stem diameter, early tuber initiation and increased tuber number 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 phosphite 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 with CaPhi or KPhi provided protection against P. infestans in all cultivars, although the degree was cultivar specific. Protection was significantly bigger in early stages of crop. Expression of â-1,3-glucanases was induced at different times after treatment but no correlation between â-1,3-glucanases expression and foliar protection level was found.   Tubers from plants treated with four foliar applications of CaPhi or KPhi had smaller colony diameter of P .infestans and a diminishing the lesion area of F. solani and Erwinia caratovora. KPhi had a larger effect than CaPhi. The same tubers had an increase in the activities chitinases, peroxidase, serin proteases inhibitor and polygalacturonase inhibiting protein, which is consistent with the expected role of these products in stimulating host resistance. Although, this was also cultivar and compound dependent. Preliminary studies showed that the periderm thickness of potato tubers increased in tubers from treated plants (KPhi), with differences 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 know if these changes in the cell wall architecture are part of the defense responses induced by KPhi. Phosphite application 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.