Phosphite compounds reduce disease severity in potato seed tubers and foliage

Abstract

Phosphites (Phi) are alkali metal salts of phosphorous acid, with the ability to protect plants against different pathogens. In this research, the effect of Phi applied to potato plants on severity of three important potato diseases in Argentina was assessed. Seed tubers and foliage of potato cvs Shepody and Kennebec were treated with Phi to assess effects on resistance against Phytophthora infestans, Fusarium solani and Rhizoctonia solani. Protection resulting from Phi treatment in seed tubers was high against P. infestans, intermediate against F. solani, and low against R. solani. In addition, seed tubers treated with calcium or potassium phosphites (CaPhi and KPhi, respectively) at 1% of commercial product emerged earlier than untreated ones. When Phi were foliarly applied two or four times at different doses, high levels of protection against P. infestans were achieved in both cultivars. Higher protection was observed in Kennebec when CaPhi was applied, while in Shepody this was true for KPhi. 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. On the other hand, Phi positive protection effects did not produce negative effects in plant growth. Leaves from CaPhi-treated plants showed a darker green colour than leaves from control plants; also an increase in Rubisco protein and a delay in crop senescence was observed.

Antimicrobial activity of phosphites against different potato pathogens

“…Highest protection levels were obtained against P. infestans, while the protection levels against the fungi F. solani and R. solani were intermediate and very low, respectively. However, in all cases, protection was equal or higher when KPhi was applied rather than CaPhi (LOBATO et al 2008a), contrary to in vitro results. This apparent contradiction can be explained by considering that the effect of acidification of the media in in vitro assays was stronger when CaPhi was added, as mentioned above.…”

“…Moreover, the defence responses were cultivar, pathogen and compound dependent (LOBATO et al 2008a). The different levels of induced resistance obtained against the pathogens studied could be explained, in part, by considering a direct action of Phi on each pathogen.…”

“…Phosphites, in general, are environmentally harmless compounds (GUEST and GRANT 1991) that can stimulate plant defence responses and also reduce disease severity in different plants (PANICKER and GANGADHARAN 1999;BÉCOT et al 2000;REUVENI et al 2003;JOHNSON et al 2004;LOBATO et al 2008a), representing a potential alternative to be used in an integrated crop management programme.…”

“…On the other hand, foliar applications of CaPhi or KPhi provided protection against P. infestans in all cultivars analysed, although protection degree was cultivar-specific (ANDREU et al 2006;LOBATO et al 2008b). Tubers from plants treated in foliage showed a smaller colony diameter of P. infestans and a reduction of the lesion area caused by F. solani and Erwinia carotovora when artificially infected; KPhi had a stronger effect than CaPhi (LOBATO et al 2008a). …”

“…Sporulation and germination of Phytophthora species have also been shown to be suppressed by these biopesticides (COHEN and COFFEY 1986;GARBELOTTO et al 2009). Indirect effects of phosphites are thought to be the activation of plant defence responses (GUEST and BOMPEIX 1990;ANDREU et al 2006;LOBATO et al 2008a).…”