COMPETITION FOR NUTRIENTS AS A MECHANISM OF ANTAGONIST ACTION OF TWO YEASTS AGAINST Penicillium expansum IN PEARS

LUTZ, C.; LOPES, C.A.; SOSA, C.; SANGORRIN, M.P.

Congreso; SAMIGE; 2012

Different mechanisms to explain the antagonist capacity of yeasts against pathogens have been described. The yeasts Pichia membranifaciens NPCC 1250 and Cryptoccocus victoriae NPCC 1263 were isolated from pears and selected for their antagonist activity against blue mold caused by Penicillium expansum in stored pears. Competition for nutrients as a potential mechanism involved in the biocontrol activity of these two yeasts was investigated in both in vitro and in vivo assays. In a first step we evaluated the ability of the two yeasts and the pathogen to assimilate 26 different nutrient sources including five sugars, 17 amino acids, three inorganic nitrogen and one iron sources. Microorganisms growth was individually evaluated in microplates containing sterile pear juice (85% v/v in water) supplemented with the respective compounds. Plates were incubated at 20°C for 80 hs, and growth was evaluated by DO measuring at 630 nm. Aspartic acid and NO3NH4 stimulated the growth of the three microorganisms. Glutamic acid, arginin and FeCl stimulated the growth of P. expansum and P. membranifaciens, while glycine, serine and FeCl stimulated the growth of P. expansum and C. victoriae. Nutrients stimulating simultaneously the growth of both microorganisms in each yeast-pathogen combination were selected to be evaluated in in situ assays on pears. Pear wounds were inoculated with each couple yeast-P. expansum with or without the respective nutrient. Both decay incidence and lesion diameters were evaluated after 60 days at -1/0ºC. P. membranifaciens and C. victoriae without addition of nutrients were very protective against P. expansum (88% and 77% protection, respectively). The addition of aspartic acid and NO3NH4 significantly reduced the biocontrol capacity of P. membranifaciens (0% and 20% protection, respectively), while glycine, aspartic and NO3NH4 significantly reduced the biocontrol capacity of C. victoriae (0% and 10% protection, respectively). The effect of NO3NH4 in the lesion diameters was also evident for the two yeasts. Due to the interesting results found with the addition of NO3NH4, we tested the effect in vitro of this compound on pathogen conidia germination. Inhibition of conidial germination caused by C. victoriae was partially suppressed in the presence of NO3NH4 (competition at germination time), while no effect was observed with P. membranifaciens (competition after germination). Overall, our data provide evidence about the fact that competition for nutrients would be one of the mechanisms involved in the biocontrol activity of P. membranifaciens and C. victoriae against postharvest P. expansum on stored pears.