Effect of CaCl2 on the inhibitory activity of Rhodotorula glutinis against Penicillium italicum on orange fruits.
Arras, G.; Sanna, P.; Astone, V.; Arru, S.;
Italus Hortus Year: 1998 Vol: 5 Issue: 5/6 Pages: 67-70 Ref: 15 ref.
1998
บทคัดย่อ
Effective antagonistic microorganisms, for potential use in the biological control of postharvest diseases, were selected from the surface of tomatoes. The fruits of 30 Citrus spp. were artificially wounded in 4 points around the button. Each wound was inoculated with 20 micro l of a suspension of antagonist and then inoculated with 20 micro l of P. italicum suspension (105 conidia ml- 1). Of 52 yeast strains isolated, Rhodotorula glutinis (strain 21A), R. rubra (isolates 19A and 12A2) and Candida famata [Torulopsis candida] (strain 16L) had strong inhibitory activity, ranging from 80 to 96%, against P. italicum on orange and satsuma fruits. Strain 21A effectively inhibited rot development (by 98.3 and 83.2%), when inoculated at high cell concentrations (108 and 107 cells ml-1, respectively); as the inoculation concentration decreased (106 and 105 cells ml-1), lower inhibition values were observed (44.5 and 15.2%, respectively). Studies indicated that R. glutinis colonizes the surface of the fru
it, the wounds, and P. italicum hyphae, probably competing with the fungus for space and nutrients in the wound site; moreover R. glutinis did not produce antibiotics. Assays were performed to test the possible enhancement of inhibitory activity of strain 21A in combination with CaCl2 using lower cell concentrations. Calcium, at 2%, significantly improved the inhibitory activity of strain 21A inoculated at 107 and 106 cells ml-1, compared to strain 21A alone. At 105 cells ml-1, calcium did not enhance yeast inhibitory activity. Calcium alone was toxic to P. italicum in vitro at 1%, probably by affecting the osmotic balance in the fungal cells, whilst inhibiting fungal pectinolytic enzymes at the wound site.