Control of blue and green mold decay of citrus fruit by Pichia membranefaciens and induction of defense responses

Penicillium italicum and Penicillium digitatum are critical pathogens for citrus fruit. In this study, the ability of yeast Pichia membranefaciens to control P. italicum and P. digitatum during storage was examined, and the possible biocontrol mechanisms were discussed. Disease incidence after treatments with autoclaved cell culture or culture filtrate of P. membranefaciens was not effective in preventing the decay and even aggravated the disease degree. Disease incidence and lesion diameter were lower in fruit treated with living yeast cell suspension and washed cell suspension when compared to the respective control. Furthermore, disease control was more efficient when P. membranefaciens was applied. Rapid wound colonization by P. membranefaciens was observed both at 4 and at 20 degrees C. Correspondingly, yeast population on the inoculated wounds increased by more than 4 and 11 folds after 48 h inoculation. In addition. citrus fruit dipped in 1 x 10(8) CFU mL(-1) P. membranefaciens had lower disease incidence, and the fruit dipped or inoculated with P. membranefaciens had increased in phenolic and flavonoid compounds content, peroxidase (POD), polyphenoloxidase (PPO), phenylalanine ammonia-lyase (PAL), chitinase (CHI) and beta-1,3-glucanase activities in citrus fruit peel, all of which were correlated with the onset of induced resistance. This result suggested that competition for nutrients and space on wounds, and induced host defenses appear to contribute to the control mechanism of P. membranefaciens. (C) 2011 Elsevier B.V. All rights reserved.