الفهرس 
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Abstract
Economic losses due to postharvest decay diseases of plants are widespread throughout the world, and chemical pesticides are the primary means to control these losses. Blue and green moulds disease caused by Penicillium italicum and Penicillium digitatum, are the most economically harmful pathogens in orange fruits.
1- Eleven moulds were isolated from infected orange fruits and leaves showing symptoms of green and blue moulds infection, two were identified as P. digitatum and P. italicum and selected in vitro assays.
2- Twenty -eight yeast isolates were obtained, 16 of them were isolated from orange leaves and 12 from the surface of fruits. All yeasts exhibited high killer activity. Twelve yeasts reduced
22.5 –70% of P. digitatum growth while seven isolates reduced 21.1- 68.5% of P. italicum growth.
The most potent yeast isolates were identified as Candida pseudotropicalis, C. salmanticensis, C. membranifaciens and Pichia guilliermondii.
3- The impact of different stressors on protection efficiency of
C. pseudotropicalis, C. salmanticensis, C. membranifacenis and
P. guilliermondii was evaluated, and were subjected to thermal treatments, pH value, water activity and oxidative stress. Pichia guilliermondii was more resistant to thermal treatments, pH value, water activity and oxidative stress against P. digitatum, while C. salmanticensis was more resistant to thermal treatments, water activity but C. pseudotropicalis was resistant to oxidative stress against P. italicum. The higher concentrations of NaCl and H2O2 reduced the antagonistic activity against
P. digitatum and P. italicum. Pichia guilliermondii and
C. salmanticensis demonstrated a great potential to combat
P. digitatum and P. italicum under a wide range of conditions, the yeast is a promising as an effective and valuable alternative to toxic fungicides.
4- Excluding C. membranifaciens, combination of the biocontrol agents with 2% sodium bicarbonate, 2% CaCl2 or 0.5% chitosan increased the effectiveness of C. pseudotropicalis and
P. guilliermondii against P. digitatum. However, excluding,
C. salmanticensis it decreased their effectiveness against
P. italicum. Excluding C. membranifaciens, application of 0.2% salicylic acid did not increase the effectiveness of the rest of antagonists against P. digitatum. Application of 2% sodium benzoate has additive effect on C. pseudotropicalis against
P. digitatum, also has additive effect on C. pseudotropicalis and
P. guilliermondii against P. italicum. All individual and some of the combined applications of killer yeasts as bio-control agents in vitro had the potential to control postharvest blue and green moulds of orange fruits.
5- Additional studies on the modes of action of these yeast strains showed that all the evaluated yeasts compete for nutrients, produce chitinase enzyme, produce cell-free and volatile antifungal compounds. Only C. pseudotropicalis can produce β- glucanase enzyme as hydrolytic enzyme, also, only
P. guilliermondii produced thermo-stable antifungal compounds, to inhibit the growth of P. digitatum and P. italicum.
A deep understanding of mode of action of the yeasts is essential to develop appropriate formulation and methods of application for controlling postharvest decay of orange fruits.
6- The biocontrol efficacy of wettable powder formulated
P. guilliermondii was evaluated against blue and green moulds in vitro and in vivo. Based on using a protective medium containing sucrose, sodium glutamate and skim milk to improve viability of wettable powder formulated P. guilliermondii using yeast extract peptone dextrose (medium A) and sugar cane molasses base (medium B) as biomass production medium. The viability and biocontrol assays were conducted between the two wettable powder formulated P. guilliermondii produced from two different biomass production medium (A) and medium (B) against P. digitatum and P. italicum in vitro.
7- After 12 months of shelf life at 4˚C of storage, the wettable powder formulated Pichia guilliermondii showed 49 and 32.4 % of the viability and retained biocontrol efficacy 58.7 and 40.4% against P. digitatum, while give 61.7 and 47.3 % against
P. italicum produced from two different biomass production medium (A) and (B), respectively, however, showed 35.6 and
19.7 % of viability , and retained biocontrol efficacy 51.3 and 36.7% against P. digitatum, while 54.1 and 39.8 % against
P. italicum at room temperature (about 37˚C) of storage of the two wettable powder formulated P. guilliermondii produced from two different biomass production medium (A) and medium (B), respectively.
8- The application of two wettable powder formulated
P. guilliermondii produced from two different biomass production medium (A) and medium (B) were evaluated, respectively against green and blue moulds on orange fruits and showed protection efficiency 60-100% and 50- 80 % against P. digitatum and the best treatment method is fogging method, while showed
protection efficiency 70- 100% and 60- 90% against
P. italicum and the best treatment method is spraying method.
9- The results showed the potential value of P. guilliermondii for commercialization and freeze - drying system is a suitable process; moreover, the wettable powder formulated
P. guilliermondii is easy to pack, store and transport, and is a cost-effective process.