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Aureobasidium pullulans suppression of green mould (Penicillium digitatum) development in mandarin var. ‘Kinnow’ through multiple modes of action

Nimal Adikaram: National Institute of Fundamental Studies

<div>The objective of the study was to develop an effective biocontrol agent with multiple modes of action against green mould (<em>Penicillium digitatum</em>) in mandarin (<em>Citrus </em><em>reticulata</em> var. `Kinnow’). <em>Aureobasidium pullulans</em> was isolated from the mandarin fruit surface. Freshly harvested mandarins were treated with a cell suspension of different <em>A. pullulans</em> isolates and two days later, the treated and control fruits were inoculated with <em>P. digitatum</em>. Treatment with <em>A. pullulans</em> Isolate Y3 significantly (p<0.05) lowered green mould incidence compared to controls and other <em>A. pullulans </em>isolates tested. Dual culture of <em>P. digitatum</em> with Y3 on PDA slowed down colony growth indicating direct inhibitory activity of Y3. SEM studies revealed that Y3 cells had become embedded in the cuticle within 2-3 days of treatment. The cuticle showed signs of digestion, depressions underneath the yeast cells and shredding-off probably due to internal pressure exerted by embedded yeast cells. Some yeast cells proliferated producing buds and others made occasional physical contact with conidia of <em>P. digitatum</em>. Treated fruit peel displayed slightly greater antifungal activity than controls on TLC bioassay. Y3 was shown to produce non-specific esterases in cutin-amended medium. Yeast cells embedded might have physically obstructed <em>P. digitatum </em>entry and competed for space; cutin monomers produced by cutinase action triggered fruit resistance contributing to lowered green mould incidence.</div>