Primary metabolites analysis of induced citrus fruit disease resistance upon treatment with oligochitosan, salicylic acid and Pichia membranaefaciens

Abstract The present study investigated the effects of oligochitosan, salicylic acid (SA), and Pichia membranaefaciens on inducing disease resistance against Geotrichum candidum in citrus fruit by using iTRAQ proteomic and physico-chemical analysis. Our finding showed that with pre-treatment of oligochitosan, SA and P. membranaefaciens, disease incidences and lesion diameter infected by G. candidum were both significantly reduced. Proteomics analysis indicated that the differentially expressed proteins (DEPs) were significantly enriched in the pathways of starch and sucrose metabolism, carbon metabolism and amino acid metabolism induced by the three elicitors. Primary metabolites analysis showed that the three elicitors significantly stimulated the accumulation of primary metabolites that closely associated with the defense response such as hexoses, xylose, oxalic acid, proline, glutamate, aspartate, cysteine, etc. Moreover, the marked accumulation of organic acid such as citric acid, α-ketoglutarate, succinic acid, malic acid and fumaric acid which affect the TCA cycle was also observed in three elicitors treated citrus. In conclusion, primary metabolites induced by oligochitosan, SA and P. membranaefaciens behaved as the source of energy and substrates or signaling molecules that directly or indirectly participated in defense responses to against sour rot in citrus fruit.