Effect of chitosan-based natural product (chitoplant) on the major postharvest diseases and the defence related enzymes in avocado

Avocado is susceptible to various pathogenic fungi that penetrate the mesocarp tissue through the fruit skin, stem-end button or wounded pedicel of unripe fruit. The aim of this study was to determine the eliciting effect of the presence of chitosan an active ingredients in chitoplant either as stand-alone or in combination with other fungicides in artificially inoculated avocado 'Fuerte'. In this study, concentrations of chitoplant solution (0.2-0.05% w/v) alone or its combination with citral, thyme oil and prochloraz were screened against Colletotrichum gloeosporioides and Lasiodiplodia theobromae. The optimal concentration of 0.2% w/v chitoplant was applied in vivo as a stand-alone or in combination with 50% prochloraz as a dip application in a curative and preventative method. The fruit was incubated for 6 days, 8 days and 14 days (cold storage) + 3 days shelf life and later assessed for the incidence, severity and its effect on the defence-related enzymes. The result showed that 50% prochloraz + 0.2% w/v chitoplant completely inhibited the radial mycelia growth of C. gloeosporioides and L. theobromae compared to other treatment. Prochloraz alone and (50% prochloraz + 0.2% w/v chitoplant) significantly reduced anthracnose and stem-end rot incidence and severity in preventatively treated fruit. However, the incorporation of half strength prochloraz enhanced total phenolic content as well as the defence enzymes with an increase in PAL (phenylalanine ammonia-lyase) and pathogenesis-related (chitinase and β-1,3-glucanase) enzymes activities in anthracnose and stem-end rot treated fruit compared to the untreated control. The combination of chitoplant with half strength prochloraz could be considered a new approach to extend fruit shelf life and retain the quality of avocado during storage.