The effects of chemical inducers on postharvest control of botrytis cinerea (Pers.:Fr.) and penicillium expansum (Link.) on apple fruit

In this thesis, the effects of resistance inducing chemicals including chitosan, methyl jasmonate, salicylic acid and silicon against Botrytis cinerea (Pers.: Fr.) and Penicillium expansum (Link.), which causes of the most important postharvest diseases in apples in vitro and in vivo were investigated. In the study, the determination of the effects of chemicals on mycelial growth of pathogens in vitro and the effects on disease development on Golden Delicious apples, the activations of phenylalanine ammonia lyase (PAL), scopoletin, scoparon, lignin, patulin formation as an important mycotoxin and the fruit quality were aimed. In vitro tests, to determine the effects of the B. cinerea and P. expansum on mycelial growth in Potato Dextrose Agar (PDA), chitosan and silicon concentrations including 0.025%, 0.05%, 0.075%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, methyl jasmonate and salicylic acid concentrations including 250, 500, 750, 1000, 1500, 2000, 2500 and 3000 ppm were tested. The applications of resistance inducing chemicals reduced the mycelial growth of B. cinerea and P. expansum at increasing concentrations. In the mean time, the concentrations of chitosan 0.2%, 0.25%, 0.3% and salicylic acid 2500, 3000 ppm prevented the mycelial growth completely. For determination of the the resistance inducing chemicals on B. cinerea and P. expansum in vivo, the chitosan doses including 0.1%, 0.2%, 0.3%, methyl jasmonate and salicylic acid doses including 1000 ppm, 1500 ppm and 2000 ppm, silicon doses including 0.25%, 0.5%, 1% and 1000 ppm dose of thiabendazole were applied to apple fruit by dipping method. After the pathogen inoculations, the fruits were stored at 2-4°C in cold storage for 75 days. At the end of the experiment, the decay rate of fruits (%) was evaluated. It was observed that the resistance inducing chemicals decreased the decay rate of inoculated fruits with both pathogen. Although silicon was the most effective against rot caused by B. cinerea, high phytotoxicity was determined at doses of 0.5% and 1%. Therefore, chitosan is the most effective chemical that did not cause phytotoxicity against the decay caused by B. cinerea. Similarly, chitosan was the most effective treatment against rot caused by P. expansum. Resistance inducing chemical applications significantly increased PAL activity in fruit compared to control. Although the increases due to dose applications were in the same statistical group, the highest increase was determined in 0.3% of chitosan against B. cinerea and 2000 ppm of salicylic acid against P. expansum. When the phytoalexin activity against the two pathogens in the fruit was evaluated; It was found that the scopoletin was synthesized by all resistance induced chemicals. All chitosan doses were the most effective applications to increase scopoletin for both pathogen. In addition, while the application of chitosan for the two pathogens promoted the increase in scoparone, no increase in scoparone in methyl jasmonate and salicylic acid was observed. At the end of the experiment, the increase in lignin content of fruits was determined. The most lignin production against both pathogens was observed in silicon applications. All applications were effective against patulin formation caused by P. expansum while all doses of chitosan prevented the mycotoxin formation. When the quality paramteres of fruit were evaluated at the end of the storage period, among the resistance inducing chemicals all doses of methyl jasmonate and salicylic acid were the most effective on maintaining firmness of the fruit for the both pathogen. However, the amount of total solube solids and the amount of titratable acid decreased, but no significant effect on the pH of the fruit was detected. As a result, the application resistance inducing chemicals are considered as effective on preventing postharvest diseases in apple fruits.