Effects of Thifluzamide Treatment on the Production of Cell Wall Degrading Enzymes in Rhizoctonia solani and Phenylpropane Metabolism in Pear Fruit

Abstract

The study aimed to investigate the effects of thifluzamide (2.67 mg/L) on 'Huangguan' pear fruit rot caused by Rhizoctonia solani during storage, as well as the activities of polygalacturonase (PG), pectin methylesterase (PME), polygalacturonic acid trans-eliminase (PGTE), pectin methyl trans-eliminase (PMTE), xylanase, and pectate lyase (PL) secreted by R. solani. The results showed that thifluzamide treatment significantly inhibited the activities of PG, PME, PGTE, PMTE, xylanase, and PL secreted by R. solani after 3 days in vitro culture, compared to the control. Thifluzamide also increased the activities of phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and 4-coumarate CoA ligase (4CL), and the contents of flavonoids and total phenolic compounds in pear fruit. Furthermore, thifluzamide increased the expression of PcPAL, PcC4H, Pc4CL, Pcβ-1,3-GA, PcLCH, PcF3H, and PcDFR involved in phenylpropanoid metabolism in pear fruit. In conclusion, thifluzamide treatment reduced the infection ability of R. solani by inhibiting the expression of the genes encoding cell wall-degrading enzymes in R. solani. At the same time, it inhibited the activities of cell wall-degrading enzymes induced resistance against R. solani infection in 'Huangguan' pears by promoting phenylpropane metabolism.

Keywords: Rhizoctonia solani; cell wall-degrading enzyme; pear fruit; phenylpropanoid pathway; thifluzamide.

Figure 1

Symptoms of postharvest fruit rot caused by R. solani in ‘Huangguan’ pear. (A) External symptoms; (B) Internal symptoms; (C) Colony on PDA; (D) Sclerotinia morphology on PDA.

Figure 2

Effects of thifluzamide on lesion diameter of the fruit rot. (A) is the therapeutic effect, (B) is the protective effect. Bars indicate standard error (±SE). Letters above columns in the graphs denote significant differences at the level of p < 0.05.

Figure 3

Effects of thifluzamide treatment on the activities of PG, PME, PL, xylanase, PGTE, and PMTE secreted by R. solani. Bars indicate standard error (±SE). Asterisks denote significant differences (p < 0.05).

Figure 4

Effects of postharvest thifluzamide treatment on the activities of PAL, 4CLand C4H in R. solani-inoculated ‘Huangguan’ pears. Bars indicate standard error (±SE). Asterisks denote significant differences (p < 0.05).

Figure 5

Effects of thifluzamide treatment on the expression of PcPAL, PcC4H, Pc4CL, Pcβ-1,3-GA, PcCHI, PcF3H, and PcDFR in R. solani-inoculated ‘Huangguan’ pears. Bars indicate standard error (±SE). Letters above columns in the graphs denote significant differences at the level of p < 0.05.

Figure 6

Total phenolic (A) and flavonoid (B) contents in pear fruit after thifluzamide treatment during storage at 20 ± 1 °C with 75 ± 5% RH. Bars indicate standard error (±SE). Letters above columns in the graphs denote significant differences at the level of p < 0.05.