Expression of class I chitinase and β-1,3-glucanase genes and postharvest fungal decay control of table grapes by high CO2 pretreatment

The effect of pretreatment with 20% CO2 plus 20% O2 for 3 days was studied with regard to its effectiveness on natural postharvest decay control and its possible induction of specific PR genes in table grapes. Full-length cDNAs encoding a class I chitinase (Vcchit1b) and β-1,3-glucanase (Vcgns1) were isolated from table grapes (Vitis vinifera L. cv. ‘Cardinal’). Our results indicate that this short-term high CO2 treatment had a residual effect and significantly reduced decay incidence of table grapes during low temperature storage and upon transfer to 20 °C. Our results indicate that during low temperature storage the expression pattern differed between the two tested PR genes. So, while the abundance of Vcgns1 transcript increased sharply at the beginning of storage at 0 °C, the increase in Vcchit1b mRNA levels was paralleled by the change in total decay. High CO2 pretreatment restrained the up-regulation of Vcgns1 gene expression and delayed the accumulation of Vcchit1b transcript as compared with non-treated grapes. Upon transfer to 20 °C after 33 days of cold storage, when attainment of maximum total decay was observed, there was a sharp increase in the accumulation of Vcchit1b mRNA in both treated and non-treated grapes, which was higher in the non-treated ones. Our results point out that the expression of class I chitinase and β-1,3-glucanase genes is not enhanced in CO2-treated grapes which control total fungal decay. These results suggest, then, that the efficacy of high CO2 pretreatment in reducing total fungal decay is not mediated by induction of the above-mentioned PR genes.