Stress Response to Climate Change and Postharvest Handling in Two Differently Pigmented Lettuce Genotypes: Impact on Alternaria alternata Invasion and Mycotoxin Production

Abstract

Many species of Alternaria are important pathogens that cause plant diseases and postharvest rots. They lead to significant economic losses in agriculture and affect human and animal health due to their capacity to produce mycotoxins. Therefore, it is necessary to study the factors that can result in an increase in A. alternata. In this study, we discuss the mechanism by which phenol content protects from A. alternata, since the red oak leaf cultivar (containing higher phenols) showed lower invasion than the green one, Batavia, and no mycotoxin production. A climate change scenario enhanced fungal growth in the most susceptible cultivar, green lettuce, likely because elevated temperature and CO₂ levels decrease plant N content, modifying the C/N ratio. Finally, while the abundance of the fungi was maintained at similar levels after keeping the lettuces for four days at 4 °C, this postharvest handling triggered TeA and TEN mycotoxin synthesis, but only in the green cultivar. Therefore, the results demonstrated that invasion and mycotoxin production are cultivar- and temperature-dependent. Further research should be directed to search for resistant cultivars and effective postharvest strategies to reduce the toxicological risk and economic losses related to this fungus, which are expected to increase in a climate change scenario.

Keywords: Alternaria alternata; climate change scenario; defense mechanisms; differently pigmented lettuce; mycotoxins; postharvest handling.

Figure 1

Effect of A. alternata inoculum and environmental conditions on the fresh biomass (A) and water content (B) of two differently-colored fresh lettuces. Light green bars represent green fresh lettuces grown without inoculum (Aa−), dark green bars represent green fresh lettuces grown with inoculum (Aa+), light red bars represent red fresh lettuces grown without inoculum (Aa−), and dark red bars represent red fresh lettuces grown with inoculum (Aa+). (ATC) refers to lettuces grown under the present climatic scenario and (ETC) to those grown under a climate change scenario. Each value represents the mean ± standard error (n = 8). Significant differences (p < 0.05) are indicated by different letters.

Figure 2

Effect of A. alternata inoculum and environmental conditions on the superoxide dismutase (SOD, (A)), ascorbate peroxidase (APX, (B)), monodehydroascorbate reductase (MDHAR, (C)), and dehydroascorbate reductase (DHAR, (D)) activities of two differently-colored fresh lettuces. Light green bars represent green fresh lettuces grown without inoculum (Aa−), dark green bars represent green fresh lettuces grown with inoculum (Aa+), light red bars represent red fresh lettuces grown without inoculum (Aa−), and dark red bars represent red fresh lettuces grown with inoculum (Aa+). (ATC) refers to lettuces grown under the present climatic scenario and (ETC) to those grown under a climate change scenario. Each value represents mean ± standard error (n = 4). Significant differences (p < 0.05) are indicated by different letters.

Figure 3

Effect of A. alternata inoculum and environmental conditions on ascorbate (A) and total phenols (B) of two differently-colored fresh lettuces. Light green bars represent green fresh lettuces grown without inoculum (Aa−), dark green bars represent green fresh lettuces grown with inoculum (Aa+), light red bars represent red fresh lettuces grown without inoculum (Aa−), and dark red bars represent red fresh lettuces grown with inoculum (Aa+). (ATC) refers to lettuces grown under the present climatic scenario and (ETC) to those grown under a climate change scenario. Each value represents mean ± standard error (n = 4). Significant differences (p < 0.05) are indicated by different letters.