Impact of Drought on Cereals Infected with Zymoseptoria tritici, the Causal Agent of Leaf Spot Disease of Wheat: An Overview

Zymoseptoria tritici (Desm. Quaedvlieg & Crous), known as the wheat leaf spot disease agent, is a highly virulent fungus that induces blotch and necrosis on leaves. Although it is known to cause severe infections under humid conditions, recent observations suggest that it can also infect wheat leaves under drought and high-temperature conditions, possibly influenced by global warming. Recent findings showed that Z. tritici could easily tolerate various abiotic stresses, including drought, water stress, salinity, and temperature. It has been evident that the fungus can tolerate pesticide stress, as indicated by the increased frequency and number of pesticide applications throughout the growing season. Under stress conditions, the fungi, unlike crop plants, could easily tolerate stress by rapidly modifying gene expression and reducing spore production and mycelial growth without downregulating major biochemical components that play significant roles in pathogenicity and virulence. Z. tritici can accumulate melanin under stress conditions; therefore, an increase in pathogenicity under drought or salinity stress is not unexpected. Recent studies have shown that the pathogenicity of the fungus is increasing, and more virulent, toxin-producing pathogens might emerge in the future. Since drought and high-temperature stresses significantly affect crop plants, the adaptation of pathogenic microorganisms to these conditions could be inevitable if abiotic stress persists. Under these circumstances, the crop loss would be more pronounced. A critical aspect of this process is the assessment of DNA integrity in both wheat and the pathogen under drought stress conditions. The organism that better maintains DNA integrity is considered to exhibit greater drought tolerance. Therefore, our main target should be DNA health when developing or breeding new wheat varieties, considering double- or even multiple-stress conditions. We should finally state that we are very optimistic about generating highly stress-tolerant wheat varieties via metabolomic and proteomic approaches without compromising quality. However, the impact and combination of stress factors are becoming increasingly complex.