Barley (Hordeum vulgare L.) occupies an important position among cereal crops and is fourth in the world in terms of harvested area and harvest quantity after wheat, rice and corn (Baik and Ullrich, 2008). Barley is used for animal feed, human nutrition, and malt production and each of these uses is fulfilled by specific barley varieties. Some biotic factors, including nematodes and fungi, can limit barley production. Barley plants are susceptible to diseases caused by Fusarium species, and most species of Fusarium graminearum, F. culmorum and F. avenaceum are reported to cause annual losses of more than $1 billion in wheat and barley production worldwide (Wegulo et al., 2015; Ferrigo et al., 2016).
Fusarium culmorum (W.G. Smith), a soil-borne fungus, is a facultative plant pathogen that causes root/root collar rot, spike blight, and a combination of mycotoxin in cereals (Hestbjerg et al., 2002). Fusarium culmorum is a significant disease of cereals, particularly in arid and semi-arid regions where irrigation is limited or absent and cereals are the predominant crop. This disease causes substantial crop losses (Chekali et al., 2013). Fusarium culmorum causes brown discoloration of roots and root collars, plant lodging, leaf discoloration, spike rot, mycotoxin production, and reduced grain yield and quality (Bouarda et al., 2022). Both spike blight and root rot become evident after flowering. Spike blight requires prolonged wet weather during flowering and grain filling, while root rot appears as white heads following periods of moisture and/or heat stress. Differences in environmental factors and the virulence of different Fusarium species and races are important factors in the differentiation of symptoms (Wang et al., 2015). It has been reported that toxin translocation from the roots can occur, therefore, when environmental conditions are favorable for root and root collar rot diseases, it will cause major crop losses and more attention should be paid to this species (Winter et al., 2013; Scherm et al., 2013).
Pratylenchus, a genus of root lesion nematodes, are parasitic and can cause significant economic losses in crop production. The most important Pratylenchus species that infect cereals are Pratylenchus thornei, Pratylenchus neglectus, Pratylenchus penetrans and Pratylenchus crenatus (Mokrini et al., 2019). Wheat is more susceptible to root lesion nematodes than barley, and P. thornei has a high incidence rate (Thompson et al., 2017). Necrotic areas are subject to secondary infections by other pathogens (Mallaiah et al., 2014). The severity of the disease caused by secondary microorganisms can vary depending on the host plant, the pathogenicity of the pathogens and the prevailing environmental conditions (Doohan et al., 2003). Nordmeyer and Sikora (1983) found significantly higher numbers of Heterodera daverti larvae in alfalfa roots treated with F. avenaceum culture filtrates. Since pectin methyl esterase enzyme was detected in the filtrates of F. avenaceum, they suggested that this enzyme may have enabled H. daverti to penetrate more easily due to its degrading effect on the cell wall of plants. Furthermore, some Fusarium species are classified as entomopathogenic fungi because of the toxic metabolites their generate (Sevim, 2015). Although F. culmorum is known to produce Deoxynivalenol (vomitoxin, DON) and derivatives of DON toxin such as 3-acetyl DON, 15 acetyl DON, Nivalenol, Fumonisin (B1, B2 and B3), ZEA, T-2 Toxin, HT-2 Toxin, Neosolaniol, Diacetoxyscirpenol, Moniliformin, Fusarin C, Wortmannin, Fusaric acid and Sambutoxin metabolites (Pasquali et al., 2016), there is no study on the interaction with root lesion nematodes. However, it has been reported that fungi producing 4,15-diacetylnivalenol and 4,15 diacetoxyscirpenol toxins have toxic effects on plant parasitic nematodes (Nitao et al., 2001).
Nematode-fungus interactions can vary depending on the plant genotype, the degree of virulence specific to the pathogen, the infection process and the secondary metabolites produced by the fungi (Back et al., 2002). Since F. culmorum is a common pathogen in cereal fields together with root lesion nematodes and can produce many secondary metabolites such as toxins and enzymes, it was thought to have the potential to form an antagonistic relationship and the interaction of 12 F. culmorum isolates with P. thornei was investigated in Göze Özdemir et al. (2023). The researchers found that only three F. culmorum isolates (YLVC16, T21 and K17) contributed positively to the reproduction rate of P. thornei, while no antagonistic relationship was found. Only one F. culmorum isolate (YLVC16) was found to contribute to the disease severity of P. thornei. Furthermore, Göze Özdemir (2021) investigated the reaction of 5 different P. thornei isolates on Tarm92 and Burakbey barley varieties and found high reproduction rates in both varieties. Based on these results, our study was designed to determine the interaction between a single P. thornei isolate and culture filtrates obtained from 12 F. culmorum isolates in 4 barley varieties under controlled conditions.