Trichoderma sp. is a fungus in the genus Trichoderma, ubiquitous in soils, on plant roots and in decaying plant residues. Due to its competitiveness and mycoparasitic potential against other microorganisms, particular strains of Trichoderma sp. are used in agriculture as biocontrol agents against plant pathogens. However, Trichoderma afroharzianum. has been recently reported as a pathogen causing ear rot disease on maize in Germany, France and Italy leading to massive infections on maize cobs. This raised the question, whether and to what extend Trichoderma can infect other cereal crops than maize and cause disease symptoms and yield losses. To address this question, two varieties of wheat, barley and sorghum millet were grown in the greenhouse and artificially inoculated with T. afroharzianum by both spray and point inoculation at the time of flowering. Disease severity was scored weekly and thousand-kernel weight and colonization rate were determined after harvest. As early as 14 days after inoculation, the first visual symptoms appeared on wheat and barley as tan or brown discoloration of the base of a floret within the spikelets. After spray inoculation, clear discolorations of the entire ear were seen, while point inoculation only showed symptoms at the injection site and above. No visible symptoms were observed on sorghum millet. The colonization rate on wheat and barley grains was significantly increased compared to the control while thousand kernel weights (TKW) were significantly reduced. No differences in colonization rate and TKW compared to the control were observed in sorghum. This is the first report of Trichoderma afroharzianum infecting wheat and barley, causing diseases symptoms and significantly reducing thousand-kernel weights.

Magnaporthe oryzae Triticum (MoT) pathotype is the causal agent of wheat blast, which has caused significant economic losses and threatens wheat production in South America, Asia and Africa. Three bacterial strains from rice and wheat seeds (B. subtilis BTS-3, B. velezensis BTS-4, and B. velezensis BTLK6A) were used to explore the antifungal effects of volatile organic compounds (VOCs) of Bacillus spp. as a potential biocontrol mechanism against MoT. All bacterial treatments significantly inhibited both mycelial growth and sporulation of MoT in vitro. We found that this inhibition was caused by Bacillus VOCs in a dose-dependent manner. In addition, biocontrol assays using detached wheat leaves infected with MoT showed reduced leaf lesions and sporulation compared to the untreated control. VOCs from B. velezensis BTS-4 alone or a consortium (mixture of B. subtilis BTS-3, B. velezensis BTS-4, and B. velezensis BTLK6A) treatments consistently suppressed MoT in vitro and in vivo. Compared to the untreated control, VOCs from BTS-4 and Bacillus consortium reduced MoT lesions in vivo by 85% and 81.25%, respectively. A total of thirty-nine VOCs (from 9 different VOC groups) from 4 Bacillus treatments were identified by gas chromatography-mass spectrometry (GC-MS), of which 11 were produced in all Bacillus treatments. Alcohols, fatty acids, ketones, aldehydes, and S-containing compounds were detected in all four bacterial treatments. In vitro assays using pure VOCs revealed that hexanoic acid, 2-methylbutanoic acid, and phenylethyl alcohol are potential VOCs emitted by Bacillus spp. that are suppressive for MoT. The minimum inhibitory concentrations for MoT sporulation were 250 mM for phenylethyl alcohol and 500 mM for 2-methylbutanoic acid and hexanoic acid. Therefore, our results indicate that VOCs from Bacillus spp. are effective compounds to suppress the growth and sporulation of MoT. Understanding the MoT sporulation reduction mechanisms by Bacillus VOCs may provide novel options to manage the further spread of wheat blast by spores.

Fusarium culmorum is a major pathogen of grain crops. Infected plants accumulate deoxynivalenol (DON), 3-acetyl-deoxynivalenol (3-ADON), or nivalenol (NIV), which are mycotoxins of the trichothecene B group. These toxins are also produced by F. graminearum species complex. New trichothecenes structurally similar to trichothecenes B but lacking the carbonyl group on C-8, designated NX toxins, were recently discovered in atypical isolates of F. graminearum from North America. Only these isolates and a few strains of a yet to be characterized Fusarium species from South Africa are known to produce NX-2 and other NX toxins. Here we report that among 20 F. culmorum strains isolated from maize, wheat, and oat in Europe and Asia over a period of 70 years, 18 strains produced NX-2 simultaneously with 3-ADON and DON or NIV. Rice cultures of strains producing 3-ADON accumulated NX-2 in amounts corresponding to 2-8% of 3-ADON (1.2 - 36 mg/kg). A strain producing NIV accumulated NX-2 and NIV at comparable amounts (13.6 and 10.3 mg/kg, respectively). In F. graminearum, producers of NX-2 possess a special variant of cytochrome P450 monooxygenase encoded by TRI1 that is unable to oxidize C-8. In F. culmorum, producers and nonproducers of NX-2 possess identical TRI1; the reason for the production of NX-2 is unknown. Our results indicate that production of NX-2 simultaneously with trichothecenes B is a common feature of F. culmorum.