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The adaptation of pathogenic fungi to plant-specialized metabolites is necessary for their survival and reproduction. The biotrophic fungus Ustilago maydis can cause maize smut and produce tumors in maize (Zea mays), resulting in reduced maize yield and significant economic losses. Qualitative analysis using UPLC-MS/MS revealed that the infection of maize variety B73 with U. maydis resulted in increased levels of phytohormones, phenolics, and alkaloids in maize seedling tissues. However, correlation analysis showed that nearly all compounds in the mechanical damage group were significantly negatively correlated with the shoot growth indexes of maize B73. The correlation coefficients of 2-hydroxy-7-methoxy-1,4-benzoxazin-3-one (HMBOA) and maize B73 shoot length and shoot weight were r = -0.56 (p < 0.01) and r = -0.75 (p < 0.001), respectively. In the inoculation group, these correlations weakened, with the correlation coefficients between HMBOA and maize B73 shoot length and shoot weight being r = 0.02 and r = -0.1, respectively. The correlation coefficients between 6-methoxy-2-benzoxazolinone (MBOA) and the shoot weight were r = -0.73 (p < 0.001) and r = -0.15 in the mechanical damage group and inoculation group, respectively. These findings suggest that increased concentrations of these compounds are more positively associated with mechanical damage than with U. maydis infection. At high concentrations, most of these compounds had an inhibitory effect on U. maydis. This study investigated the ability of U. maydis to regulate various compounds, including phytohormones, phenolic acids, and alkaloids in maize B73, providing evidence that U. maydis has adapted to the specialized metabolites produced by maize B73.

Essential oils (EOs) are often the source of insecticidal substances of high efficiency and low toxicity. From gas chromatograph-mass spectrometer, column chromatography, and nuclear magnetic resonance spectra analyses, twenty terpenes were identified from the EOs of Artemisia nakaii. These comprised mostly monoterpenes (49.01%) and sesquiterpenes (50.76%). The terpenes at the highest concentrations in the EOs of A. nakaii were feropodin (200.46 ± 1.42 μg/ml), (+)-camphor (154.93 ± 9.72 μg/ml), β-selinene (57.73 ± 2.48 μg/ml), and 1,8-cineole (17.99 ± 1.06 μg/ml), calculated using area normalization and external standards. The EOs were tested for biological activity and showed strong fumigant toxicity and significant antifeedant activity against the larvae of Spodoptera litura. Furthermore, the monoterpenes 1,8-cineole and (+)-camphor displayed significant fumigant activity against S. litura, with LC50 values of 7.00 ± 0.85 and 18.16 ± 2.31 μl/L, respectively. Antifeedant activity of the sesquiterpenes feropodin and β-selinene was obvious, with EC50 values of 12.23 ± 2.60 and 10.46 ± 0.27 μg/cm2, respectively. The EOs and β-selinene were also found to inhibit acetylcholinesterase, with IC50 values of 37.75 ± 3.59 and 6.88 ± 0.48 μg/ml, respectively. These results suggest that monoterpenes and sesquiterpenes from the EOs of A. nakaii could potentially be applied as a botanical pesticides in the control of S. litura.

The larch adelgid Adelges laricis laricis Vallot is a specialist insect parasite of Picea koraiensis (Korean spruce) and forms fish scale-like galls that damage the growth of the host plants. Our investigation reveals that both these galls and the fruits (cones) of P. koraiensis display lower concentrations of phytosynthetic pigments and accumulate anthocyanin cyanidin-3-O-glucoside and soluble sugars in the mature stages. Interestingly, high concentrations of 6-benzylaminopurine (BAP) both in the cauline gall tissues and in the larch adelgids themselves (4064.61 ± 167.83 and 3655.42 ± 210.29 ng/g FW, respectively), suggested that this vital phytohormone may be synthesized by the insects to control the development of gall tissues. These results indicate that the galls and cones are sink organs, and the development of gall tissues is possibly regulated by phytohormones in a way similar to that of the growth of cones. The concentrations of phytohormones related to growth [indole-3-acetic acid (IAA), cytokinins (CTK), and gibberellins (GAs)] and defense [salicylic acid (SA)], as well as SA-related phenolics [benzoic acid (BA) and p-hydroxybenzoic acid (pHBA)] in gall tissues were positively correlated with those in cones during the development stage. The levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in the developmental stage of the cones correlates negatively with their concentrations in the gall tissues (R = −0.92, p < 0.001), suggesting that downregulation of ACC might be the reason why galls are not abscised after a year. Our results provide a new perspective on the potential mechanism of the development of cauline galls on P. koraiensis, which are regulated by phytohormones.