Global crop production is essential for providing energy and nutrients to humans, but agricultural systems contribute substantially to environmental issues, making it crucial to find sustainable methods for crop production. In this study, we conducted extensive field monitoring of two rice paddy fields in Kyoto Prefecture, Japan, where a rice variety, Hinohikari, was cultivated to investigate how ecological communities influence rice growth and yields under two contrasting farming practices: conventional farming and no-fertilizer farming. We had three objectives: (1) to monitor rice growth and ecological dynamics to create a comprehensive ecological time series using quantitative environmental DNA metabarcoding and complementary monitoring methods, (2) to identify ecological variables that causally affect rice performance using nonlinear time series analysis, and (3) to examine the effects of the two farming practices on ecological variables and rice performance. As expected, the no-fertilizer paddy field showed lower rice growth and yields but still produced 40-50 % of the yields of the conventional field. Ecological monitoring revealed contrasting ecological communities between the two fields, particularly among plant species on the paddy ridges and microbial taxa. Twenty-five taxa had statistically clear causal influences on rice performance. While the per-abundance influences of the causal taxa were largely similar in both paddy fields, their abundances were different, contributing to the differences in the overall effects of these taxa on the rice performance. These findings suggest that the abundance of causal taxa, along with nutrient conditions, may have driven differences in rice growth between the two paddy fields.

Leptocorisa chinensis Dallas (Hemiptera: Alydidae) is a serious pest responsible for causing pecky rice grains in paddy fields. When disturbed, an adult L. chinensis emit a pungent odour-an alarm pheromone-that induces escape behaviour in conspecifics. (E)-2-Octenal (E-2-OAL) is a major component of this odour and is responsible for triggering the escape response. We hypothesized that the synthetic form of E-2-OAL could be used to control L. chinensis adults. This study aimed to reduce the incidence of pecky rice grains in paddy fields by deploying E-2-OAL dispensers. To determine an effective concentration for field application, outdoor experiments were conducted. A 1% emulsified E-2-OAL solution placed 30 cm upwind of caged adults L. chinensis effectively elicited escape behaviour. Field trials were conducted during the milk-ripe stage of rice plants in paddy fields in two regions in Japan. In a paddy field, a plot treated with 1% emulsified E-2-OAL was established, with a control plot of the same size located 30 m away in the same field. In both regions, the E-2-OAL-treated plots showed a significant reduction in pecky rice grains attributed to L. chinensis compared to the control plots. The total number of rice grains harvested did not differ significantly between treated and control plots. These results suggest that applying E-2-OAL in paddy fields can effectively alter L. chinensis behaviour, reducing pecky rice grain damage without negatively impacting rice yield.

Spider mites (Tetranychus urticae) are a major threat to economically important crops. Here, we investigated the potential of tetranins, in particular Tet3 and Tet4, as T. urticae protein-type elicitors that stimulate plant defense. Truncated Tet3 and Tet4 proteins showed efficacy in activating the defense gene pathogenesis-related 1 (PR1) and inducing phytohormone production in leaves of Phaseolus vulgaris. In particular, Tet3 caused a drastically higher Ca2+ influx in leaves, but a lower reactive oxygen species (ROS) generation compared to other tetranins, whereas Tet4 caused a low Ca2+ influx and a high ROS generation in the host plants. Such specific and non-specific elicitor activities were examined by knockdown of Tet3 and Tet4 expressions in mites, confirming their respective activities and in particular showing that they function additively or synergistically to induce defense responses. Of great interest is the fact that Tet3 and Tet4 expression levels were higher in mites on their preferred host, P. vulgaris, compared to the levels in mites on the less-preferred host, Cucumis sativus, whereas Tet1 and Tet2 were constitutively expressed regardless of their host. Furthermore, mites that had been hosted on C. sativus induced lower levels of PR1 expression, Ca2+ influx and ROS generation, i.e., Tet3- and Tet4-responsive defense responses, in both P. vulgaris and C. sativus leaves compared to the levels induced by mites that had been hosted on P. vulgaris. Taken together, these findings show that selected tetranins respond to variable host cues that may optimize herbivore fitness by altering the anti-mite response of the host plant.

Interplant interactions mediated by plant-emitted volatile organic compounds (VOCs) occur with heterospecific neighboring plants, making VOC-emitting companion plants a practical tool for pest management. In this study, we investigated the cocultivation of common bean (Phaseolus vulgaris L.) with bush basil (Ocimum basilicum L. var. minimum), which induced the expression of defense-related genes, such as pathogenesis-related protein 1, via salicylate signaling in the leaves. This coculture enhanced the defense capacity of P. vulgaris against spider mites (Tetranychus urticae) and field herbivores. Eugenol, one of the major VOCs emitted by bush basil plants, was likely responsible for conferring the antiherbivore activity on the receiver plants. Furthermore, bush basil VOCs were able to prime P. vulgaris plants to attract Phytoseiulus persimilis, a predatory mite of T. urticae, in response to T. urticae attack. Our results suggest a practical use of bush basil as companion plants in organic crop production.

We studied plant–plant communication in a system that included eggplants, herbivores as prey, and the omnivorous mirid Nesidiocoris tenuis . When uninfested eggplants were exposed to volatiles from conspecific plants infested by N. tenuis adults, the amounts of jasmonic acid (JA) and salicylic acid (SA) in the exposed plants remained to be similar to those in uninfested eggplants that were exposed to volatiles from uninfested conspecific plants (control eggplants). Subsequent artificial damage to the leaves of either the exposed or control eggplants using scissors led to a significant increase in JA content in the leaves. Furthermore, following the damage, the JA content in the exposed plants was significantly higher than in the control plants. In contrast, the amount of SA in the eggplants was not affected by either exposure or subsequent artificial damage. The fecundity of Kanzawa spider mites on the leaf disks of the exposed plants was significantly lower than that on the leaf disks of the control plants. The weight gain of 2nd stadium Spodoptera litura larvae on the exposed plants was significantly lower than on the control plants. However, the survival and fecundity of N. tenuis females on both exposed and control plants were not significantly different. This study demonstrates the potential variations in the tolerance of herbivorous and omnivorous arthropods to plant defenses in response to exposure to plant volatiles.

The zoophytophagous mirid predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is used in the augmentative biological control of Thrips palmi Karny (Thysanoptera: Thripidae), a fruit and vegetable pest in protected culture in Japan. N. tenuis can be maintained on certain plants without arthropod prey. Although such plant species may be useful as banker plants, their attractiveness to N. tenuis is underresearched. We investigated the behavioral responses of N. tenuis to (1) uninfested and conspecific-infested banker plants, Verbena × hybrida (verbena), Scaevola aemula (scaevola), Cleome hassleriana (cleome), and Lobularia maritima (sweet alyssum) and (2) conspecific-infested banker plants and T. palmi -infested eggplants, using a Y-tube olfactometer. Female N. tenuis preferred the volatiles emitted by (1) uninfested verbena over clean air but showed no preference for those emitted by the other uninfested banker plants, and (2) conspecific-infested verbena over clean air but showed no preference for those emitted by conspecific-infested scaevola over clean air. The attractiveness of the volatiles of T. palmi -infested eggplants for N. tenuis was not significantly different from those of N. tenuis -infested verbena and scaevola. As both uninfested and conspecific-infested verbena attracted female N. tenuis , this species is a promising banker plant. Chemical analyses and principal coordinate analyses of the volatiles from the headspaces of uninfested and N. tenuis -infested verbena and scaevola showed that 1-octen-3-ol, ( E )-β-caryophyllene, and ( E )-4,8-dimethyl-1,3,7-nonatriene distinguished these plant species and are candidate volatile N. tenuis attractants.

Menthyl ester of valine (MV) has been developed as a plant defense potentiator to induce pest resistance in crops. In this study, we attempted to establish MV hydrochloride (MV-HCl) in lettuce and tomato crops. When MV-HCl solutions were used to treat soil or leaves of potted tomato and lettuce plants, 1 µM MV-HCl solution applied to potted plant soil was most effective in increasing the transcript level of defense genes such as pathogenesis-related 1 (PR1). As a result, leaf damage caused by Spodoptera litura and oviposition by Tetranychus urticae were significantly reduced. In addition, MV-HCl-treated plants showed an increased ability to attract Phytoseiulus persimilis, a predatory mite of T. urticae, when they were attacked by T. urticae. Overall, our findings showed that MV-HCl is likely to be effective in promoting not only direct defense by activating defense genes, but also indirect defense mediated by herbivore-induced plant volatiles. Moreover, based on the results of the sustainability of PR1 expression in tomato plants treated with MV-HCl every 3 days, field trials were conducted and showed a 70% reduction in natural leaf damage. Our results suggest a practical approach to promoting organic tomato and lettuce production using this new plant defense potentiator.

We previously reported that the presence of pyridalyl, a selective insecticide, in aqueous honey (50% v/v) negatively affects the survival of diamondback moth (Plutella xylostella: DBM) adults. However, it remains unclear whether toxicity of pyridalyl in aqueous honey affects the fecundity of adult female DBMs. We analysed the survival and fecundity of adult DBM under the water, honey or honey + pyridalyl conditions in glass tubes containing Japanese mustard spinach (Brassica rapa: Komatsuna) leaves for 10 days. The survival of adults under the honey (50% v/v) and honey + pyridalyl (100-fold dilution) conditions was significantly higher and lower, respectively, than under the water condition during the experimental period. The number of eggs laid by DBM females each day (fecundity) under the water condition was significantly lower than that under the honey condition throughout the experimental period, except on day 1. In contrast, the numbers under the water and honey + pyridalyl conditions were not significantly different, except on day 2 (the honey + pyridalyl condition was significantly lower). To study the effects of plants grown in pots on the survival and fecundity of DBM females, we conducted experiments using acrylic cages containing potted komatsuna plants. The survival trends under the honey, and honey + pyridalyl conditions in the cages were similar to those in the glass tubes. Fecundity was evaluated based on the total number of subsequent generations (DBM larvae and pupae) on day 10. The numbers were significantly higher in the honey condition than in the water condition. In contrast, the number in the honey + pyridalyl condition was not significantly different from that in the water condition. Given our previous findings that the longevity and fecundity of Cotesia vestalis, an effective natural enemy of DBM larvae, remained unaffected by the presence of pyridalyl in honey as a food supply, our research suggests that introducing devices providing honey infused with pyridalyl in greenhouses as a nutritional source for C. vestalis could be an effective biological control strategy for managing DBM populations within greenhouse environments.

Volatiles from herbivore-infested plants function as a chemical warning of future herbivory for neighboring plants. (Z)-3-Hexenol emitted from tomato plants infested by common cutworms is taken up by uninfested plants and converted to (Z)-3-hexenyl β-vicianoside (HexVic). Here we show that a wild tomato species (Solanum pennellii) shows limited HexVic accumulation compared to a domesticated tomato species (Solanum lycopersicum) after (Z)-3-hexenol exposure. Common cutworms grow better on an introgression line containing an S. pennellii chromosome 11 segment that impairs HexVic accumulation, suggesting that (Z)-3-hexenol diglycosylation is involved in the defense of tomato against herbivory. We finally reveal that HexVic accumulation is genetically associated with a uridine diphosphate-glycosyltransferase (UGT) gene cluster that harbors UGT91R1 on chromosome 11. Biochemical and transgenic analyses of UGT91R1 show that it preferentially catalyzes (Z)-3-hexenyl β-D-glucopyranoside arabinosylation to produce HexVic in planta.

BACKGROUND Booklice Liposcelis bostrychophila are frequently found almost everywhere, including private houses and cleanrooms of factories and institutes. They often cause serious hygienic as well as agricultural problems, but a useful trap has not been developed so far. Therefore, an effective way to monitor and capture booklice is required. RESULTS We here identified a new attractant, 2,3,5,6-tetramethylpyrazine (TMP), which efficiently captured booklice in combination with UV light. When booklice placed at both right and left edges of an assay tray were exposed to light stimulus from the center, test insects gathered at the center. The attraction was stronger with shorter wavelengths than longer ones: 365-nm ultraviolet light showed the strongest attraction of four tested light wavelengths. We found that cocoa powder attracted booklice weakly but significantly under total darkness. Furthermore, the cocoa smell was confirmed to enhance the attraction to light at all tested wavelengths irrespective of the difference between two brands of cocoa powders. Gas chromatography-mass spectrometry indicated that both cocoa products contain TMP as a major odor compound. Exposure of booklice to TMP significantly enhanced the attraction to UV light: the combined use with TMP almost doubled the attraction compared to the light only. In contrast, TMP homologs, pyrazine and dimethylpyrazines, showed strong repellent activities under UV-light exposure. CONCLUSION TMP enhanced the UV light attraction for booklice while pyrazine and dimethylpyrazines diminished it. Use of these attractant and repellent pyrazine derivatives together with UV-light would enable us to develop a practical new way to monitor and capture booklice. This article is protected by copyright. All rights reserved.

Oviposition by aphidophagous predators is triggered by semiochemicals emitted from aphids and host plants, such as volatile chemicals from host plants infested by aphids and from honeydew and aphid alarm pheromones. Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) is a common, widely distributed aphidophagous predator that is used as a biological agent to control aphids in greenhouses. Previous work showed that a volatile chemical emitted from honeydew produced by Aphis gossypii Glover (Hemiptera: Aphididae) on eggplants (Solanum melongena L.) attracted adult female A. aphidimyza, and identified it as phenylacetaldehyde. There are no known oviposition stimulants for A. aphidimyza females and the function of herbivory-induced plant volatiles (HIPVs) produced by eggplants infested by A. gossypii is not clear. Therefore, this study investigated the effects of HIPVs from eggplants induced by A. gossypii infestation and volatile chemicals in honeydew produced by A. gossypii on the oviposition of A. aphidimyza in bioassay cages. We found that HIPVs from A. gossypii-infested eggplants-induced oviposition. Moreover, using gas chromatography coupled with mass spectrometry, we identified 6-methyl-5-hepten-2-one, nonanal, and decanal as the HIPVs from eggplants. A mixture of these three compounds-induced oviposition of significantly more eggs than the control, but fewer eggs than the eggplant–aphid complex. Honeydew did not induce oviposition of significantly more eggs than the control. In conclusion, oviposition by A. aphidimyza females was induced by HIPVs from A. gossypii-infested eggplants. But the statistical difference in the number of oviposited eggs between the honeydew treatment and uninfested eggplant was not significant.

Plants perceive volatiles emitted from herbivore-damaged neighboring plants to urgently adapt or prime their defense responses to prepare for forthcoming herbivores. Mechanistically, these volatiles can induce epigenetic regulation based on histone modifications that alter the transcriptional status of defense genes, but little is known about the underlying mechanisms. To understand the roles of such epigenetic regulation of plant volatile signaling, we explored the response of Arabidopsis (Arabidopsis thaliana) plants to the volatile β-ocimene. Defense traits of Arabidopsis plants toward larvae of Spodoptera litura were induced in response to β-ocimene, through enriched histone acetylation and elevated transcriptional levels of defense gene regulators, including ethylene response factor genes (ERF8 and ERF104) in leaves. The enhanced defense ability of the plants was maintained for 5 d but not over 10 d after exposure to β-ocimene, and this coincided with elevated expression of those ERFs in their leaves. An array of histone acetyltransferases, including HAC1, HAC5, and HAM1, were responsible for the induction and maintenance of the anti-herbivore property. HDA6, a histone deacetylase, played a role in the reverse histone remodeling. Collectively, our findings illuminate the role of epigenetic regulation in plant volatile signaling.

One of the characteristic aspects of odour sensing in humans is the activation of olfactory receptors in a slightly different manner in response to different enantiomers. Here, we focused on whether plants showed enantiomer-specific response similar to that in humans. We exposed Arabidopsis seedlings to methanol (control) and (+)- or (-)-borneol, and found that only (+)-borneol reduced the root length. Furthermore, the root-tip width was more increased upon (+)-borneol exposure than upon (-)-borneol exposure. In addition, root-hair formation was observed near the root tip in response to (+)-borneol. Auxin signalling was strongly reduced in the root tip following exposure to (+)-borneol, but was detected following exposure to (-)-borneol and methanol. Similarly, in the root tip, the activity of cyclin B1:1 was detected on exposure to (-)-borneol and methanol, but not on exposure to (+)-borneol, indicating that (+)-borneol inhibits the meristematic activity in the root. These results partially explain the (+)-borneol-specific reduction in the root length of Arabidopsis. Our results indicate the presence of a sensing system specific for (+)-borneol in Arabidopsis.

Prohydrojasmon (PDJ), an analog of jasmonic acid (JA), was found to induce direct and indirect defenses against herbivores in non-infested plants. To test whether PDJ can be used for pest control in crop production, we conducted experiments in pesticide-free Japanese radish fields from October 4 to December 12 in 2015. Twenty-four Japanese radish plants in three plots were treated with a 100 times-diluted commercial formulation (5%) of PDJ (treated plants), and 24 plants in three different plots were treated with water (control plants) until November 29 every week. Throughout the observation period, the number of aphids, leaf-mining fly larvae, vegetable weevils, and thrips was significantly lower on the treated plants than on the control plants. In contrast, the number of lepidopteran larvae was not significantly different between the treated and control plants throughout the study period. Parasitized aphids (mummies) were also observed in both plots. Poisson regression analyses showed that a significantly higher number of mummies was recorded on the treated plants as compared to that on the control plants when the number of aphids increased. This suggested that PDJ application to Japanese radish plants attracted more parasitoid wasps on the treated plants than on the control plants. We also identified eight terpenoids and methyl salicylate as the PDJ-induced plant volatiles in the headspace of the treated plants. Some of these volatiles might be responsible for attracting aphid-parasitoid wasps in the field. However, for other insect pests, we did not find any natural enemies. Interestingly, the genes of the JA and salicylic acid signaling pathways were differentially upregulated in the treated plants. We also observed that the PDJ treatments induced the expression of the genes related to glucosinolate biosynthesis and the subsequent isothiocyanate formation. Additionally, the weights of both the aboveground and belowground parts of the treated plants were significantly lower than those of the respective parts of the control plants. These results indicated that the treatment of Japanese radish plants with a 100 times-diluted commercial formulation of PDJ induced their direct and indirect defenses against several insect pest species to reduce their numbers, and negatively affected their biomass.

It is known that undamaged plants that have been exposed to volatiles from damaged con- or heterospecific plants become more resistant against herbivores. This is one of the plants’ induced resistant responses against herbivores. To test whether this response can be used for rice production, we conducted the following experiments over 2 years (2012 and 2013). Rice seedlings were first planted in the rice seedling bed for 2 weeks in early May. There, half of the rice seedlings were exposed to artificially damaged weed volatiles three times for 12 days (treated plants). Weeds were randomly collected from the areas that were >100 m away from the seedling bed and the rice paddy fields. The remaining seedlings were not exposed (control plants). In the middle of May, bunches (ca. three seedlings per bunch) were transplanted to the rice paddy field. In July, leaf damage was observed. The total number of leaves in the treated and control plants was not significantly different. In contrast, the total number of damaged leaves in the treated plants was significantly lower than that in the control plants. In September, rice grains were harvested. The average weight of a rice grain from the treated and control plants was not significantly different. However, the weight of grains per bunch of treated plants was significantly higher than that of control plants; this indicated a significant increase of the number of grains by 23% in 2012 and by 18% in 2013 in the treated plants compared to that in the control plants. The volatiles emitted from the weeds included monoterpenoids (40.4% in total), green leaf volatiles (46.5%), short-chain alcohols (5.3%), short-chain ketone (5.4%), short-chain acetate (0.5%), short-chain aldehyde (1.1%), and hydrocarbon (0.7%). These results suggest that exposure of volatiles from artificially damaged weeds to rice seedlings has the potential to increase rice production.

Key message This study describes biological functions of the bHLH transcription factor RERJ1 involved in the jasmonate response and the related defense-associated metabolic pathways in rice, with particular focus on deciphering the regulatory mechanisms underlying stress-induced volatile emission and herbivory resistance. RERJ1 is rapidly and drastically induced by wounding and jasmonate treatment but its biological function remains unknown as yet. Here we provide evidence of the biological function of RERJ1 in plant defense, specifically in response to herbivory and pathogen attack, and offer insights into the RERJ1-mediated regulation of metabolic pathways of specialized defense compounds, such as monoterpene linalool, in possible collaboration with OsMYC2-a well-known master regulator in jasmonate signaling. In rice (Oryza sativa L.), the basic helix-loop-helix (bHLH) family transcription factor RERJ1 is induced under environmental stresses, such as wounding and drought, which are closely linked to jasmonate (JA) accumulation. Here, we investigated the biological function of RERJ1 in response to biotic stresses, such as herbivory and pathogen infection, using an RERJ1-defective mutant. Transcriptome analysis of the rerj1-Tos17 mutant revealed that RERJ1 regulated the expression of a typical family of conserved JA-responsive genes (e.g., terpene synthases, proteinase inhibitors, and jasmonate ZIM domain proteins). Upon exposure to armyworm attack, the rerj1-Tos17 mutant exhibited more severe damage than the wildtype, and significant weight gain of the larvae fed on the mutant was observed. Upon Xanthomonas oryzae infection, the rerj1-Tos17 mutant developed more severe symptoms than the wildtype. Among RERJ1-regulated terpene synthases, linalool synthase expression was markedly disrupted and linalool emission after wounding was significantly decreased in the rerj1-Tos17 mutant. RERJ1 appears to interact with OsMYC2-a master regulator of JA signaling-and many OsJAZ proteins, although no obvious epistatic interaction was detected between them at the transcriptional level. These results indicate that RERJ1 is involved in the transcriptional induction of JA-mediated stress-responsive genes via physical association with OsMYC2 and mediates defense against herbivory and bacterial infection through JA signaling.

We previously reported that the exposure of field-grown black soybean seedlings (Glycine max 'Hyokei Kuro-3') to artificially damaged goldenrod volatiles (ADGVs) resulted in a significant increase in isoflavonoids in their seeds. Here, we used field-grown soybean seedlings to study the effects of the exposure to ADGVs on the production of seed saponins that are particularly abundant in soybean seeds. We used black soybean plants and yellow soybean plants (G. max 'Yumesayou'). The exposure of black soybean parental plants to ADGVs resulted in a significant increase in the seed saponins Ab, βa, and Bc when compared with control seeds from non-exposed parental plants. In yellow soybean seeds, exposure resulted in a significant increase in the seed saponins Af, Ab, αg, βg, γg, and γa when compared with the control. Bb and Bc, the degradation products, were detected in black soybean seeds but not in yellow soybean seeds. This is the first evidence that environmental condition such as exposure to ADGVs affects to saponin content in plants.