Search

Common ragweed (Ambrosia artemisiifolia) is an invasive annual weed that invades heavily disturbed habitats and natural habitats less disturbed by human activities with native plant species in need of protection. Achieving effective control of A. artemisiifolia for the protection of native organisms and the local ecological environment is an ongoing challenge. Based on the growth and development characteristics of A. artemisiifolia , we examined the effectiveness of herbicides in controlling this species and the optimal time for application in the field with the aim of reducing herbicide dosage. Additionally, we analyzed whether the efficiency of low-dose applications for controlling this species might improve with increasing native plant species richness. Our findings indicate that aminopyralid (33 g ai ha−1) was the most suitable herbicide for chemical control of A. artemisiifolia, with optimum application time being during vegetative growth (BBCH 32–35). Application of aminopyralid was found to kill approximately 52% of A. artemisiifolia plants, and more than 75% of the surviving plants did not bloom, thereby reducing seed yield of the population by more than 90%. Compared with the application of high-dose herbicide, the phytotoxicity of aminopyralid to native plants at the applied dose was substantially reduced. After 2 years of application, the relative coverage of A. artemisiifolia significantly decreased, with few plants remaining, whereas the relative coverage of native plants more than doubled, representing an eco-friendly control. Further, there was an increase in the A. artemisiifolia control rate in the plant community with higher native plant species richness at the same herbicide rates and a reduction in seed yield of A. artemisiifolia. Our findings help toward developing control measures to reduce the invasiveness of A. artemisiifolia with low-dose herbicides meanwhile protecting native plants, and then using the species richness of native plant communities to indirectly promote the effectiveness of low-dose herbicide application. [ABSTRACT FROM AUTHOR]

Common ragweed (Ambrosia artemisiifolia) is an invasive annual weed that invades heavily disturbed habitats and natural habitats less disturbed by human activities with native plant species in need of protection. Achieving effective control of A. artemisiifolia for the protection of native organisms and the local ecological environment is an ongoing challenge. Based on the growth and development characteristics of A. artemisiifolia, we examined the effectiveness of herbicides in controlling this species and the optimal time for application in the field with the aim of reducing herbicide dosage. Additionally, we analyzed whether the efficiency of low-dose applications for controlling this species might improve with increasing native plant species richness. Our findings indicate that aminopyralid (33 g ai ha−1) was the most suitable herbicide for chemical control of A. artemisiifolia, with optimum application time being during vegetative growth (BBCH 32–35). Application of aminopyralid was found to kill approximately 52% of A. artemisiifolia plants, and more than 75% of the surviving plants did not bloom, thereby reducing seed yield of the population by more than 90%. Compared with the application of high-dose herbicide, the phytotoxicity of aminopyralid to native plants at the applied dose was substantially reduced. After 2 years of application, the relative coverage of A. artemisiifolia significantly decreased, with few plants remaining, whereas the relative coverage of native plants more than doubled, representing an eco-friendly control. Further, there was an increase in the A. artemisiifolia control rate in the plant community with higher native plant species richness at the same herbicide rates and a reduction in seed yield of A. artemisiifolia. Our findings help toward developing control measures to reduce the invasiveness of A. artemisiifolia with low-dose herbicides meanwhile protecting native plants, and then using the species richness of native plant communities to indirectly promote the effectiveness of low-dose herbicide application.

Huanglongbing (HLB) is the most destructive citrus disease worldwide. This is associated with the phloem-limited bacterium Candidatus Liberibacter, and the typical symptom is leaf blotchy mottle. To better understand the biological processes involved in the establishment of HLB disease symptoms, the comparative proteomic analysis was performed to reveal the global protein accumulation profiles in leaf petiole, where there are massive HLB pathogens of Ca. L. asiaticus-infected Newhall sweet orange (Citrus sinensis) plants at the asymptomatic and symptomatic stages compared to their healthy counterpart. Photosynthesis, especially the pathway involved in the photosystem I and II light reactions, was shown to be suppressed throughout the whole Ca. L. asiaticus infection cycle. Also, starch biosynthesis was induced after the symptom-free prodromal period. Many defense-associated proteins were more extensively regulated in the petiole with the symptoms than the ones from healthy plants. The change of salicylic and jasmonic acid levels in different disease stages had a positive correlation with the abundance of phytohormone biosynthesis-related proteins. Moreover, the protein–protein interaction network analysis indicated that an F-type ATPase and an alpha-1,4 glucan phosphorylase were the core nodes in the interactions of differentially accumulated proteins. Our study indicated that the infected citrus plants probably activated the non-unified and lagging enhancement of defense responses against Ca. L. asiaticus at the expense of photosynthesis and contribute to find out the key Ca. L. asiaticus-responsive genes for tolerance and resistance breeding.

Huanglongbing (HLB) is the most destructive citrus disease worldwide. This is associated with the phloem-limited bacterium Candidatus Liberibacter, and the typical symptom is leaf blotchy mottle. To better understand the biological processes involved in the establishment of HLB disease symptoms, the comparative proteomic analysis was performed to reveal the global protein accumulation profiles in leaf petiole, where there are massive HLB pathogens of Ca. L. asiaticus-infected Newhall sweet orange (Citrus sinensis) plants at the asymptomatic and symptomatic stages compared to their healthy counterpart. Photosynthesis, especially the pathway involved in the photosystem I and II light reactions, was shown to be suppressed throughout the whole Ca. L. asiaticus infection cycle. Also, starch biosynthesis was induced after the symptom-free prodromal period. Many defense-associated proteins were more extensively regulated in the petiole with the symptoms than the ones from healthy plants. The change of salicylic and jasmonic acid levels in different disease stages had a positive correlation with the abundance of phytohormone biosynthesis-related proteins. Moreover, the protein–protein interaction network analysis indicated that an F-type ATPase and an alpha-1,4 glucan phosphorylase were the core nodes in the interactions of differentially accumulated proteins. Our study indicated that the infected citrus plants probably activated the non-unified and lagging enhancement of defense responses against Ca. L. asiaticus at the expense of photosynthesis and contribute to find out the key Ca. L. asiaticus-responsive genes for tolerance and resistance breeding. [ABSTRACT FROM AUTHOR]

Stomatal pores control leaf gas exchange and are one route for infection of internal plant tissues by many foliar pathogens, setting up the potential for tradeoffs between photosynthesis and pathogen colonization. Anatomical shifts to lower stomatal density and/or size may also limit pathogen colonization, but such developmental changes could permanently reduce the gas exchange capacity for the life of the leaf. I developed and analyzed a spatially explicit model of pathogen colonization on the leaf as a function of stomatal size and density, anatomical traits which partially determine maximum rates of gas exchange. The model predicts greater stomatal size or density increases the probability of colonization, but the effect is most pronounced when the fraction of leaf surface covered by stomata is low. I also derived scaling relationships between stomatal size and density that preserves a given probability of colonization. These scaling relationships set up a potential anatomical conflict between limiting pathogen colonization and minimizing the fraction of leaf surface covered by stomata. Although a connection between gas exchange and pathogen defense has been suggested empirically, this is the first mathematical model connecting gas exchange and pathogen defense via stomatal anatomy. A limitation of the model is that it does not include variation in innate immunity and stomatal closure in response to pathogens. Nevertheless, the model makes predictions that can be tested with experiments and may explain variation in stomatal size and density among plants. The model is generalizable to many types of pathogens, but lacks significant biological realism that may be needed for precise predictions. [ABSTRACT FROM AUTHOR]

Plants are sessile organisms that are continuously exposed to a wide range of environmental stresses. To cope with various stresses using limited resources, plants have evolved diverse mechanisms of "tradeoff" that enable the allocation of resources to address the most life-threatening stress. During our studies on induced disease resistance in rice, we have found some important phenomena relevant to tradeoffs between biotic and abiotic stress responses, and between stress response and plant growth. We characterized these tradeoff phenomena from viewpoints of signaling crosstalks associated with transcriptional regulation. Here, I describe following topics: (1) PTP1-dependent increased disease susceptibility of rice under low temperature and high salinity conditions, (2) OsNPR1-dependent tradeoff between pathogen defense and photosynthesis, (3) tradeoff between pathogen defense and abiotic stress tolerance in WRKY45-overexpressing rice plants, and (4) WRKY62-dependent tradeoff between pathogen defense and hypoxia tolerance. Lastly, I discuss my view regarding the significance of such tradeoffs in agricultural production that should be considered in crop breeding; that is, the tradeoffs, although they benefit plants in nature, can be rather disadvantageous in agricultural production. [ABSTRACT FROM AUTHOR]

Infectious diseases cause huge crop losses annually. In response to pathogen attacks, plants activate defense systems that are mediated through various signaling pathways. The salicylic acid (SA) signaling pathway is the most powerful of these pathways. Several regulatory components of the SA signaling pathway have been identified, and are potential targets for genetic manipulation of plants' disease resistance. However, the resistance associated with these regulatory components is often accompanied by fitness costs; that is, negative effects on plant growth and crop yield. Chemical defense inducers, such as benzothiadiazole and probenazole, act on the SA pathway and induce strong resistance to various pathogens without major fitness costs, owing to their 'priming effect.' Studies on how benzothiadiazole induces disease resistance in rice have identified WRKY45, a key transcription factor in the branched SA pathway, and OsNPR1/NH1. Rice plants overexpressing WRKY45 were extremely resistant to rice blast disease caused by the fungus Magnaporthe oryzae and bacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae (Xoo), the two major rice diseases. Disease resistance is often accompanied by fitness costs; however, WRKY45 overexpression imposed relatively small fitness costs on rice because of its priming effect. This priming effect was similar to that of chemical defense inducers, although the fitness costs were amplified by some environmental factors.WRKY45 is degraded by the ubiquitin-proteasome system, and the dual role of this degradation partly explains the priming effect. The synergistic interaction between SA and cytokinin signaling that activates WRKY45 also likely contributes to the priming effect. With a main focus on these studies, I review the current knowledge of SA-pathway-dependent defense in rice by comparing it with that in Arabidopsis, and discuss potential strategies to develop disease-resistant rice using signaling components. [ABSTRACT FROM AUTHOR]

Plants are sessile organisms that are continuously exposed to a wide range of environmental stresses. To cope with various stresses using limited resources, plants have evolved diverse mechanisms of "tradeoff" that enable the allocation of resources to address the most life-threatening stress. During our studies on induced disease resistance in rice, we have found some important phenomena relevant to tradeoffs between biotic and abiotic stress responses, and between stress response and plant growth. We characterized these tradeoff phenomena from viewpoints of signaling crosstalks associated with transcriptional regulation. Here, I describe following topics: (1) PTP1-dependent increased disease susceptibility of rice under low temperature and high salinity conditions, (2) OsNPR1-dependent tradeoff between pathogen defense and photosynthesis, (3) tradeoff between pathogen defense and abiotic stress tolerance in WRKY45-overexpressing rice plants, and (4) WRKY62-dependent tradeoff between pathogen defense and hypoxia tolerance. Lastly, I discuss my view regarding the significance of such tradeoffs in agricultural production that should be considered in crop breeding; that is, the tradeoffs, although they benefit plants in nature, can be rather disadvantageous in agricultural production.