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Alfalfa (Medicago sativa) is known to release allelopathic substances to affect the germination and growth of other plants, which have the potential to be applied in controlling weeds. Green foxtail (Setaria viridis) and barnyardgrass (Echinochloa crus-galli), as malignant weeds worldwide, also pose a serious threat to alfalfa in northern China. In this study, the sensitivity of the two weeds to the extracts from the first, second, and third stubbles of six varieties were investigated to further reveal the allelopathic interference of different varieties of alfalfa on notorious weeds. The germination rate, the length and fresh weight of seedlings, the length and fresh weight of roots were measured to elucidate the allelopathy of alfalfa extracts on the two weeds. The results suggested that: (1) The allelopathy of six alfalfa varieties tested showed obvious intraspecific differences, the inhibition of Zhongmu No.3 on green foxtail and barnyardgrass was weaker than other varieties, with the values of synthetical allelopathic effect (SAE) were -0.55 and -0.29, respectively. (2) The inhibitory effect of alfalfa extracts on green foxtail was enhanced with the increase of stubbles, while the differences between three stubbles on barnyardgrass were not clear, especially between the first and second stubbles. (3) Compared with barnyardgrass (SAE = -0.39 ~ -0.29), green foxtail (SAE = -0.65 ~ -0.52) was generally more susceptible to the extracts. (4) The inhibitory effect of alfalfa extracts on root was stronger than seedling in the same weed. For example, the third stubble extracts of Baoding variety inhibited 88.00% of the roots at the concentration of 0.01 g mL-1, but did not affect the seedlings of green foxtail. The study may help to comprehensively reveal the allelopathic effect of different alfalfa varieties in the first three stubbles on green foxtail and barnyardgrass, providing scientific evidence for weed control based on natural plant extracts in the future.

Allelopathy is a phenomenon involving beneficial or adverse effects from one plant to another by releasing compounds called allelochemicals. Essential oils, which are volatile substances responsible for plant aromas, may play a role in this phenomenon. This study aimed to evaluate the phytotoxic and cytotoxic effects of rosemary (Rosmarinus officinalis) essential oil. Phytotoxic effects of the oil (1 µL, 5 µL, 10 µL, and 20 µL) were assessed on germination and initial growth of two target species: a crop (Lactuca sativa L., lettuce) and a weed (Eragrostis plana, capim-annoni-2). The evaluated variables were germination rate, speed of germination, root length, and shoot length. The cytotoxic effects of essential oil (0.5 µL, 1 µL, and 10 µL) were assessed on L. sativa root tips, evaluating its impact on mitotic and metaphasic indexes as well as the frequency of each mitotic phase. The essential oil was extremely harmful to L. sativa germination and initial growth. The volatiles also caused an inhibitory, dose-dependent effect in E. plana germination and strongly inhibited both root and shoot growth of the species at the highest amounts tested. Rosemary essential oil interfered with the cell division of L. sativa, resulting in decreased mitotic and metaphasic indexes. Analysis of the frequency of each mitosis phase indicates that volatiles inhibited root growth by delaying cell division. These findings suggest that rosemary essential oil could serve as a potential bioherbicide.

Biodiversity is adversely affected by the growing levels of synthetic chemicals released into the environment due to agricultural activities. This has been the driving force for embracing sustainable agriculture. Plant secondary metabolites offer promising alternatives for protecting plants against microbes, feeding herbivores, and weeds. Terpenes are the largest among PSMs and have been extensively studied for their potential as antimicrobial, insecticidal, and weed control agents. They also attract natural enemies of pests and beneficial insects, such as pollinators and dispersers. However, most of these research findings are shelved and fail to pass beyond the laboratory and greenhouse stages. This review provides an overview of terpenes, types, biosynthesis, and their roles in protecting plants against microbial pathogens, insect pests, and weeds to rekindle the debate on using terpenes for the development of environmentally friendly biopesticides and herbicides.

Just as plants attack heterospecific competitors with allelopathic phytotoxins, they also attack conspecifics with phytotoxins to inhibit seedling germination and growth (autotoxicity). As a result, for many plant species, autotoxicity limits offspring germination and growth proximate to parental plants—consequently reducing deleterious density dependent effects. Autotoxicity appears to vary across species, but it also may vary within species. We tested autotoxicity and variability in six ecotypes of the model plant, Arabidopsis thaliana, using allelopathy bioassays. We found that autotoxic impacts varied across the Eurasian and African ecotypes, and the negative effects on conspecific root growth were greater from above-than belowground exudate. In half the ecotypes, root growth decreased 71% in seedlings treated with exudate from the same ecotype than when treated with exudate from other ecotypes. That the ecotypes limited themselves more than they did other ecotypes is consistent with coexistence theory, which assumes species limit themselves more than others. Moreover, it is consistent with negative density dependent theories that suggest seedling mortality is highest near conspecific adults. Finally, the variation in autotoxicity across ecotypes suggests that intraspecific genetic variability and/or local habitat influence autotoxic intensity. It is well recognized that phytotoxic effect (allelopathy and autotoxicity) varies interspecifically but ecotype-level effects suggests that plants may exhibit greater intraspecific variation in autotoxicity than currently recognized.

An organism with a single recessive loss-of-function allele will typically have a wild-type phenotype, whereas individuals homozygous for two copies of the allele will display a mutant phenotype. We have developed a method called the mutagenic chain reaction (MCR), which is based on the CRISPR/Cas9 genome-editing system for generating autocatalytic mutations, to produce homozygous loss-of-function mutations. In Drosophila, we found that MCR mutations efficiently spread from their chromosome of origin to the homologous chromosome, thereby converting heterozygous mutations to homozygosity in the vast majority of somatic and germline cells. MCR technology should have broad applications in diverse organisms.

The frequency and intensity of cyanobacterial blooms are increasing worldwide with major societal and economic costs. Interactions between toxic cyanobacteria and eukaryotic algal competitors can affect toxic bloom formation, but the exact mechanisms of interspecies interactions remain unknown. Using metabolomic and proteomic profiling of co-cultures of the toxic cyanobacterium Microcystis aeruginosa with a green alga as well as of microorganisms collected in a Microcystis spp. bloom in Lake Taihu (China), we disentangle novel interspecies allelopathic interactions. We describe an interspecies molecular network in which M. aeruginosa inhibits growth of Chlorella vulgaris , a model green algal competitor, via the release of linoleic acid. In addition, we demonstrate how M. aeruginosa takes advantage of the cell signaling compound nitric oxide produced by C. vulgaris , which stimulates a positive feedback mechanism of linoleic acid release by M. aeruginosa and its toxicity. Our high-throughput system-biology approach highlights the importance of previously unrecognized allelopathic interactions between a broadly distributed toxic cyanobacterial bloom former and one of its algal competitors.

Allelopathy is expressed through the release of plant chemicals and is considered a natural alternative for sustainable weed management. Artemisia argyi (A. argyi) is widely distributed throughout Asia, and often dominates fields due to its strong allelopathy. However, the mechanism of A. argyi allelopathy is largely unknown and need to be elucidated at the physiological and molecular levels. In this study, we used electron microscopy, ionomics analysis, phytohormone profiling, and transcriptome analysis to investigate the physiological and molecular mechanisms of A. argyi allelopathy using the model plant rice (Oryza sativa) as receptor plants. A. argyi water extract (AAWE)-treated rice plants grow poorly and display root morphological anomalies and leaf yellowing. We found that AAWE significantly inhibits rice growth by destroying the root and leaf system in multiple ways, including the integrity of ultrastructure, reactive oxygen species (ROS) homeostasis, and the accumulation of soluble sugar and chlorophyll synthesis. Further detection of the hormone contents suggests that AAWE leads to indole-3-acetic acid (IAA) accumulation in roots. Moreover, ionomics analysis shows that AAWE inhibits the absorption and transportation of photosynthesis-essential mineral elements, especially Mg, Fe, and Mn. In addition, the results of transcriptome analysis revealed that AAWE affects a series of crucial primary metabolic processes comprising photosynthesis in rice plants. This study indicates that A. argyi realizes its strongly allelopathy through comprehensive effects on recipient plants including large-scale IAA synthesis and accumulation, ROS explosion, damaging the membrane system and organelles, and obstructing ion absorption and transport, photosynthesis and other pivotal primary metabolic processes of plants. Therefore, AAWE could potentially be developed as an environmentally friendly botanical herbicide due to its strong allelopathic effects.