Aromatic plants and their volatile compounds affect seed germination and plant growth, and therefore hold potential for agriculture uses as plant growth regulators and bioherbicides. In the present study 17 major monoterpenes were selected, and their mechanisms of plant toxicity were elucidated using transgenic Arabidopsis thaliana at various growth stages. Microtubulin and the plant cell membrane were identified as the focal targets through which phytotoxicity and herbicidal activity acted. Variability in monoterpene mechanisms was observed. Limonene and (+ )-citronellal had strong antimicrotubule efficacy, whereas citral, geraniol, (−)-menthone, (+)-carvone, and (−)-citronellal demonstrated moderate antimicrotubule efficacy. Pulegone, (−)-carvone, carvacrol, nerol, geranic acid, (+)/(−)-citronellol, and citronellic acid lacked antimicrotubule capacity. An enantioselective disruption of microtubule assembly was recorded for (+)/(−)-citronellal and (+)/(−)-carvone. The (+) enatiomers were more potent than their (−) counterparts. Citral, limonene, carvacrol, and pulegone were also tested for phytotoxicity and herbicidal activity. Pulegone had no detectable effect on microtubules or membranes. Citral disrupted microtubules but did not cause membrane damage. Carvacrol lacked a detectable effect on microtubules but incited membrane leakage, and limonene disrupted microtubules and membrane leakage. Therefore, only limonene was herbicidal at the tested concentrations. In planta quantification of residues revealed that citral was biotransformed into nerol and geraniol, and limonene was converted into carvacrol, which could explain its dual capacity with respect to microtubules and membrane functionality. The results obtained are an important added value to commercial efforts in selecting appropriate aromatic plants to be sources of bioherbicidal compounds for sustainable weed management with a limited potential for herbicide resistance evolution in weed populations.

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Whitefly (Bemisia tabaci) is an important insect pest, causing severe damage to agricultural crops. The pest was recorded in a commercial rosemary (Rosmarinus officinalis, Lamiaceae) field, colonizing rosemary variety (var.) '2', but not '11'. A series of field and controlled laboratory choice bioassays confirmed the observed phenomenon. Mature potted plants of the two varieties were randomly organized in a lemon verbena (Lippia citrodora) and lemon grass (Cymbopogon spp.) fields. Seven days later var. '2' was significantly more colonized by whiteflies than var. '11'. Under lab conditions, whiteflies were significantly more attracted to var. '2' plantlets than to var. '11' following choice bioassays. Furthermore, cotton plants dipped in an essential oil emulsion of var. '2' had significantly greater colonization than cotton plants dipped in the essential oil emulsion of var. '11'. Similar results were obtained in 'plant-plant', 'plant-no plant' as well as, 'essential oil—essential oil' choice bioassay designs. Analyses of the essential oils of the two varieties identified a set of common and unique volatiles in each variety. Among these volatiles were β-caryophyllene and limonene, two compounds known to be associated with plant-insect interactions. The attraction of B. tabaci to pure (>95%) β-caryophyllene and limonene using a range of concentrations was examined in vitro by choice bioassays. The compounds were attractive to the insect at moderate concentration, but not at the lowest or highest concentrations used, where the insect was not attracted or repelled, respectively. Limonene attracted the insects at rates that were 10-fold lower than β-caryophyllene. The results emphasized the role of host plant volatiles in shaping the structure of B. tabaci populations in nature and in agricultural systems, and provided insights into the factors that contribute to the development of insect populations with unique characteristics. The results could also serve for future development of bio-pesticides and in breeding programs.

Sweet basil, Ocimum basilicum L., is a well-known culinary herb grown worldwide, but its uses go beyond the kitchen to traditional medicine, cosmetics and gardening. To date, the lack of an available reference genome has limited the utilization of advanced molecular breeding methods. We present a draft version of the sweet basil genome of the cultivar ‘Perrie’, a fresh-cut Genovese-type basil. Genome sequencing showed basil to be a tetraploid organism with a genome size of 2.13 Gbp, assembled in 12,212 scaffolds, with > 90% of the assembly being composed of 107 scaffolds. About 76% of the genome is composed of repetitive elements, with the majority being long-terminal repeats. We constructed and annotated 62,067 protein-coding genes and determined their expression in different plant tissues. We analysed the currently known phenylpropanoid volatiles biosynthesis genes. We demonstrated the necessity of the reference genome for a comprehensive understanding of this important pathway in the context of tetraploidy and gene redundancy. A complete reference genome is essential to overcome this redundancy and to avoid off-targeting when designing a CRISPR: Cas9-based genome editing research. This work bears promise for developing fast and accurate breeding tools to provide better cultivars for farmers and improved products for consumers.

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