To understand whether domestication had an impact on susceptibility and responsiveness to arbuscular mycorrhizal fungi (AMF) in tomato (Solanum lycopersicum), we investigated two tomato cultivars (\"M82\" and \"Moneymaker\") and a panel of wild relatives including S. neorickii, S. habrochaites and S. pennellii encompassing the whole Lycopersicon clade. Most genotypes revealed good AM colonisation levels when inoculated with the AMF Funneliformis mosseae. By contrast, both S. pennellii accessions analysed showed a very low colonisation, but with normal arbuscule morphology, and a negative response in terms of root and shoot biomass. This behaviour was independent of fungal identity and environmental conditions. Genomic and transcriptomic analyses revealed in S. pennellii the lack of genes identified within QTLs for AM colonisation, a limited transcriptional reprogramming upon mycorrhization and a differential regulation of strigolactones and AM-related genes compared to tomato. Donor plants experiments indicated that the AMF could represent a cost for S. pennellii: F. mosseae could extensively colonise the root only when it was part of a mycorrhizal network, but a higher mycorrhization led to a higher inhibition of plant growth. These results suggest that genetics and functional traits of S. pennellii are responsible for the limited extent of AMF colonisation.

The plant Centaurea cineraria L. subsp. cineraria has been investigated as a potential source of inhibitors of broomrape radicle growth. The latter are weeds that pose a threat to agriculture and for which there are few methods available for the control of infestations. Four sesquiterpene lactones have been isolated from C. cineraria L. subsp. cineraria aerial parts and identified as isocnicin, cnicin, salonitenolide, and 11β,13-dihydrosalonitenolide using spectroscopic, spectrometric, and optical methods. Salonitenolide and 11β,13-dihydrosalonitenolide have been isolated for the first time from this plant. Tested at 1.0-0.1 mM against the broomrape species Phelipanche ramosa, Orobanche minor, Orobanche crenata, and Orobanche cumana, isocnicin, cnicin, and salonitenolide demonstrated remarkable inhibitory activity (over 80% in most of the cases) at the highest concentrations. Structure-activity relationship conclusions indicated the significance of the α,β-unsaturated lactone ring. In addition, the synthetic acetylated derivative of salonitenolide showed the strongest activity among all compounds tested, with inhibitions close to 100% at different concentrations, which has been related to a different lipophilicity and the absence of H-bond donor atoms in its structure. Neither the extracts nor the compounds exhibited the stimulating activity of broomrape germination (induction of suicidal germination). These findings highlight the potential of C. cineraria to produce bioactive compounds for managing parasitic weeds and prompt further studies on its sesquiterpene lactones as tools in developing natural product-based herbicides.

The stigma is the terminal part of the carpel which receives pollen during the pollination process. Although the role of the stigmas in pollination is the same for all angiosperms, stigmas structures are very diverse. This study aimed to evaluate intraspecific, interspecific and intergeneric stigmas variability and then find differences of the stigma morphology amongst 24 holoparasitic Orobanche and Phelipanche species and provide new insights into its potential taxonomic value. This paper was also focused on selecting the best diagnostic features that would be used for future stigma analysis in other species of Orobanchaceae. These analyses were conducted with fresh, dry and fixed material using stereomicroscopy from different locations from Central Europe. Twenty-one quantitative or qualitative morphological features were analysed. This study highlights the variation of stigma morphology and characters which are useful to improve the taxonomic understanding of problematic taxa. Thus, two main types of stigmas were established, based on tested features: 1-oval, rarely hemispherical in shape, most often one-coloured with lobes separated in Phelipanche stigmas; 2-spherical to hemispherical, rarely oval, multi-coloured with partially fused or separated lobes in Orobanche stigmas. The best diagnostic features of the stigmas for distinguishing the Orobanchaceae are the type and subtype of stigma, the length and area of the stigma, the width of single lobes, the width in the middle part of the stigma, the length of upper and lower separation in the middle part between lobes and the angle between lobes in the upper and lower part. The morphological features of the stigmas are important criteria for distinguishing genera, sections and subsections, as well as related species. In this study, we present the first stigma morphological studies for the most numerous genera from the tribe Orobancheae and this paper may determine features possible to use in solving certain taxonomic problems and evolutionary relationships of the species.

The study of allelopathic activity of plants and the isolation and characterization of the responsible allelochemicals can lead to the development of environment friendly alternative approaches to weed control. Conyza species are invasive weeds that use allelopathic activity as part of a successful strategy to outcompete neighboring plants. Broomrape weeds are parasitic plants that use host-induced germination and the formation of a haustorium as strategies to infect host plants. The control of broomrape infection in most affected crops is limited or non-existing. In the current study, we investigated the allelopathic activity of Conyza bonariensis organic extracts in suicidal germination and radicle growth of four broomrape species (Orobanche crenata, Orobanche cumana, Orobanche minor and Phelipanche ramosa). A bioactivity-driven fractionation of Conyza bonariensis extracts led to the identification of two germination-inducing molecules and two growth-inhibitory compounds. The germination-inducing metabolites had species-specific activity being hispidulin active on seeds of O. cumana and methyl 4-hydroxybenzoate active in P. ramosa. The growth-inhibitory metabolites (4Z)-lachnophyllum lactone and (4Z,8Z)-matricaria lactone strongly inhibited the radicle growth of all parasitic weed species studied. Some structure-activity relationships were found as result of the study herein presented.

The root parasitic weed broomrapes, Phelipanche spp., cause severe damage to agriculture all over the world. They have a special host-dependent lifecycle and their seeds can germinate only when they receive chemical signals released from host roots. Our previous study demonstrated that 2-phenylethyl isothiocyanate is an active germination stimulant for P. ramosa in root exudates of oilseed rape. In the present study, 21 commercially available ITCs were examined for P. ramosa seed germination stimulation, and some important structural features of ITCs for exhibiting P. ramosa seed germination stimulation have been uncovered. Structural optimization of ITC for germination stimulation resulted in ITCs that are highly active to P. ramosa. Interestingly, these ITCs induced germination of P. aegyptiaca but not Orobanche minor or Striga hermonthica. P. aegyptiaca seeds collected from mature plants parasitizing different hosts responded to these ITCs with different levels of sensitivity. ITCs have the potential to be used as inducers of suicidal germination of Phelipanche seeds.

This invited paper summarises a career in which I became increasingly involved in research and related activities on Striga and other parasitic weeds. It also presents a personal view of the present status of parasitic weed problems and their control.

UNASSIGNED: New transgenic and biotechnological approaches may serve as a key component in achieving crop resistance to root parasitic weeds. Root parasitic weeds inflict severe damage to numerous crops, reducing yield quantity and quality. A lack of new sources of resistance limits our ability to manage newly developing, more virulent races. Having no effective means to control the parasites in most crops, innovative biotechnological solutions are needed. Several novel biotechnological strategies using regulatory RNA molecules, the CRISPR/Cas9 system, and T-DNA insertions have been acknowledged for engineering resistance against parasitic weeds. Significant breakthroughs have been made over the years in deciphering the plant genome and its functions, including the genomes of parasitic weeds. However, the basis of biotechnological strategies to generate host resistance to root parasitic weeds needs to be further developed. Gene-silencing and editing tools should be used to target key processes of host-parasite interactions, such as strigolactone biosynthesis and signaling, haustorium development, and degradation and penetration of the host cell wall. In this review, we summarize and discuss the main areas of research leading to the discovery and functional analysis of genes involved in host-induced gene silencing that target key parasite genes, transgenic host modification, and host gene editing to generate sustainable resistance to root parasitic weeds.

Parasitic plants rely on neighboring host plants to complete their life cycle, forming vascular connections through which they withdraw needed nutritive resources. In natural ecosystems, parasitic plants form one component of the plant community and parasitism contributes to overall community balance. In contrast, when parasitic plants become established in low biodiversified agroecosystems, their persistence causes tremendous yield losses rendering agricultural lands uncultivable. The control of parasitic weeds is challenging because there are few sources of crop resistance and it is difficult to apply controlling methods selective enough to kill the weeds without damaging the crop to which they are physically and biochemically attached. The management of parasitic weeds is also hindered by their high fecundity, dispersal efficiency, persistent seedbank, and rapid responses to changes in agricultural practices, which allow them to adapt to new hosts and manifest increased aggressiveness against new resistant cultivars. New understanding of the physiological and molecular mechanisms behind the processes of germination and haustorium development, and behind the crop resistant response, in addition to the discovery of new targets for herbicides and bioherbicides will guide researchers on the design of modern agricultural strategies for more effective, durable, and health compatible parasitic weed control.

Strigolactones are natural products that are exuded by plants and stimulate parasitic weed germination. Their use in herbicides is limited since they are produced in small quantities, but the synthesis of bioactive analogues provides an alternative source. In this work, eleven analogues have been synthesized. Among them, nine compounds belong to a novel family named eudesmanestrigolactones. The procedure is short (3-6 steps), the starting materials are isolated on a multigram scale, and global yields are up to 8%, which significantly enhance isolated yields. In bioassay, the compounds germinated high percentages of Phelipanche ramosa, Orobanche cumana, and Orobanche crenata seeds, even at nanogram doses (100 nM). Bioactivity was stereochemistry-dependent, and it was discussed in terms of the presence and geometry of the enol ether, orientation of the butenolide, and unsaturation of ring A. The reported compounds provide a set of readily obtained allelochemicals with potential applications as preventive herbicides.

Strigolactones (SLs) are a group of carotenoid derived plant hormones that play a key role in establishing plant architecture and adapting it to environmental changes, and are involved in plants response to biotic and abiotic stress. SLs are also released into the soil to serve as a chemical signal attracting beneficial mycorrhizal fungi. However, this signal also induces seed germination in root parasitic weeds that represent a major global threat for agriculture. This wide spectrum of biological functions has made SL research one of the most important current topics in fundamental and applied plant science. The availability of SLs is crucial for investigating SL biology as well as for agricultural application. However, natural SLs are produced in very low amounts, and their organic synthesis is quite difficult, which creates a need for efficient and easy-to-synthesize analogs and mimics. Recently, we have generated a set of SL analogs, Methyl Phenlactonoates (MPs), which resemble the non-canonical SL carlactonoic acid. In this paper, we describe the development and characterization of a new series of easy-to-synthesize MPs. The new analogs were assessed with respect to regulation of shoot branching, impact on leaf senescence, and induction of seed germination in different root parasitic plants species. Some of the new analogs showed higher efficiency in inhibiting shoot branching as well as in triggering parasitic seed germination, compared to the commonly used GR24. MP16 was the most outstanding analog showing high activity in different SL biological functions. In summary, our new analogs series contains very promising candidates for different applications, which include the usage in studies for understanding different aspects of SL biology as well as large scale field application for combating root parasitic weeds, such as Striga hermonthica that devastates cereal yields in sub-Saharan Africa.