Parasitic Weed Research Articles

Effect of Sowing Date of Resistant and Susceptible Faba Bean, <i>Vicia faba</i> L. Cultivars on <i>Orobanche crenata</i> Forsk Seed Bank and Faba Bean Production

The broomrape<i>, Orobanche crenat</i>a Forsk (Orobanchaceae) is a serious annual parasitic weed that causes considerable losses in many major crops including faba bean (Vicia faba L.). In Egypt: losses due to <i>O. crenata</i> parasitism may reach 40 to 100%. Despite using several methods to control <i>O. crenata,</i> success has not been achieved. The impact of different control tactics on <i>O. crenata </i>is not well understood<i>.</i> However, Sowing date appears to be one of the potential solutions for controlling <i>O. crenata</i>. In this work we investigated the effect of sowing dates on both the level of infection by <i>O. crenata</i> and the pod yield of faba bean using resistant (Giza 843) and susceptible (Nubaria 1) faba bean cultivars in naturally <i>Orobanche</i> infested soil. Moreover, the <i>Orobanche</i> seeds production was determined as an indication of seed bank future adding in soil. Under <i>Orobanche</i> free conditions, Nubaria 1 cultivar produces more pod yield than the resistant cultivar. The results demonstrated that, late sowing (3 weeks after normal sowing date) reduced significantly the number of emerged <i>O. crenata</i> shoots for both the resistant and the susceptible cultivars., Late sowing similarly contributed to a significant increase in pod yield (dry weight (kg)/plot) especially for Giza 843 (5.15 ± 0.02 Kg /plot), the resistant cultivar, which produced much higher pod yield than the susceptible Nubaria 1 cultivar (2.98± 0.06 Kg /plot) during the first season (2019 - 2020). During the second season (2020 - 2021), the pod yield was (3.85 ± 0.10) and (5.49± 0.76) Kg/plot for Giza 843 and Nubaria 1 cultivars, respectively, compared with the early sowing date. Furthermore, regarding both seasons, the seeds number per spike decreased significantly with the late sowing date in both the resistant and susceptible cultivars.

An Insight of Parasitic Weeds in Africa and Scientific Developments: A Review

Parasitic weeds are a major threat to food security in Africa and control measures mostly done by smallholder farmers are not effective in eradicating the parasites. This results in a yield loss up to 100%. Parasitic weeds comprise Alectra vogelii, Striga spp., Orobanche spp., Rafflesia spp., and Phoradendron spp. Parasitic attachment is successful when three necessary conditions have been fulfilled namely the compatible host, suitable environment, and parasitic weed. These species parasite plant species through special attachment features such as modified leaves, suckers, haustoria, or modified roots. In Africa, the variability of parasitic weeds is largely driven by environmental factors such as temperature, rainfall, soil type, and crop husbandry practices. Warmer temperatures create more hospitable conditions for certain parasitic weeds, and allowing them to spread to new areas. Parasitic weed control is vital for effective crop production and the control strategies can be achieved through integrated weed control method that embraces mechanical, cultural, chemical, and biological methods. However, the most effective and crucial method is the cultivation of resistant varieties that provide long-term protection against parasitic weeds. Studies have been done on host-parasite attachment where dodder can send out new roots to infected neighbouring plants and spread their parasitic behaviour. More insight and knowledge should offer new goals for control within the life cycle of the parasitic weeds and their metabolic activities. Lastly, disciplines such as agronomy, plant breeding, nutrition, economics, and IT should play their roles effectively in combating parasitic weeds.

Genetic resources and breeding of maize for Striga resistance: a review.

The potential yield of maize (Zea mays L.) and other major crops is curtailed by several biotic, abiotic, and socio-economic constraints. Parasitic weeds, Striga spp., are major constraints to cereal and legume crop production in sub-Saharan Africa (SSA). Yield losses reaching 100% are reported in maize under severe Striga infestation. Breeding for Striga resistance has been shown to be the most economical, feasible, and sustainable approach for resource-poor farmers and for being environmentally friendly. Knowledge of the genetic and genomic resources and components of Striga resistance is vital to guide genetic analysis and precision breeding of maize varieties with desirable product profiles under Striga infestation. This review aims to present the genetic and genomic resources, research progress, and opportunities in the genetic analysis of Striga resistance and yield components in maize for breeding. The paper outlines the vital genetic resources of maize for Striga resistance, including landraces, wild relatives, mutants, and synthetic varieties, followed by breeding technologies and genomic resources. Integrating conventional breeding, mutation breeding, and genomic-assisted breeding [i.e., marker-assisted selection, quantitative trait loci (QTL) analysis, next-generation sequencing, and genome editing] will enhance genetic gains in Striga resistance breeding programs. This review may guide new variety designs for Striga-resistance and desirable product profiles in maize.

First Report of the Branched Broomrape (Phelipanche schultzii (Mutel) Pomel.) on Fennel (Foeniculum vulgare Mill.) in Morocco

Holoparasitic broomrape weeds (Orobanche and Phelipanche spp.) are a major biotic constraint limiting the production of important food crops. Parasitism caused by Phelipanche spp. is considered to be a serious threat, particularly in the Mediterranean region. In this study, the broomrape species collected from infested fennel fields in Sid L’Mokhtar in the Central West of Morocco was described and identified morphologically and molecularly. For molecular identification, 700 bp ITS regions were PCR-amplified from two representative individuals, OA and OY-4. The obtained sequences exhibited more than 99% similarity with the P. schultzii sequence (MT026593). In addition, maximum likelihood analysis placed our species with other referred P. schultzii in the same clade. Through molecular analysis, the broomrape species attacking fennel was identified as P. schultzii. This is the first record of the broomrape species P. schultzii parasitizing fennel (Foeniculum vulgare syn. Foeniculum officinale) in Morocco. Therefore, it should be considered that this parasite could spread to other cultivated fields causing severe yield losses, requiring urgent action through efficient control measures to avoid further spread of this parasitic weed.

Effective Striga control and yield intensification on maize farms in western Kenya with N fertilizer and herbicide-resistant variety.

Maize production in western Kenya is limited by the spread of parasitic weed Striga hermonthica and depletion of soil nutrient stocks. Nitrogen (N) fertilizer and imidazolinone resistant (IR) maize are key elements in the agronomic toolbox to control infestations and enhance yields. The circumstances under which their use, individually or combined, is most effective on farmer fields have not been well documented. Inappropriate management decisions and low returns on investments arise from this knowledge gap, causing hunger and poverty in smallholder communities to persist. Experiments were carried out on 60 fields in three different agroecosystems of western Kenya using full-factorial treatments with non-herbicide treated maize (DH) and herbicide treated maize (IR), and N fertilizer omission and application. Trials were stratified on a field with low and high soil fertility within individual farms and repeated over two seasons. Cultivating IR maize instead of DH maize decreased the emergence of Striga with 13 shoots m-2 on average while applying N fertilizer on DH maize led to a reduction of 5 shoots m-2 on average. Decreases of Striga by use of IR maize and N fertilizer were between 6 and 23 shoots m-2 larger at the site with high levels of infestation than at the sites with medium or low emergence. Input of N fertilizer increased grain harvests by 0.59 ton ha-1 on average while use of IR maize enhanced the productivity with 0.33 ton ha-1 on average. Use of N fertilizer had similar yield effects in all three sites, whereas use of IR maize at the site with high Striga emergence increased maize production by 0.26-0.39ton ha-1 more than at the sites with medium or low emergence. The greater Striga responses to IR maize and the greater yield responses to N fertilizer demonstrate their use could be optimized according to field conditions and management goals. Combining IR maize and N fertilizer has larger added yield benefits where their individual effects on grain productivity are smaller. Findings from this study indicate that farmers in western Kenya require guidance on how to align the use of herbicide resistant maize and inorganic N inputs with the level of Striga infestation and maize yield on their fields for effectively controlling the pernicious weed and enhancing food production.

Trenchant microbiological-based approach for the control of Striga: Current practices and future prospects

Striga species are obligate parasitic weeds most of which are members of the Orobanchaceae family. They are commonly associated with staple crops and constitute threats to food security, especially in Sub-Saharan Africa. They pose deleterious impacts on staple cereal crops like maize and pearl millet, resulting in 7–10 billion dollars yield losses or, in extreme infestations, entire crop losses. Farmers' limited knowledge about the weed (genetics, ecology, nature of the damage caused, complex life cycle, interactions with its host and associated microbes) and their attitude toward its control have negatively affected its management and sustainability. With the present Striga management such as mechanical, chemicals, cultural and biological measures, it is extremely difficult to achieve its active management due to nature of the association between host plants and parasites, which requires highly selective herbicides. The use of soil microbes has not been well explored in the management of Striga infection in African countries. However, many soil microorganisms have been considered viable biological control techniques for fighting parasitic weeds, due to their vast action and roles they play in the early stage of host-Striga interaction. Their application for pest control is well perceived to be cost-effective and eco-friendly. In this review, we gave a comprehensive overview of major knowledge gaps and challenges of smallholders in Striga management and highlighted major potentials of microbial-based approach with respect to the mechanisms of host-Striga-microbe interactions, and the metagenomics roles on Striga management that include understanding the microbe and microbial systems of Striga-infested soil.

Climate change and ecological intensification of agriculture in sub-Saharan Africa – A systems approach to predict maize yield under push-pull technology

Assessing effects of climate change on agricultural systems and the potential for ecological intensification to increase food security in developing countries is essential to guide management, policy-making and future research. ‘Push-pull’ technology (PPT) is a poly-cropping design developed in eastern Africa that utilizes plant chemicals to mediate plant–insect interactions. PPT application yields significant increases in crop productivity, by reducing pest load and damage caused by arthropods and parasitic weeds, while also bolstering soil fertility. As climate change effects may be species- and/or context-specific, there is need to elucidate how, in interaction with biotic factors, projected climate conditions are likely to influence future functioning of PPT. Here, we first reviewed how changes in temperature, precipitation and atmospheric CO2 concentration can influence PPT components (i.e., land use, soils, crops, weeds, diseases, pests and their natural enemies) across sub-Saharan Africa (SSA). We then imposed these anticipated responses on a landscape-scale qualitative mathematical model of maize production under PPT in eastern Africa, to predict cumulative, structure-mediated impacts of climate change on maize yield. Our review suggests variable impacts of climate change on PPT components in SSA by the end of the 21st century, including reduced soil fertility, increased weed and arthropod pest pressure and increased prevalence of crop diseases, but also increased biological control by pests’ natural enemies. Extrapolating empirical evidence of climate effects to predict responses to projected climate conditions is mainly limited by a lack of mechanistic understanding regarding single and interactive effects of climate variables on PPT components. Model predictions of maize yield responses to anticipated impacts of climate change in eastern Africa suggest predominantly negative future trends. Nevertheless, maize yields can be sustained or increased by favourable changes in system components with less certain future behaviour, including higher PPT adoption, preservation of field edge density and agricultural diversification beyond cereal crops.

Effect of histidine covalent modification on strigolactone receptor activation and selectivity

The parasitic weed Striga has led to billions of dollars’ worth of agricultural productivity loss worldwide. Striga detects host plants using compounds of the strigolactone class of phytohormones. Early steps in the strigolactone signaling pathway involve substrate binding and hydrolysis followed by a conformational change to an “active” or “closed” state, after which it associates with a MAX2-family downstream signaling partner. The structures of the inactive and active states of strigolactone receptors are known through X-ray crystallography, and the transition pathway from the inactive to active state in apo receptors has previously been characterized using molecular dynamics simulations. However, it also has been suggested that a covalent butenolide modification of the receptor on the catalytic histidine through substrate hydrolysis promotes formation of the active state. Using molecular dynamics simulations, we show that the presence of the covalent butenolide enhances activation in both AtD14, a receptor found in Arabidopsis, and ShHTL7, a receptor found in Striga, but the enhancement is ∼50 times greater in ShHTL7. We also show that several conserved interactions with the covalent butenolide modification promote transition to the active state in both AtD14 (non-parasite) and ShHTL7 (parasite). Finally, we demonstrate that the enhanced activation of ShHTL7 likely results from disruption of ShHTL7-specific histidine interactions that inhibited activation in the apo case. These results provide a possible explanation for difference in strigolactone sensitivity seen between different strigolactone-sensitive proteins and can be used to aid the design of selective modulators to control Striga parasites.

Influence of Two Desmodium Species Root Exudates on Haustorium Initiation and Attachment in Striga hermonthica (Del.) Benth

Striga hermonthica is a parasitic weed that causes significantyield losses in many important crops and affects the livelihood of millionsof people worldwide. A study was undertaken to examine the effects ofDesmodium. uncinatum (Jacq.) DC and D. dichotomum (Klein) DC rootexudates on initiation of haustorium and attachment of S. hermonthica. Aseries of laboratory experiments was conducted at the Gezira ResearchStation, Wad Medani, Sudan. D. uncinatum and D. dichotomum rootexudates, applied 24 hours subsequent to GR 24, a synthetic germinationstimulant, or simultaneously with it, did not induce haustorium initiation.D. uncinatum and D. dichotomum curtailed striga attachment to sorghumroots.

Diversity Analysis for Grain Nutrient Content and Agronomic Traits among Newly Bred Striga-Resistant and Fusarium oxysporum f.sp. strigae (FOS)-Compatible Sorghum Genotypes

The parasitic weed, Striga species, is among the major causes of yield and quality losses of cereal and legume crops in sub-Saharan Africa. The development of nutritionally enhanced genetic resources with Striga resistance is an overriding consideration in sorghum breeding programs. The objective of this study was to determine the genetic variability among 12 elite and newly bred sorghum (Sorghum bicolor (L.) Moench) lines with variable Striga resistance for agronomic performance and nutritional traits. The sorghum genotypes were analyzed for protein, amino acid profiles, and selected minerals. For agronomic traits, significant variations were observed for yield per plant that varied from 51.74 to 15.12 g/plant, with a mean of 29.77 g/plant. The tested genotypes showed significant (p &lt; 0.05) variation in protein, amino acid, iron, and zinc contents. The crude protein content varied from 9.59 to 13.60%, with a mean of 11.64%. The lysine values ranged from 1.13 to 3.08%, with a mean of 2.15%, while methionine content varied from 0.42 to 1.58%, with a mean of 0.87%. Iron content ranged from 35.26 to 156.32 mg/kg with a mean of 78.32 mg/kg, while zinc content varied from 14.45 to 44.46 mg/kg with a mean of 24.91 mg/kg. The following genotypes: AS1, PAN8816, 672, Macia, AS436, 3984 × 630, AS426 × 672, and 105 × 654 were identified as having superior agronomic and nutritional qualities for commercialization and sorghum breeding programs.

Comparative Insights into the Microbial Diversity and Community Structure of Striga hermonthica-Infested Maize Rhizosphere

The damaging competition between crops and parasitic weeds has a negative impact on agricultural productivity; however, the impact of disturbance on the soil’s microbial community has received less attention. Hence, this study investigates the microbial composition and diversity of the maize rhizosphere infected with Striga hermonthica using a shotgun sequencing approach from two maize-growing fields (Eruwa, Nigeria and Mbuzini, South Africa). The rhizosphere soil DNA was extracted from infested soil using a Nucleospin soil genomic DNA extraction kit and sequenced on an Illumina platform. The dominant phyla were Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Acidobacteria, Chloroflexi, Cyanobacteria, Planctomycetes, Verrucomicrobia, Chlorobi, Proteobacteria, Firmicutes, Nitrospirae, Thermotogae, Synergistetes, Ascomycota, Euryarchaeota, and Crenarchaeota. Bacteria phyla were observed to be of higher proportion in the rhizosphere soil samples obtained from Striga-infested maize field in Eruwa (Es) than those recovered from Mbuzini (Ms). The alpha diversity of microbial communities indicated insignificance differences (p &gt; 0.05) between the five taxonomical groups (phylum, class, order, family, and genus), while the beta diversity produced a significant (p = 0.01, R = 0.52) difference in the microbial diversity of the infested soil. In summary, the study sheds light on the diversity and composition of the microbiome of Striga hermonthica-infested soil, which influences the microbial functions in the management and sustenance of plant health against parasitic weeds.

Synthesis of aryloxyacetylthiourea derivatives for the development of radicle elongation inhibitor of parasitic weeds

Aryloxyacetylthiourea, 1-(3,4-dichlorophenyl)-3-(2-phenoxyacetyl)thiourea (PI-28), has attracted attention as a lead compound for the development of radicle elongation inhibitors in Orobanche minor seeds germination. In this study, we synthesized PI-28 and its derivatives in two steps using commercially available phenols, 2-chloroacetamide, and N-aryl isothiocyanates. In this method, 2-aryloxyacetanilides, which are also attractive as bioactive compounds, were obtained as byproducts. According to the result of the control experiment, the formation of byproducts was due to the loss of isothiocyanate moiety from the formed aroyloxyacetylthioureas caused by the action of another aryl isothiocyanate during the reaction. Moreover, we have developed a one-pot synthesis method for PI-28 derivatives with comparable overall yields.

Identification of Host Critical Stage Affected by Orobanche crenata and Variation in the Resistance of Faba Bean Genotypes under Infested Field and Controlled Conditions in Ethiopia

Orobanche crenata is a serious parasitic weed and a major constraint on legume crops, particularly for faba bean, which causes about 75–100% of yield losses in Ethiopia. Twenty faba bean genotypes were evaluated in Orobanche infested fields and pot experiments in Tigray, Ethiopia. The aim of the study was to determine the critical stage of host plants affected by parasite and to evaluate resistance level of faba bean genotypes. The degree of infection and host resistance level was evaluated at three host growing stages (flowering, pod setting, and maturity stages) using different traits like number of Orobanche emerged per plant, per plot, incidence, and severity. The agronomic data such as stand count at emergence, flowering, pod setting, maturity, plant height, pod number, seed per pod, hundred seed weight, and grain yield were recorded from five and three randomly selected plants in the field and pot experiments, respectively. The analysis of variance showed that there were high significant variations p &lt; 0.01 in measured traits between the three host growing stages and between genotypes in agronomic traits. The effect of O. crenata on host plant was started from the flowering stage, but the pod setting stage is economically important stage at which actual effect of the parasite was observed both at field and pot experiments. Based on the result of the study, all tested traits at field and pot experiments allowed separating the faba bean genotypes into three groups: partially resistant and or tolerant genotypes “Ashange, Dide’a, and Obse,” moderately susceptible genotypes “Holleta, Selale, Wayu, Welki, Mesay, Bulga, Degaga, Gachena, Mosise, and Shalo,” and highly susceptible genotypes “Moti, Gebelcho, Dosha, Tumsa, Hachalu, and Tesfa Aloshe.”

Structure−Activity Relationship (SAR) Study of trans-Cinnamic Acid and Derivatives on the Parasitic Weed Cuscuta campestris

Cuscuta campestris Yunck. is a parasitic weed responsible for severe yield losses in crops worldwide. The selective control of this weed is scarce due to the difficult application of methods that kill the parasite without negatively affecting the infected crop. trans-Cinnamic acid is secreted by plant roots naturally into the rhizosphere, playing allelopathic roles in plant-plant communities, although its activity in C. campestris has never been investigated. In the search for natural molecules with phytotoxic activity against parasitic weeds, this work hypothesized that trans-cinnamic acid could be active in inhibiting C. campestris growth and that a study of a series of analogs could reveal key structural features for its growth inhibition activity. In the present structure-activity relationship (SAR) study, we determined in vitro the inhibitory activity of trans-cinnamic acid and 24 analogs. The results showed that trans-cinnamic acid's growth inhibition of C. campestris seedlings is enhanced in eight of its derivatives, namely hydrocinnamic acid, 3-phenylpropionaldehyde, trans-cinnamaldehyde, trans-4-(trifluoromethyl)cinnamic acid, trans-3-chlorocinnamic acid, trans-4-chlorocinnamic acid, trans-4-bromocinnamic acid, and methyl trans-cinnamate. Among the derivatives studied, the methyl ester derivative of trans-cinnamic acid was the most active compound. The findings of this SAR study provide knowledge for the design of herbicidal treatments with enhanced activity against parasitic weeds.

Genomic and Epigenomic Mechanisms of the Interaction between Parasitic and Host Plants.

Parasitic plants extract nutrients from the other plants to finish their life cycle and reproduce. The control of parasitic weeds is notoriously difficult due to their tight physical association and their close biological relationship to their hosts. Parasitic plants differ in their susceptible host ranges, and the host species differ in their susceptibility to parasitic plants. Current data show that adaptations of parasitic plants to various hosts are largely genetically determined. However, multiple cases of rapid adaptation in genetically homogenous parasitic weed populations to new hosts strongly suggest the involvement of epigenetic mechanisms. Recent progress in genome-wide analyses of gene expression and epigenetic features revealed many new molecular details of the parasitic plants' interactions with their host plants. The experimental data obtained in the last several years show that multiple common features have independently evolved in different lines of the parasitic plants. In this review we discuss the most interesting new details in the interaction between parasitic and host plants.

Are root parasitic broomrapes still a good target for bioherbicide control?

Root parasitic weeds of the genera Orobanche and Phelipanche (commonly named broomrapes) are responsible for enormous yield losses of several crops all around the world. Traditional weed management methods, including among others the use of herbicides, soil fumigation and solarisation, and mechanical, agronomic, or physical methods, may have limits of use or can provide a modicum of control. Difficulties in controlling parasitic weeds are due both to the enormous number of seeds produced by each plant that can remain viable, even in the absence of a host, for many years and to the unique physiological and biological properties of the parasite. Although considered a suitable and promising approach for a long time, biological control, in particular with the use of microbial organisms or with compounds stimulating or inhibiting seed germination, has had no commercial success, and no products have reached the market. The present article aims at making a quick overview of the bioherbicide approaches attempted until now, briefly discussing the causes of the failures and the possibility to improve biocontrol agents' effectiveness. Indeed, despite the failures, the 'bioherbicide' approach deserves a renewed interest in light of the enormous scientific and technological progress made in the last years, which offers new chances of success. This article is protected by copyright. All rights reserved.

Are pests adapting to the push-pull system? Ecologically intensified farms in Kenya maintain successful pest control over time

Ecological intensification utilizes biodiversity to maintain agricultural yields while reducing negative environmental impacts. While pest management is a common goal of ecological intensification, studies examining ecologically intensified pest management systems over longer time scales are rare. Using the push-pull system in Western Kenya, we examine whether pest abundance (for both insects and parasitic weeds) and yield vary with time since a given push-pull field was established. With a total of 1880 data points from 476 unique farmers and 24 cropping seasons, we found that pests declined with time since establishment in both push-pull and nearby control fields, while yield improved with time since establishment in push-pull fields. Although this study did not directly address mechanisms, it seems likely that pests in the push-pull system are not successfully adapting to overcome its pest management effects given the continued declines in pest abundance over time. Our data suggest that ecologically intensified agriculture may be resilient against pest adaptation over time, maintaining consistently high yields.

Mapping quantitative trait loci and predicting candidate genes for Striga resistance in maize using resistance donor line derived from Zea diploperennis.

The parasitic weed, Striga is a major biological constraint to cereal production in sub-Saharan Africa (SSA) and threatens food and nutrition security. Two hundred and twenty-three (223) F2:3 mapping population involving individuals derived from TZdEI 352 x TZEI 916 were phenotyped for four Striga-adaptive traits and genotyped using the Diversity Arrays Technology (DArT) to determine the genomic regions responsible for Striga resistance in maize. After removing distorted SNP markers, a genetic linkage map was constructed using 1,918 DArTseq markers which covered 2092.1cM. Using the inclusive composite interval mapping method in IciMapping, twenty-three QTLs influencing Striga resistance traits were identified across four Striga-infested environments with five stable QTLs (qGY4, qSC2.1, qSC2.2, qSC5, and qSC6) detected in more than one environment. The variations explained by the QTLs ranged from 4.1% (qSD2.3) to 14.4% (qSC7.1). Six QTLs each with significant additive × environment interactions were also identified for grain yield and Striga damage. Gene annotation revealed candidate genes underlying the QTLs, including the gene models GRMZM2G077002 and GRMZM2G404973 which encode the GATA transcription factors, GRMZM2G178998 and GRMZM2G134073 encoding the NAC transcription factors, GRMZM2G053868 and GRMZM2G157068 which encode the nitrate transporter protein and GRMZM2G371033 encoding the SBP-transcription factor. These candidate genes play crucial roles in plant growth and developmental processes and defense functions. This study provides further insights into the genetic mechanisms of resistance to Striga parasitism in maize. The QTL detected in more than one environment would be useful for further fine-mapping and marker-assisted selection for the development of Striga resistant and high-yielding maize cultivars.

Association mapping for broomrape resistance in sunflower.

Sunflower breeding for resistance to the parasitic plant sunflower broomrape (Orobanche cumana Wallr.) requires the identification of novel resistance genes. In this research, we conducted a genome-wide association study (GWAS) to identify QTLs associated with broomrape resistance. The marker-trait associations were examined across a germplasm set composed of 104 sunflower accessions. They were genotyped with a 600k AXIOM® genome-wide array and evaluated for resistance to three populations of the parasite with varying levels of virulence (races EFR, FGV, and GTK) in two environments. The analysis of the genetic structure of the germplasm set revealed the presence of two main groups. The application of optimized treatments based on the general linear model (GLM) and the mixed linear model (MLM) allowed the detection of 14 SNP markers significantly associated with broomrape resistance. The highest number of marker-trait associations were identified on chromosome 3, clustered in two different genomic regions of this chromosome. Other associations were identified on chromosomes 5, 10, 13, and 16. Candidate genes for the main genomic regions associated with broomrape resistance were studied and discussed. Particularly, two significant SNPs on chromosome 3 associated with races EFR and FGV were found at two tightly linked SWEET sugar transporter genes. The results of this study have confirmed the role of some QTL on resistance to sunflower broomrape and have revealed new ones that may play an important role in the development of durable resistance to this parasitic weed in sunflower.

Host-guest complexation of phthalimide-derived strigolactone mimics with cyclodextrins. Application in agriculture against parasitic weeds.

Parasitic weeds are noxious plants that damage crops of economic relevance, especially in Mediterranean and African countries. The strategy of suicidal germination was proposed to deal with this plague by using seed germination inducers that work as a pre-emergence herbicide and reduce the parasitic seed load before sowing. N-Substituted phthalimides with a furanone ring were found to be efficient in inducing the germination of Phelipanche ramosa and Orobanche cumana, two of the most problematic parasitic weeds of crops. However, the solubility of these compounds in water is low. A strategy for enhancing their aqueous solubility is the synthesis of host-guest complexes with cyclodextrins. Three bioactive phthalimide-lactones (PL01, PL04, and PL07) were selected and studied to form complexes of increased water solubility with α-, β-, HP-β-, and γ-cyclodextrin. The complexes obtained by the coprecipitation method, with increased aqueous solubility (up to 3.8 times), were studied for their bioactivity and they showed similar or slightly higher bioactivity than free phthalimide-lactones, even without the addition of organic solvents. A theoretical study using semiempirical calculations of molecular models including a solvation system confirmed the physicochemical empirical results. These results demonstrated that cyclodextrins can be used to improve the physicochemical and biological properties of parasitic seed germination inducers.