Recent research progress in combatting root parasitic weeds

2-oxoglutarate-dependent dioxygenases and BAHD acyltransferases drive the structural diversification of orobanchol in Fabaceae plants

Strigolactones (SLs), a class of plant apocarotenoids, serve dual roles as rhizosphere-signaling molecules and plant hormones. Orobanchol, a major naturally occurring SL, along with its various derivatives, has been detected in the root exudates of plants of the Fabaceae family. Medicaol, fabacyl acetate, and orobanchyl acetate were identified in the root exudates of barrel medic (Medicago truncatula), pea (Pisum sativum), and cowpea (Vigna unguiculata), respectively. Although the biosynthetic pathway leading to orobanchol production has been elucidated, the biosynthetic pathways of the orobanchol derivatives have not yet been fully elucidated. Here, we report the identification of 2-oxoglutarate-dependent dioxygenases (DOXs) and BAHD acyltransferases responsible for converting orobanchol to these derivatives in Fabaceae plants. First, the metabolic pathways downstream of orobanchol were analyzed using substrate feeding experiments. Prohexadione, an inhibitor of DOX inhibits the conversion of orobanchol to medicaol in barrel medic. The DOX inhibitor also reduced the formation of fabacyl acetate and fabacol, a precursor of fabacyl acetate, in pea. Subsequently, we utilized a dataset based on comparative transcriptome analysis to select a candidate gene encoding DOX for medicaol synthase in barrel medic. Recombinant proteins of the gene converted orobanchol to medicaol. The candidate genes encoding DOX and BAHD acyltransferase for fabacol synthase and fabacol acetyltransferase, respectively, were selected by co-expression analysis in pea. The recombinant proteins of the candidate genes converted orobanchol to fabacol and acetylated fabacol. Furthermore, fabacol acetyltransferase and its homolog in cowpea acetylated orobanchol. The kinetics and substrate specificity analyses revealed high affinity and strict recognition of the substrates of the identified enzymes. These findings shed light on the molecular mechanisms underlying the structural diversity of SLs.

Harnessing plant resistance against Striga spp. parasitism in major cereal crops for enhanced crop production and food security in Sub-Saharan Africa: a review

Given their long-lasting seed viability, 15–20-year lifespan and their high seed production levels, a significant impact of parasitic plant Striga spp. on African food production is inevitable. Over the last decades, climate change has increasingly favoured the adaptability, spread and virulence of major Striga species, S. hermonthica and S. asiatica, across arable land in Sub-Saharan Africa (SSA). These parasitic weeds are causing important yield losses on several staple food crops and endangering food and nutritional security in many SSA countries. Losses caused by Striga spp. are amplified by low soil fertility and recurrent droughts. The impact of Striga parasitism has been characterized through different phenotypic and genotypic traits assessment of their host plants. Among all control strategies, host-plant resistance remains the most pro-poor, easy-to-adopt, sustainable and eco-friendly control strategy against Striga parasitism. This review highlights the impact of Striga parasitism on food security in SSA and reports recent results related to the genetic basis of different agronomic, pheno-physiological and biochemical traits associated with the resistance to Striga in major African cereal food crops.

Agriculture without paraquat is feasible without loss of productivity-lessons learned from phasing out a highly hazardous herbicide

A small proportion of the thousands of pesticides on the market today are associated with a disproportionately high incidence of severe acute pesticide poisoning and suicide. Paraquat stands out as one of the most lethal pesticides in common use, frequently involved in fatal incidents due to suicides or accidental exposure. Even though paraquat has been banned in over 67 countries, it is still widely used in many others, particularly in Asia and Latin America. Based on a literature review and consultations, this paper identifies options for replacing paraquat and distils practical lessons from numerous successes around the world. Our aim is to support regulators, policymakers, agronomists and the supply chain sector with practical information related to phasing out paraquat. Production data consistently failed to show any negative effects of banning paraquat on agricultural productivity. A wide range of alternative approaches to weed management and crop defoliation are available, many of which do not rely on herbicides. Over 1.25 million farmers in low- and middle-income countries (LMICs) successfully produce a range of crops for private voluntary standards (PVS) in food and fiber supply chains which prohibit paraquat use. We conclude from the findings of this study that eliminating paraquat will save lives without reducing agricultural productivity. Less hazardous and more sustainable alternatives exist. To enhance successful adoption and uptake of these methods on a wide scale, farmers require training and support within an enabling policy environment.

Mycorrhiza, Charcoal, and Rocket Salad Powder as Eco-friendly Methods for Controlling Broomrape Weed in Inter-planted Faba Bean with Flax

Till now, there is no complete program that could be implemented to eradicate the parasitic weeds such as broomrape because of their complex life cycle. Therefore, the current research aimed to find new and safe agricultural practices to solve, partially at least, the issues of broomrape in faba bean fields. The experiment was conducted for two winter seasons of 2018/2019 and 2019/2020 in naturally infested field with broomrape. Treatments involved application of mycorrhiza, charcoal and rocket salad powder, glyphosate–isopropylammonium herbicide, and weedy check applied whether with sole planting of faba bean and interplanting with flax. The experiment was designed in a strip plot based on completely randomized block arrangement with six replicates. Broomrape number and weight, infested faba bean plants, faba bean agronomic traits, and seed nutrient uptake were estimated. In both seasons, glyphosate whether with sole or interplanting patterns recorded the lowest values of broomrape number plot‒1 and broomrape weight plot‒1 without significant variation with charcoal and rocket salad applied in interplanted plots. The maximum increases in faba bean seed yield were observed with application of charcoal × sole or interplanting pattern and rocket salad × interplanting pattern in the 2018/2019 season as well as charcoal, mycorrhiza, and rocket salad with sole pattern in the 2019/2020 season. Charcoal, mycorrhiza, and rocket salad were effective practices whether under sole or interplanting patterns for improving nutrient uptake, especially in the first season. In the second season, rocket salad with sole or interplanting pattern was the stable interaction for enhancing all nutrient uptake. Reducing broomrape hazards expressed in low number and weight with less infested faba bean plants was confined by application of mycorrhiza, charcoal, and rocket salad powder whether with sole planting of faba bean and interplanting with flax. Hence, faba bean farmers are advised to apply such promising safe practices for sustaining faba bean cultivation in lands infested by broomrape.

Crop diversification and parasitic weed abundance: a global meta-analysis

Parasitic weeds cause huge annual losses to food production globally. A small number of species from the genera Cuscuta, Orobanche, Phelipanche and Striga have proliferated across many agroecological zones. Their control is compromised due to the lack of efficacy of conventional herbicides and their rapid adaptation to new resistant crop cultivars. A broad range of studies suggest consistent reductions in parasitic weed densities owing to increased spatial (intercropping) and temporal diversity (crop rotation). However, to date, no synthesis of this body of research has been published. Here we report the results of a meta-analysis using 1525 paired observations from 67 studies across 24 countries, comparing parasitic weed density and crop yields from monocrop and more diverse cropping systems. We found both spatial and temporal crop diversification had a significant effect on parasitic weed density reduction. Furthermore, our results show effects of spatial diversification are stronger in suppressing parasitic weeds than temporal effects. Furthermore, the analysis indicates intercrops which alter both microclimate and soil chemistry (e.g. Crotalaria, Stylosanthes, Berseem clover and Desmodium) are most effective in parasitic weed management. This analysis serves to underline the viability of crop diversification as a tool to enhance food security globally.

Identification of risk areas for Orobanche cumana and Phelipanche aegyptiaca in China, based on the major host plant and CMIP6 climate scenarios

Parasitic broomrape of the genus Orobanche poses a formidable threat to producing many crops in Europe, Africa, and Asia. Orobanche cumana and Phelipanche aegyptiaca are two of China's most destructive root parasitic plants, causing extreme sunflower, tomato, melon, and tobacco damage. However, the potentially suitable areas of O. cumana and P. aegyptiaca in China have not been predicted, and little is known about the important environmental factors that affect their extension. Due to their invasiveness and economic importance, studying how climate change and host plants may affect broomrapes’ distribution is necessary. In the study, we first predicted the potentially suitable areas of the invasive weeds (O. cumana and P. aegyptiaca) and their susceptible host plants (Helianthus annuus and Solanum lycopersicon) using MaxEnt. Then, the risk zones and distribution shifts of two broomrapes under different climate conditions were identified by incorporating the distribution of their susceptible host plants. The results highlighted that the potential middle‐ and high‐risk zones for O. cumana and P. aegyptiaca amounted to 197.88 × 10⁴ km² and 12.90 × 10⁴ km², respectively. Notably, Xinjiang and Inner Mongolia were the highest‐risk areas within the distribution and establishment of O. cumana and P. aegyptiaca. Elevation and topsoil pH were the decisive factors for shaping O. cumana distribution; precipitation seasonality and annual precipitation were the dominant bioclimatic variables limiting the spread of P. aegyptiaca. The potentially suitable areas and risk zones of O. cumana would decrease significantly, and those of P. aegyptiaca would fluctuate slightly under future climate change scenarios. Overall, our study suggested that the two broomrapes’ risk zones will significantly northward to higher latitudes. The results will provide suggestions for preventing O. cumana and P. aegyptiaca.

Response of Faba bean to intercropping, biological and chemical control against broomrape and root rot diseases

Multispecies cropping systems contribute to sustainable agriculture with multiple ecosystem services. Effects of intercropping of various crops with faba beans on growth and yield parameters and disease severity of root rot, damping off and broomrape were investigated. This study was implemented in the laboratory, greenhouse and field to investigate the effect of the intercropping systems (fenugreek + faba bean, lupine + faba bean, garlic + faba bean and sole faba bean). The intercropping systems were combined with the application of arbuscular mycorrhiza fungi (AMF) and yeast as bio-control agents, compared to chemical application of herbicides (Glyphosate) and fungicides (Rizolex-T50), to control rot root diseases and broomrape weeds, Orobanche spp., of faba bean plants in vivo and under the naturally infested field. In vitro, yeast and Rizolex-T50 significantly inhibited mycelial growth of root pathogenic fungi. Intercropping with garlic and/or application of Rizolex-T, significantly decreased the incidence and disease index of root rot and damping-off diseases, meanwhile increased percentage of survival plants. In vivo, intercropping with fenugreek and/or application of Glyphosate, significantly reduced the number/weight of spikes/plot of broomrapes. Intercropping with fenugreek combined with AMF application promoted crop growth and significantly increased yield components. The AMF enhanced seed yield/ha when applied to the intercropping of faba bean + fenugreek and faba bean + garlic, showing the highest seed yield/ha with 3.722 and 3.568 ton/ha, respectively. Intercropping of faba bean with garlic integrated with AMF revealed the highest values of LER, 2.45, and net return, 2341 US$/ha. Our results suggested that using faba bean–garlic intercrop along with AMF inoculation can reduce root rot disease, damping off and broomrapes, as well as enhance the profitability of Egyptian farmer and sustainable production.

Current progress in Striga management

The Striga, particularly S. he rmonthica, problem has become a major threat to food security, exacerbating hunger and poverty in many African countries. A number of Striga control strategies have been proposed and tested during the past decade, however, further research efforts are still needed to provide sustainable and effective solutions to the Striga problem. In this paper, we provide an update on the recent progress and the approaches used in Striga management, and highlight emerging opportunities for developing new technologies to control this enigmatic parasite.

Applications of plant growth promoting bacteria and Trichoderma spp. for controlling Orobanche crenata in faba bean

Background

Orobanche crenata is an obligate root parasite belonging to Orbanchaceae. Broomrape causes great damage to the faba bean. Several attempts were applied for controlling parasitic weeds. So, the aim of this work is to study the application of Trichoderma spp. as well as three rhizobacteria species in comparison to herbicidal effect of Glyphosate (Glialka 48% WSC) for controlling broomrape infesting faba bean (Vicia faba).

Materials and methods

Three pot experiments were carried out in the greenhouse of the National Research Centre, Dokki, Giza, Egypt during two successive winter seasons. Trichoderma inocula were adjusted to 3.6 × 108 propagules/ml and the bacterium inocula were adjusted at 107–109 colony-forming unit (CFU)/ml. All treatments were applied, before 1 week of sowing, at rate of 50 ml per pot in experiments I and II, while 100 ml per pot in experiment III.

Results

Trichoderma spp. (T. harzianum, T. viride and T. vierns) as well as three rhizobacteria species (Pseudomonas fluorescens, Bacillus subtilis and Bacillus pumilus) enhanced the growth parameters in faba bean plants, i.e. shoot length, shoot fresh weight, shoot dry weight and leaf number in the first experiment when applied without O. crenata infection. In the second experiment, all bio-control could protect plants against O. crenata infection, where it had better juvenile number reduction, than glyphosate after 2 months of application. Both B. subtilis and B. pumilus had the highest reduction to juvenile fresh weight, while their effect was equal to herbicide for juvenile dry weight, respectively. The bio-control agents had high effects until the 4th month, but it was less than that of the herbicide. In experiment III, the bio-control agents could highly reduce the juvenile parameters after 2 months, as well as juvenile fresh weight and juvenile dry weight after 4 months, than the herbicide, respectively. The bio-control agents were effective until 6 months, but less than the herbicide effect. All bio-control treatments highly increased the plant growth parameters, than the herbicide.

Conclusion

The application of Trichoderma spp. as well as rhizobacteria species could play an important role in controlling broomrape in faba bean as a natural bioherbicide.

The Effect of Virulence and Resistance Mechanisms on the Interactions between Parasitic Plants and Their Hosts

Parasitic plants have a unique heterotrophic lifestyle based on the extraction of water and nutrients from host plants. Some parasitic plant species, particularly those of the family Orobanchaceae, attack crops and cause substantial yield losses. The breeding of resistant crop varieties is an inexpensive way to control parasitic weeds, but often does not provide a long-lasting solution because the parasites rapidly evolve to overcome resistance. Understanding mechanisms underlying naturally occurring parasitic plant resistance is of great interest and could help to develop methods to control parasitic plants. In this review, we describe the virulence mechanisms of parasitic plants and resistance mechanisms in their hosts, focusing on obligate root parasites of the genera Orobanche and Striga. We noticed that the resistance (R) genes in the host genome often encode proteins with nucleotide-binding and leucine-rich repeat domains (NLR proteins), hence we proposed a mechanism by which host plants use NLR proteins to activate downstream resistance gene expression. We speculated how parasitic plants and their hosts co-evolved and discussed what drives the evolution of virulence effectors in parasitic plants by considering concepts from similar studies of plant-microbe interaction. Most previous studies have focused on the host rather than the parasite, so we also provided an updated summary of genomic resources for parasitic plants and parasitic genes for further research to test our hypotheses. Finally, we discussed new approaches such as CRISPR/Cas9-mediated genome editing and RNAi silencing that can provide deeper insight into the intriguing life cycle of parasitic plants and could potentially contribute to the development of novel strategies for controlling parasitic weeds, thereby enhancing crop productivity and food security globally.

Exploration of resistance to Phelipanche aegyptiaca in tomato

BACKGROUND

Cultivated tomatoes are highly susceptible to the destructive parasite Phelipanche aegyptiaca. Wild relatives show the potential resistance for genetic improvement. However, their genetic and molecular mechanisms are still unknown.

RESULTS

Among 50 wild tomato accessions were evaluated for resistance to P. aegyptiaca, most of the wild relatives exhibited varying degrees of resistance compared to the cultivars. Solanum pennellii LA0716 performed the most promising and solid resistance with very low infection by the broomrape. The resistance involved in LA0716 was further confirmed by cytological analysis, and explored by employing a permanent introgression line (IL) population. Thirteen putative quantitative trait loci (QTLs) conferring the different resistance traits were identified. They are located on chromosomes 1, 2, 3, 4, 6, 8 and 9. The most attractive QTLs are positioned in IL6-2 and overlap with IL6-3. Specially, IL6-2 showed the highest and most consistent resistance for multiple traits and explained the major phenotypic variation of LA0716. Analysis of candidate genes involved in these regions showed that Beta (Solyc06g074240) and P450 (Solyc06g073570, Solyc06g074180 and Solyc06g074420) genes are substantially related to the strigolactone (SL) pathway. Transcript analysis further demonstrated that both Solyc06g073570 and Solyc06g074180 might play an important role in the reduction of P. aegyptiaca infection.

CONCLUSION

Germplasms resistant to P. aegyptiaca were found in wild tomato species. QTLs conferring P. aegyptiaca tolerance in LA0716 were identified. IL6-2 is identified as a prospective line possessing the major QTLs. The candidate genes would provide the availability to assist the introgression of the resistance in future breeding programmes. © 2020 Society of Chemical Industry.

Plant science's next top models

BACKGROUND

Model organisms are at the core of life science research. Notable examples include the mouse as a model for humans, baker's yeast for eukaryotic unicellular life and simple genetics, or the enterobacteria phage λ in virology. Plant research was an exception to this rule, with researchers relying on a variety of non-model plants until the eventual adoption of Arabidopsis thaliana as primary plant model in the 1980s. This proved to be an unprecedented success, and several secondary plant models have since been established. Currently, we are experiencing another wave of expansion in the set of plant models.

SCOPE

Since the 2000s, new model plants have been established to study numerous aspects of plant biology, such as the evolution of land plants, grasses, invasive and parasitic plant life, adaptation to environmental challenges, and the development of morphological diversity. Concurrent with the establishment of new plant models, the advent of the 'omics' era in biology has led to a resurgence of the more complex non-model plants. With this review, we introduce some of the new and fascinating plant models, outline why they are interesting subjects to study, the questions they will help to answer, and the molecular tools that have been established and are available to researchers.

CONCLUSIONS

Understanding the molecular mechanisms underlying all aspects of plant biology can only be achieved with the adoption of a comprehensive set of models, each of which allows the assessment of at least one aspect of plant life. The model plants described here represent a step forward towards our goal to explore and comprehend the diversity of plant form and function. Still, several questions remain unanswered, but the constant development of novel technologies in molecular biology and bioinformatics is already paving the way for the next generation of plant models.