A review of selected parasitic plants in Nigeria:converting harms to benefits

Parasitic plants are challenging to agricultural crops and forestry development,which are sources of major revenues in several countries,including Nigeria.Nevertheless,parasitic plants are important to human society as they have an abundance of bioactive compounds with pharmacological relevance.Thus,it becomes expedient to know the benefits of these plants and potential means of management.This review discusses four selected parasitic plants in Nigeria,namely Viscum album,Striga hermonthica,Tapinanthus bangwensis and Cuscuta campestris.Relevant information about their pharmacological relevance and biocontrol was obtained from credible databases,including the National Library of Medicine,SCOPUS,and Google Scholar.The review showed that all four plants have been extensively studied for their antioxidant and antitumor properties.Also,antimicrobial and anti-inflammatory activities are common pharmacological values among parasitic plants.These are largely due to the presence of abundant beneficial classes of phytocompounds.Furthermore,there is an increasing number of biocontrol studies on the use of microorganisms,such as Phaeobotryosphaeria visci,Sphaeropsis visci,Pandoraea pulminicol,Colletotrichum gloeosporioides,and Fusarium oxysporum in controlling and managing these seemingly disastrous plants.It is hoped that this review will spur further studies into the conservation and proper management of parasitic plants using strategically developed biocontrol.

Detection and Adaptation in Parasitic Angiosperm Host Selection

Developmental transitions in some parasitic angiosperms are tied directly to host-derived chemical cues (xenognosins). The obligate hemi-parasite Striga asiatica, initiates the root apical meristem population (germination), development of the host attachment organ (the haustorium), and shoot apical meristem initiation (seed coat shedding) in response to specific xengonosins. These checkpoints synchronize spatial and temporal tissue development. We have now exploited the external control over these developmental transitions to trace functional expression in haustorial organogenesis. Genes associated with phytohormone regulation, metabolism, vascular tissue development, and reactive oxygen species (ROS) production identified in this study suggest an elaborate and global response closely tied to plant defense and redox chemistry that may also be components of a more general quorum sensing-type mechanism in plants.

Parasitic plant in natural Boswellia papyrifera stands at Humera, Northern Ethiopia

In Boswellia papyrifera （Del.） Hochst natural stands, we stud- ied the association of parasitic plants with B. papyrifera trees from which frankincense was tapped and marketed for domestic and export markets. Data on the rate of infection of parasitic plants on B. papyrifera was collected in three transects located at separate locations around Baha kar, northern Ethiopia. Each transect had ten circular sample plots of 400 m2 and separated by 100 m. Species composition, DBH, height, crown di- ameter, number of main, secondary and tertiary branches and number of parasitic plants on individual trees were recorded. Sixteen tree species were recorded in the combined sample plots. The parasitic plant associ- ated with B. papyrifera was identified as Tapinanthus globiferus. This parasite infected 38% of Boswellia trees in sample plots. The infection rate of the parasitic plant varied from 1 to 33 per Boswellia tree. The infection of T. globiferus on B. papyrifera was predominantly limited to tertiary small branchlets arising from secondary branches; parasitic plants were absent on thick main and secondary branches. In all plots, infectionof T. globiferus was exclusively limited to Boswellia trees. The influence of T. globiferus parasitism on growth of Boswellia trees and its influence on yield of incense production needs further investigation. Management of natural stands for frankincense production should include measures to reduce infection by T. globiferus.

Viral pathogens and plant parasitic nematode

This special focus is dedicated to three parts：i）One of the most ubiquitous viral pathogens of stone fruit tree,Plum pox virus（PPV）;ii）a re-emerging pathogen,Wheat streak mosaic virus（WSMV）of cereal crops in Central Europe;and iii）a less studied plant parasitic,cyst-forming nematode in cereal crops Heterodera avenae.

Identification of Arceuthobium globosum using unmanned aerial vehicle images in a high mountain forest of central Mexico

The identification of forests infested by parasitic plants is important for the design of appropriate control and prevention strategies.Satellite images and geographic information systems are commonly used to analyze the presence of pest and parasitic plants in the forests.However there is a need for finer resolution.In the last decade,the use of unmanned aerial vehicles has become increasingly common for capturing aerial images(<10 cm per pixel).The objective of the study was to obtain RGB values(Red,Green and Blue)through the colorimetric ranges for use in identification of Yellow Dwarf Mistletoe(YDM)(Arceuthobium globosum)in aerial images taken in a forest of central Mexico via a programmed algorithm.Three tonalities of YDM were classified according to its phenological stages,viz.green(young stage),yellow(adult stage),and brown(senescence stage),considering two light intensities,sunny and cloudy.Non-parametric tests were used in statistical analyses.The Spearman test showed significant negative correlation(p<0.001)between phenological stage and colour,indicating that lower RGB values were associated with greater age.The differences between groups were analysed using Kruskal–Wallis(p<0.01)and Mann–Whitney tests(p<0.01).The applied algorithm identified the presence and predominant colours of YDM according to its phenological stage.

Genotypic Variation for Low Striga Germination Stimulation in Sorghum “Sorghum bicolor (L.) Moench” Landraces from Eritrea

Sorghum (Sorghum bicolour (L.) Moench), the second most important staple crop in Sub-Saharan Africa (SSA) after maize, is well adapted to marginal environments of drought stress and high temperatures. But besides drought stress, the obligate root-parasitic flowering plant Striga hermonthica is an equally economically important biotic stress in agro-ecological zones where soils are marginal. Notwithstanding widespread and intense Striga infestation, genetic variations in defence mechanisms against the parasite have been reported. Sorghum variants, producing low levels of chemical stimulants such as sorgolactones that deter the advance of Striga seed germination and are therefore deemed resistant to the parasite, have been also reported in a few studies. But the existence of sorghum genetic variation for this resistance especially among farmers’ landraces is yet to be demonstrated. The objective of this study was therefore to determine the levels of Striga germination stimulants in response to each of the 111 collected sorghum landraces and their progenies from Eritrea. The ability of a sorghum genotype to cause germination of a Striga seed as a measure of the amount of the germination stimulant produced was used to assess the resistance of these accessions. The data were recorded as Striga germination percentage by counting the number of germinated Striga seeds. Landraces EG47, EG1261, EG830, EG1076, EG54 and EG746 with 14.68%, 15.32%, 11.85%, 13.05%, 15.74% and 16.5% germination percentages respectively were found to stimulate low levels of Striga germination percentage compared to commercial checks, IS9830, SRN39, Framida, with 22.46%, 22.67%, 23.27% germination respectively. While these variants did not show complete resistance against Striga seed germination, the low level production of stimulant indicated their high level of resistance to Striga . These results implied that these accessions are likely potential sources of resistance against Striga infestation in SSA sorghum breeding programs.

Effects of the Residues of Cuscuta campestris and Mikania micrantha on Subsequent Plant Germination and Early Growth

Cuscuta campestris, a dodder, can parasitize and suppress a scrambling herbaceous to semi-woody perennial vine, Mikania micrantha, one of the most destructive weeds in the world. To assess the effects of the mixed residue of C. campestris and M. micrantha on the subsequent plant community, we conducted a one-year experiment on the germination and seedling growth of subsequent plant community after the application of C. campestris. Seven treatments of varying proportions of C. campestris and M. mierantha residue on 21 subject trees and shrubs, which were commonly found in South China, resulted in a germination rate of 35.3% for all 8 715 seeds from 18 species, ranging from 5.7 to 81.9%; the remaining 3 species failed to germinate. ANOVA analysis showed that the residue did not affect the germination, growth, or mortality of the trees and shrubs. The germinated C. campestris seeds from the residue coiled the seedlings of most of the species, but less than 4% host death caused by C. campestris. In addition, the residue did not affect the germination of the herbaceous seedlings originating from the loam, and the similarity coefficients of the germinated seedlings between the treatments were very high. These results suggested that the residue had no negative impact on the germination and early seedling stages of the tree, shrub and grass species of the subsequent plant community. The use of C. campestris residue had a positive effect on the growth of M. micrantha, but it did not change the trend of M. micrantha being suppressed because re-parasitization occurred soon after the growth restarted. No negative effect was detected on the other species as a result of the parasitization of C. campestris or by the use of the mixed residue. This suggests that C. campestris is likely to be an effective and promising ecologically safe native herbaceous agent for controlling M. micrantha.

Growth characteristics and reproductive output of dwarf mistletoeinfected Juniperus polycarpos in Iran

Dwarf mistletoes are parasitic flowering plants that infect conifers, resulting in substantial loss of growth and mortality. Recently, forest managers in Iran are contemplating whether infection of Juniperus polycarpos C. Koch forests by dwarf mistletoe, Arceuthobium oxycedri （DC.） M. Bieb, influences tree vigor and contributes to insuffieient natural regeneration. The present study aimed at assessing the severity of infection and its impact on growth and reproductive output of./., polycar- pos. Infected and uninfected trees （n =20 each） were selected for assess- ment of diameter, height, crown area, and crown volume as well as quantity and quality of cones and seeds. The severity of infection of trees was determined by Hawksworth＇s 6-class dwarf mistletoe rating （DMR） system. The DMR system revealed that 40% of the infected sample trees were lightly infected （DMR =1-2） and 60% were moderately infected （DMR =3--4）. Growth characteristics did not differ significantly （p 〉 0.05） between infected and uninfected trees. However, moderate infec- tion affected the reproductive output of./. polycarpos by significantly （p 〈0.05） reducing the mean number of cones per unit area of the crown, increasing the number of damaged seeds, and reducing seed size and seedgermination capacity. We conclude that reproductive output of J.. poly- carpos is more sensitive than growth characters to moderate infection by juniper dwarf mistletoe, and this might partly account for poor natural regeneration.

The Use of RNA Interference in Enhancing Plant Resistance against Nematodes

Plant-parasitic nematodes caused severe yield loss in major crops all over the world.The most wild-used strategies to combat the nematodes is the chamical nematicides,but the overuse of synthetic nematicides threaten sustainable agriculture development.Other strategies,like resistance cultivars and crop rotation,have limited efficiency.Thus,the utilization of molecular biotechnology like RNA interference(RNAi)would be one of the alternative ways to enhance plant resistance against nematodes.RNAi has already used as a tool for gene functional analysis in a wide range of species,especially in the non-parasitic nematode,Caenorhabtidis elegans.In plant-parasitic nematodes,RNAi is induced by soaking nematodes with double strand RNA(dsRNA)solution mixed with neurostimulants,which is called in vitro RNAi delivery method.In another way around,in planta RNAi method,which is Host-mediated RNAi approach also showed a great success in conferring the resistance against root-knock nematodes.Two main advantages of RNAi-based transgenics are RNAi technology do not produce any functional foreign proteins and it target organisms in a sequence-specific way.Even though the development of RNAi-based transgenics against plant-parasitic nematodes is still in the initial phase,it offers the prospect into a novel nematode control strategy in the future.

Unravelling host-mediated effects on hemiparasitic Mexican mistletoe Psittacanthus calyculatus(DC.)G.Don traits linked to mutualisms with pollinators and seed dispersers

Aims While the influence of mistletoe-host interactions on each other’s evolution is well-recognized,the role of interactions between mis-tletoes and its mutualistic pollinators and seed dispersers mediated by host species is relatively unexplored.Methods Here,we examine the effects of host species(Mexican hawthorn Crataegus mexicana DC,black cherry Prunus serotina Ehrh.,leather-leaf Mexican oak Quercus crassipes Bonpl.)on flower morphology,nectar production,pollinator visitation rate and female reproduct-ive fitness in hemiparasitic Mexican mistletoe Psittacanthus caly-culatus(DC.)G.Don(Loranthaceae)populations at three different locations.We first measured the lengths of corolla,style,stamen,exerted stamen and anther,the length and width of the ovary and nectar availability for mistletoe flowers in natural populations.Then,we evaluated flower visitation and measured(length and width)and weighed the fruits and its seeds of mistletoes growing on each of the three host species.Finally,we evaluated the effects of host species,location and flower traits on fruit or seed size variation(both as proxies of reproductive fitness).Important Findings We found mistletoes growing on natural hosts P.serotina and Q.crassipes produced larger flowers,fruits and seeds than mistle-toes on cultivated C.mexicana.However,these differences varied across space.The amount of available nectar and hummingbird vis-itation rates in flowers of mistletoes on C.mexicana was higher at the three sites than in flowers of mistletoes on P.serotina or Q.cras-sipes.The effects of host species,study site and floral trait covariates affected significantly all fitness measures,indicating that mistletoes’reproductive fitness is affected differently depending on the host species and their site of occurrence.These host-associated differ-ences in reproduction might have implications for interactions with mutualistic vectors.

New Strigolactone Analogs as Plant Hormones with Low Activities in the Rhizosphere

Strigolactones （SLs） are known not only as plant hormones, but also as rhizosphere signals for establishing symbiotic and parasitic interactions. The design of new specific SL analogs is a challenging goal in understanding the basic plant biology and is also useful to control plant architectures without favoring the development of parasitic plants. Two different molecules （23 （3＇-methyI-GR24）, 31 （thia-3＇-methyl-debranone-like molecule）） already described, and a new one （AR36）, for which the synthesis is presented, are biologically compared with the well-known GR24 and the recently identified CISA-1. These different structures emphasize the wide range of parts attached to the D-ring for the bioactivity as a plant hormone. These new compounds possess a common dimethylbutenolide motif but their structure varies in the ABC part of the molecules： 23 has the same ABC part as GR24, while 31 and AR36 carry, respectively, an aromatic ring and an acyclic carbon chain. Detailed information is given for the bioactivity of such derivatives in strigolactone synthesis or in perception mutant plants （pea rmsl and rms4, Arabidopsis max2 and, max4） for different hormonal functions along with their action in the rhizosphere on arbuscular mycorrhizal hyphal growth and parasitic weed germination.

Efficient Mimics for Elucidating Zaxinone Biology and Promoting Agricultural Applications

Zaxinone is an apocarotenoid regulatory metabolite required for normal rice growth and development.In addition,zaxinone has a large application potential in agriculture,due to its growth-promoting activity and capability to alleviate infestation by the root parasitic plant Striga through decreasing strigolactone(SL)production.However,zaxinone is poorly accessible to the scientific community because of its laborious organic synthesis that impedes its further investigation and utilization.In this study,we developed easy-to-synthesize and highly efficient mimics of zaxinone(MiZax).We performed a structure-activity relationship study using a series of apocarotenoids distinguished from zaxinone by different structural features.Using the obtained results,we designed several phenyl-based compounds synthesized with a high-yield through a simple method.Activity tests showed that MiZax3 and MiZax5 exert zaxinone activity in rescuing root growth of a zaxinone-deficient rice mutant,promoting growth,and reducing SL content in roots and root exudates of wild-type plants.Moreover,these compounds were at least as efficient as zaxinone in suppressing transcript level of SL biosynthesis genes and in alleviating Striga infestation under greenhouse conditions,and did not negatively impact mycorrhization.Taken together,MiZax are a promising tool for elucidating zaxinone biology and investigating rice development,and suitable candidates for combating Striga and increasing crop growth.

Confirming Stereochemical Structures of Strigolactones Produced by Rice and Tobacco

Major strigolactones （SLs） produced by rice （Oryza sativa L. cv. Nipponbare） and tobacco （Nicotiana tabacum L. cv. Michinoku No. 1） were purified and their stereochemical structures were determined by comparing with optically pure synthetic standards for their NMR and CD data and retention times and mass fragmentations in ESI-LC/MS and GC-MS. SLs purified from root exudates of rice plants were orobanchol, orobanchyl acetate, and ent-2＂-epi-5-deoxystr- igol. In addition to these SLs, 7-oxoorobanchyl acetate and the putative three methoxy-5~deoxystrigol isomers were detected by LC-MS/MS. The production of 7-oxoorobanchyl acetate seemed to occur in the early growth stage, as it was detected only in the root exudates collected during the first week of incubation. The root exudates of tobacco contained at least 11 SLs, including solanacol, solanacyl acetate, orobanchol, ent-2＂-epi-orobanchol, orobanchyl acetate, ent-2＇- epi-orobanchyl acetate, 5-deoxystrigol, ent-2＂-epi-5-deoxystrigol, and three isomers of putative didehydro-orobanchol whose structures remain to be clarified. Furthermore, two sorgolactone isomers but not sorgolactone were detected as minor SLs by LC-MS/MS analysis. It is intriguing to note that rice plants produced only orobanchol-type SLs, derived from ent-2＂-epi-5-deoxystrigol, but both orobanchol-type and strigol-type SLs, derived from 5-deoxystrigol were detected in tobacco plants.

New species and new records of Meliolaceae from Panama

Three new species of Meliolaceae,Appendiculella monsterae on Monstera deliciosa(Araceae),Asteridiella nitidae on Buddleja nitida(Scrophulariaceae),and Irenopsis chrysophylli on Chrysophyllum sp.(Sapotaceae),are described based on material collected in Panama.Eighteen species of Meliolaceae are reported for the first time for Panama,which include four first records for the Americas,viz.Ast.formosensis,Meliola indica,and M.pisoniae,previously known only from Asia,and M.dissotidis hitherto known only from Africa.Six species of plants are cited as hosts for meliolaceous fungi for the first time.In a phylogenetic hypothesis based on 28S nrDNA sequences,the position of Meliolales,including Appendiculella,Asteridiella,Endomeliola,Irenopsis,and Meliola,is found to be basal to Sordariomycetidae,Hypocreomycetidae,and Xylariomycetidae within Sordariomycetes.The five genera of Meliolaceae form a strongly supported clade.We suggest adopting the concept of the subclass Meliolomycetidae.The monophyly of Asteridiella cannot be confirmed.A hypothetical close relationship between Asteridiella and Appendiculella is not supported,but Endomeliola appears closely related to a species of Asteridiella.Two Meliola species on the same host family are closely related.