Genetic analysis of the maximum germination distance of Striga under Fusarium oxysporum f.sp.strigae biocontrol in sorghum

Maximum germination distance（MGD） is an important component of Striga resistance in sorghum. The objective of this study was to determine gene action influencing MGD of Striga hermonthica and Striga asiatica among selected sorghum lines treated with a biocontrol agent, Fusarium oxysporum f. sp. strigae（FOS） for effective breeding with Striga resistance, and FOS compatibility. Twelve sorghum genotypes were selected based on their Striga resistance, FOS compatibility, and superior agronomic performance. Selected genotypes were crossed using a bi-parental mating design to generate six families for genetic analysis. Agar-gel assays were used to determine low haustorium initiation factor（LHF） using the 12 parental lines, their F_1 progenies, backcross derivatives, and F_2 segregants in two sets. One set had S. hermonthica seed and the other one had S. asiatica seed. Both were treated with and without FOS. Genotypes were evaluated using a split-plot design with three replications and MGD data were recorded followed by generation mean analysis. FOS reduced MGD by 1cm under both S. hermonthica and S. asiatica infestations. Additive, dominance, and epistatic gene actions were involved in the control of MGD of the two Striga species in the evaluated populations. On average, the relative contribution of additive, additive×additive and dominance×dominance genetic effects on the MGD of S. hermonthica and S. asiatica, with FOS, were 20, 33, and 36%; and 21, 32, and 35%, respectively. Breeding methods exploiting these genetic effects may provide enhanced response to selection for Striga resistance and FOS compatibility in integrated Striga management（ISM） programmes.

Maize-Soybean Integration for Managing Striga hermonthica (Del.) Benth in the Sudan Savannah Zone of Ghana

Field experiments were conducted at Gore near Zebila in Bawku West District of the Upper East Region of Ghana during the 2015 and 2016 cropping season on four Striga tolerant maize varieties in maize/soybean integration alongside maize monocrop as a means of managing the devastating effects of Striga. The study determined the relative Striga tolerance of the maize varieties in terms of yield and yield components, as well as the most effective intercrop for the reduction of Striga seed bank. The treatment differences were not significant (p < 0.05) in affecting plant height, plant population, leaf area index (LAI), Striga count and Striga biomass. Similarly, yield components of maize such as height of cob attachment, cob length, cob weight, 100 seed weight, grain yield, as well as straw weight were not significantly affected by the treatments. There was no relativity of Striga stress tolerance in terms of yield and yield components of the four maize varieties. All the entries efficiently tolerated the biotic stress of Striga and further supported growth and grain yield equally. There was reduced S. hermonthica seed bank production in the soil in both cropping systems. The four maize varieties are proven tolerant materials to Striga infestation and are therefore recommended for long-term Striga seed bank depletion in the study area.

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.

Parasitic Plants <i>Striga</i>and <i>Phelipanche</i>Dependent upon Exogenous Strigolactones for Germination Have Retained Genes for Strigolactone Biosynthesis

Strigolactones are plant hormones with multiple functions, including regulating various aspects of plant architecture such as shoot branching, facilitating the colonization of plant roots by arbuscular mycorrhizal fungi, and acting as seed germination stimulants for certain parasitic plants of the family Orobanchaceae. The obligate parasitic species Phelipanche aegyptiaca and Striga hermonthica require strigolactones for germination, while the facultative parasite Triphysaria versicolor does not. It has been hypothesized that P. aegyptiaca and S. hermonthica would have undergone evolutionary loss of strigolactone biosynthesis as a part of their mechanism to enable specific detection of exogenous strigolactones. We analyzed the transcriptomes of P. aegyptiaca, S. hermonthica and T. versicolor and identified genes known to act in strigolactone synthesis (D27, CCD7, CCD8, and MAX1), perception (MAX2 and D14) and transport (PDR12). These genes were then analyzed to assess likelihood of function. Transcripts of all strigolactone-related genes were found in P. aegyptiaca and S. hermonthica, and evidence points to their encoding functional proteins. Gene open reading frames were consistent with homologs from Arabidopsis and other strigolactone-producing plants, and all genes were expressed in parasite tissues. In general, the genes related to strigolactone synthesis and perception appeared to be evolving under codon-based selective constraints in strigolactone-dependent species. Bioassays of S. hermonthica root extracts indicated the presence of strigolactone class stimulants on germination of P. aegyptiaca seeds. Taken together, these results indicate that Phelipanche aegyptiaca and S. hermonthica have retained functional genes involved in strigolactone biosynthesis, suggesting that the parasites use both endogenous and exogenous strigolactones and have mechanisms to differentiate the two.

Evaluation of antidiabetic activity of plants used in Western Sudan

Objective: To investigate the traditional antidiabetic uses of some indigenous Sudanese plants on streptozotocin-induced diabetes rats. Methods: Diabetic rats were treated with a 400 mg/kg dose of aqueous extracts of five plant species orally for 2 h(acute) or 14 days(chronic). In acute model blood glucose levels were monitored at specific intervals. In the chronic model blood samples were collected from overnight fasted diabetic rats on day 15 to estimate blood glucose level. And the body weight, serum lipid profile and activities of liver and kidney enzymes were measured. Histopathological observations of liver sections were also studied.Results: In the case of acute treatment, aqueous extracts of Tinospora bakis(T. bakis), Nauclea latifolia(N. latifolia) and Randia nilotica(R. nilotica) at 400 mg/kg significantly lowered(P < 0.05) blood glucose levels in diabetic rats whereas, chronic treatment of diabetic rats with 400 mg/kg of T. bakis, N. latifolia, R. nilotica and Mitragyna inremis proved to have significant(P < 0.05) antihyperglycemic effect and have the capacity to correct the metabolic disturbances associated with diabetes. Histopathological studies showed that the aqueous extracts of these four plants reinforced the healing of liver. However, Striga hermonthica aqueous extract did not exert any antihyperglycemic effect to diabetic rats. Conclusions: This study demonstrated that T. bakis, N. latifolia, R. nilotica and Mitragyna inremis have therapeutic value in diabetes and related complications and thus supporting the traditional uses of these plants in Sudanese traditional medicine.

Evaluation of Cereal-Legume Cropping on Striga Control and Maize Yield

Striga hermonthica(Del.)Benth is ranked as the number one constraint to maize productivity in Eastern Uganda.The use of trap crops is one of the control measures suggested for farmers with limited resources in Striga infested areas.In this study the main focus was on the effectiveness of intercropping in reducing Striga infestation and hence overall land productivity.The major objective was to identify suitable legumes in the control of Striga.In order to achieve this,on-farm experiments were conducted in Tororo and Busia districts of Eastern Uganda where the effect of the legumes on the Striga prevalence was evaluated.Maize(Zea mays)was intercropped with common beans(Phaseolus vulgaris),soybean(Glycine max)and silver leaf desmodium(Desmodium uncinatum)with sole maize(Z.mays)as the control.Soybean,beans and desmodium decreased the infestation of Striga by 26%,40%and 72%,respectively.There was a significant(p<0.05)difference in the number of emerged Striga and maize yield attained by desmodium and the rest of the legumes.Desmodium was found to be the most effective of the legumes in the control of Striga.

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.

Induced Mutation for Developing Mutant Rice Lines Tolerant to the Parasitic Weed Striga asiatica (L.) Kuntze

This work aims to screen mutant rice lines tolerant to Striga asiatica.Two rainfed sensitive rice varieties B22 and F154 were used.Plants survival rates of the two parents were significantly lower respectively(9.74a and 11.83a)than those of mutant lines(55.36c to 74.36b);Striga plants emergence/pot were significantly higher for the parents(13.96c and14.89c)compared to the mutants(0.12a to 1.5b);the infection rate of parents(7.37b;7.86b)was higher compared to the mutants(2.27a to 2.74a);fertility rate/plant of parents was lower(20.98%b;22.29%b)but much higher than mutants(72.19%b to 78.35%b);the average panicle number/plant of parents was significantly lower(0.5a;1a)than those of mutants(1.5b to 2.4bc)and the 100 g grain weight of parents are lower(2.35a;2.56a)than those of mutants(3.19b to 3.23b).The culture of those mutant lines may increase rice production and contribute to enhancing food security in Madagascar.

Assessing the Impact of Different Cropping Systems in Maize Field Infested by Striga asiatica (Madagascar)

The main problem of maize plantations is the attack of Striga asiatica in the poor soil,leading to the reduction of maize yield.The Arbuscular Mycorrhizal Fungi(AMF)helps the host plants to fight against the attack of biotic stress,increasing the water and their nutrients elements.The objective of this study was to enhance maize production,particularly Plata maize variety,by restoring the AMF in soil under Striga asiatica infestation.During 3 years period from 2016 to 2019,three cropping systems were installed on an experimental field of FOFIFA station,Madagascar,using Mulch-based-Cropping System(MCS)of Stylosanthes,and Green Cover System(GCS)using Vigna unguiculata and a Control Plot(CP).A laboratory study was also conducted to determine the mycorrhizal rate in maize roots.The best results on root mycorrhization were found in MCS 16.53%and in GCS 11.65%against 2.01%for the CP.The average number of Striga asiatica plants per plot(100 m^(2) areas)emerging soil was 1 for MCS,3 for GCS,and 15 for CP.The yield production for MCS,GCS,and CP was respectively 4.43 t/ha,2.56 t/ha,and 1.40 t/ha.The high roots colonization mycorrhizal of 16.53%reduces the average Striga asiatica plants number emerging 1 per 100 m^(2) and increases maize grain production by 4.43 t/ha for MCS.The use of MCS of Stylosanthes is the best way to increase the maize yield,reduce Striga plants emerging,and improve the AMF restoration in maize culture.

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.

独脚金SRAP-PCR反应体系的优化及引物筛选

为建立适用于独脚金的SRAP-PCR反应体系并筛选扩增条带丰富的引物组合,本研究以独脚金基因组DNA为模板,采用单因素分析法对影响SRAP-PCR反应的5个主要因素dNTP浓度、Taq酶浓度、Mg^(2+)浓度、引物浓度、DNA浓度进行优化;并利用优化的反应体系对引物进行筛选。结果表明,独脚金SRAP-PCR最优反应体系为10μL,其中dNTP 0.06 mmol/L,Taq酶0.3 U,Mg^(2+)2.0 mmol/L,引物1.0μmol/L,DNA 25 ng,10×PCR Buffer 1μL;利用该体系从95对引物中共筛选出扩增条带清晰、稳定、丰富引物组合39对。本研究所优化的反应体系和筛选的引物组合为后续独脚金种质资源遗传多样性研究奠定有力基础。

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.