Arbuscular mycorrhizal fungal association in Asteraceae plants growing in the arid lands of Saudi Arabia

The present research was undertaken to explor the possibility of arbuscular mycorrhizal(AM) association with Asteraceae plants in the arid lands of Saudi Arabia(Al-Ghat, Buraydah, Thumamah and Huraymila). AM fungal colonization in the roots, spore numbers in the rhizosphere soil, fungal species diversity and correlation between AM properties and soil properties were determined. The highest colonization was in Conyza bonariensis(65%) from Al-Ghat, Anthemis cotula(52%) from Buraydah and C. bonariensis(53%) from Thumamah. The lowest was in Vernonia schimperi(41%) from Al-Ghat, Pulicaria undulata(25%) from Buraydah, Acanthospermum hispidum(34%) from Thumamah, Asteriscus graveolens(22%) and V. schimperi(22%) from Huraymila. Vesicular and arbuscular colonization were also presented in all plant species examined. The number of spores were 112–207 in Al-Ghat, 113–133 in Buraydah, 87–148 in Thumamah and 107–158 in Huraymila. Funneliformis mosseae, Glomus etunicatum, G. fasciculatum and G. aggregatum were identified. Relative frequency of AM fungal species varied widely and was irrespective of location and plant species. Diversity index varied with the rhizosphere soils of different plant species at various locations. Soil properties varied with locations and no distinct correlations were observed among the soil properties, root colonization and the number of spores. The results of the present study specified the association of AM fungi in different plants of Asteraceae and its significance in the ecological functioning of annual plants in the punitive environments of the rangelands in Saudi Arabia.     

甘肃省红豆草病原真菌鉴定及病害发生动态调查

为明确甘肃省红豆草的病害种类、发生动态和危害状况,采用病原物分离与培养、形态学及分子生物学鉴定和致病性测定确定红豆草病害种类,于2012—2013年在通渭、渭源、榆中和碌曲4县调查各病害的发病率以确定发生动态,观察病害田间发生特点并结合调查数据评价其重要性。结果表明,4县共发生真菌性病害12种,分别为大茎点霉叶斑病(病原为大茎点霉属真菌Macrophoma sp.)、壳针孢叶斑病(病原为歪头菜壳针孢Septoria orobina)、炭疽病(病原为白蜡树刺盘孢Colletotrichum spaethianum)、黑秆病(病原为红豆草壳二孢Ascochyta onobrychis、菠菜刺盘孢C.spinaciae和链格孢Alternaria alternata混合侵染)、壳二孢叶斑病、茎点霉叶斑病、尾孢叶斑病、柱格孢白斑病、匍柄霉叶斑病、链格孢黑斑病、锈病和白粉病,其中大茎点霉属真菌、白蜡树刺盘孢和菠菜刺盘孢在红豆草上首次发现;尾孢叶斑病和壳针孢叶斑病为甘肃新记录病害;大茎点霉叶斑病为世界新病害,仅于碌曲县发现。白粉病、锈病、链格孢黑斑病发生于红豆草生长后期,其它病害则始于6月;6—9月危害加重的为黑秆病和柱格孢白斑病,发病率最高达89.7%和96.0%;危害渐轻的为茎点霉叶斑病、壳二孢叶斑病和壳针孢叶斑病,发病率最高达88.7%、57.4%和45.1%。黑秆病和茎点霉叶斑病在甘肃省目前危害最重。     

Impact of volatility reduction agents on dicamba and glyphosate spray solution pH,droplet dynamics,and weed control

BACKGROUND

Regulations in 2021 required the addition of a volatility reduction agent (VRA) to dicamba spray mixtures for postemergence weed control. Understanding the impact of VRAs on weed control, droplet dynamics, and spray pH is essential.

RESULTS

Adding glyphosate to dicamba decreased the solution pH by 0.63 to 1.85 units. Across locations, potassium carbonate increased the tank-mixture pH by 0.85 to 1.65 units while potassium acetate raised the pH by 0.46 to 0.53 units. Glyphosate and dicamba in tank-mixture reduced Palmer amaranth control by 14 percentage points compared to dicamba alone and decreased barnyardgrass control by 12 percentage points compared to glyphosate alone 4 weeks after application (WAA). VRAs resulted in a 5-percentage point reduction in barnyardgrass control 4 WAA. Common ragweed, common lambsquarters, and giant ragweed control were unaffected by herbicide solution 4 WAA. Dicamba alone produced a larger average droplet size and had the fewest driftable fines (% volume < 200 μm). Potassium acetate produced a larger droplet size than potassium carbonate for D_v0.1 and D_v0.5. The addition of glyphosate to dicamba decreased droplet size from the entire spray droplet spectrum (D_v0.1, D_v0.5, D_v0.9).

CONCLUSION

A reduction in spray pH, droplet size, and weed control was observed from mixing dicamba and glyphosate. It may be advisable to avoid tank-mixtures of these herbicides and instead, apply them sequentially to maximize effectiveness. VRAs differed in their impacts on spray solution pH and droplet dynamics, but resulted in a minimal negative to no impact on weed control. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Population dynamics of postharvest decay antagonists growing epiphytically and within wounds on grapefruit

ABSTRACT Coating formulations of shellac, sucrose ester, and cellulose were tested that support populations of bacterial and yeast antagonists of postharvest Penicillium decay of grapefruit. Surface populations of Pseudomonas syringae, P. fluorescens, and P. putida were stable between 10(3) and 10(4) CFU/cm(2) on shellacked fruit over 4 months at 13 degrees C, but numbers of the yeast Candida oleophila rose steadily from 2.35 x 10(3) to nearly 10(5). Through the first 15 days of cold storage, surface populations of P. syringae and C. oleophila were greater when applied to fruit within the pH 7.2 shellac than when applied by dipping fruit into an antagonist suspension and drying the fruit prior to shellacking; numbers were generally equivalent thereafter. Within wounds of shellacked fruit, populations of P. syringae were equal regardless of the method of application and increased from 10(4) to more than 1.2 x 10(7) CFU within 2 weeks. In contrast, numbers of C. oleophila in wounds over the first 2 weeks of storage were greater in fruit dipped and coated with shellac than when the antagonist was incorporated in this material; populations stabilized at approximately 6 x 10(6) CFU after 2 weeks. Incorporation of P. syringae and C. oleophila into ester and cellulose coatings, however, initially fostered greater numbers of both antagonists in wounds ( approximately 10(6) CFU) than did the preliminary dip application, and significant population differences persisted for several weeks. In cold storage, although application method did not affect the efficacy of P. syringae, C. oleophila was more efficacious after 3 and 4 months when applied in the shellac than when applied by a preliminary immersion and subsequent drying of fruit prior to shellacking.     

Parasitism of macroconidia, chlamydospores and hyphae of Fusarium culmorum by mycoparasitic Pythium species

Parasitism of macroconidia and endoconidial chlamydospores of Fusarium culmorum by Pythium oligandrum was studied on water agar (WA), corn-meal agar (CMA) and glass slides. Loss of cytoplasmic content in F. culmorum spores was followed by complete degradation, and P. oligandrum produced an abundance of oogonia on the parasitized macroconidia. A simple method for assessing the relative aggressiveness of isolates is presented, based on the percentage of macroconidial cells devoid of cytoplasm. Parasitism of macroconidia by P. acanthophoron , P. oligandrum and P. periplocum , but not by the plant pathogenic species, P. tracheiphilum , was demonstrated by this method. Interactions between hyphae of P. oligandrum and F. culmorum on WA resulted in an increase in the number of oogonia of P. oligandrum and a decrease in the sporulation of F. culmorum . The ability of isolates of P. oligandrum , P. periplocum , P. acanthophoron and P. mycoparasiticum to suppress disease symptoms caused by F. culmorum on barley seedlings was demonstrated in a greenhouse test.     

The crucial role of calcium interacting with soil pH in enhanced biodegradation of metam-sodium

Enhanced biodegradation of soil-applied pesticides has long been correlated with soil pH above ca 6.5-7.5, but the possibility of confounding or interdependence with calcium, given that soil calcium concentration increases exponentially as pH rises above that range, has not previously been studied. Enhanced biodegradation of the broad-spectrum biocide metam-sodium was readily induced de novo in a naturally acid sandy soil (pH 4.2 measured in 0.01 M CaCl2) by multiple treatments, but only when the pH and calcium concentration were raised simultaneously using calcium carbonate (lime). Enhanced biodegradation was not induced when soil pH alone was raised with magnesium carbonate, nor when calcium alone was raised using calcium chloride. In limed sand treated monthly for 12 months, the degradation rate increased to where dissipation was complete within 24 h of application after the fifth metam-sodium treatment at pH 7.8 and after the eighth metam-sodium treatment at pH 6.8. Pesticide concentration was reduced, but not eliminated, at pH 5.8 and was unchanged at pH 4.8. When metam-sodium was applied bi- and tri-monthly, the degradation rate also increased when soil pH was raised with calcium carbonate, but to a lesser extent than with monthly applications. In an acid loam soil amended to the same pH values with calcium carbonate and treated monthly, there was no correlation between soil pH or calcium concentration and degradation. The results reveal the crucial interdependence of pH and calcium concentration in enhancement of biodegradation of soil-applied pesticides, but confirm that the phenomenon ultimately depends on interaction with soil type and frequency of application factors, all of which probably together act to affect the abundance, composition and activity of the soil microbial biomass.     

Antagonistic rhizoplane bacteria induce diverse morphological alterations in Peronosporomycete hyphae during <Emphasis Type="Italic">in vitro</Emphasis> interaction

A total of 150 bacteria were isolated from rhizoplanes of the host and non-host plants of a phytopathogenic Peronosporomycete Aphanomyces cochlioides. Upon screening, 5% of the isolates were evaluated as antagonists as they inhibited radial growth of A. cochlioides AC-5 hyphae in a dual culture assay. In addition, those antagonistic bacteria also induced characteristic morphological alterations in the A. cochlioides AC-5 hyphae that grew towards bacterial colonies. Hyphal morphological alterations observed in AC-5 and other tested strains of Peronosporomycetes included excessive branching, curly growth, unusually longer and pointed tip formation and swelling; all of these were comparable to the alterations induced by known antimicrobial compounds. Among the antagonistic bacteria, Pseudomonas sp. strain EC-S101 induced a unique branching pattern (tree-like) in AC-5 hyphae by continuous apical bifurcation of successive hyphae, where increases in number of branches and hyphal area were linearly correlated with time up to 10 h. Our observations suggested that the pathogen might have lost its ability of normal branch production; however maintained the capability of self-branching. Soluble extracts from the culture fluids of Pseudomonas sp. strain EC-S101 and Stenotrophomonas maltophilia EC-S105 induced similar excessive branching and curly growth in A. cochlioides hyphae as the respective bacterium. These results revealed that bacterial metabolites appeared to be responsible for induction of morphological alterations. Interestingly, the antagonistic bacteria that induced hyphal morphological alterations, also efficiently suppressed in vivo damping-off disease caused by AC-5. We suggest that antagonistic rhizoplane bacteria have the capability to induce diverse morphological alterations in Peronosporomycetes hyphae during in vitro interactions. Hyphal morphological alterations associated with growth inhibition and the induction of characteristic morphological changes indicate antagonistic activity against the Peronosporomycete.     

Growth,population dynamics,and diversity of <Emphasis Type="Italic">Fusarium equiseti</Emphasis> in ginseng fields

Fusarium equiseti is prevalent in ginseng soil, straw mulch and in ginseng root tissues and is the cause of a root surface discolouration on ginseng grown in British Columbia. Population levels of the fungus in ginseng fields ranged from 3.8 × 10³ cfu g⁻¹ soil to 1.4 × 10⁴ cfu g⁻¹ soil and were highest at 0–5 cm soil depths compared to 10–15 cm. Soil population levels were negatively correlated with S content in soil and positively correlated with Zn levels. Barley or wheat straw added to soil significantly increased population levels under laboratory conditions. Mycelial growth in culture was highest at 26–30°C and at pH 7.2–7.8. Samples of flowers and berries, and harvested seed, contained DNA of F. equiseti detected using a Fusarium-specific DNA array and the fungus was isolated from these tissues on agar medium. A high degree of genetic variation in the EF-1 alpha gene sequence was present among 52 isolates of F. equiseti which originated from ginseng fields. At least seven clades were identified. Inoculum dispersal from straw mulch used in ginseng gardens can result in seed contamination by the fungus. In addition, fungal growth near the soil surface under warm summer conditions can result in infection and crown discolouration of ginseng roots.     

Infection and colonization of peanut pods by Aspergillus parasiticus and the expression of the aflatoxin biosynthetic gene,nor-1, in infection hyphae

The aflatoxigenic fungi, Aspergillus flavus and A. parasiticus infect a wide variety of crops, all of which produce oil-rich seed. A histological study of the host–pathogen interaction between peanut,Arachis hyphogea , and A. parasiticus was performed in a system where peanuts remained attached to the plant and were inoculated without wounding. For infection studies, a genetically-tagged strain of A. parasiticus, G5, was engineered to harbor the β-glucuronidase (GUS) reporter gene under control of the nor-1 promoter from the aflatoxin biosynthetic pathway. There was a similar temporal pattern of aflatoxin B1 production and appearance of GUS activity in cultures ofA. parasiticus G5. This strain was used to follow infection and aflatoxin production during colonization of undamaged, drought-stressed peanuts. The fungus colonized all tissues of the peanut pod and appeared to gain ingress through the corky layer of the pericarp. Both intra- and inter-cellular colonization were observed. Fungal colonization of the cotyledons resulted in visible depletion of storage bodies within cells. Two morphologically distinct types of hyphae, wider hyphae and narrower hyphae, were seen throughout the pod tissues. Statistical analysis revealed that the narrower hyphae were significantly more likely to produce GUS activity than wider ones. GUS activity was found in hyphae infecting the pericarp, embryo and cotyledons indicating expression of aflatoxin biosynthetic genes in these tissues. Interestingly, GUS activity was not observed in the hyphae colonizing the testa.     

Communication: the fastest growing part of the management of plant invasions in Saxony‐Anhalt,Germany

The Coordination Centre for Invasive Plants in protected areas of Saxony‐Anhalt (KORINA) has been active in Halle/Saale, Germany since 2010. Communication is an important part of an integrated action plan for managing invasive plant species. The first task of KORINA was to establish a network of stakeholders. Cooperation among the stakeholders was essential to collect information about invasive plants and, when necessary, to implement coordinated actions against some of these species. The second task was to engage the public in collecting information on invasive plants and in controlling them. A strategy was developed for this purpose that identified the tools and tasks to involve different target groups. The aim was to increase awareness among large portions of society. The strategy included a wide range of communication tools such as oral presentations and workshops, field trips and a smartphone application. The KORINA‐website ( www.korina.info ) is central in data collection through online recording and bringing species information to the people involved.     

Involvement of FgMad2 and FgBub1 in regulating fungal development and carbendazim resistance in Fusarium graminearum

Resistance to carbendazim of Fusarium graminearum is conferred by point mutation in the β₂‐tubulin gene that plays an important role in spindle assembly. The spindle assembly checkpoint is a cellular surveillance system that is critical for maintaining genomic stability. Predicted protein Mad2‐ and Bub1‐encoding genes in F. graminearum (FgMad2 and FgBub1) were isolated and characterized. There was no difference in FgMad2 and FgBub1 expression levels between carbendazim‐sensitive and ‐resistant strains; however, after carbendazim treatment FgMad2 expression increased while FgBub1 expression stayed the same. Both the FgMad2 and FgBub1 deletion mutants became more sensitive to carbendazim. The FgMad2 deletion mutants grew more slowly, produced fewer conidia and both hyphae and conidia were malformed. Conversely, deletion of FgBub1 had no effect on fungal development other than a reduction in conidia production. FgMad2 deletion mutants exhibited a severe decrease in perithecia production and pathogenicity along with a down‐regulation of trichothecene production, whereas FgBub1 deletion mutants exhibited only a slight reduction in perithecia production and was accompanied by a twofold increase in trichothecene production. Overall, the results indicate that both FgMad2 and FgBub1 are involved in carbendazim resistance and trichothecene biosynthesis, and FgMad2 plays an important role in fungal development in F. graminearum.     

生长季马铃薯植株冠层空气中Alternaria solani分生孢子飞散动态及其影响因素

 对生长季马铃薯冠层空气中Aternaria solani (Ell. & G. Martin ) 分生孢子的数量和马铃薯早疫病发生程度进行了系统调查,并对空气中分生孢子数量与早疫病发生程度之间的相关性以及影响空气中分生孢子数量的因素进行了分析。结果表明:在马铃薯出苗至收获(6~8月份)期间,当病情指数低于4时两者之间呈显著线性相关关系,随着病情指数的增高二者的线性相关性降低。天气条件对空气中A. solani 分生孢子数量的影响明显,通常降雨2 d后空气中孢子的数量会有一个高峰,日平均气温(地上2 m)低于18℃的条件下,空气中孢子数量会显著减少。一天中6∶00 am至16∶00 pm空气中A. solani分生孢子数量较多,17∶00 pm至次日5∶00 am孢子数量较少,分别占全天总量的 60.95%和 39.05%,各小时孢子飞散量占全天比例与空气相对湿度呈显著负相关,而与空气温度呈显著正相关。