Sources of inoculum and reappearance of spot blotch of wheat in rice–wheat cropping

A study was undertaken to examine the main source of inoculum of Bipolaris sorokiniana responsible for its reappearance in rice–wheat cropping regions of eastern India. Soil samples were collected at monthly intervals during April–October in the years 2000 and 2001 from fields having rice–wheat cropping. Bipolaris sorokiniana conidia were isolated and their viability was found to decline sharply with the onset of flooding in the month of August. In contrast to 82% in April, viability was 4% and <1% in August and September, respectively. Viable conidia were multiplied in the laboratory and inoculated on to susceptible cv. Sonalika under controlled conditions for test of pathogenicity. Appearance of symptoms typical to spot blotch were recorded after 7 days. Twenty-two different species (weeds and grasses) normally found to be associated with rice–wheat fields were tested for the presence of B. sorokiniana to evaluate their possible role as alternative hosts. Only three species, i.e. Setaria glauca, Echinochloa colonum and Pennisetum typhoids, were found to naturally harbour B. sorokiniana. Isolates from these hosts were tested for pathogenicity and also for their possible spread to wheat. When reisolated from these hosts, the pathogen did not infect wheat. Seeds of 25 different wheat genotypes were tested for B. sorokiniana infection. All genotypes were infected and the incidence of infection varied from 26% to 86%. Five isolates of wheat and one isolate from each of the three species (S. glauca, E. colonum and P. typhoids) were subjected to RAPD analysis. Two broad clusters were formed, suggesting that the wheat isolates were different from the isolates originating from other hosts. The results indicate that seeds are the most important source of inoculum for the reappearance of spot blotch of wheat in rice-wheat cropping systems in eastern India.     

Toxicity of insecticides to the tsetse fly,Glossina palpalis palpalis in Nigeria and comparison of tolerances in 1974–1975 and 1979–1982

Abstract

Toxicities o1 12 chemical insecticides to wild‐caught tsetse flies, Glossina palpalis palpalis in Nigeria were measured by topical application. Median lethal doses (as ng per fly) at 48 h after application for older flies, males (females), were: DDT 331 (700), dieldrin 14 (46), endosulfan 8 (15), malathion 193 (273), fenitrothion 47, pirimiphos methyl 31 (45), tetrachlorvinphos 14 (33), sumicidin 28 (58), neopynamin 12 (15), sumithrin 10 (8), permethrin 4.4 (5.9), deltamethrin 0.45 (0.94). Lethality expressed as dose per whole fly can be termed effective toxicity/tolerance and those expressed as dose per weight unit of fly can be termed intrinsic (or true) toxicity/tolerance. Generally, effective tolerance was greater for females than males, especially for older flies. However, intrinsic tolerance was often about equal for the sexes or greater for males. Regardless of sex, effective tolerance increased with increasing fly age and intrinsic tolerance increased during later ageing but not during early ageing. This suggested that protecting mechanisms developed during ageing. Flies fed a few hours before treatment in 1979–1982 were more tolerant of three organochlorines and three organophosphates than flies fed the day before treatment in 1974–1975, probably due to diversion of poisons from sites of action into inert undigested blood. However, results and statistical analysis suggested a slight increase in true tolerance of males to DDT during the intervening years. Continued monitoring of tolerance in the fly populations is recommended.     

Impact of push–pull cropping system on pest management and occurrence of ear rots and mycotoxin contamination of maize in western Kenya

Push–pull involves intercropping of cereals with Desmodium as a “push” crop and planting Napier grass/Brachiaria as the “pull” crop at the border. The technology has been reported to effectively control stemborers, striga weed, and fall armyworm (FAW), and to improve soil nutrition, resulting in increased grain yield. This study evaluated the impact of stemborer and FAW management using this technology on incidence of maize ear rots and preharvest contamination of grains with aflatoxin and fumonisin in western Kenya. The study was conducted during three cropping seasons on maize grown under the push–pull system and as a monocrop. Incidence of stemborer and FAW damage was determined as percentage of damaged plants, while incidence of ear rots was determined as percentage of ears with symptoms. At harvest, fungi were isolated from kernels and aflatoxin and fumonisin were quantified using enzyme-linked immunosorbent assay. Stemborer and FAW damage was significantly (p = .001) reduced by over 50% under the push–pull system. There was also a significant (p < .001) reduction in the incidence of Fusarium verticillioides (60%) and Aspergillus flavus (86%), which was reflected in a reduced incidence of ear rots (50%) with the push–pull system (p = .001). Fumonisin in maize from push-pull farms was significantly (p = .048) reduced (39%) but the technology had no significant (p > .05) effect on aflatoxin. The study showed that push–pull is an effective strategy for managing maize ear rots and fumonisins, and therefore could play a role in improving food safety among smallholder maize farmers in the region.     

Cuticular penetration of β-cypermethrin in insecticide-susceptible and resistant strains of Bactrocera dorsalis

Semi-thin sectioning and transmission electron microscope techniques were employed to investigate the cuticle thickness, integument structure, and fat body of larvae from susceptible and resistant strains of Bactrocera dorsalis. The results showed that the cuticle of β-cypermethrin-resistant strains (25.96 ± 1.00 μm) was thicker than that of susceptible strains (19.36 ± 0.82 μm). The number of chitin layers in the endocuticle of β-cypermethrin-resistant strains (98.00 ± 3.61 layers) was more than that in susceptible strains (75.67 ± 2.40 layers). Compared with susceptible strains, the laminated structure of the chitin layers in the endocuticle of resistant strains revealed higher density and more distinctive structure, and the interspace of epidermal cells was thicker. Fat body in the resistant insects contained more fat granules than those in susceptible insects. Moreover, HPLC analysis showed that the cuticular penetration of β-cypermethrin into larvae of resistant strains was slower than that of susceptible strains. In addition, the metabolism of β-cypermethrin in resistant strains was faster than that in susceptible strains, indicating that the resistant strains could enhance detoxification metabolism. These results indicated that cuticle thickness, fat body, laminated structure of the chitin layers, and interspace of epidermal cells might be correlated with cuticular penetration between susceptible and resistant strains, suggesting that the resistant strains could decrease the rate of penetration of insecticide into the internal cavity.     

Occurrence of boscalid resistance in cucumber powdery mildew in Japan and molecular characterization of the iron–sulfur protein of succinate dehydrogenase of the causal fungus

A total of 74 mass isolates of cucumber powdery mildew fungus (Podosphaera xanthii) were collected from commercial greenhouses with a history of boscalid use in Ibaraki Prefecture, Japan, and tested in a leaf disk assay for their sensitivity to boscalid. The mildew development of 40 of 74 isolates and five sensitive reference isolates on the disks was completely suppressed at 5 μg boscalid/ml. The minimum inhibitory concentrations (MIC) for the remaining 34 isolates were 50 μg/ml or higher, and 21 of these isolates also grew well at 500 μg/ml. Six single-spore isolates were resistant to boscalid with MIC values higher than 500 μg/ml; four of these were moderately resistant (MR), and two were very highly resistant (VHR) isolates. The growth of MR isolates was almost completely suppressed at 500 μg/ml, whereas two VHR isolates grew vigorously at 500 μg/ml. In foliar inoculation tests of potted cucumber plants, the efficacy of boscalid (500 μg/ml) against both MR and VHR isolates was very low. Partial DNA fragment of the iron–sulphur protein subunit (SdhB) gene of succinate dehydrogenase was PCR-amplified from five sensitive and five resistant isolates and directly sequenced, revealing that VHR isolates possess a substitution from a highly conserved histidine (CAT) to tyrosine (TAT) in a third cysteine-rich center of a putative SdhB, whereas MR isolates so far have not been found to have such substitution in SdhB.     

Characterization of moderate resistance to QoI fungicides in Pestalotiopsis longiseta and polymorphism in exon–intron structure of cytochrome b gene

Qo inhibitor (QoI) fungicides are used to control gray blight caused by Pestalotiopsis longiseta in Japanese tea cultivation. However, field isolates of P. longiseta highly resistant to QoI fungicides were found in 2008, resulting in failure of QoI fungicidal control. This resistance was attributed to a mutation in the cytochrome b gene (cytb) in which alanine was substituted for glycine at position 143 (G143A). In 2009–2010, we detected field isolates that had an intermediate reaction between sensitive and resistant isolates in a preliminary assay. These isolates showed intermediate sensitivity to azoxystrobin and kresoxim-methyl on PDA plates. The intermediate reaction to azoxystrobin was also confirmed on detached tea leaves. Consequently, they were considered moderately resistant to QoI fungicides. Nucleotide sequencing of cytb showed that moderate resistance correlated with a single point mutation; leucine was substituted for phenylalanine at amino acid position 129 (F129L). Sequence analysis also revealed two types of cytb, with or without an intron between codons 131 and 132, in P. longiseta. F129L and G143A mutations were detected in both types of cytb according to their QoI resistance. This result suggests that G143A and F129L mutations have each occurred at least twice in the P. longiseta population.     

Spatiotemporal variation of forest land and its driving factors in the agropastoral ecotone of northern China

As an important natural resource,forest land plays a key role in the maintenance of ecological security.However,variations of forest land in the agropastoral ecotone of northern China(AENC)have attracted little attention.Taking the AENC as an example and based on remote-sensing images from 2000,2010 to 2020,we explored the spatiotemporal variation of forest land and its driving factors using the land-use transfer matrix,spatial autocorrelation analysis and spatial error model.The results showed that from 2000 to 2020,the total area of forest land in the AENC increased from 75,547.52 to 77,359.96 km² and the changes were dominated by the transformations among forest land,grassland and cropland,which occurred mainly in areas with the elevation of 500-2000 m and slope of 15°-25°.There was obvious spatial agglomeration of forest land in the AENC from 2000 to 2020,with hot spots of forest land gathered in the southern marginal areas of the Yanshan Mountains and the low mountainous and hilly areas of the Loess Plateau.The sub-hot spots around hot spots moved southward,the sub-cold spots spread to the surrounding areas and the cold spots disappeared.The spatiotemporal variation of forest land resulted from the interactions of natural environment,socioeconomic and policy factors from 2000 to 2020.The variables of average annual precipitation,slope,terrain relief,ecological conversion program and afforestation policy for barren mountains affected the spatial pattern of forest land positively,while those of annual average temperature,slope and road network density influenced it negatively.     

Farmers’ perceptions of sorghum production constraints and Striga control practices in semi-arid areas of Tanzania

The objectives of this study were to investigate constraints affecting sorghum production and farmers' approaches of Striga management in the semi-arid regions of Tanzania. Focus group discussions based on a semi-structured questionnaire and observations following transect walks were used for data collection. Only 35%, 15%, and 10% of the farmers from Igunga, Kishapu, and Meatu districts, respectively, reported growing newly released varieties. The major constraints affecting sorghum production in the study areas included Striga infestation, drought, storage pests, damage by birds, a lack of access to improved varieties, and a lack of access to production inputs, such as fertilizers, insecticides, fungicides and herbicides. Hand weeding, crop rotation, fallowing, intercropping, and organic manure application were the most common practices of farmers for reducing Striga infestations, but most farmers (79.7%) had little knowledge of the best recommended Striga management practices. About 65% of the farmers did not use fertilizers and herbicides for soil fertility improvement and weed management, respectively, creating favourable conditions for Striga infestation. A systematic breeding programme aiming at improving sorghum varieties for Striga resistance, including farmers' preferred traits, should be designed and implemented to increase the adoption of these new varieties by the farmers.     

Efficacy and dose–response relationship in biocontrol of Fusarium disease in maize by Streptomyces spp.

Two isolates of Streptomyces spp. DAUFPE 11470 and DAUFPE 14632 were evaluated to determine the antagonist–pathogen inoculum concentration relationship under greenhouse conditions. Pathogen and antagonist concentration, significantly (P < 0.05) affected development of Fusarium disease in maize with a significant interaction between pathogen and antagonist concentration. Dose–response relationship also differed significantly (P < 0.05) between the two isolates, but both isolates demonstrated effective control of Fusarium disease, regardless of pathogen concentration. The isolate DAUFPE 11470 provided the most effective control. The lowest value for disease incidence occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentration (10⁶ cfu ml⁻¹) for both isolates. The disease incidence for control plants ranged from 19% to 76%. However, in relation to control the lowest disease reduction occurred at low pathogen (10³ chlamydospore g⁻¹ soil) and high antagonist concentrations (10⁶ cfu ml⁻¹). These reductions were 10.6% and 13% for DAUFPE 14632 and DAUFPE 11470, respectively. The highest disease reductions, in relation to control plants, occurred at high pathogen (10⁶ chlamydospore g⁻¹ soil) and antagonist (10⁶ cfu ml⁻¹) concentrations for both isolates. These values were 55% and 62.2% for DAUFPE 14632 and DAUFPE 11470, respectively. The chlamydospore germination of Fusarium moniliforme was affected by glucose addition, antagonist isolates and type of inoculum. The lowest chlamydospore germination was observed with bacterial suspensions of the isolates, for all glucose additions. The results suggested that both Streptomyces spp. isolates were effective at different doses as biocontrol agents against F. moniliforme. Also, there was evidence for at least two mechanisms of biocontrol and that apparently, both isolates showed the same mechanisms of biocontrol action related to production of bioactive compounds and competition for carbon. Further studies will be developed to improve the level and effectiveness of control by these isolates.     

Prediction of meteorological drought in arid and semi-arid regions using PDSI and SDSM: a case study in Fars Province,Iran

Drought is one of the most significant environmental disasters,especially in arid and semi-arid regions.Drought indices as a tool for management practices seeking to deal with the drought phenomenon are widely used around the world.One of these indicators is the Palmer drought severity index(PDSI),which is used in many parts of the world to assess the drought situation and continuation.In this study,the drought state of Fars Province in Iran was evaluated by using the PDSI over 1995-2014 according to meteorological data from six weather stations in the province.A statistical downscaling model(SDSM)was used to apply the output results of the general circulation model in Fars Province.To implement data processing and prediction of climate data,a statistical period 1995-2014 was considered as the monitoring period,and a statistical period 2019-2048 was for the prediction period.The results revealed that there is a good agreement between the simulated precipitation(R2>0.63;R2,determination coefficient;MAE<0.52;MAE,mean absolute error;RMSE<0.56;RMSE,Root Mean Squared Error)and temperature(R2>0.95,MAE<1.74,and RMSE<1.78)with the observed data from the stations.The results of the drought monitoring model presented that dry periods would increase over the next three decades as compared to the historical data.The studies showed the highest drought in the meteorological stations Abadeh and Lar during the prediction period under two future scenarios representative concentration pathways(RCP4.5 and RCP8.5).According to the results of the validation periods and efficiency criteria,we suggest that the SDSM is a proper tool for predicting drought in arid and semi-arid regions.     

Evidence for the involvement of Aphanomyces cochlioides and Pythium spp. in ‘girth scab’ disease of sugar beet in Bavaria

Journal of Plant Diseases and Protection - The term ‘girth scab’ describes a chronic disease of sugar beet roots (Beta vulgaris ssp. vulgaris) for which the causes still remain unclear....     

Origin and circulation of saline springs in the Kuqa Basin of the Tarim Basin,Northwest China

It is widely accepted that hydrogeochemistry of saline springs is extremely important to understand the water circulation and evolution of saline basins and to evaluate the potential of potassium-rich evaporites.The Kuqa Basin,located in the northern part of the Tarim Basin in Northwest China,is a saline basin regarded as the most potential potash-seeking area.However,the origin and water circulation processes of saline springs have yet to be fully characterized in this saline basin.In this study,a total of 30 saline spring samples and 11 river water samples were collected from the Qiulitage Structural Belt(QSB)of the Kuqa Basin.They were analyzed for major(K^+,Ca2^+,Na^+,Mg2^+,SO42-,Cl-and HCO3-)and trace(Sr2^+and Br-)ion concentrations,stable H-O-Sr isotopes and tritium concentrations in combination with previously published hydrogeochemical and isotopic(H-O)data in the same area.It is found that the water chemical type of saline springs in the study area belonged to the Na-Cl type,and that of river water belonged to the Ca-Mg-HCO3-SO4 type.The total dissolved solid(TDS)of saline springs in the QSB ranged from 117.77 to 314.92 g/L,reaching the brine level.On the basis of the general chemical compositions and the characteristics of the stable H-O-Sr isotopes of saline springs,we infer that those saline springs mainly originated from precipitation following river water recharging.In addition,we found that saline springs were not formed by evapo-concentration because it is unlikely that the high chloride concentration of saline springs resulted in evapo-concentration and high salinity.Therefore,we conclude that saline spring water may have experienced intense evapo-concentration before dissolving the salty minerals or after returning to the surface.The results show that the origin of salinity was mainly dominated by dissolving salty minerals due to the river water and/or precipitation that passed through the halite-rich stratum.Moreover,there are two possible origins of saline springs in the QSB:one is the infiltration of the meteoric water(river water),which then circulates deep into the earth,wherein it dissolves salty minerals,travels along the fault and returns to the surface;another is the mixture of formation water,or the mixture of seawater or marine evaporate sources and its subsequent discharge to the surface under fault conditions.Our findings provide new insight into the possible saltwater circulation and evolution of saline basins in the Tarim Basin.     

Detection and characterization of a phytoplasma associated with witches’-broom disease of Salvadora persica in India

Salvadora persica trees with symptoms of witches’-broom, little leaf and severe leaf curling were observed in the Biodiversity Park, North Delhi (India) during February 2010. Using a nested-PCR assay targeting two phytoplasma specific loci (16S ribosomal RNA and the ribosomal protein gene) and sequence analysis of the amplified products, we identified the associated phytopathogen as a phytoplasma of group 16SrI. RFLP-mediated characterization revealed that the phytoplasma belongs to subgroup 16SrI-B. Phylogenetic reconstruction also grouped the phytoplasma within group 16SrI. The study reports a new host of phytoplasma in India and worldwide.     

Development of a qPCR test to detect and quantify Elsinoë piri in unsprayed and organic apple orchards and assessment of apple cultivar susceptibility to the disease

Recently, Elsinoë piri has become an important pathogen in unsprayed and organic apple orchards. The increasing demand for organic apples as well as the limited use of fungicides imposed by European legislation has turned this pathogen, which has been known for over a century in Europe, into a resurgent phytosanitary threat. It also represents a new trait to be taken into account in apple breeding programmes. As E. piri is extremely difficult to isolate and causes symptoms that can be confused with those caused by other pathogens, a quantitative PCR (qPCR) test has been developed based on the internal transcribed spacer (ITS) region of the rDNA gene. This test, which displays a low limit of detection, allows the early detection of the fungus in apple leaves. As a quantitative method, it is a promising tool for breeding purposes as it can be used on leaves to assess the level of quantitative resistance of apple cultivars to the disease. The molecular test is also useful to gain knowledge on the epidemiology of this re-emerging fungal disease. Spore trapping conducted in 2015, 2016 and 2020 using Rotorod devices and the qPCR test showed that airborne inoculum is released at the end of the growing season. Tests were also carried out to demonstrate that the pathogen was detected in buds during winter. A comparison of 18 E. piri isolates based on the sequencing of five genome regions highlighted a high genotypic diversity. All these isolates were detected with the qPCR test developed in this study.     

Andropogon annulatus and Ischaemum rugosom – Two New Weeds of Sugarcane in Trinidad

Abstract

Potato cyst-nematode species are believed to have evolved in South America but now have a worldwide distribution and can be major and persistent pests except in the warmest soils. Both species contain pathotypes and their correct identification, although difficult, is important when planning control with resistant potatoes. Some closely related and very similar species are of minor economic importance. Resistant cultivars available at present are effective against only some pathotypes and except where high crop values make use of nematicides economic, it is important to combine extended crop rotation with such cultivars.