Characterisation of benzimidazole resistance of Cercospora beticola in Serbia using PCR-based detection of resistance-associated mutations of the β-tubulin gene

A survey to detect and characterise benzimidazole resistance within populations of Cercospora beticola in Serbia was performed. From 52 field isolates collected from sugar beet and beet root, only eight were found to be benzimidazole-sensitive based on the inhibition of mycelial growth by discriminatory concentrations of carbendazim and thiophanate-methyl. Sensitivity tests revealed the presence of three resistant phenotypes among the tested isolates: high-resistance (HR), low-resistance (LR) and moderate-resistance (MR). The benzimidazole resistant isolates were characterised based on the DNA sequence of the β-tubulin gene and temperature sensitivity. The HR isolates showed no temperature sensitivity regardless of carbendazim concentration, whereas the LR and MR isolates were sensitive at lower temperatures. Analysis of the β-tubulin gene sequence revealed two amino acid replacements in the benzimidazole-resistant isolates of C. beticola. One was a glutamic acid to alanine change at position 198 (codon GAG to GCG) that was identified in HR isolates; this mutation has previously been reported to be associated with the development of benzimidazole resistance in C. beticola. The second replacement was a novel point mutation of phenylalanine (TTC) to tyrosine (TAC) at position 167, identified in low and moderate benzimidazole-resistant isolates, sharing a single LR/MR β-tubulin genotype. A diagnostic PCR-RFLP assay utilising a BsaI restriction site present in the benzimidazole sensitive and LR/MR genotypes but absent in the HR genotype was developed for the routine detection of high resistance. A mutation-specific PCR assay was developed for the diagnosis of LR/MR genotype based on a mutation from T to A at codon 167, which is unique to this genotype.     

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.     

Insect Pests of Cotton – Western Herbaceum Region of India

Abstract

Pre-plant and pre-emergence herbicides were tested for effective weed control in a seed crop of okra during 1974–75 and 1975–76. All treatments significantly decreased the weed population and increased the seed yield as compared to the unweeded control. Fluchloralin (0.90 and 1.20 kg a.i./ha pre-plant), alachlor (2.50 kg a.i./ha pre-em) and EPTC plus alachlor (3.75 kg a.i./ha pre-plant and 1.25 kg a.i./ha pre-em) proved to be the most effective and economical treatments. No residual effects were observed with any herbicide on the succeeding crops of radish, carrot, turnips, peas and spinach.     

Evaluation of efficiency of hemi-nested PCR assay for the detection of ‘Candidatus Liberibacter’ infecting citrus

Journal of Plant Diseases and Protection - The present study reports the development and evaluation of a hemi-nested polymerase chain reaction (hnPCR) assay for the efficient detection of...     

Evidence of the Presence of Two Serotypes of Rice Yellow Mottle Sobemovirus in Côte d'Ivoire

Serological variability of isolates of rice yellow mottle virus (RYMV) collected in Côte d'Ivoire was assessed by immunological tests with polyclonal and monoclonal antibodies (MAbs). Two serotypes (named S1 and S2) were distinguished. The S1 isolates had common epitopes which were absent in S2 isolates, whereas they lacked epitopes shared by S2 isolates. There was no evidence of S1 and S2 mixtures, although S1 and S2 isolates were sometimes found in nearby sites. Serotype S2 was more prevalent in Côte d'Ivoire than S1, and was in a large majority in the centre and the south of the country. By contrast, S1 occurred more widely in the north. S1 isolates were also found in neighbouring countries at the north of Côte d'Ivoire. In tests with monoclonal antibodies, three additional serotypes were found, one in West-Africa and two in East-Africa. Using the primers developed against an S2 isolate from Côte d'Ivoire, all S2 but not the S1 isolates were transcribed and amplified by RT-PCR, and another set of primers was developed to amplify S1 isolates. S1 and S2 have different biological properties, and competition between isolates of the two strains was apparent resulting in S2 dominance over S1. This was assessed using S1 and S2 strain specific MAbs, and it occurred whatever the pattern of inoculation or the rice variety tested. Differences in pathogenicity and virus titre did not account for strain competition, as there was no relation between symptom severity, virus content and serotype of the isolates in Oryza sativa indica cultivars.     

Preference of female rats for the odours of non-parasitised males: the smell of good genes?

Many animals obtain reliable information about potential mates, including whether they are parasitised or not, mostly from olfactory cues in urine. Previous experiments with rodents have shown that females can detect parasites in males that are potentially transmissible during copulation, so that females can directly avoid infection by discriminating against parasitised males. Here, using choice tests, we examine whether female rats can distinguish males infected with the tapeworm Hymenolepis diminuta Rudolphi, 1819, a parasite with a complex life cycle and thus not directly transmissible among rats. Female rats tended to spend more time investigating the urine of non-parasitised males than that of parasitised males. The magnitude of the parasite burden in the infected males had no effect on the females' preference for the non-parasitised males. We also found that parasitised males had lover testosterone levels in their blood than non-parasitised males. These results suggest that females use cues in male urine reflecting either the presence of the parasite and/or lower testosterone levels to avoid parasitised males and possibly secure resistance genes for their offspring.     

Mode of action of acibenzolar-S-methyl against sheath blight of rice, caused by Rhizoctonia solani Kühn

The mode of action of acibenzolar-S-methyl (BTH) was investigated against sheath blight of rice and its pathogen, Rhizoctonia solani. BTH exhibited limited fungitoxicity against R solani, in the form of reduced mycelial growth, hyphal browning and sclerotia formation. Parasite fitness of mycelia and sclerotia formed on BTH-amended media was also reduced. When applied as soil drench or foliar spray, BTH inhibited both disease development on inoculated sheaths and its spread to the younger sheaths. The degree of protection against sheath blight increased with increase in duration between BTH application and inoculation. The curative effect of BTH was poor. When applied through roots a protective effect of BTH was visible even with only a 1-h interval between application and inoculation. However, in the case of foliar application, protective effect was recorded only when the gap between application and inoculation was 24 h. BTH reduced the frequency of penetration by R solani, colonization of host tissue and spread of the hyphae from primary lesions to form secondary lesions. BTH induced swelling of hyphal tips on the sheath surface, formation of papillae, browning of penetrated epidermal cells and degeneration of intra-cellular hyphae colonizing epidermal and mesophyll cells. Therefore, the protective effect of BTH against sheath blight was due to combination of its host defence-inducing activity and its adverse effect on growth and vigor (parasite fitness) of the pathogen.     

Addition of Oil to Pesticide Sprays—Downwind Movement of Droplets

Abstract

An investigation of the downwind movement, distribution and distance covered from a spray source of insecticide to which oil is an additive. Vertical targets were placed at distances ranging from 0.25 to 64 m and at three heights, 35, 70 and 150 cm, downwind from the spray source. There was an increase in the number of droplets arriving at the targets when 20% oil was added to the aqueous solution. An even greater increase was seen when oil only was sprayed; these results are compared with sprays containing water and a 5% wetting agent. Droplet size and air turbulence effects are discussed, as is the faster evaporation of water-based sprays. The work was carried out on rhododendron leaves using Saturn yellow fluorescent dye as a tracer using a Micron Mini-ULVA and Ulvapron oil. A comparison is made with the use of Shell oil A and Risella 33 used by pest workers.     

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.     

Is tile drainage water representative of root zone leaching of pesticides?

Given the methods presently available, determination of flux-averaged concentrations of pesticides in structured soils is always a compromise. Most of the available methods entail major uncertainties and limitations. Tile drainage monitoring has several advantages, but the extent to which it is representative of overall leaching has been questioned because it comprises a mixture of water of different origins. This literature review evaluates whether drainage water pesticide concentrations are representative of root zone leaching of pesticides. As there are no reports quantifying the extent to which the flux-averaged concentration of pesticides in drainage water differs from that found between the drains, evidence-based conclusions cannot be drawn. Nevertheless, the existing literature does suggest that the concentration in drainage water does not always correspond to the concentration at drain depth between the drains; depending on the conditions pertaining, the concentrations may be higher or lower. As to whether the flux-averaged concentration of pesticides in drainage water is representative of the interdrain concentration at drain depth it is concluded that (1) the representativeness of drainage water concentrations can be questioned on very well-drained soils and on poorly drained soils with little capacity for lateral transport beneath the plough layer, (2) the conditions provided by relatively porous soils and moderate climatic conditions are conducive to the drainage water concentration being representative and (3) drainage water will be more representative in the case of weakly sorbed pesticides than for strongly sorbed pesticides. Used critically, it is thus believed that drainage water concentrations can serve to characterize the flux-averaged concentration of pesticides at drain depth. However, the use of drainage water for determining average concentrations necessitates thorough investigation and interpretation of precipitation, percolation, drain outflow and concentration dynamics.     

Comparison of Pathogenicity and Nucleotide Sequences of 3′-terminal Regions of Bean yellow mosaic virus Isolates from Gladiolus

Sixty-four isolates of Bean yellow mosaic virus (BYMV) from cultivated and naturalized gladioli were divided into two pathogenic groups, necrotic spot (NS) and chlorotic spot (CS) groups on Chenopodium quinoa. NS-type isolates (S-22N and E-24N), CS-type isolates (S-22C and E-92C), and broad bean isolates (Sb-50C and Sb-12C) differed in their pathogenicity on Antirrhinum majus, Nicotiana benthamiana, Phaseolus vulgaris, Spinacia oleracea and Vigna unguiculata. The four gladiolus isolates were different from BYMV-B, -P, -O and C1YVV-N in their pathogenicity on these plants, while the two broad bean isolates were similar to BYMV-B, originally from broad bean. The nucleotide (nt) sequences of the 3′-terminal region of the BYMV RNA genome of the two NS-type isolates, the two CS-type isolates, the two broad bean isolates and BYMV-B, -P and -O were determined. In a phylogenetic tree based on the CP amino acid (aa) sequences, the two NS-type isolates clustered together (identity 98.4% and 98.2% at the nt and aa level, respectively). The two CS-type isolates clustered with BYMV-O (93.2 to 99.3% nt identity and 95.6 to 98.5% aa identity). The two broad bean isolates clustered with BYMV-B (99.0 to 99.5% nt identity and 98.9 to 99.6% aa identity). BYMV-P clustered with BYMV-CS (identity 97.7% and 99.3% at the nt and aa level, respectively). The obtained sequences were compared with those of the 3′-terminal regions of seven published BYMV isolates. In a phylogenetic tree based on deduced aa sequences, BYMV isolates were divided into four clusters. Received 1 July 1999/ Accepted in revised form 22 May 2000     

Assessment of Losses of Hybrid Sorghum ‘CSH-1’ to Earhead Caterpillars,and Comparison of Insecticidal Controls

Abstract

In hybrid sorghum ‘CSH-1’ severe infestation of the earhead caterpillars Cydia sp., Ectomyelois sp., Eublemma sp. nr. gayneri Roths., Heliothis armigera Hub., and Euproctis limbata Wlk, was recorded at Jabalpur (Madhya Pradesh) during 1968. The first two were relatively more serious. The loss in grain yield was estimated to be 18.26 per cent, i.e. about 717 kg/ha.

Among different insecticides tested, carbaryl 0.2 per cent spray proved most effective, followed by endosulfan 0.05 per cent spray. Dichlorvos 0.05 per cent gave good initial kill, but showed little persistent effect.     

Sequence of the 3′-terminal region of the RNA of a mite transmitted potyvirus fromHordeum murinum L.

The 3026 nucleotides upstream of the 3-polyadenylated tract of a mite transmitted virus fromHordeum murinum L. were cloned and sequenced, and portions of the sequence were expressed inEscherichia coli. Sequence comparisons with wheat streak mosaic virus (WSMV), Agropyron mosaic virus (AgMV) and Hordeum mosaic cirus (HoMV), three mite transmitted potyviruses, and potato virus Y (PVY), the type member of the genusPotyvirus, revealed that the virus is probably a potyvirus, but distinct from WSMV, AgMV, HoMV, and PVY. Serological tests further demonstrated these differences and that the virus is serologically related to another potyvirus, brome streak mosaic virus (BrSMV). We conclude that the virus should be named as the Hordeum isolate of BrSMV.     

Effect of Soil–matric Potential and Phylloplanes of Rotation-crops on the Survival of a Bioluminescent Xanthomonas campestris pv. campestris

The survival of the bacterial pathogen, Xanthomonas campestris pv. campestris (Xcc), was studied in plant debris-infested soil with different matric potentials (0, –10, –30, –50, –100, –200, and –900kPa), and on the phylloplane of crops used for rotation with cabbage. Populations of cellulolytic and proteolytic microorganisms were studied in relation to soil matric potential and Xcc. The survival of Xcc was negatively correlated (r=–0.710; P=0.06) with soil matric potential and with the abundance of cellulolytic microorganisms (P=0.05). In saturated soil, Xcc survived for only 19–28 days, while at –900kPa there was no significant change in the bacterial population within this period. Survival of Xcc on the phylloplane of cabbage (Brassica oleracea var. capitata) (host) was similar to that on mustard and lettuce (48 days), whereas the pathogen was detected for only 9 days on rice. It appears that high matric potentials reduced populations of Xcc in soil, whereas epiphytic survival of this pathogen depended on the plant species.