The dynamics of Phytophthora infestans populations in the major potato-growing regions of Asia – A review

Asia is now the largest potato-producing region of the world and late blight, caused by Phytophthora infestans, is the most important pathogen limiting production. This review documents, in both the historical and the current context, the population structure of P. infestans in the major areas of potato production in Asia. Information from diverse sources regarding the stated or inferred clonal pathogen lineages present, population changes, and possible migration routes of the pathogen into the countries of this region have been reviewed to aid researchers and those involved in managing late blight in Asia. The single most important factor for population change and resultant epidemics in this region has been found to be migration of pathogen genotypes from Europe and the Americas. Reducing the impact of such migration in the future will necessitate putting in place improved phytosanitary measures. To achieve this, data sharing using global networks such as AsiaBlight and EuroBlight is imperative.     

Banning of methyl bromide for seed treatment: could Ditylenchus dipsaci again become a major threat to alfalfa production in Europe?

In Europe, the stem and bulb nematode Ditylenchus dipsaci has been listed as a quarantine pest by EPPO: without any control, it may cause complete failure of alfalfa crops. Movement of nematodes associated with seeds is considered to be the highest‐risk pathway for the spread of this pest. Since the 2010 official withdrawal of methyl bromide in Europe, and in the absence of any alternative chemical, fumigation of contaminated seed batches is no longer possible, which makes the production of nematode‐free alfalfa seeds difficult to achieve and leads to unmarketable seed batches. Thermotherapy is being considered as a realistic alternative strategy, but its efficiency still remains to be validated. The combination of the currently available methods (i.e. use of resistant cultivars, seed production according to a certification scheme, mechanical sieving, seed batch inspection) could significantly reduce the likelihood of seed contamination. However, it does not guarantee a total eradication of the nematode. Although it is already widely distributed all over Europe, reclassification of D. dipsaci as a regulated non‐quarantine pest to reduce the possibility of further introductions and the rate of spread of this pest appears to be a risky strategy because of the lack of up‐to‐date documented data to evaluate damage thresholds and determine acceptable tolerance levels. [[ArtCopyrightmsg]]     

Mechanisms of powdery mildew resistance of wheat – a review of molecular breeding

Powdery mildew (Blumeria graminis f. sp. tritici) results in serious economic loss in wheat production. Exploration of plant resistance to wheat powdery mildew over several decades has led to the discovery of a wealth of resistance genes and quantitative trait loci (QTLs). We have provided a comprehensive summary of over 200 powdery mildew genes (permanently and temporarily designated genes) and QTLs reported in common bread wheat. This highlights the diverse and rich resistance sources that exist across all 21 chromosomes. To manage different data for breeders, here we also present a bridged mapping result from previously reported powdery mildew resistance genes and QTLs with the application of a published integrated wheat map. This will provide important insights to empower further breeding of powdery mildew resistant wheat via marker-assisted selection (MAS).     

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.     

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.     

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...     

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.     

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.