Frequency of brown rot fungi on blossoms and fruit in stone fruit orchards in Greece

Brown rot is a devastating disease of stone fruits caused by Monilinia spp. This study was conducted to investigate the disease aetiology on blossoms and fruit in peach, apricot, sweet cherry and plum orchards, in Greece. In total, 1433 isolates obtained from orchards located in the main stone fruit production regions of Greece were identified to species based on the presence/size of a cyt b intron. Monilinia laxa and M. fructicola were detected at frequencies of 59 and 41%, respectively, while M. fructigena was absent. Monilinia fructicola was more common on fruit whereas M. laxa occurred in similar frequency on blossoms and fruit. Monilinia laxa was replaced by M. fructicola in fruit infections of peach in both regions investigated and in fruit infections of plum in the Imathia region. Assessments of aggressiveness of 30 isolates of both species on the petals and fruits of the hosts showed that M. fructicola isolates were more aggressive. This suggests that the predominance of M. laxa on the blossoms cannot be explained by higher aggressiveness. Measurements of the effect of temperature on mycelial growth showed that M. laxa isolates had a higher growth rate than M. fructicola at the lowest temperature tested of 5°C, whereas M. fructicola isolates showed higher growth rates at higher temperatures. The observed high frequency of M. fructicola in Greece represents a major threat for stone fruit production. Furthermore, the information obtained about delineation of species and plant organ preference could be useful for the implementation of disease management strategies.     

Characterization of Sclerotinia minor populations in Texas peanut fields

In the summer of 2004 an epidemic of sclerotinia blight of peanut, a disease caused by Sclerotinia minor, occurred in Texas in fields where the disease was never previously detected. The disease was observed on many plants within one of the fields (>3000 disease foci), although most foci were <1 m. It is hypothesized that these observations were inconsistent with the recent introduction of a monocyclic pathogen, even if disease developed under conducive environmental conditions. The pattern of disease is most suggestive of the presence of foliar (ascospore) infections, although air temperature was above the known limits for apothecia development if the pathogen had arrived in the field in 2004 peanut seed. To further examine this epidemic, 232 isolates were collected, across a variety of spatial scales spanning this field and other Texas peanut fields, and evaluated for aggressiveness, fungicide sensitivity and genotypic diversity. There was wide variation among isolates for the phenotypic characteristics measured, but there was no evidence that a genotypically unique, highly aggressive, and fungicide resistant isolate had been introduced or evolved. The predominant genotype, TX1, which contained 154 isolates, was found in every county and field population.     

Influence of competition and host plant resistance on selection in Phytophthora infestans populations in Michigan, USA and in Northern Ireland

Competition between genotypes of Phytophthora infestans was studied by inoculating potato cultivars with differing susceptibility to late blight in field experiments over three years in Northern Ireland, UK, and Michigan, USA. Multiple isolates of six genotype groups of P. infestans were chosen from the local populations in both N. Ireland and Michigan for inoculation of separate field trials planted in 2003, 2004 and 2005. Four cultivars were used in each trial; two (susceptible cv. Atlantic and the partially resistant cv. Stirling) were common to both locations, whereas the two additional cultivars (with partial resistance to late blight) were cvs Santé and Milagro in N. Ireland and cvs Pike and Jacqueline Lee in Michigan. Single-lesion isolates of P. infestans were obtained from leaves at 1% level of infection, characterized using pre-assigned markers and re-assigned to their respective genotype groups. Extreme selection occurred within the population of genotypes of P. infestans in N. Ireland in each year, with different genotype groups dominating the infection of different cultivars. Selection was observed on all cultivars tested, but was greatest on the more resistant cultivars. Over the 3 years, all of the 114 isolates obtained from cv. Milagro belonged to a single group, whereas among the 118 isolates from cv. Atlantic all six groups were represented. By contrast, in Michigan, the US-8 genotype dominated infection in all cultivars in each year; only 12 of 374 isolates characterized belonged to other genotypes (11 US-14 and a single US-10 isolate).     

Greater aggressiveness in the 2_A1 lineage of Phytophthora infestans may partially explain its rapid displacement of the US-1 lineage in east Africa

The displacement in east Africa of the US-1 clonal lineage of Phytophthora infestans by 2_A1 clonal lineage has been very rapid. This study tested the hypothesis that dominance of 2_A1 could be due, at least in part, to the increased aggressiveness of 2_A1 over US-1, using both a detached leaf assay (DLA) and a tuber slice assay. The assays were conducted in Uganda and Kenya but US-1 was only assayed in Uganda, because isolates could not be moved across borders and no potato US-1 isolates were available in Kenya. All isolates were collected from potato and compared on two potato cultivars (Kachpot-1 and Sarpo Mira), with the 2_A1 isolates also tested on tomato cultivar Rio Grande. Additionally, a tuber slice assay was done to test whether the capacity to infect tubers differed between 2_A1 and US-1. The aggressiveness of the isolates in the DLA varied significantly both within and among isolates classified according to clonal lineage and for type of host. The 2_A1 isolates were significantly more aggressive than US-1 isolates on both potato varieties evaluated. There were no significant effects of clonal lineage or potato cultivar used in the tuber assay. No significant correlation between foliar and tuber pathogenicity was observed. The 2_A1 isolates were significantly more aggressive on potato than on tomato. An effect of location was also observed in the DLA, on both hosts. It can be concluded from this study that greater pathogenicity of 2_A1 is at least partly attributable to its increased aggressiveness on potato.     

Cell wall-degrading enzymes produced in vitro by isolates of Phaeosphaeria nodorum differing in aggressiveness

The relationships between in vitro production of cell wall-degrading enzymes and aggressiveness of three Phaeosphaeria nodorum isolates were investigated. When grown in liquid medium containing 1% cell wall from wheat leaves as the carbon source, the isolates secreted xylanase, α-arabinosidase, β-xylosidase, polygalacturonase, β-galactosidase, cellulase, β-1,3-glucanase, β-glucosidase, acetyl esterase and butyrate esterase. Time-course experiments showed different levels of enzyme production and different kinetics between isolates. A highly aggressive isolate produced more xylanase, cellulase, polygalacturonase and butyrate esterase than did the two weakly aggressive isolates. Xylanase was the most active polymer-degrading enzyme produced, suggesting a key role during pathogenesis by P. nodorum .     

Characterization of Fusarium asiaticum and F. graminearum isolates from gramineous weeds in the proximity of rice fields in Korea

Fusarium graminearum species complexes (FGSCs), such as Fusarium asiaticum and F. graminearum, are important pathogens that cause Fusarium head blight (FHB) in several cereal crops worldwide. In this study, we collected 342 gramineous weed samples in the proximity of rice fields from May to June 2018 in Korea. Among the 500 Fusarium isolates from the weed samples, 13 species of Fusarium were identified, and F. asiaticum (41.2%), F. avenaceum (18.0%), F. acuminatum (16.4%) and F. graminearum (14.8%) were the most frequently isolated. The trichothecene genotype analysis showed that 206 F. asiaticum strains consisted of the nivalenol (NIV) genotype (n = 195, 94.7%) and 3-acetyldeoxynivalenol (3ADON) genotype (n = 11, 5.3%), whereas 74 F. graminearum strains consisted of the 15-acetyldeoxynivalenol (15ADON) genotype (n = 58, 78.4%) and 3ADON genotype (n = 16, 21.6%). Geographical differences were observed in the FGSC and trichothecene genotype compositions, which appeared host-dependent between the southern provinces and mid-eastern provinces. The aggressiveness assessment of FHB showed that the 3ADON chemotype was most aggressive followed by the 15ADON and NIV chemotypes in wheat, while the NIV chemotype was most aggressive followed by the 3ADON and 15ADON chemotypes in rice. The F. asiaticum strains grew slowly and produced fewer conidia and perithecia than the F. graminearum strains, regardless of their chemotypes. The results of this study suggest that F. asiaticum with the NIV chemotype has a host preference for rice, and FHB-causing pathogens can be harboured in gramineous weeds, which play a role in the dispersal of FHB pathogens to rice and other cereal crops.     

Reaction of cultivars of populus spp. to radiation induced virulent mutants of melampsora medusae

Summary Infection Type (IT) and Uredinial Number per Leaf Disk (ULD), induced on eleven cultivars of poplar in vitro, were employed to compare five radiation induced, mono-uredinial mutant lines of Melampsora medusae Thum. with the wild type race 5A from which they were derived. IT produced by the mutants was higher than (eight cultivars), similar to (two cultivars) and pronouncedly less than (IT from 4 to 1 in P. deltoides cv. 7–2) that of race 5A. Although the five mutants produced a uniform IT within a particular cultivar. ULD varied significantly between mutants on individual cultivars and there was a significant differential interaction of the mutant lines with cultivars. The ranking of mutant lines for aggressiveness on cultivars was not consistent while the differences among the mutants in mean ULD over all cultivars were not associated with the dosage level of irradiation from which they were isolated. The implications of the results in the interaction of leaf rust with poplar cultivars are discussed.     

Reactions of poplar clones to physiologic races of Melampsora larici-populina Kleb.

Summary Four mono-uredospore isolates of Melampsora larici-populina Kleb. produced qualitatively distinct reactions on four half-sib clones of Populus deltoides Marsh. and thus were recognisable as races. Two of the races could be distinguished equally readily by the distinctness of their reactions (three quantitative parameters) on four compatible clones of Populus spp. The pronounced race specific reactions of the clones of P. deltoides, allied to the less distinct, but nevertheless race specific reactions, of the compatible clones are consistent with an integrated rather than a disjunctive concept of resistance in Populus spp. to M. larici-populina.     

Toxicity of halogenated oxyquinolines in dogs. A clinical study. II. History, symptoms, laboratory findings, therapy, and follow-up

Intoxication due to short-term oxyquinoline therapy was studied in 100 dogs, which had been so treated because of diarrhoea (except in 2 cases). The latter condition was in itself mild and uncomplicated. The main symptoms of intoxication were listlessness or excitation and nervousness, aggressiveness, tremor, convulsions, and salivation. Clinical examination revealed myocarditis and liver injury. Mortality, i.e. the sum of spontaneous deaths and euthanasia, amounted to 30 %. The treatment considered to be most important was sedation and anticonvulsant measures. It was further essential to correct the dehydration, which was often present. A follow-up investigation showed that approx. 1/3 of the dogs which had recovered from the acute intoxication developed recurrent convulsions within the next 3 years.     

Differential effects of behaviour,propensity to migrate and recruitment season on glass eels and elvers’ growing performance

Abstract –  Social interactions impact growth rate of animals in different ways such as direct or indirect competition for food and/or territories. In this study, behaviour of glass eels and elvers was described throughout three trials of 9 days spread out over 3 months. The impact of recruitment season (spring and autumn runs) and glass eels’ propensity to migrate (assessed thanks to an experimental sorting) on individual growth was studied. Overall, spring elvers were more aggressive and active than autumn elvers while autumn fish were more gregarious and reached a higher specific growth rate than spring fish. At the individual level, gregariousness and swimming, respectively, promote and impair growth rate. In addition, skinny individuals and individuals with high motivation to get food achieved better growth rate suggesting catch‐up growth processes. These findings may help in clarifying the complex relations between behaviour, growth, river basin colonisation and future sex (which is environmentally determined in eel) and then contribute to the urgent need of scientific knowledge to guide the stocking programme of this endangered species.