Pathotype characterization of Aphanomyces euteiches isolates collected from pea breeding nurseries

Introduction

Aphanomyces euteiches Drechsler is an oomycete pathogen that affects legume crops, causing root rot, a severe disease of peas (Pisum sativum L.) worldwide. While significant research progress has been made in breeding pea-resistant varieties, there is still a need for a deeper understanding of the diversity of pathogen populations present in breeding nurseries located in various legume-growing regions around the world.

Methods

We analysed the diversity of 51 pea-infecting isolates of A. euteiches, which were recovered from four American (Athena, OR; Le Sueur, MN; Mount Vernon, WA; Pullman, WA) and three French (Riec-sur-Belon, Templeux-le-Guérard, Dijon) resistance screening nurseries. Our study focused on evaluating their aggressiveness on two sets of differential hosts, comprising six pea lines and five Medicago truncatula accessions.

Results

The isolates clustered into three groups based on their aggressiveness on the whole pea set, confirming the presence of pathotypes I and III. Pathotype I was exclusive to French isolates and American isolates from Athena and Pullman, while all isolates from Le Sueur belonged to pathotype III. Isolates from both pathotypes were found in Mount Vernon. The M. truncatula set clustered the isolates into three groups based on their aggressiveness on different genotypes within the set, revealing the presence of five pathotypes. All the isolates from the French nurseries shared the same Fr pathotype, showing higher aggressiveness on one particular genotype. In contrast, nearly all-American isolates were assigned to four other pathotypes (Us1, Us2, Us3, Us4), differing in their higher aggressiveness on two to five genotypes. Most of American isolates exhibited higher aggressiveness than French isolates within the M. truncatula set, but showed lower aggressiveness than French isolates within the P. sativum set.

Discussion

These results provide valuable insights into A. euteiches pathotypes, against which the QTL and sources of resistance identified in these nurseries displayed effectiveness. They also suggest a greater adaptation of American isolates to alfalfa, a more widely cultivated host in the United States.

Didymella fabae Punith.: mating type occurrence, distribution and phenotyping of the anamorph Ascochyta fabae Speg. in Tunisia

Faba bean ascochyta blight, caused by Ascochyta fabae Speg. (teleomorph: Didymella fabae Punith.), is one of the most devastating diseases of the crop. It can cause yield losses that reach 95% in conducive weather conditions. Surveys were carried out in five regions of Tunisia: Beja, Bizerte, Jendouba, Kef and Tunis-Cap Bon. A total of 513 fungal isolates were collected from 2011 to 2013. A molecular characterization was conducted to identify the mating type of each individual using a mating type specific PCR. Results revealed that the two mating types MAT1-2 and MAT1-1 coexisted in all surveyed regions. An imbalance in favor of MAT1-2 was observed particularly in Bizerte and Jendouba regions (sex ratio was 18:85 and 32:80, respectively). Moreover, morphological and pathogenic characterization of 122 isolates among the collection revealed a significant variability in conidia type (one celled or two celled conidia) frequency, in conidia mean size and in aggressiveness toward Badii faba bean cultivar (incubation period, IP; percentage necrotic leaf area, S; and area under disease progression curve, AUDPC). A principal component analysis (PCA) performed on morphologically studied parameters (frequency of conidia cell number and conidia mean size) identified three groups of isolates based on morphological traits: one celled (1C) and two celled (2C) conidia rates, one celled and two celled conidia length and width (1L, 1W, 2L and 2W, respectively). A second PCA using aggressiveness parameters (IP: Incubation period, S1, S4 and S9: percentage of necrotic leaf area respectively 5, 20 and 45 days after inoculation) identified three distinct pathogenic groups: poorly pathogenic AG1, moderately pathogenic AG2 and highly pathogenic AG3. Morphological and pathogenic groups and mating type data were used to conduct a multiple factorial correspondence analysis (MFCA) which revealed a correlation between the variables studied. Five groups were identified, each associated with a morphological and pathogenic trait and mating type. The most pathogenic group belonged to MAT1-2 suggesting that in locations where MAT1-2 is prevalent the epidemic risk is more important.

Aggressiveness of Diverse French Aphanomyces euteiches Isolates on Pea Near Isogenic Lines Differing in Resistance Quantitative Trait Loci

Aphanomyces root rot is a major disease in many pea growing regions worldwide. Development of resistant varieties is necessary to manage the disease. Near isogenic lines (NILs) carrying resistance alleles at main quantitative trait loci (QTLs) were developed by marker-assisted backcrossing. This study aimed to evaluate the aggressiveness of diverse French isolates of Aphanomyces euteiches on NILs carrying different resistance QTLs. Forty-three A. euteiches isolates from different French pea growing regions were tested for aggressiveness on eight NILs carrying single or combinations of resistance QTLs and two susceptible or resistant control lines, in controlled conditions. Three clusters of isolates, unrelated to geographical origin, were identified, including 37, 56, and 7% of isolates with high, moderate, and low average levels of aggressiveness, respectively. Three groups of pea lines were also identified. The first group consisted of a pea resistant control line, moderately to highly resistant to all of the isolates. The second group included five NILs carrying a major-effect resistance allele at QTL Ae-Ps7.6, with a medium to broad range of effects on the isolates. The third group consisted of three NILs carrying minor-effect resistance alleles, with a narrow range of effects on the isolates. The results suggest that highly aggressive isolates occur naturally, which may be selected by future partially resistant pea varieties carrying QTLs and increase the risk of erosion of QTL effect. QTL pyramiding strategies for a higher level and a broader range of effect of quantitative resistance on A. euteiches populations will be required for breeding for durable pea resistant varieties.

Genetic and Pathogenicity Diversity of Aphanomyces euteiches Populations From Pea-Growing Regions in France

Aphanomyces euteiches is an oomycete pathogen with a broad host-range on legumes that causes devastating root rot disease in many pea-growing countries and especially in France. Genetic resistance is a promising way to manage the disease since consistent QTL controlling partial resistance have been identified in near isogenic lines of pea. However, there are still no resistant pea varieties cultivated in France. This study aimed to evaluate the phenotypic and genetic diversity of A. euteiches populations from the major pea-growing regions in France. A collection of 205 isolates, from soil samples collected in infested pea fields located in five French regions, was established and genotyped using 20 SSR markers. Thirteen multilocus genotypes were found among the 205 isolates which displayed a low genotypic richness (ranged from 0 to 0.333). Two main clusters of isolates were identified using PCoA and STRUCTURE, including a predominant group comprising 88% of isolates and another group representing 12% of isolates mainly from the Bourgogne region. A subset of 34 isolates, representative of the fields sampled, was phenotyped for aggressiveness on a set of resistant and susceptible varieties of four legume hosts (pea, faba bean, vetch, alfalfa). Significant differences in disease severity were found among isolates and three groups of aggressiveness comprising 16, 17, and 2 isolates, respectively, were identified using HCA analysis. A higher diversity in pathogen aggressiveness was observed among isolates from Bourgogne, which included different legumes in its crop history. Little relationship was observed between genetic clusters and pathogenicity in the subset of 34 isolates, as expected using neutral markers. This study provides useful knowledge on the current state of low to moderate diversity among A. euteiches populations before resistant pea varieties are grown in France. New insights and hypotheses about the major factors shaping the diversity and evolution of A. euteiches are also discussed.

A single, plastic population of Mycosphaerella pinodes causes ascochyta blight on winter and spring peas (Pisum sativum) in France

Plant diseases are caused by pathogen populations continuously subjected to evolutionary forces (genetic flow, selection, and recombination). Ascochyta blight, caused by Mycosphaerella pinodes, is one of the most damaging necrotrophic pathogens of field peas worldwide. In France, both winter and spring peas are cultivated. Although these crops overlap by about 4 months (March to June), primary Ascochyta blight infections are not synchronous on the two crops. This suggests that the disease could be due to two different M. pinodes populations, specialized on either winter or spring pea. To test this hypothesis, 144 pathogen isolates were collected in the field during the winter and spring growing seasons in Rennes (western France), and all the isolates were genotyped using amplified fragment length polymorphism (AFLP) markers. Furthermore, the pathogenicities of 33 isolates randomly chosen within the collection were tested on four pea genotypes (2 winter and 2 spring types) grown under three climatic regimes, simulating winter, late winter, and spring conditions. M. pinodes isolates from winter and spring peas were genetically polymorphic but not differentiated according to the type of cultivars. Isolates from winter pea were more pathogenic than isolates from spring pea on hosts raised under winter conditions, while isolates from spring pea were more pathogenic than those from winter pea on plants raised under spring conditions. These results show that disease developed on winter and spring peas was initiated by a single population of M. pinodes whose pathogenicity is a plastic trait modulated by the physiological status of the host plant.

Landscape epidemiology of plant diseases

Many agricultural landscapes are characterized by a high degree of heterogeneity and fragmentation. Landscape ecology focuses on the influence of habitat heterogeneity in space and time on ecological processes. Landscape epidemiology aims at applying concepts and approaches originating from landscape ecology to the study of pathogen dynamics at the landscape scale. However, despite the strong influence that the landscape properties may have on the spread of plant diseases, landscape epidemiology has still received little attention from plant pathologists. Some recent methodological and technological progress provides new and powerful tools to describe and analyse the spatial patterns of host-pathogen interactions. Here, we review some important topics in plant pathology that may benefit from a landscape perspective. These include the influence of: landscape composition on the global inoculum pressure; landscape heterogeneity on pathogen dynamics; landscape structure on pathogen dispersal; and landscape properties on the emergence of pathogens and on their evolution.

Infective endocarditis in a collegiate wrestler

A 21-year-old collegiate wrestler was admitted to the hospital suffering from acute left lower quadrant abdominal pain. Blood cultures taken at the time of admission showed Staphylococcus aureus. The results of a computed tomography scan and a two-dimensional echocardiogram were consistent with a diagnosis of infective endocarditis. Therapy consisted of a 14-day hospitalization, a 28-day course of parenteral antibiotics, and subsequent follow-up visits. He returned to full participation in wrestling after 15 weeks.

Inhibition of lymphocyte protein kinase C by unsaturated fatty acids

Oleic, arachidonic, eicosapentaenoic and docosahexaenoic acids inhibited lymphocyte protein kinase C activity in the presence of Ca2+, phospholipid and a phorbol ester. Linoleic and alpha-linolenic acids did not affect protein kinase C activity in this way and none of the fatty acids affected protein kinase A activity. These findings indicate direct inhibitory effects of some unsaturated fatty acids upon protein kinase C. Culture of lymphocytes in the presence of oleic, arachidonic, eicosapentaenoic or docosahexaenoic acids resulted in a reduction in protein kinase C activity (by up to 45%). Culture with linoleic or alpha-linolenic acids did not affect protein kinase C activity and none of the fatty acids affected total protein kinase A activity or the percentage in the active form. These results show for the first time that fatty acids have long term effects upon protein kinase C activity, perhaps as a result of altering the rate of turnover of the enzyme. It is suggested that the inhibition of lymphocyte functions caused by unsaturated fatty acids may in part be due to their effect on protein kinase C.

Risk factors and 10-year breast cancer survival in northern Alberta

1,121 women in northern Alberta diagnosed as having breast cancer between 1971-74 were followed for 10 years. Risk factors for breast cancer were studied with respect to their possible influence on survival by comparing survival curves, using both Logrank and Cox's regression model, and controlling for intercurrent death, stage and axillary node status. A complex interaction was found between age and menopausal status and survival rates. Premenopausal women aged 45-55 had a better survival rate than postmenopausal women of the same age. However, one subgroup of premenopausal women aged 35-39 had a significantly worse prognosis than those aged 40-44 as did a group of post menopausal women aged 70-74. No cause was found other than the effect of age. There was a significant trend to worsening survival with heavier weight at time of diagnosis and with breast feeding. Parity of five or more and family history of breast cancer were less consistently associated with worse survival. Oral contraceptive use was only associated with worsened prognosis significantly when stage was controlled for; there was no overall effect. Age at menarche and age at first birth did not influence prognosis. Theories to explain the findings are discussed.

The behavior of the expanding point .25 ACP ammunition in the human body

We examined six cases (four homicides, two suicides) involving gunshot wounds with .25 ACP ammunition. The nature of these cases is described in this article.

Reproductive events and family history as risk factors for breast cancer in northern Alberta

Reproductive events and family history as risk factors for breast cancer in northern Alberta were investigated with the use of data from a computerized population-based registry. Women aged 30 to 79 years attending diagnostic breast clinics at the Cross Cancer Institute from 1971 through 1975 constituted the two study groups; 1232 women had diagnosed breast cancer (malignant disease group) and 602 women were clinically free of all types of breast disease (control group). An increased relative risk of breast cancer was found in women with a family history of breast cancer, those who gave birth to their first term infant at age 30 years or older, those in whom more than 15 years elapsed between menarche and that birth, and those with a late natural menopause. There was a decreased risk, relative to nulliparity, in the postmenopausal women who first gave birth to a term infant 5 years or less after menarche. Artificial menopause (bilateral oophorectomy), parity and age at menarche had no apparent effect on the risk. The pattern of risk factors in northern Alberta differed from that reported for other geographic areas, including other provinces of Canada, thus emphasizing the need for local studies in the planning of screening programs.