Appearance of race Pfs:5 of spinach downy mildew fungus, Peronospora farinosa f. sp. spinaciae, in Japan

The races for the causal agent of spinach downy mildew Peronospora farinosa f. sp. spinaciae were identified by inoculation of race-differential cultivars. One isolate was identified as Pfs:5s and the others belonged to a new race. This is the first report of race Pfs:5 and another new race in Japan.     

Factors governing oospore production by Peronospora farinosa f. sp. spinaciae in cotyledons of spinach

Oospore production inPeronospora farinosa f. sp.spinaciae was induced in spinach seedlings. This was done in detached cotyledons as wel as in undetached cotyledons on living plants, and in growth chambers as well as in the field. In young leaf tissue the fungus, produced oospores more often than in old tissue. The four spinach cultivars tested, viz. Breedblad Scherpzaad, Symphony, Novires and Huro, did not show significant differences in numbers of cotyledons with oospores, nor in numbers of oospores per cotyledon, though cv. Breedblad Scherpzaad was less susceptible to oospore formation in the field. Comparison of various inoculum densities showed a tendency to a smaller number of cotyledons with oospores with a lower inoculum density. Oospores were abundantly formed, when the plants were exposed to stress conditions in the second half of the latent period.Samenvatting Methoden werden ontwikkeld om oosporenvorming doorPeronospora farinosa f. sp.spinaciae in kiemplanten van spinazie te induceren. Dit gebeurde met afgeplukte kiembladeren en in kiembladeren aan de levende plant, zowel in klimaatcellen als tevelde.In jonge kiembladeren werden vaker en meer oosporen gevormd, dan in oudere kiembladeren. De vier getoetste cultivars Breedblad Scherpzaad, Symphony, Novires en Huro vertoonden geen opvallende verschillen in aantallen kiembladeren met oosporen en aantallen oosporen per kiemblad, hoewel cultivar Breedblad Scherpzaad in het veld als minst vatbaar voor oosporenvorming naar voren kwam.Vergelijking van verschillende inoculum dichtheden toonde een tendens aan voor een kleiner aantal cotylen met oosporen bij lagere inoculumdichtheden. Er werden overvloedig oosporen gevormd wanneer de planten in de tweede helft van de latentieperiode in een stress situatie werden gebracht.     

Production of conidia by Peronospora farinosa f. sp. spinaciae

Conidium production byPeronospora farinosa f. sp.spinaciae (pathotype 3) was measured daily on colonies induced on leaves of spinach cvs Breedblad Scherpzaad (BS) and Huro. Distinction was made between colonies grown at temperatures of 10 and 15°C. Spore production was expressed as number of spores produced per stoma. There was a significant difference between total spore production on lesions on BS at 10 °C and that on lesions on the three other cultivartemperature combinations tested. Also a significant difference in the average sporulation period was observed between lesions produced at 10 and those at 15 °C. The same significant difference in response to temperature was found in the sporulation per stoma in the course of time.Samenvatting De conidiënproduktie vanPeronospora farinosa f. sp. spinaciae (fysio 3) werd dagelijks bepaald aan kolonies, welke op bladeren van de spinaziecultivars Breedblad Scherpzaad (BS) en Huro werden geïnduceerd. Daarbij werd onderscheid gemaakt tussen kolonies welke zich bij 10 en bij 15 °C hadden ontwikkeld. De sporenproduktie werd omgerekend naar het aantal sporen per huidmondje. Er was een significant verschil tussen de totale sporenproduktie op lesies op BS bij 10 °C en die op lesies op de drie andere getoetste cultivar-temperatuur combinaties. Er kon ook een significant verschil in de gemiddelde sporulatieperiode worden waargenomen tussen de lesies ontstaan bij 10 en bij 15 °C. Een dergelimk significant verschil in temperatuurreactie kon ook worden gevonden in het verloop van de soorulatie per huidmondje in de tijd.     

Germination of Peronospora farinosa f. sp. spinaciae conidia: a two-topped temperature curve

Samenvatting Bij verschillende herkomsten vanP. farinosa f. sp.spinaciae werden twee optima geconstateerd in de curve welke het verband aangeeft tussen conidiënkiemingspercentage en temperatuur.     

Proteomic analysis of a compatible interaction between Pisum sativum (pea) and the downy mildew pathogen Peronospora viciae

A proteomic approach was used to identify host proteins altering in abundance during Peronospora viciae infection of a susceptible cultivar of pea (Pisum sativum cv. Livioletta). Proteins were extracted from fully developed pea leaflets at 4 days post-inoculation, before visible symptoms were apparent. Cytoplasmic proteins and membrane- and nucleic acid-associated proteins from infected and control leaves were examined using two-dimensional difference gel electrophoresis. The majority of proteins had a similar abundance in control and infected leaves; however, several proteins were altered in abundance and twelve were found to have increased significantly in the latter. These proteins were selected for either matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry or electro-spray ionisation quadrupole time-of-flight tandem mass spectrometry analysis following trypsin digestion, with sequence identity being assigned to eight of the proteins. These included the ABR17 stress-response protein, the pathogen-induced PI176 protein, three photosynthetic proteins, a glycine-rich RNA binding protein and two glyceraldehyde 3-phosphate dehydrogenases (cytosolic and chloroplastic) which can be induced by a range of abiotic and biotic stresses in many plant species. The possible roles of these proteins in the response of the pea plant during P. viciae infection are discussed. This study represents the first proteomic analysis of downy mildew infection of pea leaves, and provides the basis for further work to elucidate molecular mechanisms of compatibility in P. viciae infections.     

Variation for virulence among Scandinavian isolates of Peronospora viciae f.sp. pisi (pea downy mildew) and responses of pea genotypes

Variation for virulence among Scandinavian isolates of Peronospora viciae f.sp. pisi (downy mildew) on different pea genotypes was investigated. Variation for virulence was found within and between mass-conidial isolates which were originally obtained from oospore populations. Virulence towards pea cultivars that have not been commerically cultivated in Scandinavia was observed. The specific resistance of the pea cultivars Puget, Cobri, Gastro, Starcovert and Starnain was confirmed. One pea breeding line showed a stable partial resistance to different isolates of the fungus and it was also highly resistant to race 8'from The Netherlands which is considered to be virulent on most pea genotypes carrying known specific resistance factors.     

New genes for resistance to downy mildew (Peronospora parasitica) in oilseed rape (Brassica napus ssp. oleifera)

The response of cotyledons of oilseed rape ( Brassica napus ssp. oleifera ) accessions to infection by isolates of Peronospora parasitica under controlled conditions was assessed on a 0–7 scale (disease reaction). In interactions scored 0–3, 4–5 and 6–7, the host was considered resistant, partially resistant and susceptible, respectively. Accession RES-26, selected from the spring oilseed rape cultivar Janetzkis, was partially resistant to isolate R1 and resistant to isolate P003 of P. parasitica , which distinguishes it from three previously described differential response groups ('A', 'B' and 'C') of accessions in B. napus . The resistance of RES-26 to isolate P003 seemed to be conditioned by a single, partially dominant gene and the resistance of RES-02, which belongs to group 'A' (resistant to R1 and P003), by two independent partially dominant genes. The gene for resistance to P003 in RES-26 is either closely linked, allelic or identical to one of the two genes for resistance in RES-02. Resistance of RES-02 to R1 is conditioned by a single, incompletely dominant gene. The genes for resistance to isolates R1 and P003 in RES-02 are either closely linked, allelic or identical. The cotyledonary leaves of each seedling responded independently when inoculated simultaneously each with a different isolate of the pathogen.     

The identification of a gene for race-specific resistance to Peronospora parasitica (downy mildew) in Brassica napus var. oleifera (oilseed rape)

The oilseed rape cultivar Cresor was resistant to 14 isolates of Peronospora parasitica derived from crops of Brassica napus in the UK. Segregation for resistance to one isolate among F₂ plants and F₃ progeny of crosses between Cresor and the susceptible cultivars Victor and Jet Neuf indicated that resistance was controlled by a single gene. There was evidence that genetic background and environment could influence the phenotypic expression of this resistance. Two sexual progeny isolates derived from a homothallic isolate of P. parasitica avirulent on Cresor were completely virulent on this cultivar. This suggested that the parental isolate was heterozygous at a matching locus or loci for avirulence and demonstrated the race-specific nature of the resistance.     

Seedling and adult plant resistance to downy mildew (Peronospora parasitica) in cauliflower (Brassica oleracea convar. botrytis var. botrytis)

Seedlings of six cauliflower cultivars ( Brassica oleracea convar. botrytis var. botrytis ) were assessed for resistance to a Danish isolate of Peronospora parasitica , under controlled conditions. Resistance, characterized by restricted sporulation and necrotic dark flecks at the inoculation site on the cotyledons, was expressed in the hybrids 9306 F1, 9311 F1, and the open pollinated cultivar Perfection. Testing of the parent lines and F2 generations of the two resistant hybrids suggested that resistance was a dominantly inherited trait controlled by a single gene. Inoculation of the cultivars with seven isolates, from different geographical origins, showed that the resistance was isolate specific. The two hybrid cultivars expressing cotyledon resistance and two hybrids expressing susceptibility were assessed for adult plant resistance under field conditions. The AUDPC (Area Under the Disease Progress Curve), based on disease incidence and severity, revealed significant differences between the cultivars. At harvest, the cultivars exhibited significantly different levels of defoliation and curd attack. The cultivars 9306 F1 and 9311 F1 showed high levels of resistance in all assessments, whereas the two cultivars exhibiting susceptibility at the seedling stage, 9304 F1 and 9305 F1, also exhibited susceptibility through the adult plant stage. Thus, the resistance exhibited under field conditions resembled that identified at the seedling stage under controlled conditions. The results suggest that cotyledon resistance similar to that described could provide resistance throughout the adult plant stage, including curds.     

Induction of resistance to downy mildew (Peronospora parasitica) in cauliflower by DL-β-amino-n-butanoic acid (BABA)

Of the three isomers of aminobutyric acid, only the β isomer (BABA) was effective in inducing resistance against Peronospora parasitica , the causal agent of downy mildew, in cauliflower ( Brassica oleracea var. botrytis ). A single foliar spray applied to 7-day-old seedlings protected the plants against Peronospora parasitica for at least 15 days. Of the enantiomers (R and S), only the R was effective. Resistance was accompanied by a hypersensitive-like reaction (necrotic spots) which was evident before inoculation. BABA was systemically effective when applied to the roots, but failed to protect cotyledons adjacent to treated ones. Unlike other chemical inducers, BABA was effective when applied several hours postinoculation. It had no effect on P. parasitica spore germination. In cauliflower seedlings, BABA did not induce the accumulation of the pathogenesis-related protein PR-1, PR-2, PR-3, PR-5 and PR-9. Only treated and challenged seedlings accumulated PR-2.     

Effect of leaf wetness duration and temperature on infection of downy mildew (Peronospora sp.) of basil

Journal of Plant Diseases and Protection - The effect of leaf wetness duration and temperature on the development of downy mildew of basil, incited by Peronospora sp., was studied under controlled...     

Recent races of spinach downy mildew pathogen <Emphasis Type="Italic">Peronospora farinosa</Emphasis> f. sp. <Emphasis Type="Italic">spinaciae</Emphasis> in Japan

Isolates of spinach downy mildew fungus, Peronospora farinosa f. sp. spinaciae, collected at seven sites in Japan from December 2013 to March 2016, were identified as belonging to races 8, 10, 12 and 13, and one was unauthorized. Races 10, 12, 13 and the unauthorized were first found in Japan.     

拟南芥霜霉病抗性分子机制研究进展

随着近年分子生物学技术的发展与应用,植物霜霉病抗性的研究有了长足的进展。本文就拟南芥抗霜霉病基因的克隆与结构分析,抗病信号传导,防卫反应和系统获得抗性,以及寄主-寄生菌共进化冲突方面进行了综述,并就今后的研究进行了展望。     

拟南芥霜霉病抗眭分子机制研究进展

随着近年分子生物学技术的发展与应用，植物霜霉病抗性的研究有了长足的进展。本文就拟南芥抗霜霉病基因的克隆与结构分析，抗病信号传导，防卫反应和系统获得抗性，以及寄主一寄生菌共进化冲突方面进行了综述，并就今后的研究进行了展望。     

Seasonal development of ontogenic resistance to downy mildew in grape berries and rachises

ABSTRACT Clusters of Vitis vinifera and V. labrusca are reported to become resistant to Plasmopara viticola at stages of development ranging from 1 to 6 weeks postbloom. It has been suggested that resistance is associated with loss of the infection court as stomata are converted to lenticels, but the time of onset, cultivar variation, and seasonal variation in ontogenic resistance has remained uncertain, as has the comparative susceptibility of stem tissue within the fruit cluster. In New York, we inoculated clusters of V. vinifera cvs. Chardonnay and Riesling and V. labrusca cvs. Concord and Niagara at stages from prebloom until 5 to 6 weeks postbloom. Berries were infected and supported profuse sporulation until 2 weeks postbloom, and pedicel tissue remained susceptible until 4 weeks postbloom. Although berries on later-inoculated clusters failed to support sporulation, discoloration and necrosis of berry tissues was often noted, and necrosis of the pedicel within such clusters often led to further discoloration, shriveling, reduced size, or loss of berries. When the epidermis of discolored berries that initially failed to support sporulation was cut, the pathogen emerged and sporulated through incisions, indicating that lack of sporulation on older symptomatic berries was due to infection at an early stage of berry development followed by conversion of functional stomata to lenticels during latency. We repeated the study on Chardonnay and Riesling vines in South Australia and found that the period of berry and rachis susceptibility was greatly increased. The protracted susceptibility of the host was related to the increased duration and phenological heterogeneity of bloom and berry development in the warmer climate of South Australia. The time of onset and subsequent expression of ontogenic resistance to P. viticola may thus be modified by climate and should be weighed in transposing results from one climatic area to another. Our results can be used to refine forecast models for grapevine downy mildew to account for changes in berry and rachis susceptibility, and to focus fungicide application schedules upon the most critical periods for protection of fruit.     

Further characterization of field resistance in lettuce to Bremia lactucae (downy mildew)

The development of five Bremia lactucae isolates on the field-resistant crisphead lettuce cultivar Iceberg was compared under field conditions with that on the more susceptible crisphead cultivar Ithaca. With each of five isolates, the epidemic developed more rapidly on Ithaca than Iceberg; lesions on Ithaca were more numerous, larger and sporulated more profusely than on Iceberg. There was no evidence for adaptation of isolates to Iceberg, which provides some additional evidence that the resistance of this cultivar could be non-differential (horizontal). There was, however, evidence of non-specific differences between isolates in their quantitative virulence.