Crown rot caused by Phytophthora cactorum in Norwegian strawberry production

Crown rot of strawberry, caused by Phytophthora cactorum , was detected for the first time in Norway in 1992. This paper reports on surveys for P. cactorum in Norwegian certified strawberry plant production and on the distribution of the pathogen in regular strawberry production. In 1996 and 1997, samples of plant material from all certified strawberry plant growers in the country were investigated by isolation on artificial growth medium and using an enzyme-linked immunosorbent assay (ELISA). P. cactorum was not detected in any of the samples. A total of 171 isolations from plants with symptoms resembling crown rot were made from plants in a survey of the distribution of Phytophthora fragariae var. fragariae and from other samples. P. cactorum was detected at 35 different strawberry-producing farms in 11 of the 19 counties of Norway. The fungus was most frequently isolated from cv. Korona (at 18 locations), followed by cv. Inga (at 10 locations).     

Control of crown rot (Phytophthora cactorum) of apple trees with the systemic fungicides metalaxyl and fosetyl-aluminium

Four fungicides were evaluated as combined soil drench and trunk treatments for the control of crown rot, caused by Phytophthora cactorum, in naturally infected apple trees. In a 3-year preliminary study, metalaxyl at 1 and fosetyl-aluminium at 8 g a. i. per tree, applied twice a year, prevented death of infected trees showing only initial, but not more severe, symptoms of crown rot. This indicates that these fungicides have the ability to arrest further symptom development in naturally infected trees if they are treated as soon as symptoms appear. Healthy trees remained free of infection if they were treated with these fungicides, suggesting a preventative action. Repeated bi-annual application of metalaxyl or fosetyl-aluminium should be sufficient to prevent the loss of trees to crown rot.     

The occurrence of crown rot caused by Phytophthora cactorum in the apple rootstock MM 104

Samenvatting In het voorjaar van 1968 vertoonde een aantal bomen op het onderstammen proefveld te Kraggenburg (N.O.P.) een slechte bladstand. Vóór januari 1969 waren alle bomen van de appelrassen Cox's Orange Pippin, James Grieve en Lombartscalville en één enkel geplante Stark Earliest, alle geënt op onderstam MM 104, afgestorven. Slechts de vijf bomen van het ras Golden Dilicious op MM 104 vertoonden een normale stand. Uit de aangetaste wortels konPhytophthora cactorum geïsoleerd worden. Vermoedelijk heeft het pathogeen door een hoge grondwaterstand gedurende de winter 1967/1968 de kans gekregen de onderstam MM 104 te infecteren. Doordat de vijf Golden Delicious bomen op MM 104 aan het windscherm grensden, waar het relatief droger is, zijn deze waarschijnlijk aan infectie ontsnapt.     

Phytophthora crown rot of almonds in Australia 1

Phytophthora crown rot, caused primarily by Phytophthora cambivora, has caused considerable losses in almond orchards in the Willunga and northern plains areas approximately 50 km north and south of Adelaide (AU), respectively. Other Phytophthora species including P. citrophthora, P. cryptogea, P. megasperma and P. syringae have also been associated with diseased trees. Tree losses have been associated with P. cactorum isolated from trunk cankers on scaffold limbs on trees in the Riverland almond-growing area approximately 350 km north-east of Adelaide. The Al mating type of P. cambivora was the most pathogenic to almond seedlings. Cvs Mission and Chellaston, which are commonly used as rootstocks, were highly susceptible to crown rot whereas peach cv. Nemaguard was resistant. An excised twig assay has been developed to screen micropropagated shoots for resistance to P. cambivora. Metalaxyl applied at 5 g active substance per tree in spring, winter and autumn in a shallow trench close to the trunk prevented the development of trunk cankers. Foliar sprays of phosphonate (H₃PO₃) at 2 g active substance per litre in autumn and spring also inhibited canker development.     

Incidence of Phytophthora pod rot disease of cacao at different heights in the tree

The rate of infection of pods byP. palmivora at the lower trunk of a cacao tree is always higher than of those in the canopy. This is often held as a proof that the soil is the primary source of infection. An experiment has indicated that climatic conditions at the beginning of the rainy season in Western Nigeria do not favour infection of pods in the canopy, which may also explain the said phenomenon.Samenvatting In Nigeria evenals in andere landen is waargenomen dat doorP. palmivora aangetaste cacaokolven in het begin van de regentijd vooral voorkomen aan de stam en dat het aantastingspercentage van de stamvruchten over het gehele seizoen genomen aanzienlijk hoger light dan dat van de vruchten in de kroon. Een proef waarbij ongeveer 10% van de stamvruchten en ook van de vruchten in de kroon werd geïnoculeerd bij het begin van de regentijd, wees uit dat in deze periode van het jaar de klimaatomstandigheden in de kroon waarschijnlijk ongunstig zijn voor infectie.Een hoog percentage aangetaste stamvruchten in genoemde periode mag derhalve niet zonder meer gezien worden als bewijs dat de grond in het begin van de regentijd de enig belangrijke besmettingsbron van de ziekte zou zijn.     

Phytophthora root and crown rot of raspberry in Bulgaria

Root and crown rot of raspberry (Rubus idaeus L.) was observed in a plantation at the experimental station of small fruits in Kostinbrod, Bulgaria. Isolates ofPhytophthora spp. were obtained from diseased plants. Colony morphology, growth rates, features of asexual and sexual structures were studied and as a result twoPhytophthora species were identified:Phytophthora citricola Saw. andPhytophora citrophthora (R.E. Sm. & E.H. Sm.) Leonian. Their pathogenicity was confirmed in artificial inoculation experiments. The isozyme (-esterase) patterns ofP. citrophthora andP. citricola isolates from raspberry and from the collection of the CBS, Baarn the Netherlands were compared, using micro-gel electrophoresis. Both species are reported for the first time as pathogens of raspberry in Bulgaria. This is only the second report in phytopathological literature ofP. citrophthora on raspberry, the first being from Chile [Latorre and Munoz, 1993].     

Etiology of a newly described root rot of guar (Cyamopsis tetragonoloba) in Australia caused by Phytophthora cryptogea

An isolate of Phytophthora obtained from diseased roots and stems of guar ( Cyamopsis tetragonoloba ) growing in waterlogged soil from Dalby. Queensland. was identified as Phytophothora cryptogea ( P. drechsleri ). Sex organs were not observed, Pathogenicity to guar seedlings was established under glasshouse conditions either by using a hypocotyl-wound inoculation technique, or adding motile zoospores to seedlings growing under saturated conditions. This appears to be the first report of this disease. Seven isolates of P. drechsleri from hosts other than guar were shown to be pathogenic to guar following hypocotyls-wound inoculation.
The host range of the guar isolate was studied using both hypocotyl-wound inoculation and zoospores. After hypocotyl inoculation, the following species were found to be susceptible^: cantaloupe. cowpea, cucumber, mungbean, pea. pigeon-pea, safflower. sunflower, tomato and watermelon. Slight symptoms were observed on bean and chickpea. When zoospores were used as the inoculum, only pea. pigeon-pea, sunflower and safflower were highly susceptible. A range of guar cultivars and breeding lines were screened for resistance using zoospore inoculum, and although no genotypes were highly resistant, there were significant differences between disease reactions.     

Evaluation of antisera raised against Phytophthora fragariae for detecting the red core disease of strawberries by enzyme-linked immunosorbent assay (ELISA)

Antiserum was raised against pooled mycelial suspensions from five isolates (designated Pf 1, Pf 2, Pf 3, Pf 10 and Pf 11) representing five physiologic races of Phytophthora fragariae. In enzyme-linked immunosorbent assay (ELISA), this antiserum detected homologous soluble antigens at protein concentrations as low as 2 ng/ml.
Fungal antigens could also be detected in extracts of strawberry plants infected with P. fragariae. Root extracts prepared from the alpine strawberry Fragaria vesca and F. ananassa cv. Cambridge Favourite infected with any of the five isolates studied produced strong reactions in ELISA. In F. vesca , ELISA-positive material was detectable 6-8 days after inoculation before macroscopic symptoms appeared. The cultivar Red Gauntlet, which is resistant to Pf 1, 2 and 3 but susceptible to Pf 10 and 11, reflected this differential response in ELISA; the absorbance produced by extracts of plants infected with virulent isolates was significantly higher than that obtained with the corresponding extracts of plants inoculated with a virulent isolates. The recently introduced cultivars Hapil, Ostara and Providence were found to be susceptible to all isolates in this study: the corresponding root extracts were also positive in ELISA.
The antiserum also detected P cactorum infections. Nevertheless, the ELISA test described should prove valuable in screening certified strawberry stocks.     

32份木薯种质对疫霉根腐病的抗性评价和农艺性状分析

通过田间自然发病和室内离体接种方法对32份木薯种质进行了棕榈疫霉根腐病抗病性评价,结果表明,供试的32份木薯种质中,高抗种质7份,抗病种质7份,中感种质8份,感病种质7份,高感种质3份。其中高抗种质为‘H360’、‘华南11号’、‘华南8号’、‘H588’、‘桂热3号’、‘H873’和‘H971’;抗病种质为:‘F556’、‘H502’、‘GR911’、‘C-4’、‘F10’、‘南植188’和‘H47’。对其中14份抗棕榈疫霉根腐病木薯种质的农艺性状进行了鉴定和评价,结果表明‘华南8号’、‘GR911’、‘F556’、‘C-4’、‘H360’可以进一步加以利用。     

Phytophthora species causing crown and root rot of tomato in southern Italy*

Phytophthora capsici, Phytophthora cryptogea and Phytophthora nicotianae were isolated from tomato plants with symptoms of crown and root rot in plastic‐house crops in Sicilia and Calabria (southern Italy). The species were identified primarily on the basis of morphological and cultural characteristics. The identification was confirmed using molecular methods, polyacrylamide gel electrophoresis (PAGE) of mycelial proteins and polymorphism of DNA sequences amplified by polymerase chain reaction using random primers (RAPD‐PCR). P. capsici caused significant losses in tomato crops that had succeeded capsicum crops. P. cryptogea was found to be the most frequent species causing basal stem rot of tomato, a disease of increasing importance in commercial tomato crops in plastic houses in Sicilia. P. nicotianae was common in plastic houses where poor drainage resulted in standing water.     

Causes of incipient rot and rot in regrowth Eucalyptus diversicolor (karri) trees

Eucalyptus diversicolor (karri) is the second most important commercial timber tree in Western Australia. Sawlogs from regrowth trees often have a discoloration in the heartwood that is more abundant than in sawlogs from mature trees. Other symptoms in regrowth logs include white rot, white pocket rot and brown rot. Fungal isolations and pathogenicity tests were conducted to determine whether this discoloration was incipient rot, and if so, what caused it and which rot(s) would eventually develop. A combined sample of 329 discs from recently felled trees and freshly cut scantling had discoloration in 48%, white rot in 14%, white pocket rot in 12% and brown rot in 4% of pieces of wood. Hymenochaete semistupposa was isolated from 22% of discoloured wood and 39% of white pocket rot samples. Stereum hirsutum was isolated from 4% of discoloured wood and 13% of white rot samples. Koch's postulates in regrowth karri trees showed that H. semistupposa caused extensive discoloration, with white pocket rot developing in the heartwood within 4 years, while S. hirsutum caused extensive discoloration, with white rot developing in both the heartwood and sapwood within 2 years. It was concluded that the discoloration was incipient rot, which would eventually develop into either white rot or white pocket rot.     

Tomato late blight (Phytophthora infestans) in Uganda

A survey on the tomato late blight situation and current practices for disease management was carried out in Uganda using an informal structured questionnaire approach. Ten districts from different agroclimatic zones were selected for the survey. Phytophthora infestans isolates from tomatoes were obtained from the zones and only the A1 mating type was recovered. Tomato cultivation is practised year-round. The major commercial varieties grown, Moneymaker, Marglobe, Heinz and Roma, were susceptible to late blight. Late blight and bacterial wilt ( Pseudomonas solanacearum ) were the major diseases, with bollworm ( Helicoverpa armigera ) and thrips ( Thrips spp .) the major insect pests. Fungicides, mostly mancozeb, were the predominant control method used by farmers. Sanitation is practised by some farmers, but only in association with fungicides, to control late blight. Plant nutrition is not perceived as playing a major role in late blight management. Problems associated with pesticides and poor marketability were identified as major constraints to tomato production in Uganda.     

Identification and development of molecular markers linked to Phytophthora root rot resistance in pepper (Capsicum annuum L.)

Phytopthora root rot in pepper (C. annuum) is caused by Phytophthora capsici L., which exhibits a high level of pathogenic diversity. Resistance to this disease is conditioned by a number of quantitative trait loci. Pyramiding resistance alleles is desirable and could be simplified by the use of molecular markers tightly linked to the resistance genes. The purpose of this study was development of molecular markers linked to Phytophthora root rot resistance. An F₈ recombinant inbred line (RIL) population derived from a cross between YCM334 and a susceptible cultivar ‘Tean’ was used in combination with bulk segregant analysis utilizing RAPD and conversion of AFLP markers linked to Phytophtora root rot resistance into sequence-characterized amplified region (SCAR) markers. In conversion: one marker was successfully converted into a co-dominant SCAR marker SA133_4 linked to the trait. In bulked segregant analysis (BSA): three RAPD primers (UBC484, 504, and 553) produced polymorphisms between DNA pools among 400 primers screened. Genetic linkage analysis showed that the SCAR and RAPD markers were located on chromosome 5 of pepper. Quantitative trait locus (QTL) analysis showed that the SA133_4 and UBC553 were linked to Phytophtora root rot resistance. These markers were correctly identified as resistant or susceptible in nine promising commercial pepper varieties. These markers will be beneficial for marker-assisted selection in pepper breeding.     

Phytophthora oleae sp. nov. causing fruit rot of olive in southern Italy

A homothallic Phytophthora species was found to be consistently associated with a rot of mature fruits of two local cultivars of olive (Olea europaea) in Calabria, southern Italy. The phylogenetic analysis of sequences of the ITS1‐5.8S‐ITS2 region and cox1 gene enabled its identification as a new species of clade 2, with a basal position compared to previously described subclades. The new species is described formally with the epithet Phytophthora oleae, referring to the natural matrix from which it was isolated. A unique combination of molecular and morphological characters clearly separates P. oleae from other already described Phytophthora species. This new species produced semipapillate, occasionally bipapillate, persistent sporangia on simple sympodially branching sporangiophores as well as globose and smooth‐walled oogonia, paragynous antheridia and spherical, plerotic oospores. The pathogenicity of P. oleae was confirmed in inoculation trials on fruits of three olive cultivars, including the two local cultivars from which the pathogen had been isolated.     

First report of Phytophthora palmivora as a causal pathogen of citrus brown rot in Japan

A fruit rot, similar to brown rot, occurred on extremely early ripening Satsumas in Saga Prefecture in the early autumn of 1999. A single species of Phytophthora was isolated from the affected fruit. After nonwounding inoculation of healthy fruits of Citrus spp. including Satsuma with the isolated fungus, the fungus was reisolated from fruit with symptoms similar to those in nature. On the basis of its morphology and molecular analysis of the rDNA-internal transcribed spacer regions, the pathogen was identified as P. palmivora. This is the first report of P. palmivora as a causal pathogen of citrus brown rot in Japan.