Phylogeny of the frosty pod rot pathogen of cocoa

Morphological, cytological and molecular evidence is presented which confirms that the frosty pod rot pathogen of cocoa, formerly classified as the mitosporic fungus Moniliophthora roreri (Deuteromycota), belongs to the hymenomycetous genus Crinipellis (Basidiomycota) and that two varieties should now be recognized: Crinipellis roreri var. roreri and the new variety C. roreri var. gileri . The latter was collected on Theobroma gileri , an endemic tree of submontane forests in north-west Ecuador, and can be distinguished from Ecuadorian and Peruvian isolates from cocoa ( T. cacao ) on the basis of spore morphology, incompatibility and nucleotide sequence data. As with var. roreri , meiosis is shown to occur within the dispersive and infective spore stage of var. gileri and these meiospores are interpreted to represent a much modified probasidium. In addition, in a field inoculation experiment, an isolate from T. gileri proved to be noninfective to cocoa pods when compared with positive control strains isolated from T. cacao in western Ecuador and T. bicolor in eastern Ecuador. It is concluded that var. gileri is the vestigial progenitor of the frosty pod rot pathogen of cocoa, with a host range and distribution restricted to T. gileri in the mesic forests of north-west South America.     

Comparison of cuprous oxide and metalaxyl with mixtures of these fungicides for thecontrol of Phytophthora pod rot of cocoa

Experiments were conducted using small-scale, detached pod evaluation methods to compare the likely effectiveness in controlling black pod of cuprous oxide-metalaxyl mixtures with these fungicides alone at approximately equivalent cost doses. All fungicide treatments were about equally effective and persistent except when rain fell soon afterspraying. Treatments containing cuprous oxide then gave very poor control of artificialinoculations with Phytophthora palmivora zoospores . Further laboratory' scale tests confirmed that cuprous oxide was readily leached by washing before the deposit completely dried whereas metalaxyl was very rapidly adsorbed on to ihe pods. A black pod control strategy is proposed using metalaxyi during critical wet periods and cuprous oxide for the rest of the year to reduce the possibility of metalaxyl resistance becoming apractical problem.     

Phytophthora rot of alpine delphinium caused by Phytophthora sp. kelmania

Severe stunting and root rot were observed on alpine delphinium plants (Delphinium elatum) from Aomori Prefecture, Japan, in 2010 and 2011. A Phytophthora isolate from the diseased crown was identified as Phytophthora sp. kelmania based on morphological characteristics and DNA sequence data. Inoculation of alpine delphinium plants with the isolate produced a similar root rot. Pathogenicity of the isolate on four species of plants that are known hosts for P. sp. kelmania was confirmed. We propose the name “Phytophthora rot” (eki-byo in Japanese) for the present new disease on alpine delphinium.

     

Root rot of lavender caused by Phytophthora nicotianae

Lavender (Lavandula angustifolia) plants with rotted roots and discoloured vascular systems consistently yielded cultures of fungi that were identified as Phytophthora nicotianae van Breda de Haan (= P. parasitica). Inoculation experiments using either zoospore suspensions or mycelial fragments were successful in reproducing symptoms originally observed on wilting and dying plants. Lavender is a new host for P. nicotianae.     

Root rot of cabbage caused by Phytophthora drechsleri

A root rot of cabbage is reported from South Africa. The causal pathogen was identified as Phytophthora drechsleri , based on morphological characters and electrophoretic patterns of soluble proteins.     

Spatio-temporal dynamics on a plot scale of cocoa black pod rot caused by <Emphasis Type="Italic">Phytophthora megakarya</Emphasis> in Cameroon

Black pod disease is caused by several species of Phytophthora. In Cameroon, the disease is mainly due to Phytophtora megakarya. The pathogen attacks cocoa pods and can lead to almost total production losses in a plot if no control measures are applied. To control the disease, several research programmes are being conducted: breeding for increased resistance, development of several biocontrol or agronomic methods. However, for better use of a specific method it is useful to have a good understanding of several epidemiological processes and more effectively know how the disease is distributed in the field. The purpose of this study was to describe the spatial development of the disease in several cocoa fields in Cameroon. In particular, we determined the spatial relation of the disease using several tools, including geostatistics models and Moran indices. The results indicated that the disease was not randomly distributed, while correlations between neighbouring cocoa trees existed. The relationships were detected up to a distance of between 7 and 9 m, revealing the wide dispersal pattern of the pathogen over short distances. No spatial structure was found in the spread of the disease in the oldest cocoa plantations and the inoculum was dispersed throughout the plot. Disease dispersal over short distances should make it possible to adapt control methods by attempting to confine the first disease foci in young plots. Research should also be undertaken to limit inoculum dispersal.     

Root rot of tree lucerne caused by Phytophthora nicotianae

Phytophthora nicotianae Breda de Haan was consistently isolated from rotted roots and discoloured vascular tissues of tree lucerne ( Chamaecytisus palmensis ). It was identified with the aid of total DNA restriction fragment length polymorphisms and morphological characters. Pathogenicity was demonstrated by inoculation. This is the first record of P. nicotianae on tree lucerne in South Africa.     

Storage rot of swede caused by Phytophthora sp.

During long-term storage trials of swedes ( Brassica napus ) carried out during five seasons between 1982 and 1987, storage rots caused by a Phytophthora sp. were observed, the first report of the disease in the UK.     

Irvingia, a forest host of the cocoa black-pod pathogen, Phytophthora megakarya, in Cameroon

Phytophthora megakarya is an increasingly important invasive pathogen of cocoa in West Africa, where it forms part of the black-pod disease complex together with the more widespread, but less aggressive, P. palmivora . Its purported centre of diversity, based on evidence from molecular studies and mating types, lies on the Cameroon–Nigeria border, from where it has spread throughout both countries and more recently into Ghana and the Ivory Coast. A survey undertaken in an ancient primary forest (Korup National Park) in western Cameroon, adjacent to the Nigerian border, identified Irvingia sp., close to I. gabonensis (Irvingiaceae), as a wild host of P. megakarya , using both morphological and molecular characterization. ITS fingerprinting of two additional Phytophthora isolates, obtained during a supplementary survey in central Cameroon, showed identical banding patterns for the isolate from a cocoa pod, whilst the isolate from an unknown forest fruit proved to belong to P. heveae . This is the first authenticated record of P. heveae from the African continent. Subsequent AFLP analysis grouped the two P. megakarya isolates with other Cameroonian isolates held in the CABI Genetic Resource Collection, but separated them from the Ghanaian isolates.     

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).     

Soybean root suberin and partial resistance to root rot caused by Phytophthora sojae

Phytophthora sojae is the causal agent of root and stem rot of soybean (Glycine max). Various cultivars with partial resistance to the pathogen have been developed to mitigate this damage. Herein, two contrasting genotypes, the cultivar Conrad (with strong partial resistance) and the line OX760-6 (with weak partial resistance), were compared regarding their amounts of preformed and induced suberin components, and to early events during the P. sojae infection process. To colonize the root, hyphae grew through the suberized middle lamellae between epidermal cells. This took 2 to 3 h longer in Conrad than in OX760-6, giving Conrad plants more time to establish their chemical defenses. Subsequent growth of hyphae through the endodermis was also delayed in Conrad. This cultivar had more preformed aliphatic suberin than the line OX760-6 and was induced to form more aliphatic suberin several days prior to that of OX760-6. However, the induced suberin was formed subsequent to the initial infection process. Eventually, the amount of induced suberin (measured 8 days postinoculation) was the same in both genotypes. Preformed root epidermal suberin provides a target for selection and development of new soybean cultivars with higher levels of expression of partial resistance to P. sojae.     

Effects of fungicides on apple crown rot caused by Phytophthora cactorum

The mycelial growth of Phytophthora cactorum on corn meal agar was completely inhibited by metalaxyl or mancozeb at 50 or 100 μg ml^?1, but not by fosetyl-aluminium at the same concentrations. Soil drenches with metalaxyl, followed by metalaxyl+mancozeb, around the base of naturally infected trees under orchard conditions, prevented the growth of P. cactorum in the infected bark of the tree. Soil drenchs with metalaxyl, followed by metalaxyl+mancozeb, also prevented the infection of apple trees with P. cactorum under orchard conditions. The trunk circumference and spur length were not significantly affected by any of the fungicide treatments in all the trials over 2 years, except in one of the four orchards used in the study. Soil drench with metalaxyl alone, or followed by metalaxyl+mancozeb, may provide an effective control method for crown rot of apple trees.     

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.     

Factors influencing external fruit rot of cucumber caused by Didymella bryoniae

Several factors influencing the occurrence and extent of external fruit rot caused byDidymella bryoniae on cucumbers in the post harvest period were studied.The minimum, optimum and maximum temperatures for growth of the fungus on fruits were circa 10, 23 and 35°C, respectively. The influence of the temperature on the growth of the fungus in vitro and in vivo was about similar. The fitness of the fungus diminished by storing inoculated fruits at about the maximum temperature for growth of the fungus for one day, but this temperature influenced fruit quality negatively. Storing at 10 to 12°C is more advisable.Isolates ofD. bryoniae showed variation in virulence. There was a linear relationship between growth on fruits and growth in vitro of these isolates, but no correlation was found with disease incidence on plants.The degree of fruit rot was increased by more severe wounding, by storing in the dark instead of in the light and by higher nitrogen fertilization of the crop. Relative humidity during storage had no effect on fruit decay. It is very likely that the amount and composition of available nutrients for fungus growth determine the degree of rotting of the fruits.With the present cultivars, external fruit rot can be best controlled by reducing the changes of wounding in the pre- and post-harvest period.Samenvatting Verschillende factoren die van invloed kunnen zijn op het ontstaan en de mate van uitwendig vruchtrot op komkommers in de periode na de oogst, veroorzaakt doorDidymella bryoniae, zijn onderzocht.De minimum, optimum en maximum temperatuur voor de groei van de schimmel op vruchten waren respectievelijk circa 10, 23 en 35°C. De invloed van de temperatuur op de groei van de schimmel in vitro en in vivo was nagenoeg gelijk. Door geïnoculeerde vruchten een dag bij de maximum temperatuur voor de groei van de schimmel te bewaren, werd de groeikracht van de schimmel verminderd, maar de vruchtkwaliteit werd door deze temperatuur negatief beïnvloed. Het is raadzamer de vruchten bij 10–12°C te bewaren.Isolaten vanD. bryoniae vertoonden een variatie in virulentie. Tussen de groei van deze isolaten op vruchten en de groei in vitro bleek een lineair verband te bestaan, maar er bestond geen verband met de aantasting van planten.De mate van vruchtrot nam toe door de vruchten ernstiger te verwonden, ze in het donker in plaats van in het licht te bewaren en door een hogere stikstofbemesting tijdens de teelt. De relatieve luchtvochtigheid tijdens de bewaarperiode had geen effect op de vruchtaantasting. De hoeveelheden en de samenstelling van de voor de groei van de schimmel beschikbare voedingsstoffen bepalen zeer waarschijnlijk de mate van vruchtrot.Uitwendig vruchtrot kan bij de huidige cultivars nog het best worden tegengegaan door de mogelijkheden van verwonding, zowel in de periode voor als na de oogst, te verkleinen.     

Factors influencing internal fruit rot of cucumber caused by Didymella bryoniae

Several factors influencing the incidence of internal fruit rot of cucumber caused byDidymella bryoniae were studied.Internal infection of fruits is achieved via the flower. However, in most cases the majority of the fruits escaped infection after flower inoculation. It took more than two days for the fungus to reach the fruit after infection of the style. A mechanical barrier was not detected in the fruit tip within three days after inoculation of the open flower.Inoculation of wilted flowers resulted in 60% less infection than inoculation of fresh flowers. Blossom excision reduced fruit infection with ca 75%. Growing plants under drought stress markedly increased the incidence of internal fruit rot.Neither the method of inoculation, nor the composition of the inoculum, nor the relative humidity influenced the incidence of internal fruit rot. Fruit thinning, duration of fruit growth, flowering period and the removal of parts of the flower had no effect either on fruit infection.Cultivars resistant to powdery mildew were also resistant to internal fruit infection. The resistance was associated with a long style and a short flowering period.Growing cultivars in which the flowers quickly fall away from the fruitlets or in which the flowers have no style may solve the problem of internal fruit rot in cucumber.Samenvatting Factoren die van invloed kunnen zijn op het ontstaan van inwendig vruchtrot van komkommer, veroorzaakt doorDidymella bryoniae, werden onderzocht.Inwendige vruchtinfectie vindt plaats via het bloempje. Bijna altijd ontsnapte echter het grootste deel van de vruchten aan een aantasting als de bloem werd geïnoculeerd. Het duurde meer dan twee dagen voordat de schimmel via de stijl de vrucht had geïnfecteerd. In de punt van de vrucht werd binnen drie dagen na inoculatie van de open bloem geen mechanische barrière gevonden.Na inoculatie van verwelkte bloemen kwam 60% minder aantasting voor dan na inoculatie van bloemen die pas open waren. Het verwijderen van het bloempje reduceerde de aantasting met ca. 75%. Het optreden van inwendig vruchtrot nam aanzienlijk toe door de planten onder droge omstandigheden te telen.Noch de methode van inoculatie, noch de samenstelling van het inoculum, noch de relatieve luchtvochtigheid beïnvloedden het optreden van inwendig vruchtrot. Vruchtdunning, duur van de vruchtgroei, bloeiduur en het verwijderen van delen van de bloem hadden ook geen effect op de aantasting.Cultivars die resistent waren tegen echte meeldauw vertoonden ook resistentie tegen inwendige vruchtaantasting. De resistentie was gecorreleerd met een lange stijl en met een korte bloeiduur.De teelt van cultivars waarvan de bloemdelen snel van de vruchtbeginsels afvallen, of waarvan de bloempjes geen stijl hebben, zou het probleem van inwendig vruchtrot bij komkommer kunnen oplossen.     

On-farm selection for quality and resistance to pest/diseases of cocoa in Sulawesi: (ii) quality and performance of selections against Phytophthora pod rot and vascular-streak dieback

The cocoa industry in Sulawesi, the main region of cocoa production in Indonesia, is threatened by destructive diseases, including vascular-streak dieback (VSD) caused by the basidiomycete Oncobasidium theobromae and stem canker and Phytophthora pod rot (PPR) or black pod, caused by Phytophthora palmivora. Using the considerable genetic diversity of cocoa on farms, host resistance was identified and tested with the participation of farmers. Forty-nine local and international cocoa selections with promising resistance characteristics (as well as susceptible controls) were side-grafted onto mature cocoa in a replicated trial with single-tree plots. Developing grafts were assessed in the dry season for severity of VSD infection, scored from 0 (no infection) to 4 (graft death). All of the 49 clones in the trial became infected with VSD in at least some replicates. Average severity varied from 0.2 to 1.6. Potential VSD-resistance was found in eight clones, including DRC 15, KA2 106 and a local Sulawesi selection, VSD2Ldg. Some of the most susceptible clones were local Sulawesi selections from areas with a history of little or no VSD. Thirty-four pod-bearing clones were evaluated over a 2-year period for yield, quality and resistance to natural infections of PPR. Cumulative PPR incidence for all clones was 22% but varied from 8.6 to 43% among clones. Clones with less than 15% PPR incidence were designated as resistant, including DRC 16 and local Sulawesi selections, Aryadi 1, Aryadi 3 and VSD1Ldg. Scavina 12 was moderately resistant in the trial with a PPR incidence of 23%. Cumulative incidences of the mirid, Helopeltis spp., determined in the same evaluation period, indicated that DRC16 was the most susceptible clone with an incidence of 52% in ripe pods and 23% in immature pods. In comparison, KKM4 showed evidence of resistance to Helopeltis spp., with incidences of 34 and 0.8% in ripe and immature pods, respectively. The impact of diseases and pests (including cocoa pod borer) on bean losses and bean quality varied between clones but generally the bean size (or bean count) was affected more than the fat content or shell content.