Yeast populations associated with Ghanaian cocoa fermentations analysed using denaturing gradient gel electrophoresis (DGGE)

The yeast populations associated with the fermentation of Ghanaian cocoa were investigated using denaturing gradient gel electrophoresis (DGGE). Samples were collected at 12-24 h intervals from heap and tray fermentations, at three different fermentation sites and different periods during the season. Eukaryotic universal primers were used to amplify a fragment of the 26S rRNA gene. The DGGE profiles were relatively complex, underlining that the fermentation of cocoa is a complex microbial process. The identities of selected fragments in the denaturing gels were revealed by sequencing. Hanseniaspora guilliermondii, Candida krusei and Pichia membranifaciens were detected from most fermentations, indicating their possible important role in the fermentation of Ghanaian cocoa. Saccharomyces cerevisiae and Candida zemplinina were almost exclusively detected during tray fermentations. The developed DGGE protocol was compared with traditional culture-based isolations. The results were comparable but slightly different, as one yeast species (C. zemplinina) was only detected using DGGE. On the other hand, Trichosporon asahii yielded only faint bands in the denaturing gels, despite the fact that it was detected using culture-based methods. Analysis of pure cultures showed that the targeted region of the 26S rRNA gene was poorly amplified in T. asahii, whereas all other investigated isolates were amplified efficiently using the chosen PCR approach. Cluster analysis revealed that the DGGE profiles clustered according to fermentation method and fermentation site. Furthermore, clustering according to progress in the fermentation was observed. The DGGE technique therefore seems to offer a relatively fast and reliable method for studying yeast population dynamics during cocoa fermentations.

Biochemical changes during the development of witches' broom: the most important disease of cocoa in Brazil caused by Crinipellis perniciosa

Witches' broom disease (WBD) is caused by the hemibiotrophic basidiomycete fungus Crinipellis perniciosa, which is one of the most important diseases of cocoa in the western hemisphere. In this study, the contents of soluble sugars, amino acids, alkaloids, ethylene, phenolics, tannins, flavonoids, pigments, malondialdehyde (MDA), glycerol, and fatty acids were analysed in cocoa (Theobroma cacao) shoots during the infection and development of WBD. Alterations were observed in the content of soluble sugars (sucrose, glucose, and fructose), asparagine and alkaloids (caffeine and theobromine), ethylene, and tannins. Ethylene and tannins increased prior to symptom development and declined with the death of the infected tissues. Furthermore, MDA and glycerol concentrations were higher in infected tissue than in the controls, while fatty acid composition changed in the infected tissues. Chlorophylls a and b were lower throughout the development of the disease while carotenoids and xanthophylls dropped in the infected tissue by the time of symptom development. These results show co-ordinated biochemical alterations in the infected tissues, indicating major stress responses with the production of ethylene. Ethylene levels are hypothesized to play a key role in broom development. Some of the other biochemical alterations are directly associated with ethylene synthesis and may be important for the modification of its effect on the infected tissues.

International outbreak of Salmonella Oranienburg due to German chocolate

BACKGROUND

This report describes a large international chocolate-associated Salmonella outbreak originating from Germany.

METHODS

We conducted epidemiologic investigations including a case-control study, and food safety investigations. Salmonella (S.) Oranienburg isolates were subtyped by the use of pulsed-field gel electrophoresis (PFGE).

RESULTS

From 1 October 2001 through 24 March 2002, an estimated excess of 439 S. Oranienburg notifications was registered in Germany. Simultaneously, an increase in S. Oranienburg infections was noted in other European countries in the Enter-net surveillance network. In a multistate matched case-control study in Germany, daily consumption of chocolate (matched odds ratio [MOR]: 4.8; 95% confidence interval [CI]: 1.3-26.5), having shopped at a large chain of discount grocery stores (MOR: 4.2; CI: 1.2-23.0), and consumption of chocolate purchased there (MOR: 5.0; CI: 1.1-47.0) were associated with illness. Subsequently, two brands from the same company, one exclusively produced for that chain, tested positive for S. Oranienburg. In two other European countries and in Canada chocolate from company A was ascertained that also contained S. Oranienburg. Isolates from humans and from chocolates had indistinguishable PFGE profiles. No source or point of contamination was identified. Epidemiological identification of chocolate as a vehicle of infections required two months, and was facilitated by proxy measures.

CONCLUSIONS

Despite the use of improved production technologies, the chocolate industry continues to carry a small risk of manufacturing Salmonella-containing products. Particularly in diffuse outbreak-settings, clear associations with surrogates of exposure should suffice to trigger public health action. Networks such as Enter-net have become invaluable for facilitating rapid and appropriate management of international outbreaks.

Diversity of endophytic fungal community of cacao (Theobroma cacao L.) and biological control of Crinipellis perniciosa, causal agent of Witches' Broom Disease

The basidiomycete fungus Crinipellis perniciosa (Stahel) Singer is the causal agent of Witches' Broom Disease of Cacao (Theobromacacao L.) which is the main factor limiting cacao production in the Americas. Pod losses of up to 90% are experienced in affected areas as evidenced by the 50% drop in production in Bahia province, Brazil following the arrival of the C. perniciosa in the area in 1989. The disease has proven particularly difficult to control and many farmers in affected areas have given up cacao cultivation. In order to evaluate the potential of endophytes as a biological control agent of this phytopathogen, the endophytic fungal community of resistant and susceptible cacao plants as well as affected branches was studied between 2001 and 2002. The fungal community was identified by morphological traits and rDNA sequencing as belonging to the genera Acremonium, Blastomyces, Botryosphaeria, Cladosporium, Colletotrichum, Cordyceps, Diaporthe, Fusarium, Geotrichum, Gibberella, Gliocladium, Lasiodiplodia, Monilochoetes, Nectria, Pestalotiopsis, Phomopsis, Pleurotus, Pseudofusarium, Rhizopycnis, Syncephalastrum, Trichoderma, Verticillium and Xylaria. These fungi were evaluated both in vitro and in vivo by their ability to inhibit C. perniciosa. Among these, some were identified as potential antagonists, but only one fungus (Gliocladium catenulatum) reduced the incidence of Witches' Broom Disease in cacao seedlings to 70%.

Occurrence and diversity of yeasts involved in fermentation of West African cocoa beans

Samples of cocoa beans were taken on two separate occasions during heap and tray fermentations in Ghana, West Africa. In total 496 yeast isolates were identified by conventional microbiological analyses and by amplification of their ITS1-5.8S rDNA-ITS2 regions. For important species the identifications were confirmed by sequencing of the D1/D2 domain of the 5' end of the large subunit (26S) rDNA. Assimilations of organic acids and other carbon compounds were conducted. For dominant yeasts intraspecies variations were examined by determination of chromosome length polymorphism (CLP) using pulsed-field gel electrophoresis. For the heap fermentations maximum yeast cell counts of 9.1 x 10(7) were reached, whereas maximum yeast counts of 6.0 x 10(6) were reached for the tray fermentations. Candida krusei was found to be the dominant species during heap fermentation, followed by P. membranifaciens, P. kluyveri, Hanseniaspora guilliermondii and Trichosporon asahii, whereas Saccharomyces cerevisiae and P. membranifaciens were found to be the dominant species during tray fermentation followed by low numbers of C. krusei, P. kluyveri, H. guilliermondii and some yeast species of minor importance. For isolates within all dominant species CLP was evident, indicating that several different strains are involved in the fermentations. Isolates of C. krusei, P. membranifaciens, H. guilliermondii, T. asahii and Rhodotorula glutinis could be found on the surface of the cocoa pods and in some cases on the production equipment, whereas the origin of e.g. S. cerevisiae was not indicated by the results obtained. In conclusion, the results obtained show that fermentation of cocoa beans is a very inhomogeneous process with great variations in both yeast counts and species composition. The variations seem to depend especially on the processing procedure, but also the season and the post-harvest storage are likely to influence the yeast counts and the species composition.

Performance comparison of the BioSys optical assay and the violet red bile agar method for detecting coliforms in food products

Coliform counts in a variety of foods, including dairy products (raw milk, pasteurized milk, yogurt, butter, and ice cream), meats (pork sausage, ground beef, and raw chicken), raw eggs, and chocolate, were performed by the rapid automated BioSys optical assay and the conventional method with violet red bile agar (VRBA). The standard deviation (SD) among five replicate counts for the optical assay was similar to or better than that obtained with VRBA plates for all foods tested. The average SD for all foods tested was 0.21 for the optical assay and 0.30 for the VRBA plates. At very low concentrations of coliforms (1 to 10 CFU/ml for liquid products and 10 to 100 CFU/g for solid samples), the average SDs were 0.26 and 0.47, respectively. The optical assay was less susceptible to interference by noncoliform organisms. In naturally contaminated samples, bacteria such as Serratia liquefaciens, Pantoea spp., Vibrio fluvialis, Aeromonas hydrophilia, and Pseudomonas spp. formed typical colonies in VRBA, resulting in false-positive results or a need to verify colonies in brilliant green lactose broth. The optical assay appeared to be more selective than the VRBA conventional method, detecting fewer noncoliforms. There was close agreement in test results between the two methods, as indicated by correlation coefficients of 0.92 to 0.99 obtained for the regression analysis of the two methods. In most cases both methods distinguished accurately between positive samples containing coliforms and negative controls. All products tested using the automated BioSys Optical Assay for coliforms yielded results more quickly (typically 10 to 12 h) than did those tested with the conventional VRBA method (24 to 72 h with confirmation).

Survival, growth, and thermal resistance of Listeria monocytogenes in products containing peanut and chocolate

Outbreaks of listeriosis associated with the consumption of ready-to-eat foods have raised interest in determining growth, survival, and inactivation characteristics of Listeria monocytogenes in a wide range of products. A study was undertaken to determine the thermal tolerance of L. monocytogenes in a peanut-based beverage (3.1% fat), whole-fat (3.5%) milk, wholefat (4.0%) and reduced-fat (1.0%) chocolate milk, a chocolate-peanut spread (39% fat), and peanut butter (53% fat). The D60 degrees C value (decimal reduction time at 60 degrees C) in peanut beverage (3.2 min) was not significantly different (P > 0.05) than the D60 degrees C value in whole-fat milk (3.3 min) or whole-fat chocolate milk (4.5 min) but significantly lower (P < or = 0.05) than the D60 degrees C value in reduced-fat chocolate milk (5.9 min). The pathogen was significantly more resistant to heat when enmeshed in chocolate-peanut spread (water activity [aw] of 0.46; D60 degrees C = 37.5 min) and peanut butter (aw of 0.32; D60 degrees C = 26.0 min) than in liquid products. At 10 degrees C, the pathogen grew most rapidly in whole-fat chocolate milk and slowest in peanut beverage. At 22 degrees C, populations increased significantly within 12 and 16 h in whole-fat milk and reduced-fat chocolate milk, respectively, and within 8 h in whole-fat chocolate milk and peanut beverage. Initial populations (3.37 to 4.42 log CFU/g) of L. monocytogenes in chocolate-peanut spread and peanut butter adjusted to an aw of 0.33 and 0.65 declined, but the pathogen was not eliminated during a 24-week period at 20 degrees C. Survival was enhanced at reduced aw. Results indicate that a pasteurization process similar to that used for full-fat milk would be adequate to ensure the destruction of L. monocytogenes in peanut beverage. The pathogen survives for at least 24 weeks in chocolate-peanut spread and peanut butter at an aw range that encompasses that found in these products.

Survival of Escherichia coli O157:H7, O111:H− and O26:H11 in artificially contaminated chocolate and confectionery products

To date, the survival of Escherichia coli O157:H7 and other verocytotoxin-producing E. coli (VTEC) in chocolate and other confectionery products has not been fully established, unlike Salmonella, which have been responsible for occasional outbreaks of infection linked to contaminated chocolate and related products, although none of these outbreaks have been related to products produced in the United Kingdom. The United Kingdom Biscuit, Cake, Chocolate and Confectionery Alliance commissioned this study to obtain information on the decline and potential survival of E. coli, particularly verocytotoxin-producing strains, in reduced aw confectionery products chocolate, biscuit cream and mallow. These products were artificially contaminated with high (4 log10 cfu/g) and low (2 log10 cfu/g) levels of E. coli O157:H7, O111:H- and O26:H11 and their survival, as affected by storage temperature (10, 22 and 38 degrees C), was monitored over 12 months. Preliminary studies to establish the best inoculation and recovery procedures indicated that differences between counts on selective and non-selective media used were not sufficiently different to influence the outcome of this study. Irrespective of sample type, rapid decline was observed in products stored at 38 degrees C and increased survival occurred in products stored at 10 degrees C. In chocolate (average aw 0.40), these bacteria were detected for up to 43 days in samples stored at 38 degrees C. At 22 degrees C they survived for up to 90 days and in product stored at 10 degrees C they could still be detected after 366 days storage. In biscuit cream (average aw 0.75) they survived for 2 days at 38 degrees C, 42 days at 22 degrees C and 58 days at 10 degrees C. Whilst mallow (aw ca. 0.73) was not stored at 38 degrees C, these bacteria could still be detected in samples stored for up to 113 and 273 days at 22 and 10 degrees C, respectively. The observed prolonged survival of these bacteria under conditions of reduced aw and lowered storage temperature in this study is supported by previous studies with Salmonella and E. coli O157:H7 in other foods. In the same way that Salmonella bacteria can survive for long periods, in excess of 12 months, in chocolate, this study provides evidence that E. coli, including pathogenic strains, can also survive for similar periods of time. Assuming the routes of transmission are similar, controls currently used by the confectionery industry to prevent contamination by Salmonella should also be effective against E. coli, including VT-producing strains, providing that all raw materials have been suitably processed, stored and handled before and during manufacture.

The Microbiology of Cocoa Fermentation and its Role in Chocolate Quality

The first stage of chocolate production consists of a natural, seven-day microbial fermentation of the pectinaceous pulp surrounding beans of the tree Theobroma cacao. There is a microbial succession of a wide range of yeasts, lactic-acid, and acetic-acid bacteria during which high temperatures of up to 50 degrees C and microbial products, such as ethanol, lactic acid, and acetic acid, kill the beans and cause production of flavor precursors. Over-fermentation leads to a rise in bacilli and filamentous fungi that can cause off-flavors. The physiological roles of the predominant micro-organisms are now reasonably well understood and the crucial importance of a well-ordered microbial succession in cocoa aroma has been established. It has been possible to use a synthetic microbial cocktail inoculum of just 5 species, including members of the 3 principal groups, to mimic the natural fermentation process and yield good quality chocolate. Reduction of the amount of pectin by physical or mechanical means can also lead to an improved fermentation in reduced time and the juice can be used as a high-value byproduct. To improve the quality of the processed beans, more research is needed on pectinase production by yeasts, better depulping, fermenter design, and the use of starter cultures.

Evaluation of VIDAS Salmonella (SLM) immunoassay method with Rappaport-Vassiliadis (RV) medium for detection of Salmonella in foods: collaborative study

A collaborative study was conducted to compare the VIDAS Salmonella (SLM) with Rappaport-Vassiliadis (RV) method for detection of Salmonella in foods to the current standard method presented in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) and the culture method presented in AOAC's Official Methods of Analysis. The VIDAS SLM with RV method uses tetrathionate broth in combination with RV medium in place of selenite cystine broth for selective enrichment, thereby eliminating the hazardous waste issue for laboratories. Twenty five laboratories participated in the evaluation, each testing one or more of 8 test products: nonfat dry milk, dried egg, soy flour, lactic casein, milk chocolate, raw ground pork, raw ground turkey, and raw peeled shrimp. Results of the study showed no significant differences in the numbers of confirmed positive samples with the VIDAS SLM with RV procedure and the BAM/AOAC culture procedure. The VIDAS SLM with RV method was effective for rapid detection of Salmonella in foods. It is recommended that AOAC INTERNATIONAL modify the VIDAS Salmonella SLM procedure to include the RV method.

Isolation and purification of functional total RNA from different organs of cacao tree during its interaction with the pathogen Crinipellis perniciosa

Witches' broom disease, caused by Crinipellis perniciosa, is one of the major fungal diseases causing severe losses to cacao tree (Theobroma cacao L.) plantations in South America. One of the challenges associated with the understanding of the cacao and Crinipellis interaction in genomic studies is the isolation of intact nucleic acids. In this report, we describe a new, successful, and reliable procedure for the isolation of RNA from tissues of cacao tree, both infected and uninfected by Crinipellis. This protocol overcomes the problems associated with the very high amount of polyphenols and polysaccharides present in cacao organs that are not easily removed by conventional extraction procedures. The protocol requires few reagents, uses ultracentrifugation and inexpensive consumables, and can be easily applied in any laboratory. This method produced high-quality RNA that was suitable for subsequent purposes, such as reverse transcription PCR and cDNA library construction. We also report the first evidence of RNA isolation from cacao organs infected by C. perniciosa such as meristems and fruits.

Preservation methodology for Rosellinia species

Many small (temporary) collections of fungi maintained by plant pathologists during their research receive inadequate attention to ensure stability. Maintaining collections of fungi in pure and viable conditions, minimising physiological and morphological changes is, however, a necessity. The objective of this study was to find preservation techniques for three Rosellinia isolates used in our plant pathogenic research. Various inert and nutritious carriers, solid as well as liquid, were used to test their suitability for conserving these Rosellinia isolates. Different cryoprotectants, cooling rates and thawing rates were tested to optimise liquid nitrogen storage procedures. Survival and/or growth rate were assessed over time. Rosellinia bunodes was the most difficult to store with survival not exceeding six to nine months using traditional storage methods in mineral oil and silica gel. Storage of Rosellinia necatrix and Rosellinia pepo was successful for periods up to at least 16 months in several carriers and for up to two years for R. necatrix in silica gel. Storage in liquid nitrogen proved no problem for R. necatrix or R. pepo with a 100% survival in all cases, although radial growth rates after recuperation were affected by cryoprotectant and thawing rates. Storage of R. bunodes was more difficult and survival as well as growth rates were affected by cryoprotectant and thawing rates. Cooling rates did not affect radial growth in any of the isolates. The results showed that development of a generalised procedure for storage of our Rosellinia species was not possible and successful storage protocols had to be developed for individual isolates.

[Ability of the strains of the thermophilic fungus Thermomyces lanuginosus to hydrolyze cocoa fat and lard]

The purpose of the study was the estimation of the lipolytic activity of the thermophilic fungus Thermomyces lanuginosus on the solid base with the cocoa fat and the lard. The material was 144 strains isolated from biohumus, garden compost, leaf compost, mushroom compost, hazelnuts and raw coffee beans. The study proved, that all species was able to hydrolyze both the cocoa oil and the lard. The index of the lipolytic activity was the same on the medium with cocoa oil and on the medium with the lard.

Fungal endophytes limit pathogen damage in a tropical tree

Every plant species examined to date harbors endophytic fungi within its asymptomatic aerial tissues, such that endophytes represent a ubiquitous, yet cryptic, component of terrestrial plant communities. Fungal endophytes associated with leaves of woody angiosperms are especially diverse; yet, fundamental aspects of their interactions with hosts are unknown. In contrast to the relatively species-poor endophytes that are vertically transmitted and act as defensive mutualists of some temperate grasses, the diverse, horizontally transmitted endophytes of woody angiosperms are thought to contribute little to host defense. Here, we document high diversity, spatial structure, and host affinity among foliar endophytes associated with a tropical tree (Theobroma cacao, Malvaceae) across lowland Panama. We then show that inoculation of endophyte-free leaves with endophytes isolated frequently from naturally infected, asymptomatic hosts significantly decreases both leaf necrosis and leaf mortality when T. cacao seedlings are challenged with a major pathogen (Phytophthora sp.). In contrast to reports of fungal inoculation inducing systemic defense, we found that protection was primarily localized to endophyte-infected tissues. Further, endophyte-mediated protection was greater in mature leaves, which bear less intrinsic defense against fungal pathogens than do young leaves. In vitro studies suggest that host affinity is mediated by leaf chemistry, and that protection may be mediated by direct interactions of endophytes with foliar pathogens. Together, these data demonstrate the capacity of diverse, horizontally transmitted endophytes of woody angiosperms to play an important but previously unappreciated role in host defense.

Identification of QTLs related to cocoa resistance to three species of Phytophthora

This study aimed to compare the genetic control of cacao resistance to three species of Phytophthora: Phytophthora palmivora, Phytophthora megakarya and Phytophthora capsici. The study was conducted on 151 hybrid progenies created in Côte d'Ivoire and grown in a green-house in Montpellier. Phytophthora resistance was screened by leaf-test inoculation with two different strains per species. Selection of the best individuals for resistance to P. palmivora at a 10% selection rate, would lead to a genetic progress of 47% in the disease evaluation for this species and a genetic progress of 42% and 21% for the two other species. A genetic map with a total length of 682 cM was built with 213 markers, 190 AFLPs and 23 microsatellites. QTLs were identified using composite interval mapping. QTLs were found located in six genomic regions. One of these was detected with five strains belonging to the three Phytophthora species. Two other regions were detected with two or three strains of two different species. Three additional QTLs were detected for only one species of Phytophthora. Each QTL explained between 8 to 12% of the phenotypic variation. For each strain, between 11.5% to 27.5% of the total phenotypic variation could be explained by the QTLs identified. The identification of multiple QTLs involved in resistance to Phytophthora offers the possibility to improve durability of resistance in cocoa by a possible cumulation of many different resistance genes located in different chromosome regions using marker-aided selection.

Identification of QTLs related to cocoa resistance to three species of Phytophthora

This study aimed to compare the genetic control of cacao resistance to three species of Phytophthora: Phytophthora palmivora, Phytophthora megakarya and Phytophthora capsici. The study was conducted on 151 hybrid progenies created in Côte d'Ivoire and grown in a green-house in Montpellier. Phytophthora resistance was screened by leaf-test inoculation with two different strains per species. Selection of the best individuals for resistance to P. palmivora at a 10% selection rate, would lead to a genetic progress of 47% in the disease evaluation for this species and a genetic progress of 42% and 21% for the two other species. A genetic map with a total length of 682 cM was built with 213 markers, 190 AFLPs and 23 microsatellites. QTLs were identified using composite interval mapping. QTLs were found located in six genomic regions. One of these was detected with five strains belonging to the three Phytophthora species. Two other regions were detected with two or three strains of two different species. Three additional QTLs were detected for only one species of Phytophthora. Each QTL explained between 8 to 12% of the phenotypic variation. For each strain, between 11.5% to 27.5% of the total phenotypic variation could be explained by the QTLs identified. The identification of multiple QTLs involved in resistance to Phytophthora offers the possibility to improve durability of resistance in cocoa by a possible cumulation of many different resistance genes located in different chromosome regions using marker-aided selection.

The microbial ecology of cocoa bean fermentations in Indonesia

Cocoa beans are the principal raw material of chocolate manufacture. The beans are subject to a microbial fermentation as the first stage in chocolate production. The microbial ecology of bean fermentation (Forastero and Trinitario cultivars) was investigated at three commercial fermentaries in East Java, Indonesia by determining the populations of individual species at 12-h intervals throughout the process. The first 2-3 days of fermentation were characterised by the successional growth of various species of filamentous fungi, yeasts, lactic acid bacteria and acetic acid bacteria. The principal species found were Penicillium citrinum, an unidentified basidiomycete, Kloeckera apis, Saccharomyces cerevisiae, Candida tropicalis, Lactobacillus cellobiosus, Lactobacillus plantarum and Acetobacter pasteurianus. The later stages of fermentation were dominated by the presence of Bacillus species, mostly, Bacillus pumilus and Bacillus licheniformis. Glucose, fructose, sucrose and citric acid of the bean pulp were utilised during fermentation, with the production of ethanol, acetic acid and lactic acid that diffused into the beans. The filamentous fungi were notable for their production of polygalacturonase activity and probably contributed to the degradation of bean pulp.

Salmonella in foods: new enrichment procedure for TECRA Salmonella Visual Immunoassay using a single rv(R10) only, TT only, or dual rv(R10) and TT selective enrichment broths (AOAC official method 998.09): collaborative study

A collaborative study was conducted to compare a new enrichment procedure for the TECRA Salmonella Visual Immunoassay (TSVIA) with the reference method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (7th Ed.). Three food types (milk powder, pepper, and soy flour) were analyzed in Australia and 3 food types (milk chocolate, dried egg, and raw turkey) were analyzed in the United States. Thirty-eight collaborators participated in the study. The TECRA method was evaluated using both Rappaport-Vassiliadis R10 (RV(R10)) and tetrathionate (TT) broths for selective enrichment. M broth cultures arising from each of the 2 selective enrichment broths were tested in the TSVIA using 2 individual wells, one for each selective broth, and a single well to test the pooled selective enrichment broths. The results for the pooled enrichment broths were reported elsewhere. This study presents the results for the use of single enrichment broths, i.e., RV(R10) only or TT only, with the TSVIA. No significant differences (p > 0.05) were observed for the pairwise comparison of the proportion of positive samples for either RV(R10) or TT used as a single enrichment broth for the TSVIA with that for the reference method.

Population dynamics of epiphytic mycoparasites of the genera Clonostachys and Fusarium for the biocontrol of black pod (Phytophthora palmivora) and moniliasis (Moniliophthora roreri) on cocoa (Theobroma cacao)

Mycoparasites collected from aerial parts of the cocoa plant (Theobroma cacao) have shown great promise in the control of black pod, caused by Phytophthora palmivora, and moniliasis, caused by Moniliophthora roreri. However, the ecology of epiphytic mycoparasites is still poorly understood although it has a direct bearing on applied biocontrol practices, ranging from the identification and isolation of promising biocontrol candidates to formulation needs and required application frequency. One objective of this study was to determine the natural abundance of mycoparasites on cocoa flowers and pods in relation to crop development stage and cultivar. For this purpose, native mycoparasites were detected on cocoa flowers and pods using the precolonised plate baiting technique. Furthermore, the survival of an applied Clonostachys rosea isolate on cocoa pods on shaded and non-shaded trees was compared as well as the recolonisation patterns of surface-sterilised pods by native mycoparasites under these conditions. Clonostachys spp. were the most commonly isolated native mycoparasites, followed by Fusarium spp. No differences in the occurrence of native, epiphytic mycoparasites were observed between the three main cocoa cultivars, 'Criollo', 'Forastero' and 'Trinitario', nor between clones within these groups. Thus, a single biocontrol inoculum can be suitable for application to cultivar mixtures of cocoa commonly grown together in a field. Different susceptibility classes of segregating F1 populations of hybrids with resistance against M. roreri and P. palmivora supported similar population levels and taxonomic assemblages of mycoparasites. Therefore, we reject the hypothesis that these antagonists mediate resistance. Mycoparasite abundance and genetic disease resistance to black pod and moniliasis are independent phenomena and should lead to additive effects if employed simultaneously in an integrated disease management programme. The survival of applied C. rosea was not affected by the shading regime or any other meteorological parameter measured. On the other hand, recolonisation of surface-sterilised cocoa pods by most native mycoparasites was faster in the shade. Only Trichoderma spp. colonised pods exposed to direct sunlight faster than shaded ones. The implications for the design of biocontrol inocula and formulation technology are discussed.

Mapping QTL for yield components, vigor, and resistance to Phytophthora palmivora in Theobroma cacao L

Quantitative trait loci (QTL) mapping for agronomic traits was carried out in cocoa (Theobroma cacao L.). Regions of the genome involved in yield, vigor, and resistance to Phytophthora palmivora were identified. Three heterozygous clones, one upper Amazon Forastero (IMC78) and two Trinitario (DR1 and S52), were crossed with the same male parent, a lower Amazon Forastero (Catongo), known to be highly homozygous. Observations were made on progeny over nine consecutive years. One to three QTL related to yield were detected in each of the three populations, located on chromosomes 1, 2, 4, 5, 9, and 10. They explained between 8.1 and 19.3% of the phenotypic variation and showed various levels of repeatability. In IMC78, the QTL detected on chromosome 5 was the most repeatable over years. The QTL for the average individual pod weight on chromosome 4 was the most significant with an LOD of 17.3 and an R2 of 43.7. QTL related to these traits were identified in the same region of the genome in clones of different genetic groups. This suggests that molecular markers can be used to improve cocoa varieties.

Proteomic analysis of asexual development of Phytophthora palmivora

Two-dimensional gel electrophoresis was used to analyse stage-specific proteins from Phytophthora palmivora, a pathogen of cocoa and other economically important tropical crops. Approximately 1% of proteins appeared to be specific for each of the mycelial, sporangial, zoospore, cyst and germinated cyst stages of the life-cycle. Three proteins excised from protein gels of P. palmivora were identified as isoforms of actin by database searches to public libraries of Phytophthora infestans. The protein profiles of parallel samples of P. palmivora and P. infestans demonstrated that 30% of proteins precisely co-migrated suggesting that proteomics may be used to examine changes in the specific stages in the life cycles of Phytophthora spp.

Electrophoretic karyotype analysis of Crinipellis perniciosa, the causal agent of witches' broom disease of Theobroma cacao

Pulse-field gel electrophoresis (PFGE) was used to determine the genome size and characterize karyotypic differences in isolates of the cacao biotype of Crinipellis perniciosa (C-biotype). The karyotype analysis of four isolates from Brazil revealed that this biotype could be divided into two genotypes: one presenting six chromosomal bands and the other presenting eight. The size of the chromosomes ranged from 2.7 to 5.3 Mb. The different genotypes correlate with telomere-based PCR analysis. The isolates with six chromosomal bands had two that appeared to be doublets, as shown by densitometric analysis, indicating that the haploid chromosome number for this biotype is eight. The size of the haploid genomes was estimated at approximately 30 Mb by both PFGE and Feulgen-image analysis. DNA hybridization revealed that the rDNA sequences are clustered on a single chromosome and these sequences were located on different chromosomes in an isolate dependent manner. This is the first report of genome size and chromosomal polymorphism for the C-biotype of C. perniciosa.

Cocoa-based media for culturing Phytophthora palmivora (Butl.) Butl., causal agent of black pod disease of cocoa

Green cocoa pod husk agar (GCPA), ripe cocoa pod husk agar (RCPA), green cocoa bean agar (GCBA), ripe cocoa bean agar (RCBA), green cocoa mucilage agar (GCMA) and ripe cocoa mucilage agar (RCMA) were prepared and assessd for their clarity and for potential to support mycelial growth and sporulation of P. palmivora. Oatmeal agar (OMA), potato-dextrose agar (PDA), vegetable 8 juice agar (V8JA) and pineapple crown agar (PCA) were included for comparison. The highest radial growth rates of 8.3 and 7.2 mm/day were recorded, respectively, on OMA and GCPA but these were not significantly different (P < 0.05) from each other. The two media also supported good aerial mycelial growth but were not clear. Radial mycelial growth rates of 6.5, 7.0 and 6.6 mm/day were obtained on GCMA, RCPA and V8JA, respectively, and these rates were also not significantly different from each other. Of the three media, only the GCMA was clear and supported the best aerial mycelial growth. In comparison, the RCMA supported a significantly lower radial growth (4.6 mm/day) of P. palmivora than the three media. Growth rates were least on RCBA, PCA and PDA but sporulation was poorest on PDA, PCA and V8JA. GCMA was found to be the best medium based on all the growth parameters and media characteristics. GCMA has been used effectively to isolate/detect P. palmivora from infected cocoa pod tissues. Apart from differences in radial growth rate, both the GCMA and RCMA were similar in all other respects and are recommended for culturing P. palmivora.

Nuclear and mitochondrial rDNA variability in Crinipellis perniciosa from different geographic origins and hosts

Genetic variability in Crinipellis perniciosa, the causal organism of witches' broom disease in Theobroma cacao, was determined in strains originating from T. cacao and other susceptible host species Heteropterys acutifolia and Solanum lycocarpum in Brazil, in order to clarify host specificity and geographical variability. RFLP analysis of the ribosomal DNA ITS regions (rDNA ITS), and the mitochondrial DNA small subunit ribosomal DNA gene (mtDNA SSU rDNA) did not reveal any genetic variability in 120 tested strains, possibly serving only as species level markers. Genetic variability was observed in the ribosomal DNA IGS spacer region, in terms of IGS size, RFLPs and sequence data. Phylogenetic analyses (using CLUSTAL W, PHYLIP and TREEVIEW) indicated considerable differences between C. perniciosa strains from T. cacao and those from H. acutifolia (85-86%) and S. lycocarpum (95-96%). Sequence differences also indicated that C. perniciosa from T. cacao in Bahia is less variable (98%) when compared to the pathogen on T. cacao in Amazonas (97-98%), perhaps reflecting a recent introduction to T. cacao in Bahia.