Witches' broom disease on cocoa in Rondonia, Brazil: pod infection in relation to pod susceptibility, wetness, inoculum, and phytosanitation

Infection of cocoa pods by Crinipellis perniciosa was examined in the field in relation to pod susceptibility and variations in inoculum and climate over 2 years. The disease was incubated for 13 or 14 weeks in pods inoculated when 2 and 4 weeks old, and for 12 weeks in pods inoculated 6-12 weeks old. Pods were uniformly susceptible to natural infection during the 12 weeks after pollination. Over 75% of rain showers started between 12.00 and 02.00 h, providing sufficient water to rehydrate basidiocarps as well as to wet pods. Pods remained wet after rainfall for decreasing periods when rain occurred after 13.00 h. Incidence of pod disease was shown to be related to the number of wetness periods longer than 4 h, and to the number of open turgid basidiocarps occurring 12 weeks earlier. Wetness periods had a greater influence on disease. Pod infection was modelled by assuming that infection was limited by either wetness periods or turgid basidiocarp numbers; critical numbers of wetness periods when both factors were of equal weight were defined by an exponential equation. The model was used to predict reductions in pod disease associated with different amounts of broom removal in each year.     

Factors influencing the production of basidiocarps and the deposition and germination of basidiospores of Crinipellis perniciosa, the causal fungus of witches' broom on cocoa (Theobroma cacao)

The production of basidiocarps by Crinipellis perniciosa on detached, dead witches'brooms from cocoa was assessed in relation to temperature, light, cocoa clone, age of broom and type of tissue, in cabinets with a daily cycle of 8 h wet and 16 h dry. More basidiocarps formed and matured at 20–25°C than at 25–30°C. In the latter regime the pilei were smaller and white, instead of the usual crimson colour, and the stipes were longer. No basidiocarps formed at 30–35°C. At 20–25°C. more basidiocarps formed and matured with light at 100 μE m^-2 s^-1 during the wet period than at 10 μE m^-2 s ^-1. Only one basidiocarp and five primordia developed on 20 brooms kept in the dark. Brooms from 10 cocoa clones at Pichilingue. Ecuador, differed in basidiocarp productivity. most basidiocarps forming on brooms from Seavina and least on ICS clones. The numbers of basidiocarps produced on brooms aged 1.2.3 or 4 months when detached from cocoa trees were similar but time to initiation of the first primordium differed considerably. More basidiocarps formed at nodes than internodes.
The discharge of basidiospores was optimal at 20–25°C and 80% RH: germination was optimal in water agar films. Neither process was dependent on light.     

Molecular Fingerprinting Suggests Two Primary Outbreaks of Witches' Broom Disease (Crinipellis perniciosa) of Theobroma cacao in Bahia, Brazil

Crinipellis perniciosa (Stahel) Singer is the causal agent of witches' broom disease in the Sterculiaceae, Solanaceae, and Bixaceae families. The disease is endemic to the Brazilian Amazon, and was first reported infecting Theobroma cacao (cocoa) in the State of Bahia, Brazil, in 1989. Random amplified polymorphic DNA (RAPD) analyses were performed on 46 isolates of C. perniciosa from cocoa that were collected from 15 counties in Bahia and the Brazilian Amazon. A total of 258 RAPD loci from 20 primers and three mixed primers were analyzed. Of these loci, 108 (42%) were polymorphic, with an average of 4.7 polymorphic loci per primer produced. Genetic similarities were estimated using Nei and Li's index and UPGMA clustering. Bootstrap analysis divided the phenogram into four significantly different clusters: two groups contained isolates from Ariquemes and from Ouro Preto, Rondônia, and the other two separated the isolates from Bahia into two major groups of C. perniciosa, classified as Group 1 (G1) and Group 2 (G2). The two groups of isolates from Bahia differed for their genetic similarity with the isolates from the Brazilian Amazon. The geographic distribution of the groups in Bahia suggests two independent focal points of introduction. Ongoing programs to screen for resistant cocoa genotypes should consider both groups of isolates.     

Some experiments and considerations on the identification of witches' broom viruses,especially in clovers,in the Netherlands and Italy

Witches' broom phenomena (witches' broom growth + antholysis) observed inTropaeolum majus and in clovers in the Netherlands and in several wild and cultivated plants in Italy were demonstrated to be due to virus infection. The virus(es) could be transmitted by grafting, through dodder and by means of leaf-hoppers (Euscelis spp. primarily). The virus isolates found in both countries did not differ appreciably in the symptoms they caused. Many of the deviations concerned have been known for a long time as teratological phenomena. In the extensive literature considerable confusion exists concerning the identity of several witches' broom virus diseases. They constitute a good example of the problem of virus variability. A continuous splitting of witches' broom viruses on the basis of slight differences in symptom expression or of vector specificity does not seem justified. Since no intrinsic properties of the virus(es) concerned are known, the only conclusion that can be drawn from the information available is that the Dutch and the Italian isolates show a great similarity to aster yellows virus as well as to tomato big bud, stolbur and other witches' broom viruses.     

Population structure and migration of the witches’ broom pathogen Moniliophthora perniciosa from cacao and cultivated and wild solanaceous hosts in southeastern Brazil

Moniliophthora perniciosa, causal agent of witches’ broom disease in cacao plantations in South America and the Caribbean Islands, has co‐evolved with its host cacao, but the pathogen has also emerged in many solanaceous hosts in Brazil, including economically important food crops and wild species. This study was carried out to: (i) determine the existence of host subpopulations of M. perniciosa in Brazil; (ii) estimate gene and genotypic diversity of M. perniciosa host subpopulations infecting solanaceous hosts in southeastern Bahia and Minas Gerais states, Brazil; and (iii) estimate the amount and directionality of historical migration of M. perniciosa subpopulations. Up to 203 M. perniciosa isolates collected from solanaceous hosts with symptoms from Bahia and Minas Gerais states in Brazil and from Theobroma spp. (cacao) and Herrania spp. were characterized with 11 microsatellite markers. Factorial correspondence analyses, minimum‐spanning network and Bayesian clustering revealed genetic clusters associated with their host of origin. Significant subpopulation differentiation was evident (Φ_ST = 0.30, P ≤ 0.05) among M. perniciosa host subpopulations. Most of the multilocus microsatellite genotypes (MLMGs) were host‐specific, with few MLMGs shared among subpopulations. Pairwise comparisons among M. perniciosa host subpopulations were significant, except between jurubeba (Solanum paniculatum) and cultivated solanaceous subpopulations. The combined analyses rejected the null hypothesis that M. perniciosa in Brazil is a single genetic population not structured by host. These findings support a scenario of introduction and subsequent adaptation to solanaceous hosts that should be taken into consideration to improve mitigation and management of M. perniciosa.     

Effect of moisture, inoculum production, and planting substrate on disease reaction of field bindweed (Convolvulus arvensis L.) to the fungal pathogen, Phomopsis convolvulus

Phomopsis convolvulus Ormeno is being evaluated as a possible bioherbicide for field bindweed (Convolvulus arvensis L.) control. A granular barley formulation was applied pre-emergence onto the soil surface of pots containing pregerminated field bindweed seeds. Covering the pots with transparent plastic bags immediately after application increased disease incidence and resulted in up to 81% reduction in above-ground dry biomass, whereas a treatment of interrupted dew periods (8 h day^-1) for six days, resulted in only 56% biomass reduction. The size of container used for producing and for incubating the fungus granules had no significant effect on disease incidence and subsequent weed control of field bindweed. Likewise, no significant differences in efficacy were observed using inoculum that was milled once and then sieved or repeatedly milled and non-sieved. For early application dates, the use of two different planting substrates led to major differences in disease development. Pre-emergence application of inoculum on the surface of field collected soil on the same day that field bindweed seeds were planted resulted in an 81% mortality of seedlings emerging. In contrast, only 50% of emerging seedlings were killed when inoculum was applied on the surface of peat moss. Findings in this study indicate that moisture conditions and planting substrate may affect disease incidence and subsequent control of field bindweed by pre-emergence application of the selective fungal pathogen, P. convolvulus.     

Asian grapevine leaf rust caused by Phakopsora euvitis: an important disease in Brazil

Anthropogenic influences such as tourism and climate change affect ecosystems. One consequence is that invasive species can spread to and colonize novel areas. A recent example of this scenario is the appearance, in the early 2000s in Brazil and Australia, of the plant pathogenic fungus Phakopsora euvitis, which causes Asian grapevine leaf rust. It is speculated that the disease was introduced either by long distance transport of spores in the atmosphere or the import of contaminated plant material. While the disease could be eradicated from the Australian continent it is still present in Brazil. The pathogen has spread successfully throughout most Brazilian grapevine‐growing regions, most probably because of the lack of resistant plant cultivars. Today, the disease is endemic in Brazil. This review was written to highlight the increasing impact of the disease in Brazil and summarizes the current knowledge on the disease monocycle under different environmental conditions and the consequences for grapevine management. Gaps in the present state of knowledge are highlighted with the purpose of stimulating further research aimed at identifying efficient strategies to combat the disease.     

Detection of Acidovorax valerianellae in corn-salad seeds, seed transmission of the pathogen and disease development in the field

Acidovorax valerianellae , the causal agent of bacterial black spot of corn salad and responsible for severe economic losses to this vegetable in France, was successfully transmitted to corn-salad plants by artificially inoculated seeds in glasshouse and field experiments. In the field experiments, climatic data recorded under plastic tunnels indicated that increasing temperature and relative humidity increased symptom development. To investigate the possible contamination of commercial seedlots of corn salad, a seed test was developed consisting of soaking batches of seeds (five batches each of 5000, 1000, 500 and 100 seeds) overnight at 4°C in distilled sterile water, followed by dilution-plating of seed extracts on TSAV (tryptic soya agar for A. valerianellae ) semiselective medium. Suspected colonies were identified by biochemical and pathogenicity tests or, within 24 h, using antibodies specific to A. valerianellae . Acidovorax valerianellae was detected in three lots. Seed infection levels ranged from 0·10 to 0·89% of contaminated seeds and a single seed carried up to 1800 A. valerianellae colony-forming units.     

Stem rot disease incidence on faba beans in an artificially infested field

Journal of Plant Diseases and Protection - Stem rot, a destructive fungal disease caused by Sclerotinia trifoliorum Eriksson, is a serious problem for many important crops including faba beans...     

Control of late blight in organic potato production: evaluation of copper-free preparations under field,growth chamber and laboratory conditions

In order to replace copper fungicides in organic potato production, 53 copper-free preparations (CFPs) based on natural compounds, including plant extracts and microorganisms, and five copper preparations were evaluated for their potential to control Phytophthora infestans, the pathogen that causes late blight of potatoes. In in vitro assays, 30% of the CFPs inhibited indirect germination of sporangia, 26% mycelial growth and in growth chamber experiments, 21% efficiently reduced foliar blight of tomato plants. In micro-plot field trials with applications twice a week, the copper preparations were the most effective and reduced foliar blight by 99%. Of the CFPs tested, Oekofluid P, Mycosin and other sulphuric clays, and C-2000 reduced late blight the most, from 63% to 37%. In small-plot trials in 2001, 2002 and 2004, 27 CFPs with different formulations and four copper preparations were examined. In 2004, copper preparations at full and reduced rates and sulphuric clays were applied either weekly or according to the decision support system Bio-PhytoPRE. With Bio-PhytoPRE, copper preparations reduced foliar blight of potatoes by 23–77% and increased tuber yield by 2–28%, depending on the copper rate applied and year. With CFPs, maximal efficacy was 17% and no effect on tuber yield was observed. In vitro and in vivo trials showed that the rainfastness and the persistence of CFPs was low compared with copper preparations. This indicates that the failure of CFPs under field conditions is probably due to a lack of stability under prevailing environmental conditions and not to a lack of efficacy. Until stable formulations for CFPs are developed, an optimised and restricted use of copper fungicides using a decision support system could help to control late blight in organic potato production and to reduce copper input into the environment.     

Manifestation of black spot disease (Alternaria brassicicola) in intact leaves and detached leaf segments of cabbage plants grown in nutrient solutions without N,P, K and Ca

Journal of Plant Diseases and Protection - In two experiments young cabbage plants in the 4/6-leaf stage were supplied for eight weeks with nutrient solutions without nitrogen (oN), phosphorus...     

Giant calyx: a disease of eggplant (Solanum melongena) associated with a mycoplasma-like organism in Brazil

A disease of eggplant ( Solanum melongena ) associated with a mycoplasma-like organism (MLO) was found in the Federal District, Brazil. Symptoms were characterized by teratological changes in the flowering structure, reduction and malformation of leaves, proliferation of lateral buds, and an overall plant stunting. Evidence for the association between MLO infection and disease symptoms was obtained through graft-transmission experiments and electron microscopy. This is the first record of an eggplant disease associated with MLOs in Brazil.     

Powdery mildew on winter wheat in Bulgaria, 1980: Relations between disease incidence,disease severity,and yield

Mildew epidemics in 1980 on winter wheat cv. Sadovo 1 near Sofia, Bulgaria, were studied in detail. Half of the experimental plots were artificially inoculated, whereas the others were naturally infected. Fungicide treatments on all plots consisted of from nil to three applications of triadimefon. On four days, mildew severity, plant height and the yield components ear length, number of kernels, and grain weight per ear were determined. Mildew incidence showed to be a simple and reliable predictor of yield loss. It is suggested that mildew incidence can be used for decision making in the supervised control of wheat mildew in Bulgaria.Samenvatting Sofia, Bulgarije, in detail bestudeerd. Van 32 veldjes van 1 m² groot, in vier blokken van acht veldjes verdeeld over een groot tarweperceel, werd de helft kunstmatig geïnfecteerd met meeldauw, terwijl de andere helft aan natuurlijke infectie werd blootgesteld. De bespuitingen variëerden van een tot drie bespuitingen met triadimenfon, alsmede een onbespoten controle. Op drie dagen werden aantastingsgraad en incidentie van meeldauw bepaald aan de drie bovenste bladlagen. Een aantal relaties werd berekend tussen incidentie, aantastingsgraad en opbrengstvariabelen (planthoogte, aarlengte, aantal korrels per aar, korrelgewicht per aar). In ontwikkelingsstadium F 10.1 bleek meeldauw-incidentie een eenvoudige en betrouwbare maat te zijn voor toekomstige opbrengstderving. Meeldauw-incidentie kan als maat gebruikt worden bij de geleide bestrijding van meeldauw in Bulgarije, maar er zullen nog veel proeven nodig zijn om dit doel te bereiken.     

Effects of α-difluoromethylornithine on photosynthetic oxygen evolution,respiration and polyamine concentrations in detached barley leaves

Detached barley leaves were treated with the polyamine biosynthesis inhibitor, α-difluoromethylornithine (DFMO; 1 mM ) for either 30 min or 12 h. Exposure to DFMO for 30 min led to a substantial reduction in photosynthesis, expressed either on a unit leaf-area or unit chlorophyll basis. On the other hand, photosynthesis (expressed on a unit chlorophyll basis) was increased in leaves exposed to DFMO for 12 h, although when expressed on a unit leaf-area basis, photosynthesis remained unchanged at lower photon flux densities (0-300 μmol m^?2) and was slightly reduced at higher photon flux densities (300-800 μmol m^?2 s^?1) s^?1). Respiration was unaltered in leaves exposed to DFMO for 30 min or 12 h. Exposure to DFMO for 30 min resulted in significant increases in chlorophyll concentrations, while carotenoid concentrations remained unaltered. However, chlorophyll concentrations were reduced in leaves treated with DFMO for 12 h, although no change in carotenoid concentration was observed. Polyamine concentrations were not significantly affected by exposure of detached barley leaves to DFMO for 24 h.