Corynespora blight of sweet pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis>) caused by <Emphasis Type="Italic">Corynespora cassiicola</Emphasis> (Berk. &; Curt.) Wei

In 2004, Corynesopra cassiicola was isolated from dark brown spots on leaves and fruits and from black blights on stems of sweet pepper plants in Kochi Prefecture, Japan. The isolated fungus was then used to inoculate sweet pepper plants and subsequently reisolated from the plants with dark brown spots and black blights, showing that C. cassiicola is a new pathogen causing Corynespora blight on sweet pepper plants. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases as accession numbers AB366649 (TS-C11), AB366650 (TS-C21), AB366651 (TI-C32) and AB366652 (TI-C51)     

Bicarbonate solutions control powdery mildew (Leveillula taurica) on sweet red pepper and reduce the development of postharvest fruit rotting

Disease severity of powdery mildew (causal agentLeveillula taurica (Lév.) Arn.) on pepper (Capsicum annuum), defoliation and fruit sunscald rating were significantly reduced (P=0.05) by foliar applications of sodium or potassium bicarbonate solutions, compared with water or penconazole (Ophir). Preharvest application of bicarbonate solutions significantly reduced (P=0.05) postharvest decay development on sweet red pepper fruits.     

Resistance toLeveillula Taurica mildew (=Oidiopsis taurica) inCapsicum annuum

Several studies ofLeveillula taurica have been carried out in India, France, Israel and the USA. This report describes a promising source ofL. taurica resistance that can be incorporated into Mediterranean pepper cultivars. The present data suggest that full resistance depends on three pairs of genes.     

Effect of cultural practices on the development of arabica coffee berry disease,caused by <Emphasis Type="Italic">Colletotrichum kahawae</Emphasis>

In the high altitude regions of Africa, coffee berry disease (CBD), caused by Colletotrichum kahawae, is the main constraint for arabica coffee (Coffea arabica) production. However, certain agricultural practices can reduce losses caused by the disease and thereby promote optimum production. On small family farms in Cameroon, mixed cropping with fruit trees, intercropping with food crops and maintenance pruning of coffee trees are very widespread agricultural practices that can affect CBD epidemics. Consequently, an epidemiological study was conducted to assess how cultural practices affected the disease in an arabica coffee smallholding in Cameroon. The disease was monitored on a weekly basis over four successive years (2002–2005) on coffee trees in diverse cultural situations. Cultural practices likely to reduce losses due to CBD were identified. The infection rate was significantly lower on coffee trees grown intensively than on coffee trees grown in the traditional manner. Coffee trees located under the shade of fruit trees were significantly less attacked than those located in full sunlight. In addition, berries on the leafless parts of branches, near the main trunk of the coffee tree, were less infected than those on leafy sections. These results show that maintenance pruning, removal of mummified berries, and mixed cropping with shade plants are cultural practices which create environmental conditions that limit CBD development.     

Behavior and mutation of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> in <Emphasis Type="Italic">Solanum toxicarium</Emphasis> grown in aseptic culture

To study the behavior and mutation of Ralstonia solanacearum in Solanum toxicarium, which is resistant to bacterial wilt, S. toxicarium was grown in aseptic culture and inoculated with R. solanacearum. Although 60%–80% of the inoculated plants were wilting after 2 to 3 days, most wilted plants had recovered by 20 days after inoculation. The pathogen was reisolated from over 98% of inoculated plant stems, but the percentage of recovery decreased the closer the isolation sites were toward the upper stem sections. Three colony types, characterized as fluidal white, nonfluidal red, and a mixture of fluidal white and nonfluidal red, were reisolated from the stems. Nonfluidal red colonies were less virulent on tomato plants than fluidal white colonies.     

Status of biological control of the weed,Lantana camara in India

Abstract

A glasshouse study was conducted to determine the effect of shade on the uptake, translocation and activity of paraquat on Mikania micrantha H.B.K. The uptake, translocation and activity of paraquat were significantly enhanced at low light intensity. Placement of plants grown initially under 75% shade and transferred to 0% shade resulted in significantly higher uptake of paraquat than those initially grown under 0% and 50% shade. The uptake and activity of paraquat were also significantly increased when treated plants were placed in darkness. The rate of efflux of paraquat from leaf segments of plants grown in high light intensity was considerably slower than from plants grown in low light intensity.     

Light quality affects incidence of powdery mildew,expression of defence-related genes and associated metabolism in cucumber plants

To determine whether light quality affects the incidence of disease, we exposed cucumber (Cucumis sativus L. cv. Jinyan No. 4) plants at the 4-leaf stage to white and other monochromatic lights and tested the effects on plant response to Sphaerotheca fuliginea, defence-related gene expression and metabolic changes. Exposure to red light resulted in higher levels of H₂O₂ and salicylic acid (SA), and stronger expression of defence genes such as PR-1 than exposure to white or other monochromatic lights. In comparison, plants grown under purple and blue light had higher activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO) and higher level of flavonoids than plants grown under other lights. Furthermore, plants grown under red light were more resistant whilst plants grown under other monochromatic lights were less resistant to Sphaerotheca fuliginea than plants grown under white light. These results suggest a role of red light in light-enhanced resistance, which correlates with enhanced SA-dependent signaling pathway.     

Resistance to Leveillula taurica in the genus Capsicum

One hundred and sixty-two Capsicum genotypes were evaluated for powdery mildew (Leveillula taurica) resistance, following inoculations with a suspension of 5 × 10⁴ conidia mL⁻¹ on 10-leaved to 12-leaved plants. Genotypes were graded into five resistance classes, based on the areas under the disease progress curves calculated from disease incidence (percentage infected leaves per plant) and severity (total number of colonies per plant). Results revealed a continuum from resistance to susceptibility, with the majority (70%) of C. annuum materials being classified as moderately to highly susceptible to L. taurica. Conversely, C. baccatum, C. chinense and C. frutescens were most often resistant, indicating that resistance to L. taurica among Capsicum species is found mainly outside the C. annuum taxon. Nevertheless, some resistant C. annuum material was identified that may be useful for resistance breeding. Eight genotypes were identified as immune to the pathogen: H-V-12 and 4638 (previously reported), and CNPH 36, 38, 50, 52, 279 and 288. Only H-V-12 and 4638 are C. annuum, while all others belong to the C. baccatum taxon. Latent period of disease on a set of commercial sweet pepper genotypes varied, indicating diverse levels of polygenic resistance. The latent period progressively reduced with plant maturity, from 14·3 days in plants at the mid-vegetative stage to 8·6 days in plants at the fruiting stage. Young plants of all commercial genotypes tested at the early vegetative stage were immune, irrespective of the reaction of the genotype at later stages, demonstrating widespread juvenile resistance to L. taurica in the Capsicum germplasm. Inoculation of plants of different botanical taxa with a local isolate indicated a wide host range. Some hosts, including tomato (Lycopersicon esculentum), artichoke (Cynara scolymus) and poinsettia (Euphorbia pulcherrima), produced large amounts of secondary inoculum. Other hosts included okra (Abelmoschus esculentus), eggplant (Solanum melongena), cucumber (Cucumis sativus), Solanum gilo, Chenopodium ambrosioides and Nicandra physaloides.     

Weed hosts of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> in cotton fields in Turkey and characterization of <Emphasis Type="Italic">V. dahliae</Emphasis> isolates from weeds

A weed survey conducted in 2004 and 2005 in Aydin province of Turkey showed that Solanum nigrum, Xanthium strumarium, Amaranthus retroflexus, Portulaca oleracea, Sonchus oleraceus and Datura stramonium were the most prevalent weeds in the cotton fields exhibiting Verticillium wilt. Verticillium dahliae Kleb. was recovered from A. retroflexus and X. strumarium in those cotton fields. This is the first report of V. dahliae occurring naturally in A. retroflexus in Turkey. Pathogenicity tests on cotton and weeds showed that the virulence of V. dahliae isolates from weeds was higher on cotton plants than on weeds, with the disease severity ranging from 31.7% to 98.0%. Disease severity of V. dahliae isolates was 54.7–93.9% on eggplant, 23.7–51.6% on cucumber and 11.0–16.4% on tomato, whereas it did not cause any disease symptoms, or only low levels, on pepper and bell pepper. Two vegetative compatibility groups (VCGs) were identified among seven tested weed isolates: VCG2A (two isolates) and VCG2B (three isolates) using international reference strains.     

Competition between Solanum nigrum and pepper in the presence of Meloidogyne incognita

The influence of the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood on the competitive relationships between pepper (Capsicum annuum L.) and Solanum nigrum L. (black nightshade) was investigated in a glasshouse experiment. Seven competition treatments were set up: two intraspecific for the crop and the weed and five interspecific treatments in which the emergence of S. nigrum plants was progressively delayed with respect to that of the pepper. Nematodes reproduced in every inoculated plant and their multiplication rates were high in both pepper and S. nigrum. The parasite reduced all growth and yield parameters of the crop, but did less harm to the weed. The negative effect of S. nigrum on pepper peaked in the treatment in which the weed and pepper plants emerged together. S. nigrum was a stronger competitor than pepper under both nematode-infested and nematode-free conditions. The effect of nematodes on pepper yield was less than that of competition, but both appeared to be additive.     

Sequence comparison and transmission of <Emphasis Type="Italic">Blackcurrant reversion virus</Emphasis> isolates in black,red and white currants with black currant reversion disease and full blossom disease symptoms

We collected samples from black, red and white currants showing symptoms of blackcurrant reversion disease (BRD) and full blossom disease (FBD), cultivated in the Czech Republic. Blackcurrant reversion virus (BRV) was detected in all symptomatic plants. After amplification, a substantial part of the 3′ non-translated region (3′-NTR) of RNA2 of 15 new isolates of BRV was sequenced and compared with sequences available in the literature and GenBank. We did not find significant sequence diversity among isolates associated with either FBD or BRD. BRV was graft-transmitted from FBD infected red currant to black currant where symptoms of BRD were observed. Further sequence analysis of BRV isolates resulted in a phylogenetic tree with four branches, each consisting of six to nine isolates. No correlation with geographic origin was visible on the tree as isolates from various countries occurred in all four branches. We also found no correlation between the host and the topology of the tree: most of black currant isolates occurred in branches 3 and 4, but also occurred in branches 1 and 2. Only one white currant and one red currant isolate occurred in branches 3 and 4, respectively. The sequence identity of the Czech isolates in this region ranged from 91.9 to 99.8%. The 17 plant species growing within and in the close vicinity of the BRD-infested plantation were tested negative for BRV by RT-PCR as natural hosts of BRV. BRV was successfully transmitted by mechanical inoculation from black currant to Nicotiana occidentalis and N. tabacum cv. Xanthi, the latter being a new host for BRV. The infection was confirmed by PCR and sequencing.     

Effect of a UV-deficient environment on the biology and flight activity of<Emphasis Type="Italic">Myzus persicae</Emphasis> and its hymenopterous parasite<Emphasis Type="Italic">Aphidius matricariae</Emphasis>

Laboratory and field experiments were conducted to study the effect of UV filtration on the population growth, distribution and flight activity of the green peach aphidMyzus persicae (Sulzer) (Homoptera: Aphididae), and on the fecundity and host-finding behavior of the parasitic waspAphidius matricariae (Haliday) (Hymenoptera: Braconidae). The work was done in the Arava Valley of Israel, in walk-in tunnels covered with polyethylene film, to compare the effects of UV-absorbing filmversus those of regular film. Following artificial aphid infestation on pepper grown under the tested films, aphid population growth and spread under the UV-absorbing films were significantly less than under the regular films. The greatest impact of UV-absorbing film on aphid behavior was observed in winter and early spring, when temperature conditions favor aphid development. Elimination of UV by UV-absorbing film did not affect the parasitic activity ofA. matricariae. Previous results had indicated that covering the greenhouse with UV-absorbing films inhibited the invasion of aphids and other insect pests into it. That effect, in combination with those described in the present paper, makes the use of UV-absorbing films an effective component of IPM that aims to reduce the application of toxic insecticides. Contribution from the Agricultural Research Organization, No. 524/2002. http://www.phytoparasitica.org posting Oct. 13, 2003.     

Plant growth enhancement and disease control byTrichoderma harzianum in vegetable seedlings grown under commercial conditions

Trichoderma harzianum was applied to cucumber and pepper seedlings as a peat-bran preparation incorporated into the propagative mixture in a commercial production nursery. On marketing day (after 18 and 30 days for cucumber and pepper, respectively), significant increases of 23.8% and 17.2% in seedling height, 96.1% and 50% in leaf area, and 24.7% and 28.6% in plant dry weight were observed in cucumber and pepper seedlings, respectively, as compared to their non-treated counterparts.Trichoderma-treated seedlings were much more developed and vigorous and had higher chlorophyll contents. No significant differences were found in N, P or K content between treatments. Cucumber seedlings were then transplanted to a commercial greenhouse and analyzed over two successive growth cycles following soil fumigation with methyl bromide (500 kg/ha). Results revealed theTrichoderma-treated plants to be more resistant to damping-off disease. During the first cycle, immediately after soil fumigation, no damping-off was observed with either treatment, except in border beds where 4% of the non-treated plants died, as compared to no damping-off in theTrichoderma-treated plants. During the second growing cycle however, significant reductions in damping-off of 67% and 52% were obtained in middle and border beds, respectively, as compared to the non-treated controls.     

Growth of bell pepper plants (Capsicum annuum) affected by coloured covers

While a plant utilizes the full spectrum of visible light, some colours of light have more important applications than others. The aim of this study was to evaluate the responses of bell pepper plants grown under coloured covers. Bell pepper plants (Capsicum annuum) were grown hydroponically in a greenhouse in Tunja, Colombia, under different light quality regimes that were obtained with polypropylene films (yellow, green, blue, transparent, red, and a control without a plastic film cover). Conventional growth indices were calculated or measured as response variables. All of the evaluated parameters were influenced in a different ways by the colour of the covers, e.g. the leaf area was higher under the green and blue covers. The highest water uptake was found in the plants grown under the blue film. Plants under the yellow cover presented higher water use efficiency than the other treatments. The chlorophyll content index was higher under the blue, green and transparent covers. Based on these results, a coloured cover that favors most of the growth indices of plants cannot be selected; however, according to the needs of growers, the supplemental light quality can be used to achieve a specific effect.     

Factors affecting glyphosate activity in Imperata cylindrica (L.) Beauv. and Cyperus rotundus L. II: effect of shade

Imperata cylindrica and Cyperus rotundus were grown under three different light regimes; unshaded, 50% shade, and 75% shade and no shade plus 75% shade before and after spraying, (temporary shade) in a heated greenhouse. Six weeks after the start of the experimenis, glyphosate was applied to the plants at 0·2, 0·4 and 0·8 kg/ha (for Imperata) or 0·3, 0·6 and 1·2 kg/ha (for Cyperus). Glyphosate toxicity was enhanced as shade increased. In Imperata, all shade regimes at all rates of glyphosate eaused greater damage to the plants than the unshaded regime. The reduction in shoot dry weight, rhizome dry weight and total carbohydrate content of Imperate rhizotties at 75% continuous and temporary shaiie conditions, with the lowest rate of glyphosate, was almost twice as much as the reduction in the same features m the unshaded plants caused by the highest rate of glyphosate. In Cyperus. glyphosate at the intermediate and highest rates decreased the shoot dry weight at 75% continuous shade by 79% and 98% respectively. Plants in 50% shade were significantly affected only at the highest rate of glyphosate. Sprouting ability of the tubers al 75% continuous shade was inhibited when the tubers were replanted for recovery. Enhanced toxicity of glyphosate in reduced light intensity was attributed to the morphological changes in the nature of the leaves caused by shade.     

Reducing the spread of aphid-transmitted viruses in peppers by coarse-net cover

Spread of the aphid-transmitted cucumber mosaic virus (CMV) and potato virus Y (PVY) in pepper plots was markedly reduced by growing the plants under a white coarse-net cover permitting normal development of the plants. This net also reduced the winged aphid population on the plants by more than 40 times. Light grey and yellow nets also reduced virus spread and aphid populations, but were much less effective than white ones. The nets do not act as a mechanical barrier to aphids. It is suggested that under white and grey netting, aphid repellency and microclimatic conditions are the primary causes of virus check, while the controlling effect of the yellow nets may be explained by their being more attractive to aphids than the plants. A reduction of “background effect” and a limiting of the aphids’ vision range by nets are probably other factors involved in the protective mechanism.     

Phylogenetic analyses of plant-growth-promoting rhizobacteria isolated from tomato,lettuce, and Japanese pepper plants in Hyogo Prefecture,Japan

Approximately 30,000 fluorescent bacterial strains isolated from tomato, lettuce, eggplant, Chinese cabbage, and Japanese pepper plants at seven different locations in Hyogo Prefecture, were screened for plant-growth-promoting (PGP) activity to induce disease resistance against bacterial wilt in tomato. The 37 strains that had higher PGP activity were subjected to molecular phylogenetic analyses using the sequences of the 16S rRNA, gyrB and rpoD genes. Most of the strains were identified as Pseudomonas fluorescens or its close relative, P. putida, while a few strains were grouped with more distantly related bacterial species such as Enterobacter and Stenotrophomonas. The phylogenetic relationships among tomato and lettuce isolates mostly coincided with the source locality and host plants, with a few exceptions. In contrast, isolates from Japanese pepper plants did not form their own cluster but represented several different bacterial species.     

Tackling black leaf streak disease and soil fertility constraints to enable the expansion of plantain production to grassland in the humid tropics

In Central Africa, plantain is traditionally grown after a forest fallow. Given increasing urban demand and a lack of forest fallows near urban centres, as well as poor roads and environmental concerns to reduce pressure on forests, research is needed to identify suitable shade, fertility management and cultivars to shift production of plantain to grasslands and to reduce losses to diseases such as black leaf streak disease (BLSD). Effects of light level (full, 67%, 33% light), and nitrogen (N)-amendment on BLSD-tolerant (FHIA-21) and BLSD-susceptible (Batard) cultivars planted on soil from paired grassland and forest sites were determined. BLSD and growth were monitored until 5 months after planting. Three months after planting, leaf area attacked on cultivar FHIA-21 was less than half that on Batard. Plants grown under 33% and 67% light had less leaf area attacked (2.9% and 4.6%, respectively) than those grown in full light (7.3%). Leaf area and dry matter (DM) were higher under shade and when grown on forest soils. Compared to growing BLSD-susceptible plantain on forested land under shade, a shift onto grasslands and a reduction in shade use is predicted to reduce yields. Using cultivar FHIA-21 may limit, but not eliminate, yield loss.     

Seedborne fungi detected on stored solanaceous berry seeds and their biological activities

We isolated 629 fungi from 1296 berry seeds of solanaceous plants, including tomato (Lycopersicon esculentum), eggplant (Solanum melongena), bell pepper (Capsicum annuum), and red pepper (Capsicum annuum var. annuum) preserved for long and short terms. The isolates were classified into 22 genera excluding unidentified fungi, and the fungal floras were divided into two types: the tomato–eggplant and pepper groups. The results of cluster analysis with unweighted pair-group method with arithmetic average also supported these groups. Most tomato seeds infested with Geotrichum candidum germinated and grew the same as uninfested seeds. Cladosporium sphaerospermum and Arthrinium sp. isolated from eggplant seeds strongly suppressed germination, and Penicillium variabile suppressed seminal root elongation on eggplant. Alternaria alternata, Botrytis cinerea, and Myrothecium verrucaria detected from red pepper or bell pepper seeds were pathogenic to the fruits and the seedlings after artificial inoculation.     

Plant Phenology Influences the Effect of Mycorrhizal Fungi on the Development of Verticillium-induced Wilt in Pepper

Verticillium dahliae alters water status and consequently, growth and production of pepper plants. On the other hand, arbuscular mycorrhizal fungi (AMF) can reduce damage caused by specific soil-borne plant pathogens and improve drought resistance of pepper. Therefore, one objective of this research was to assess if AMF can modify the development of Verticillium-wilt in pepper plants. A second objective was to study the influence of plant phenology at the moment when V. dahliae was inoculated on the possible biocontrol of the disease by AMF. Results suggested that AMF reduce the deleterious effect of V. dahliae on pepper growth and yield. However, bioprotection against Verticillium-wilt was conditioned by plant phenology at the moment of pathogen attack. The highest efficacy of AMF occurred when V. dahliae was inoculated during the vegetative stage of plants. AMF allowed leaf relative water content to be maintained for longer and delayed both the appearance of disease symptoms and the decrease of photosynthesis in Verticillium-inoculated plants. These benefits on plant physiology increased pepper yield.