Susceptible Pepper Research Articles

Aconitase B is required for optimal growth of Xanthomonas campestris pv. vesicatoria in pepper plants.

The aerobic plant pathogenic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) colonizes the intercellular spaces of pepper and tomato. One enzyme that might contribute to the successful proliferation of Xcv in the host is the iron-sulfur protein aconitase, which catalyzes the conversion of citrate to isocitrate in the tricarboxylic acid (TCA) cycle and might also sense reactive oxygen species (ROS) and changes in cellular iron levels. Xcv contains three putative aconitases, two of which, acnA and acnB, are encoded by a single chromosomal locus. The focus of this study is aconitase B (AcnB). acnB is co-transcribed with two genes, XCV1925 and XCV1926, encoding putative nucleic acid-binding proteins. In vitro growth of acnB mutants was like wild type, whereas in planta growth and symptom formation in pepper plants were impaired. While acnA, XCV1925 or XCV1926 mutants showed a wild-type phenotype with respect to bacterial growth and in planta symptom formation, proliferation of the acnB mutant in susceptible pepper plants was significantly impaired. Furthermore, the deletion of acnB led to reduced HR induction in resistant pepper plants and an increased susceptibility to the superoxide-generating compound menadione. As AcnB complemented the growth deficiency of an Escherichia coli aconitase mutant, it is likely to be an active aconitase. We therefore propose that optimal growth and survival of Xcv in pepper plants depends on AcnB, which might be required for the utilization of citrate as carbon source and could also help protect the bacterium against oxidative stress.

SseF, a type III effector protein from the mammalian pathogen Salmonella enterica, requires resistance‐gene‐mediated signalling to activate cell death in the model plant Nicotiana benthamiana

Type III effector proteins (T3Es) of many Gram-negative pathogenic bacteria manipulate highly conserved cellular processes, indicating conservation in virulence mechanisms during the infection of hosts of divergent evolutionary origin. In order to identify conserved effector functions, we used a cross-kingdom approach in which we expressed selected T3Es from the mammalian pathogen Salmonella enterica in leaves of Nicotiana benthamiana and searched for possible virulence or avirulence phenotypes. We show that the T3E SseF of S. enterica triggers hypersensitive response (HR)-like symptoms, a hallmark of effector-triggered immunity in plants, either when transiently expressed in leaves of N. benthamiana by Agrobacterium tumefaciens infiltration or when delivered by Xanthomonas campestris pv vesicatoria (Xcv) through the type III secretion system. The ability of SseF to elicit HR-like symptoms was lost upon silencing of suppressor of G2 allele of skp1 (SGT1), indicating that the S. enterica T3E is probably recognized by an R protein in N. benthamiana. Xcv translocating an AvrRpt2-SseF fusion protein was restricted in multiplication within leaves of N. benthamiana. Bacterial growth was not impaired but symptom development was rather accelerated in a compatible interaction with susceptible pepper (Capsicum annuum) plants. We conclude that the S. enterica T3E SseF is probably recognized by the plant immune system in N. benthamiana, resulting in effector-triggered immunity.

Influence of Phytophthora capsici L. inoculation on disease severity, necrosis length, peroxidase and catalase activity, and phenolic content of resistant and susceptible pepper (Capsicum annuum L.) plants

This study explored the level of infection caused by different inoculum concentrations (10^2, 10^3, and 10^4 zoospores mL^-^1) of Phytophthora capsici in 3 pepper cultivars at days 2, 4, and 6. The effect that the infection induced on the peroxidase (POX), catalase (CAT), and phenolics of resistant and sensitive seedlings, as well as the defense mechanism against the pathogen, were also investigated. The resistance of PM-702 against the isolate used was high, whereas KM-Hot and DEM-8 displayed sensitive reactions. As a result of analyses of the leaves and stems from the 3 pepper cultivars, important changes in biochemical parameters were observed between resistant and sensitive cultivars after inoculation with the root rot pathogen P. capsici. The maximum increase of POX and CAT was observed in the resistant PM-702 cultivar. However, with a high inoculum concentration (10^4 zoospores mL^-^1), a loss of CAT activity was determined, especially in susceptible cultivars. The maximum increase in phenolics was detected in leaves of susceptible DEM-8 and stems of PM-702 on day 6 following infection. The results suggest that during Phytophthora root rot development there is a relation between the disease induced by P. capsici and the antioxidant system.

Transient expression of pepper Bs2 gene in Citrus limon as an approach to evaluate its utility for management of citrus canker disease

The pepper Bs2 gene confers resistance to Xanthomonas campestris pv. vesicatoria (Xcv) pathogenic strains containing the avrBs2 avirulence gene in susceptible pepper and tomato. The avrBs2 gene is highly conserved in the Xanthomonas genus and when bacteria lack this gene their growth in a susceptible host is diminished, indicating that the avrBs2 gene product could confer an adaptive advantage to the pathogen. The avrBs2 of Xanthomonas citri subsp. citri (Xcc), cause of citrus canker, shares 96% homology with avrBs2 of Xcv. To evaluate if Bs2 could recognize avrBs2 of Xcc in citrus plants and thereby activate plant defence mechanisms to increase resistance to canker, transient expression experiments were conducted using Agrobacterium tumefaciens in lemon plants subsequently challenged with wildtype Xcc. The results showed that transient expression of Bs2 reduced canker formation in lemon and induced plant defence mechanisms, as shown by callose deposition and PR‐1 expression. Moreover, when an avrBs2 mutant of Xcc was used, no decrease in disease symptoms was observed. This work shows that the Bs2 gene from Solanaceae is functional in lemon, a member of the Rutaceae family. Therefore, Bs2 is a potential candidate gene for stable expression in transgenic citrus plants in order to improve resistance to canker disease.

Tunisian Potato virus Y isolates with unnecessary pathogenicity towards pepper: support for the matching allele model in eIF4E resistance–potyvirus interactions

The pathogenic properties of Potato virus Y (PVY; genus Potyvirus, family Potyviridae) isolates collected in naturally infected pepper (Capsicum annuum) fields in Tunisia were evaluated against recessive resistance alleles at the pvr2 locus of pepper. Two pathotypes were observed. Pathotype (0,1,3) isolates were able to infect plants carrying the susceptibility allele pvr2+, together with pvr21/pvr21 and pvr23/pvr23 plants, but not pvr22/pvr22 plants. Pathotype (0) isolates were only able to infect pvr2+/pvr2+ plants. On the other hand, sequence data and phylogenetic analyses revealed three major groups of isolates, each characterized by particular amino acid residues in the central part of the VPg, the pathogenicity factor towards pvr2. Correspondence between pathogenic properties and phylogeny suggested a single evolutionary step for pathogenicity towards the pvr21 and pvr23 resistances, possibly under the selective pressure of pvr21. Indeed, 23% of the pepper plants in this area were shown to carry the pvr21 resistance, while pvr23 was not detected. The data suggested that pathogenicity towards pvr21 and pvr23 were not costly for PVY to infect susceptible pepper genotypes and supported the matching allele model for pepper–PVY interactions.

Comparative analysis of pathogenesis-related protein 10 (PR10) genes between fungal resistant and susceptible peppers

To elucidate the functional roles of PR10 genes from two pepper species during plant-pathogen interactions, PR10 genes were isolated from fungal-resistant (Capsicum baccatum var. PBC80) and fungal-susceptible (C. annuum var. Yeoju) pepper fruits infected with anthracnose fungus (Colletotrichum acutatum). Despite strong nucleotide sequence identity, there were significant differences in the patterns of gene expression and protein accumulation between the genes from the two host species. Induced expression of the PR10 mRNA in PBC80 (bacPR10) was highly maintained from 24 h after infection (HAI) rather than that in Yeoju (annPR10). These mRNA expression patterns were correlated with the level of respective protein that was detected as two or three bands in each species. Substantial induction of bacPR10 proteins was confirmed by 2D-gel analysis followed by immunoblotting. Immunolocalization study showed that deposition of bacPR10 was exclusively observed in the pericarp of PBC80 fruits after fungal infection, suggesting functional significance in defence. Additionally, in vitro analysis of the enzymatic properties of PR10 proteins revealed that recombinant bacPR10 had higher ribonucleolytic activity and exhibited less sensitivity to proteinase treatment than did annPR10. Taken together, these results support the idea that relative abundance and prolonged longevity of bacPR10 in PBC80 fruits may contribute to their increased resistance in response to the anthracnose fungus, as compared with Yeoju fruit.

Accelerated leaf senescence takes part in enhanced resistance in cucumber mosaic virus inoculated pepper leaves

Altered photosynthetic reactions in cucumber mosaic virus (CMV) inoculated leaves of virus resistant lines L113 and L57 and susceptible pepper (Capsicum annuum L.) plants cv. Albena grown in controlled environment and in the field were investigated. The CMV inoculated leaves of virus resistant lines developed different symptoms—necrotic local lesions on L113 and chlorotic spots on L57 while the same leaves of susceptible cv. Albena were symptomless. The changes in Photosystem II (PSII) and PSI electron transport were evaluated by chlorophyll fluorescence, and far-red (FR) light induced leaf absorbance A 810–860. CMV infection caused a decrease in maximal PSII quantum yield, F v/F m, in susceptible leaves. Increased non-photochemical fluorescence quenching in CMV-inoculated leaves of both resistant lines were observed. In CMV-inoculated leaves of all tested plants FR light induced P700 oxidation was decreased. In the present study, the viral-infected pepper plants grown in controlled environment to avoid the effects of abiotic factors were used as model system that allow us to investigate the differences in leaf senescence in CMV-inoculated leaves of susceptible and resistant pepper lines expressing different symptoms. Earlier leaf falls of inoculated leaves as a result of accelerated leaf senescence is important for building successful secondary virus resistance strategy following fast responses such as hypersensitive reaction.

The reproductive potential of the root-knot nematode Meloidogyne incognita is affected by selection for virulence against major resistance genes from tomato and pepper

The emergence of virulent root-knot nematode populations, able to overcome the resistance conferred by some of the resistance genes (R-genes) in Solanaceous crops, i.e., Mi(s) in tomato, Me(s) in pepper, may constitute a severe limitation to their use in the field. Research has been conducted to evaluate the durability of these R-genes, by comparing the reproduction of several laboratory-selected and wild virulent Meloidogyne incognita isolates, on both susceptible and resistant tomatoes and peppers. We first show that the Me1 R-gene in pepper behaves as a robust R-gene controlling avirulent and virulent Me3, Me7 or Mi-1 isolates. Although the reproductive potential of the virulent isolates was highly variable on susceptible and resistant plants, we also confirm that virulence is highly specific to a determined R-gene on which selection has occurred. Another significant experimental result is the observation that a reproductive fitness cost is associated with nematode virulence against Mi-1 in tomato and Me3 and Me7 in pepper. The adaptative significance of trade-offs between selected characters and fitness-related traits, suggests that, although the resistance can be broken, it may be preserved in some conditions if the virulent nematodes are counter-selected in susceptible plants. All these results have important consequences for the management of plant resistance in the field.

Defence responses in leaves of resistant and susceptible pepper ( Capsicum annuum L.) cultivars infected with different inoculum concentrations of Phytophthora capsici Leon

Three pepper cultivars (PM-702: resistant, Demre-8 and KM-hot: susceptible) with different resistances to Phytophthora capsici-22 ( P. capsici-22) were inoculated with different concentrations of zoospores to analyze the time course of phenylalanine ammonia lyase (PAL) activity, malondialdehyde (MDA), hydrogen peroxide (H 2O 2), proline and total protein. Samples were collected from the leaves of three pepper cultivars on the 2nd, 4th, and 6th days after infection; important differences were observed in PAL activity, MDA amount, H 2O 2, proline, and total protein with respect to zoospore concentration, infection time, and type of pepper cultivars. Activity of phenylalanine ammonia-lyase (PAL), the first enzyme in the phenylpropanoid biosynthetic pathway, was increased in inoculated leaves of all three cultivars. The increase in production of PAL upon challenge was higher in the infected plants compared to the non-infected (control) plants. An early induction of PAL was observed in the leaves of all peppers infected with P. capsici within two days, making it one of the detected earlier responses to infection. Moreover, pathogen stress increased the rate of lipid peroxidation (which is indicated by increasing MDA content). Production of reactive oxygen species, H 2O 2, and lipid peroxidation increased in pepper leaves by increasing time of infection and inoculum concentration. The findings suggested that PM-702 pepper cultivar was inherently better protected against lipid peroxidation under P. capsici stress than KM-hot and Demre-8. In addition, it was observed that proline content in the leaves of infected susceptible cultivars increased with time, but highest proline and total protein in non-infected (control) leaves were recorded in resistant cultivar.

Biological and Structural Mechanisms of Disease Development and Resistance in Chili Pepper Infected with the Root-knot Nematode

Biological and structural mechanisms of the nematode disease development in chili pepper caused by the root-knot nematode, Meloidogyne incognita, were investigated. Out of 39 chili pepper cultivars/lines tested, six were found resistant, while 33 were susceptible to M. incognita, of which a susceptible cultivar Chilseongcho and three resistant cultivar/lines CM334, 02G132 and 03G53 with different resistance degrees were selected for microscopic studies on the disease development. Gall formation was greatly reduced in the resistant cultivars/lines. Nematode penetration occurred both in the susceptible and resistant chili pepper roots; however, the penetration rates were significantly lowered in the three resistant peppers compared to the susceptible pepper cv. Chilseongcho. In the susceptible pepper, giant cells were extensively formed with no discernible necrosis around the nematode feeding sites. In the highly resistant pepper cultivar CM334, no giant cell was formed, but extensive necrosis formation was observed around the penetrating nematodes. In the other two resistant pepper lines (02G132 and 03G53), both giant cells and prominent necroses were formed, and the necrotic responses appeared to inhibit the further development of giant cells or accelerate their early degeneration. Although the nematode penetration was retarded significantly in the resistant cultivar/lines, all of the above results suggest that the disease resistance of pepper may be related to post-infectional defense mechanisms (nematode growth and development) more than pre-infectional ones (penetration and establishment). Variations in structural modifications in the resistant cultivar/lines may reflect their genetic differences related to the nematode resistance.

Managing Phytophthora Crown and Root Rot in Bell Pepper Using Fungicides and Host Resistance.

A resistant pepper cultivar and nine fungicides were tested in both the field and greenhouse and their ability to limit Phytophthora crown and root rot was demonstrated. In both settings, the resistant pepper 'Paladin' and the susceptible pepper 'Red Knight' were inoculated with prepared millet seed infested with Phytophthora capsici. Foliar sprays were applied to the pepper plants on a 7-day interval in the field, and foliar sprays or drenches were applied at 7- or 14-day intervals in the greenhouse. Cv. Paladin had significantly less plant death than Red Knight. In the field, plants treated with fluopicolide or mandipropamid had significantly less plant death than the untreated control plants and, in the greenhouse, all fixed effects, including cultivar, fungicide treatment, application method, and application interval, were significant. The interactions among fungicide-cultivar, application method-cultivar, application method-fungicide, and fungicide-cultivar-application method were also significant in the greenhouse. Treatments applied as drenches provided greater control of P. capsici than those applied foliarly. Combining a resistant cultivar with a fungicide applied as a drench may help reduce the incidence of crown and root rot in pepper.

A Point Mutation in the Polymerase of Potato virus Y Confers Virulence Toward the Pvr4 Resistance of Pepper and a High Competitiveness Cost in Susceptible Cultivar

To understand why the Pvr4 resistance of pepper against Potyvirus spp. remained durable in field conditions while virulent Potato virus Y (PVY) variants could be selected in the laboratory, we studied the molecular mechanisms which generated these variants and the consequences on viral fitness. Using a reverse genetics approach with an infectious cDNA clone of PVY, we found that the region coding for the NIb protein (RNA-dependent RNA polymerase) of PVY was the avirulence factor corresponding to Pvr4 and that a single nonsynonymous nucleotide substitution in that region, an adenosine to guanosine substitution at position 8,424 of the PVY genome (A(8424)G), was sufficient for virulence. This substitution imposed a high competitiveness cost to the virus against an avirulent PVY variant in plants devoid of Pvr4. In addition, during serial passages in susceptible pepper plants, the only observed possibility of the virulent mutant to increase its fitness was through the G(8424)A reversion, strengthening the high durability potential of the Pvr4 resistance. This is in accordance with the fact that the NIb protein is one of the most constrained proteins expressed by the PVY genome and, more generally, by Potyvirus spp., and with a previously developed model predicting the durability of virus resistances as a function of the evolutionary constraint applied on corresponding avirulence factors.

고추 탄저병균(Colletotrichum acutatum)의 분생포자 비산과 과실병반에 형성된 전염원 밀도

본 연구는 고추 탄저병균인 Collerorichum acutaum의 강우에 따른 비산량과 비산거리 및 포장에서 감염 후 병증상의 발현시기 그리고 병반에 형성된 전염원의 밀도 등을 알아보기 위해 수행하였다. 고추탄저병균의 분생포자는 비가 오는 날에 99.2%가 비산되었고 맑은 날에는 단지 0.8%의 포자만이 비산하였다. 포자의 비산량은 전염원과의 거리와 정의 상관이 있었다. 고추 탄저병균 포자의 93.3%는 점염원과 30 cm 수평거리에서 60 cm 높이 이하로 전파되었으며 120 cm 높이까지 비산하는 것으로 조사되었다. 노지에서 상대적으로 감수성이 높은 품종의 고추 과실과 낮은 품종의 과실은 각각 4일과 6일 후에 최초로 외부 병 증상을 나타내었다. 하지만 10일 후에 병 증상을 나타내기도 하여 기상환경에 따라 병원균의 잠복기간이 10일 이상일 가능성도 있을 것으로 판단되었다. 고추 병반에 형성된 전염원인 분생포자의 수는 병방의 크기가 클수록 많았는데 병반의 길이가 1.5 cm 이상일 경우에는 병반 당 천만 개 이상의 포자가 형성되었으며 여러 개의 병반 당 천만 개 이상의 포자가 형성되었으며 여러 개의 병반이 합쳐서 병반 길이가 4 cm가 넘을 경우 1억개가 넘는 포자가 형성되기도 하였다. 이상의 결과로 고추 탄저병균인 C. acutatum이 빗물에 튀어서 전파되고 비바람의 강도에 따라 상당히 먼 거리로 전파될 수 있으며 기상환경에 따라 감염 후 10일 이상의 잠복기를 가질 수 있으며 한 개의 큰 병반에는 수 천만개의 전염원인 형성되는 것을 확인되었다. 따라서 고추 탄저병의 가장 효과적인 방제수단은 빗물을 직접 맞지 않도록 하는 비가림 시설이며, 노지에서는 병든 과실을 조기에 제거하고 병 발생 초기에 적절한 약제를 살포하여 전염원의 밀도를 낮추는 것이 무엇보다 중요하다. This study was aimed to understand conidial disperse of the pepper anthracnose fungus Colletotrichum acutatum, elapse time for the disease development, and inoculum potentials on infected fruits. Most (99.2%) conidia of the fungus disseminated from inoculum source on the rainy day, while only 0.8% conidia dispersed on the sunny day. Among the conidia 93.3% were caught under 60 cm height at 30 cm distance; however, conidia were detected at 120 cm height at the distance. Relatively susceptible pepper fruits to anthracnose showed first visible symptoms at 4 days after infection under a mimic field condition. However, it seemed that over 10 days are required for the disease to develop on moderately resistant pepper fruits under unfavorable conditions. The number of conidia formed on a lesion was positively correlated with the lesion size (<TEX>$R^{2}=0.88$</TEX>). Over 10 millions of conidia were formed at a normal lesion size 1.5 cm in length. In some large coalesced lesions ca. 4cm in length produced over 100 millions of the fungal conidia. Results further confirmed that the rainfall is the key factor for the inoculum disperse of the pepper anthracnose pathogen, Colletotrichum acutatum, and a long distance dissemination is plausible according to rain and wind intensity. Consequently, rain-proof structures are ideal to avoid the disease, and removal of infected fruits and timely chemical spray are indispensible to reduce the inoculum potential in the field.

Mycelium homogenates from a virulent strain of Phytophthora capsici promote a defence-related response in cell suspensions from Capsicum chinense

We analysed changes in the transcript population produced in habanero pepper (Capsicum chinense) cell suspensions by the addition of whole mycelium homogenates from a pathogenic isolate of Phytophthora capsici, to identify plant cellular processes modified by the oomycete effectors. The elicitation produced several defence-like cellular responses: alkalinisation of the medium, a two-step oxidative burst, induction of β-1,3-glucanases, and activation of mitogen-activated protein kinases. The elicitation modified the accumulation of transcripts representative of diverse metabolic pathways, including ethylene biosynthetic enzymes, MAP kinases and defence-related products, like PR proteins, but did not affect the expression of C. chinense NPR1 and WRKY orthologue genes, which are important modulators of plant defence responses. Interestingly, apart from some defence-related genes, inoculation of six-leaf-stage habanero pepper plantlets with the pathogenic isolate revealed few systemic modifications in the transcript patterns. All plantlets ultimately died, even though the in planta inoculation induced the strong accumulation of two MAPK transcripts. As few resistance-related genes were expressed in susceptible habanero pepper plantlets that died, either the extent or the timing of the defence response could be insufficient to establish a proper response against Phytophthora blight.

Histological and Cytological Changes Associated with Susceptible and Resistant Responses of Chili Pepper Root and Stem to Phytophthora capsici Infection

Microscopic study of chili pepper (Capsicum annuum L.) infected with Phytophthora capsici, causing Phytophthora blight of chili pepper, was conducted to compare histological and cytological characteristics in the root and stem of susceptible (C. annuum cv. Bugang) and resistant (C. annuum cv. CM334) pepper cultivars. The susceptible pepper roots and stems were extensively penetrated and invaded by the pathogen initially into epidermal cells and later cortical and vascular cells. Host cell walls adjacent to and invaded by the infecting hyphae were partially dissolved and structurally loosened with fine fibrillar materials probably by cell wall-degrading enzymes of the pathogen. In the resistant pepper, the pathogen remained on root epidermal surface at one day after inoculation, embedded and captured in root exudation materials composed of proteins and polysaccharides. Also the pathogen appeared to be blocked in its progression at the early infection stages by thickened middle lamellae. At 3 days after inoculation, the oomycete hyphae were still confined to epidermal cells of the root and at most outer peripheral cortical cells of the stem, resulting from their invasion blocked by wound periderms formed underneath the infection sites and/or cell wall appositions bounding the hyphal protrusions. All of these aspects suggest that limitation of disease development in the resistant pepper may be due to the inhibition of the pathogen penetration, infection, invasion, and colonization by the defense structures such as root exudation materials, thickened middle lamellae, wound peridems and cell wall appositions.

Efficacy of Muscodor albus for the Control of Phytophthora Blight of Sweet Pepper and Butternut Squash.

The efficacy of Muscodor albus, a potential soil biofumigant, to control root and stem rot by Phytophthora capsici, was examined in a greenhouse study. P. capsici-infested potting mix was treated with three rates of M. albus, mefenoxam (Ridomil Gold EC, Syngenta Crop Protection, Inc.), or nothing. Seedlings of five sweet pepper cultivars and one butternut squash cultivar were transplanted into the treated potting mix. After 7 days, the plants were rated on a scale of 0 (healthy) to 5 (dead). The experiment was conducted three times and there was a significant interaction between pepper cultivar and soil treatment. Treatment with the highest rate of M. albus resulted in a slight but significant reduction in disease severity on Alliance, Aristotle, Paladin, and Revolution pepper compared with the pathogen-only control, while no significant decreases in disease severity were observed with butternut squash or the highly susceptible pepper cv. Red Knight. Of the four less-susceptible pepper cultivars, Paladin (the most tolerant cultivar) was the only one on which M. albus, as applied in this study, reduced disease severity to commercially acceptable levels.

Differential activation of defense-related genes in susceptible and resistant pepper cultivars infected with Phytophthora capsici

This study investigated the expression pattern of genes encoding for a basic PR-1 protein, a basic beta-1,3-glucanase, a peroxidase, and a sesquiterpene cyclase involved in defense responses in three pepper cultivars with different levels of resistance to Phytophthora capsici. All genes were up-regulated in infected stems of the pepper cultivars, with expression being detected 8h post-inoculation. mRNA levels of these genes increased markedly by 24h post-inoculation, and maximal induction levels were observed for the PR-1 and sesquiterpene cyclase genes. PR-1, peroxidase, and sesquiterpene genes were always expressed at higher levels in resistant cultivars than in the susceptible cultivar, although up-regulation was observed in both, suggesting that the differences between these pepper genotypes in susceptibility and resistance are a matter of the timing and magnitude of the defense response.

Effect of Poultry Manure on Pepper Veinal Mottle Virus (PVMV), Yield and Agronomic Parameters of Pepper (&lt;i&gt;Capsicum annuum&lt;/i&gt;) in Nigeria

Four fertilizer treatments were applied to two PVMV susceptible pepper (Capsicum annuum) varieties (NHV1-D96 and NHV1-E96) and one PVMV tolerant variety (NHV1-G96) to determine their effects in reducing the incidence and severity of pepper veinal mottle virus disease and on yield and agronomic parameters. The treatments were: (1) no manure application, (2) poultry litter organic manure at the rate of 10 tons/ha, (3) poultry litter organic manure at the rate of 20 tons/ha, and (4) NPK (20:10:10) at the rate of 0.26 tons/ha inorganic fertilizer. Broadcasting method was used for all the fertilizer applications. The experiment was carried out both in the field using a randomized complete block design and in 5 kg sterilized soil-potted experiment in the greenhouse in complete randomized design. The treatments showed a significant effect (P < 0.01) on PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant, and fruit yield both in the field and greenhouse plants. The interactions between the treatments were also significant (P < 0.05) for PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant and fruit yield. Mean PVMV disease incidence and severity, plant height, leaf number, internodes distance, number of fruit per plant and fruit yield, varied significantly (P < 0.05) in all the treatments applied. The application of 10 tons/ha and 20 tons/ha poultry manure showed a significant (P < 0.01) effect in reducing the incidence and severity of PVMV disease on the three pepper varieties. The poultry manure treatments were also observed to have positively and significantly contributed (P < 0.05) to the plant height, leaf number and fruit yield of PVMV infected pepper plants in all the three pepper varieties used both in the field and in the greenhouse. The yield of pepper decreased with increasing PVMV disease incidence and severity in all the treatments. Keywords: Capsicum annuum; Pepper Veinal Mottle Virus; Poultry Organic Manure East African Journal of Sciences Vol. 1 (2) 2007: pp. 104-111

Differentiation in two populations of Meloidogyne incognita from Greece in relation to reproduction on resistant tomato and pepper

The reproduction of two Meloidogyne incognita populations from Crete, Greece was assessed on ten pepper cultivars in pots in controlled conditions. One was virulent on the Mi gene of resistant tomato and was unable to reproduce on pepper while the other was avirulent on the Mi gene and produced galls and egg masses in all pepper cultivars. It has been previously reported by other researchers that various isolates of M. incognita virulent on the Mi gene (selected or natural) have a zero or decreased reproduction on the nematode susceptible peppers California Wonder and Doux Longdes Landes. This observation is confirmed in our study with a population of M. incognita from Crete on commercially grown pepper cultivars.

Implication of a pepper h-type thioredoxin in type I- and II-nonhost resistance to Xanthomonas axonopodis

Thioredoxins (TRXs) are distributed ubiquitously in prokaryotic and eukaryotic organisms. Plants have the most complex forms of TRXs. The functional roles of such TRXs have been studied in abiotic stress but their roles in plant defense responses against biotic stresses have been less well studied. Here, we identified an h-type TRX gene from pepper, CaTRXh1, and characterized its possible effect on Type II nonhost resistance, which entails localized programmed cell death in response to nonhost pathogens. Peptide sequences of CaTRXh1 showed a high degree of similarity with TRXhs from tobacco and Arabidopsis thaliana. Southern blot analyses revealed that CaTRXh1 was present as a single copy in the pepper genome. Intriguingly, leaf infiltration by Xanthomonas axonopodis pv. glycines 8ra, eliciting a visible type II nonhost hypersensitive response (HR), and its type III secretion-system null mutant 8–13, eliciting a type I nonhost non-HR, both induced CaTRXh1 at a level similar to that of pathogenesis-related protein 4, an HR marker gene in pepper. More surprisingly, expression of CaTRXh1 was significantly increased when X. axonopodis pv. vesicatoria race 3 infiltrated the leaf of a pepper cultivar containing a resistance gene, but not with infiltration of a susceptible pepper cultivar. Taken together, our study suggests that the expression of CaTRXh1 has a critical role in HR-mediated active defense responses in pepper.