Stability of resistance to Meloidogyne incognita (Kofoid &White) Chitwood was determined in pepper (Capsicum chinense Jacq. and C. annuum L.) at 24, 28, and 32 °C. Reactions of the C. annuum cultivars Charleston Belle and Keystone Resistant Giant and the C. chinense cultigens PA-426 and PA-350 to M. incognita were compared. Charleston Belle is homozygous for the N gene that confers resistance to M. incognita in C. annuum, and Keystone Resistant Giant is the susceptible recurrent parent of Charleston Belle. PA-426 is homozygous for a single dominant resistance gene that is allelic to the N gene, and PA-350 is susceptible. Root galling, egg-mass production, numbers of eggs per g fresh root, and reproductive factor of M. incognita increased for all pepper genotypes as temperature increased. Severity of root galling and nematode reproduction were less for PA-426 and Charleston Belle compared to PA-350 and Keystone Resistant Giant at all temperatures. However, both PA-426 and Charleston Belle exhibited a partial loss of resistance at the higher temperatures. For example, at 32 °C, the numbers of M. incognita eggs per g fresh root and the reproductive index for PA-426 and Charleston Belle were in the susceptible range. Nevertheless, the gall index for both cultivars was still within the resistant range. Both PA-350 and Keystone Resistant Giant exhibited highly susceptible reactions at 28 and 32 °C. Although the resistances of PA-426 and Charleston Belle were somewhat compromised at high temperatures, cultivars possessing these resistances will still be useful for managing M. incognita under high soil temperatures.
Capsicum annuum L.; C. chinense Jacq.; habanero; heat stability; Meloidogyne incognita; resistance; root-knot nematode; Scotch Bonnet pepper; soilborne pathogen; soil temperature; vegetable breeding
Pre-plant soil fumigation with methyl bromide and host resistance were compared for managing the southern root-knot nematode (Meloidogyne incognita) in pepper. Three pepper cultivars (Carolina Cayenne, Keystone Resistant Giant, and California Wonder) that differed in resistance to M. incognita were grown in field plots that had been fumigated with methyl bromide (98% CH₃Br : 2% CCl₃NO₂ [w/w]) before planting or left untreated. Carolina Cayenne is a well-adapted cayenne-type pepper that is highly resistant to M. incognita. The bell-type peppers Keystone Resistant Giant and California Wonder are intermediate to susceptible and susceptible, respectively. None of the cultivars exhibited root galling in the methyl bromide fumigated plots and nematode reproduction was minimal (<250 eggs/g fresh root), indicating that the fumigation treatment was highly effective in controlling M. incognita. Root galling of Carolina Cayenne and nematode reproduction were minimal, and fruit yields were not reduced in the untreated plots. The root-galling reaction for Keystone Resistant Giant was intermediate (gall index = 2.9, on a scale of 1 to 5), and nematode reproduction was moderately high. However, yields of Keystone Resistant Giant were not reduced in untreated plots. Root galling was severe (gall index = 4.3) on susceptible California Wonder, nematode reproduction was high, and fruit yields were reduced (P ≤ 0.05) in untreated plots. The resistance exhibited by Carolina Cayenne and Keystone Resistant Giant provides an alternative to methyl bromide for reducing yield losses by southern root-knot nematodes in pepper. The high level of resistance of Carolina Cayenne also suppresses population densities of M. incognita.
Capsicum annuum; Meloidogyne incognita; methyl bromide alternatives; nematode management; nematode resistance; pepper; root-knot nematodes
To determine the presence and level of root-knot nematode (Meloidogyne spp.) infestation in Southern California bell pepper (Capsicum annuum) fields, soil and root samples were collected in April and May 2012 and analyzed for the presence of root-knot nematodes. The earlier samples were virtually free of root-knot nematodes, but the later samples all contained, sometimes very high numbers, of root-knot nematodes. Nematodes were all identified as M. incognita. A nematode population from one of these fields was multiplied in a greenhouse and used as inoculum for two repeated pot experiments with three susceptible and two resistant bell pepper varieties. Fruit yields of the resistant peppers were not affected by the nematodes, whereas yields of two of the three susceptible pepper cultivars decreased as a result of nematode inoculation. Nematode-induced root galling and nematode multiplication was low but different between the two resistant cultivars. Root galling and nematode reproduction was much higher on the three susceptible cultivars. One of these susceptible cultivars exhibited tolerance, as yields were not affected by the nematodes, but nematode multiplication was high. It is concluded that M. incognita is common in Southern California bell pepper production, and that resistant cultivars may provide a useful tool in a nonchemical management strategy.
bell pepper; Capsicum annuum; Meloidogyne incognita; resistance; root-knot nematode
Resistance of pepper species (Capsicum annuum, C. baccatum, C. chinense, C. chacoense, and C. frutescens), cultivars and accessions to the root-knot nematodes Meloidogyne incognita race 2 and M. javanica, and their graft compatibility with commercial pepper varieties as rootstocks were evaluated in growth chamber and greenhouse experiments. Most of the plants tested were highly resistant to M. javanica but susceptible to M. incognita. Capsicum annuum AR-96023 and C. frutescens accessions as rootstocks showed moderate and relatively high resistance to M. incognita, respectively. In M. incognita-infested soil in a greenhouse, AR-96023 supported approximately 6-fold less nematode eggs per gram root and produced about 2-fold greater yield compared to a nongrafted commercial variety. The commercial variety grafted on AR-96023 produced a yield as great as the non-grafted variety in the root-knot nematode-free greenhouse. Some resistant varieties and accessions used as rootstocks produced lower yields (P < 0.01) than that of the non-grafted variety in the noninfested greenhouse. Use of rootstocks with nematode-resistance and graft compatibility may be effective for control of root-knot nematodes on susceptible pepper.
Capsicum spp.; graft compatibility; Meloidogyne incognita; Meloidogyne javanica; nematode control; pepper; resistance; root-knot nematodes; rootstock
Of the Capsicum peppers (Capsicum spp.), cultivated C. annuum is the most commercially important, but has lacked an intraspecific linkage map based on sequence-specific PCR markers in accord with haploid chromosome numbers. We constructed a linkage map of pepper using a doubled haploid (DH) population derived from a cross between two C. annuum genotypes, a bell-type cultivar ‘California Wonder’ and a Malaysian small-fruited cultivar ‘LS2341 (JP187992)’, which is used as a source of resistance to bacterial wilt (Ralstonia solanacearum). A set of 253 markers (151 SSRs, 90 AFLPs, 10 CAPSs and 2 sequence-tagged sites) was on the map which we constructed, spanning 1,336 cM. This is the first SSR-based map to consist of 12 linkage groups, corresponding to the haploid chromosome number in an intraspecific cross of C. annuum. As this map has a lot of PCR-based anchor markers, it is easy to compare it to other pepper genetic maps. Therefore, this map and the newly developed markers will be useful for cultivated C. annuum breeding.
pepper (Capsicum annuum L.); SSR markers; genetic map; 12 linkage groups
Meloidogyne mayaguensis is a damaging root-knot nematode able to reproduce on root-knot nematode-resistant tomato and other economically important crops. In a growth chamber experiment conducted at 22 and 33°C, isolate 1 of M. mayaguensis reproduced at both temperatures on the Mi-1-carrying tomato lines BHN 543 and BHN 585, whereas M. incognita race 4 failed to reproduce at 22°C, but reproduced well at 33°C. These results were confirmed in another experiment at 26 ± 1.8°C, where minimal or no reproduction of M. incognita race 4 was observed on the Mi-1-carrying tomato genotypes BHN 543, BHN 585, BHN 586 and ‘Sanibel’, whereas heavy infection and reproduction of M. mayaguensis isolate 1 occurred on these four genotypes. Seven additional Florida M. mayaguensis isolates also reproduced on resistant ‘Sanibel’ tomato at 26 ± 1.8°C. Isolate 3 was the most virulent, with reproduction factor (Rf) equal to 8.4, and isolate 8 was the least virulent (Rf = 2.1). At 24°C, isolate 1 of M. mayaguensis also reproduced well (Rf ≥ 1) and induced numerous small galls and large egg masses on the roots of root-knot nematode-resistant bell pepper ‘Charleston Belle’ carrying the N gene and on three root-knot nematode-resistant sweet pepper lines (9913/2, SAIS 97.9001 and SAIS 97.9008) carrying the Tabasco gene. In contrast, M. incognita race 4 failed to reproduce or reproduced poorly on these resistant pepper genotypes. The ability of M. mayaguensis isolates to overcome the resistance of tomato and pepper genotypes carrying the Mi-1, N and Tabasco genes limits the use of resistant cultivars to manage this nematode species in infested tomato and pepper fields in Florida.
Capsicum annuum; bell pepper; resistance; root-knot nematodes; Solanum lycopersicum; sweet pepper
Meals produced when oil is extracted from seeds in the Brassicaceae have been shown to suppress weeds and soilborne pathogens. These seed meals are commonly used individually as soil amendments; the goal of this research was to evaluate seed meal mixes of Brassica juncea (Bj) and Sinapis alba (Sa) against Meloidogyne incognita. Seed meals from Bj ‘Pacific Gold’ and Sa ‘IdaGold’ were tested alone and in combinations to determine rates and application times that would suppress M. incognita on pepper (Capsicum annuum) without phytotoxicity. Rates of soil application (% w/w) for the phytotoxicity study were: 0.5 Sa, 0.2 Bj, 0.25 Sa + 0.25 Bj, 0.375 Sa + 0.125 Bj, 0.125 Sa + 0.375 Bj, and 0, applied 0 – 5 weeks before transplant. Overall, 0.2% Bj was the least toxic meal to pepper seedlings. By comparison, 0.5% S. alba seed meal did not reduce lettuce (Lactuca sativa) seed germination at week 0, but all seed meal treatments containing B. juncea prevented or significantly reduced germination at week 0. The seed meals did not affect lettuce seed germination at weeks 1-5, but hypocotyl growth was reduced by all except 0.2% Bj at weeks 1, 4 and 5. Brassica juncea and Sa meals were tested for M. incognita suppression at 0.2, 0.15, 0.1 and 0.05%; mixtures were 0.1% Sa + 0.1% Bj, 0.15% Sa + 0.05% Bj, and 0.05% Sa + 0.15% Bj. All treatments were applied 2 weeks before transplant. The 0.2% Bj and 0.05% Sa + 0.15% Bj treatments overall had the longest shoots and highest fresh weights. Eggs per g root were lowest with 0.1 – 0.2% Bj amendments and the seed meal mixtures. The results indicate that Bj and some Bj + Sa mixtures can be applied close to transplant to suppress M. incognita populations on pepper; consequently, a seed meal mixture could be selected to provide activity against more than one pest or pathogen. For pepper, care should be taken in formulating mixtures so that Sa rates are low compared to Bj.
amendment; biofuel byproducts; Brassica; glucosinolate; management; Meloidogyne incognita; mustard seed meal; root-knot nematode; Sinapis
The efficacy of clean fallow, bermudagrass (Cynodon dactylon) as a rotational crop, and fenamiphos for control of root-knot nematode (Meloidogyne incognita race 1) and soilborne fungi in okra (Hibiscus esculentus), snapbean (Phaseolus vulgaris), and pepper (Capsicum annuum) production was evaluated in field tests from 1993 to 1995. Numbers of M. incognita in the soil and root-gall indices were greater on okra than on snapbean or pepper. Application of fenamiphos at 6.7 kg a.i./ha did not suppress numbers of nematodes on any sampling date when compared with untreated plots. The lack of efficacy could be the result of microbial degradation of the nematicide. Application of fenamiphos suppressed root-gall development on okra following fallow and 1-year sod in 1993, but not thereafter. A few galls were observed on roots of snapbean following 2- and 3-year fallow but none following 1-, 2-, and 3-year bermudagrass sod. Population densities of Pythium aphanidermatum, P. myriotylum, and Rhizoctonia solani in soil after planting vegetables were suppressed by 2- or 3-year sod compared with fallow but were not affected by fenamiphos. Yields of snapbean, pepper, and okra did not differ between fallow and 1-year sod. In the final year of the study, yields of all crops were greater following 3-year sod than following fallow. Application of fenamiphos prior to planting each crop following fallow or sod did not affect yields.
Bermudagrass; Capsicum annuum; Gynodon dactylon; Cyperus esculentus; fenamiphos; Hibiscus esculentus; management; Meloidogyne incognita; nematicide; nematode; nutsedge; okra; pepper; Phaseolus vulgaris; resistance; root-knot nematode; snapbean; sod-based rotation
The tobamovirus resistance gene L3 of Capsicum chinense was mapped using an intra-specific F2 population (2,016 individuals) of Capsicum annuum cultivars, into one of which had been introduced the C. chinenseL3 gene, and an inter-specific F2 population (3,391 individuals) between C. chinense and Capsicum frutescence. Analysis of a BAC library with an AFLP marker closely linked to L3-resistance revealed the presence of homologs of the tomato disease resistance gene I2. Partial or full-length coding sequences were cloned by degenerate PCR from 35 different pepper I2 homologs and 17 genetic markers were generated in the inter-specific combination. The L3 gene was mapped between I2 homolog marker IH1-04 and BAC-end marker 189D23M, and located within a region encompassing two different BAC contigs consisting of four and one clones, respectively. DNA fiber FISH analysis revealed that these two contigs are separated from each other by about 30 kb. DNA fiber FISH results and Southern blotting of the BAC clones suggested that the L3 locus-containing region is rich in highly repetitive sequences. Southern blot analysis indicated that the two BAC contigs contain more than ten copies of the I2 homologs. In contrast to the inter-specific F2 population, no recombinant progeny were identified to have a crossover point within two BAC contigs consisting of seven and two clones in the intra-specific F2 population. Moreover, distribution of the crossover points differed between the two populations, suggesting linkage disequilibrium in the region containing the L locus.
Electronic supplementary material
The online version of this article (doi:10.1007/s00122-008-0848-6) contains supplementary material, which is available to authorized users.
The successful exploitation of germplasm banks, harbouring plant genetic resources indispensable for plant breeding, will depend on our ability to characterize their genetic diversity. The Vegetable Germplasm Bank of Zaragoza (BGHZ) (Spain) holds an important Capsicum annuum collection, where most of the Spanish pepper variability is represented, as well as several accessions of other domesticated and non-domesticated Capsicum spp from all over the five continents. In the present work, a total of 51 C. annuum landraces (mainly from Spain) and 51 accessions from nine Capsicum species maintained at the BGHZ were evaluated using 39 microsatellite (SSR) markers spanning the whole genome. The 39 polymorphic markers allowed the detection of 381 alleles, with an average of 9.8 alleles per locus. A sizeable proportion of alleles (41.2%) were recorded as specific alleles and the majority of these were present at very low frequencies (rare alleles). Multivariate and model-based analyses partitioned the collection in seven clusters comprising the ten different Capsicum spp analysed: C. annuum, C. chinense, C. frutescens, C. pubescens, C. bacatum, C. chacoense and C. eximium. The data clearly showed the close relationships between C. chinense and C. frutescens. C. cardenasii and C. eximium were indistinguishable as a single, morphologically variable species. Moreover, C. chacoense was placed between C. baccatum and C. pubescens complexes. The C. annuum group was structured into three main clusters, mostly according to the pepper fruit shape, size and potential pungency. Results suggest that the diversification of C. annuum in Spain may occur from a rather limited gene pool, still represented by few landraces with ancestral traits. This ancient population would suffer from local selection at the distinct geographical regions of Spain, giving way to pungent and elongated fruited peppers in the South and Center, while sweet blocky and triangular types in Northern Spain.
Commercial strains of entomopathogenic fungi were evaluated for control of chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), an invasive pest of ornamental and vegetable plants in the Caribbean and southeastern United States. In laboratory assays, LC50 values against adult S. dorsalis were 5.1 × 104 CFU/mL for Beauveria bassiana GHA, with higher values 3.1 × 105 for Metarhizium brunneum F52 and 3.8 × 105 for Isaria fumosorosea Apopka 97. Second instars were comparatively less susceptible to all isolates, ostensibly due to moulting, with LC50 values of 1.1 × 108, 7.0 × 105, and 9.9 × 105 CFU/spores per mL for GHA, F52, and Apopka 97 strains, respectively. In greenhouse cages, compared with controls, three applications of mycoinsecticides and other biorational insecticides at 7 to 14 day intervals reduced overall S. dorsalis populations on pepper plants Capsicum annuum cv. California Wonder: spinosad reduced populations by 94–99%, M. brunneum F52 by 84–93%, B. bassiana GHA by 81–94%, I. fumosorosea PFR-97 by 62–66%, and different horticultural oils by 58–85%. The proportion of marketable fruit was significantly increased by M. brunneum F52, B. bassiana GHA, and 2% SuffOil-X treatments. Slightly lower levels of control were observed in nursery tests with ornamental rose shrubs, Rosa sp. Red Double Knock Out®, during hot sunny conditions. Four applications reduced thrips populations over 10 weeks: spinosad by an average of 91%, M. brunneum F52 by an average of 81%, B. bassiana GHA by an average of 62%, SuffOil-X by an average of 50%, and I. fumosorosea PFR-97 by an average of 44%. The data show that mycoinsecticides can be used in management strategies for low to moderate populations of S.
dorsalis and provide resistance management tools for the limited number of insecticides that are effective against this pest.
Beauveria bassiana; Isaria fumosorosea; Metarhizium brunneum; Rosa spp.; sweet pepper
An overview of the metabolic diversity in ripe fruits of a collection of 32 diverse pepper (Capsicum sp.) accessions was obtained by measuring the composition of both semi-polar and volatile metabolites in fruit pericarp, using untargeted LC–MS and headspace GC–MS platforms, respectively. Accessions represented C. annuum, C. chinense, C. frutescens and C. baccatum species, which were selected based on variation in morphological characters, pungency and geographic origin. Genotypic analysis using AFLP markers confirmed the phylogenetic clustering of accessions according to Capsicum species and separated C. baccatum from the C. annuum–C. chinense–C. frutescens complex. Species-specific clustering was also observed when accessions were grouped based on their semi-polar metabolite profiles. In total 88 semi-polar metabolites could be putatively identified. A large proportion of these metabolites represented conjugates of the main pepper flavonoids (quercetin, apigenin and luteolin) decorated with different sugar groups at different positions along the aglycone. In addition, a large group of acyclic diterpenoid glycosides, called capsianosides, was found to be highly abundant in all C. annuum genotypes. In contrast to the variation in semi-polar metabolites, the variation in volatiles corresponded well to the differences in pungency between the accessions. This was particularly true for branched fatty acid esters present in pungent accessions, which may reflect the activity through the acyl branch of the metabolic pathway leading to capsaicinoids. In addition, large genetic variation was observed for many well-established pepper aroma compounds. These profiling data can be used in breeding programs aimed at improving metabolite-based quality traits such as flavour and health-related metabolites in pepper fruits.
Electronic supplementary material
The online version of this article (doi:10.1007/s11306-012-0432-6) contains supplementary material, which is available to authorized users.
Capsicum; Metabolite profiling; Semi-polar compounds; Volatiles; Pungency; AFLP
Resistance to the southern root-knot nematode, Meloidogyne incognita races 1 and 3, has been identified, incorporated, and deployed into commercial cultivars of tobacco, Nicotiana tabacum. Cultivars with resistance to other economically important root-knot nematode species attacking tobacco, M. arenaria, M. hapla, M. javanica, and other host-specific races of M. incognita, are not available in the United States. Twenty-eight tobacco genotypes of diverse origin and two standard cultivars, NC 2326 (susceptible) and Speight G 28 (resistant to M. incognita races 1 and 3), were screened for resistance to eight root-knot nematode populations of North Carolina origin. Based on root gall indices at 8 to 12 weeks after inoculation, all genotypes except NC 2326 and Okinawa were resistant to M. arenaria race 1, and races 1 and 3 of M. incognita. Except for slight root galling, genotypes resistant to M. arenaria race 1 responded similarly to races 1 and 3 of M. incognita. All genotypes except NC 2326, Okinawa, and Speight G 28 showed resistance to M. javanica. Okinawa, while supporting lower reproduction of M. javanica than NC 2326, was rated as moderately susceptible. Tobacco breeding lines 81-R-617A, 81-RL- 2K, SA 1213, SA 1214, SA 1223, and SA 1224 were resistant to M. arenaria race 2, and thus may be used as sources of resistance to this pathogen. No resistance to M. hapla and only moderate resistance to races 2 and 4 of M. incognita were found in any of the tobacco genotypes. Under natural field infestations of M. arenaria race 2, nematode development on resistant tobacco breeding lines 81-RL-2K, SA 1214, and SA 1215 was similar to a susceptible cultivar with some nematicide treatments; however, quantity and quality of yield were inferior compared to K 326 plus nematicides.
Javanese root-knot nematode; Meloidogyne species; nematode; resistance; southern root-knot nematode; tobacco
Field trials were conducted during 1986, 1988, 1989, and 1991 to compare the effects of 1,3-dichloropropene, fenamiphos, and carbofuran on yield and quality of chile peppers (Capsicum annuum) in soil infested with Meloidogyne incognita. When compared with untreated plots, numbers of M. incognita juveniles recovered from soil 60 and(or) 90 days after chile pepper emergence were reduced (P = 0.05) following 1,3-D treatment every year except 1986. Nematode numbers were also reduced (P = 0.05) by fenamiphos in 1989. Chile pepper yields were significantly higher than those in untreated control plots (P = 0.05) all 4 years in plots treated with 1,3-D and in 1989 in plots treated with fenamiphos. Use of carbofuran did not significantly reduce nematode numbers or enhance yields in these experiments. Green chile pepper fruit quality was enhanced (P = 0.05) following 1,3-D treatments in 1988 and 1989 but was unaffected by fenamiphos or carbofuran application. Increasing placement depth of 1,3-D from 28 to 48 cm increased (P = 0.05) red chile pepper yield compared with that obtained with conventional placement in 1988 only, and did not affect green chile pepper yield.
application technique; Capsicum annuum; carbofuran; chile pepper; crop quality; depth of placement; fenamiphos; fumigation; Meloidogyne incognita; nematode; 1,3-dichloropropene; root-knot nematode; yield
The effects of Meloidogyne incognita on the Big Jim, Jalapeno, and New Mexico No. 6 chile (Capsicum annuum) cultivars were investigated in microplots for two growing seasons. All three cultivars were susceptible to M. incognita and reacted similarly to different initial populations of this nematode. Severe stunting and yield suppressions occurred at all initial M. incognita densities tested ranging from 385 to 4,230 eggs and larvae/500 cm³ soil. Regression analysis of the microplot data from a sandy loam soil showed yield losses of 31% for the 1978 season and 25% for the 1979 season for the three cultivars for each 10-fold increase in the initial population of M. incognita.
Capsicum annuum; Meloidogyne incognita; root-knot nematode; pepper
The widely cultivated pepper, Capsicum spp., important as a vegetable and spice crop world-wide, is one of the most diverse crops. To enhance breeding programs, a detailed characterization of Capsicum diversity including morphological, geographical and molecular data is required. Currently, molecular data characterizing Capsicum genetic diversity is limited. The development and application of high-throughput genome-wide markers in Capsicum will facilitate more detailed molecular characterization of germplasm collections, genetic relationships, and the generation of ultra-high density maps. We have developed the Pepper GeneChip® array from Affymetrix for polymorphism detection and expression analysis in Capsicum. Probes on the array were designed from 30,815 unigenes assembled from expressed sequence tags (ESTs). Our array design provides a maximum redundancy of 13 probes per base pair position allowing integration of multiple hybridization values per position to detect single position polymorphism (SPP). Hybridization of genomic DNA from 40 diverse C. annuum lines, used in breeding and research programs, and a representative from three additional cultivated species (C. frutescens, C. chinense and C. pubescens) detected 33,401 SPP markers within 13,323 unigenes. Among the C. annuum lines, 6,426 SPPs covering 3,818 unigenes were identified. An estimated three-fold reduction in diversity was detected in non-pungent compared with pungent lines, however, we were able to detect 251 highly informative markers across these C. annuum lines. In addition, an 8.7 cM region without polymorphism was detected around Pun1 in non-pungent C. annuum. An analysis of genetic relatedness and diversity using the software Structure revealed clustering of the germplasm which was confirmed with statistical support by principle components analysis (PCA) and phylogenetic analysis. This research demonstrates the effectiveness of parallel high-throughput discovery and application of genome-wide transcript-based markers to assess genetic and genomic features among Capsicum annuum.
Mature pepper (Capsicum sp.) fruits come in a variety of colors, including red, orange, yellow, brown, and white. To better understand the genetic and regulatory relationships between the yellow fruit phenotype and the capsanthin-capsorubin synthase gene (Ccs), we examined 156 Capsicum varieties, most of which were collected from Northwest Chinese landraces. A new ccs variant was identified in the yellow fruit cultivar CK7. Cluster analysis revealed that CK7, which belongs to the C. annuum species, has low genetic similarity to other yellow C. annuum varieties. In the coding sequence of this ccs allele, we detected a premature stop codon derived from a C to G change, as well as a downstream frame-shift caused by a 1-bp nucleotide deletion. In addition, the expression of the gene was detected in mature CK7 fruit. Furthermore, the promoter sequences of Ccs from some pepper varieties were examined, and we detected a 176-bp tandem repeat sequence in the promoter region. In all C. annuum varieties examined in this study, the repeat number was three, compared with four in two C. chinense accessions. The sequence similarity ranged from 84.8% to 97.7% among the four types of repeats, and some putative cis-elements were also found in every repeat. This suggests that the transcriptional regulation of Ccs expression is complex. Based on the analysis of the novel C. annuum mutation reported here, along with the studies of three mutation types in yellow C. annuum and C. chinense accessions, we suggest that the mechanism leading to the production of yellow color fruit may be not as complex as that leading to orange fruit production.
In plants, eIF4E translation initiation factors and their eIFiso4E isoforms are essential susceptibility factors for many RNA viruses, including potyviruses. Mutations altering these factors are a major source of resistance to the viruses. The eIF4E allelic series is associated with specific resistance spectra in crops such as Capsicum annum. Genetic evidence shows that potyviruses have a specific requirement for a given 4E isoform that depends on the host plant. For example, Tobacco etch virus (TEV) uses eIF4E1 to infect Capsicum annuum but uses eIFiso4E to infect Arabidopsis thaliana. Here, we investigated how TEV exploits different translation initiation factor isoforms to infect these two plant species.
A complementation system was set up in Arabidopsis to test the restoration of systemic infection by TEV. Using this system, Arabidopsis susceptibility to TEV was complemented with a susceptible pepper eIF4E1 allele but not with a resistant allele. Therefore, in Arabidopsis, TEV can use the pepper eIF4E1 instead of the endogenous eIFiso4E isoform so is able to switch between translation initiation factor 4E isoform to infect the same host. Moreover, we show that overexpressing the pepper eIF4E1 alleles is sufficient to make Arabidopsis susceptible to an otherwise incompatible TEV strain. Lastly, we show that the resistant eIF4E1 allele is similarly overcome by a resistance-breaking TEV strain as in pepper, confirming that this Arabidopsis TEV-susceptibility complementation system is allele-specific.
We report here a complementation system in Arabidopsis that makes it possible to assess the role of pepper pvr2-eIF4E alleles in susceptibility to TEV. Heterologous complementation experiments showed that the idiosyncratic properties of the 4E and iso4E proteins create a major checkpoint for viral infection of different hosts. This system could be used to screen natural or induced eIF4E alleles to find and study alleles of interest for plant breeding.
Potyvirus; Translation initiation factor; eIF4E; Arabidopsis thaliana; Capsicum annuum
This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F1 , F 2 , BC 1 Pr, and BC 1 Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 , Pn Ko2 and Pn Kr1 , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 , Pn Bz2 and Pn Kr2 , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance.
additive model; best fit model; gene effect; heredity
The discovery of Meloidogyne mayaguensis is confirmed in Florida; this is the first report for the continental United States. Meloidogyne mayaguensis is a virulent species that can reproduce on host cultivars bred for nematode resistance. The perineal patterns of M. mayaguensis isolates from Florida show morphological variability and often are similar to M. incognita. Useful morphological characters for the separation of M. mayaguensis from M. incognita from Florida are the male stylet length values (smaller for M. mayaguensis than M. incognita) and J2 tail length values (greater for M. mayaguensis than M. incognita). Meloidogyne mayaguensis values for these characters overlap with those of M. arenaria and M. javanica from Florida. Enzyme analyses of Florida M. mayaguensis isolates show two major bands (VS1-S1 phenotype) of esterase activity, and one strong malate dehydrogenase band (Rm 1.4) plus two additional weak bands that migrated close together. Their detection requires larger amounts of homogenates from several females. Amplification of two separate regions of mitochondrial DNA resulted in products of a unique size. PCR primers embedded in the COII and 16S genes produced a product size of 705 bp, and amplification of the 63-bp repeat region resulted in a single product of 322 bp. Nucleotide sequence comparison of these mitochondrial products together with sequence from 18S rDNA and ITS1 from the nuclear genome were nearly identical with the corresponding regions from a M. mayaguensis isolate from Mayaguez, Puerto Rico, the type locality of the species. Meloidogyne mayaguensis reproduced on cotton, pepper, tobacco, and watermelon but not on peanut. Preliminary results indicate the M. mayaguensis isolates from Florida can reproduce on tomato containing the Mi gene. Molecular techniques for the identification of M. mayaguensis will be particularly useful in cases of M. mayaguensis populations mixed with M. arenaria, M. incognita, and M. javanica, which are the most economically important root-knot nematode species in Florida, and especially when low (<25) numbers of specimens of these species are recovered from the soil.
isozyme; Meloidogyne arenaria; M. incognita; M. javanica; M. mayaguensis; mitochondrial DNA; molecular diagnosis; morphology; nematode; root-knot nematode; taxonomy
Meloidogyne incognita-infected and noninfected tubers of yellow nutsedge (Cyperus esculentus) and purple nutsedge (Cyperus rotundus) were treated with 56 L/ha 1,3-dichloropropene (1,3-D) in microplots and subsequently examined for tuber and nematode viability in the greenhouse using a chile pepper (Capsicum annuum) bioassay system. The study was conducted three times. Nutsedge tuber viability and M. incognita harbored in both yellow and purple nutsedge tubers were unaffected by 1,3-D treatment. Nematode reproduction on nutsedges and associated chile pepper plants varied among years, possibly due to differing levels of tuber infection or soil temperature, but was not affected by fumigation. The presence of M. incognita resulted in greater yellow nutsedge tuber germination and reproduction. The efficacy of 1,3-D for management of M. incognita in chile pepper production is likely to be reduced when nutsedges are present in high numbers, reinforcing the importance of managing these weeds and nematodes simultaneously.
Capsicum annuum; chile pepper; Cyperus esculentus; Cyperus rotundus; 1,3-dichloropropene; fumigant; management; Meloidogyne incognita; nematicide; perennial weed; purple nutsedge; root-knot nematode; tuber; yellow nutsedge
A sound knowledge of the genetic diversity among germplasm is vital for strategic germplasm collection, maintenance, conservation and utilisation. Genomic simple sequence repeats (SSRs) and random amplified microsatellite polymorphism (RAMPO) markers were used to analyse diversity and relationships among 48 pepper (Capsicum spp.) genotypes originating from nine countries. These genotypes covered 4 species including 13 germplasm accessions, 30 improved lines of 4 domesticated species and 5 landraces derived from natural interspecific crosses. Out of 106 SSR markers, 25 polymorphic SSR markers (24 %) detected a total of 76 alleles (average, 3.04; range, 2–5). The average polymorphic information content (PIC) was 0.69 (range, 0.29–0.92). Seventeen RAMPO markers produced 87 polymorphic fragments with average PIC of 0.63 (range, 0.44–0.81). Dendrograms based on SSRs and RAMPOs generated two clusters. All 38 Capsicum annuum genotypes and an interspecific landrace clustered together, whereas nine non-annuum (three Capsicum frutescens, one Capsicum chinense, one Capsicum baccatum and four interspecific landraces) genotypes clustered separately. Genetic variation within non-annuum genotypes was greater than the C. annuum genotypes. Distinctness of interspecific derivative landraces grown in northeast India was validated; natural crossing between sympatric Capsicum species has been proposed as the mechanism of their origin.
Electronic supplementary material
The online version of this article (doi:10.1007/s12298-013-0185-3) contains supplementary material, which is available to authorized users.
Capsicum; SSR; RAMPO; Interspecific derivatives; Sympatric population
Phenylalanine ammonia-lyase (PAL) is an inducible enzyme that responds to biotic and abiotic stresses. Results suggest the potential significance of pepper PAL1 in the plant defence response to microbial pathogens.
Phenylalanine ammonia-lyase (PAL) has a crucial role in secondary phenylpropanoid metabolism and is one of the most extensively studied enzymes with respect to plant responses to biotic and abiotic stress. Here, we identified the pepper (Capsicum annuum) PAL (CaPAL1) gene, which was induced in pepper leaves by avirulent Xanthomonas campestris pv. vesicatoria (Xcv) infection. CaPAL1-silenced pepper plants exhibited increased susceptibility to virulent and avirulent Xcv infection. Reactive oxygen species (ROS), hypersensitive cell death, expression of the salicylic acid (SA)-dependent marker gene CaPR1, SA accumulation, and induction of PAL activity were significantly compromised in the CaPAL1-silenced pepper plants during Xcv infection. Overexpression (OX) of CaPAL1 in Arabidopsis conferred increased resistance to Pseudomonas syringae pv. tomato (Pst) and Hyaloperonospora arabidopsidis infection. CaPAL1-OX leaves exhibited restricted Pst growth, increased ROS burst and cell death, and induction of PR1 expression and SA accumulation. The increase in PAL activity in healthy and Pst-infected leaves was higher in CaPAL1-OX plants than in wild-type Arabidopsis. Taken together, these results suggest that CaPAL1 acts as a positive regulator of SA-dependent defence signalling to combat microbial pathogens via its enzymatic activity in the phenylpropanoid pathway.
Arabidopsis; defence; pepper; phenylalanine ammonia-lyase; Xanthomonas campestris pv. Vesicatoria.
Systemic acquired resistance (SAR) can be elicited by virulent and avirulent pathogenic strains and SAR against plant-parasitic nematodes has been documented. Our objective was to determine whether co-infection of cotton by Meloidogyne incognita and Rotylenchulus reniformis affects the population level of either nematode compared to infection by each species individually. Split-root trials were conducted in which plants were inoculated with i) R. reniformis only, ii) M. incognita only, iii) both R. reniformis and M. incognita, or iv) no nematodes. Half of the root system was inoculated with R. reniformis or M. incognita on day 0 and the other half with M. incognita or R. reniformis on day 0 or day 14 depending on the experiment. Experiments were conducted on cotton cultivar DP 0935 B2RF (susceptible to both nematodes), LONREN-1 (germplasm line resistant to R. reniformis), and M-120 RNR (germplasm line resistant to M. incognita), and tests were terminated 8 wk after the last inoculation. Both soil (vermiform) and roots (egg) extracted from each half of the root system to determine the total nematode population levels, and root galling was rated on a 0 to 10 scale. Mixed models analysis and comparison of least squares means indicated no differences in root galling (except on LONREN-1) or population levels when the two nematode species were introduced on the same day. When M. incognita was introduced 14 d after R. reniformis, reduction in galling (36% on DP 0935 and 33% on LONREN-1) and M. incognita population levels (35% on DP 0935 and 45% on LONREN-1) were significant (P ≤ 0.05). When R. reniformis was inoculated 14 d after M. incognita, reduction in R. reniformis population levels (18% on DP 0935 and 26% on M-120) were significant. This study documents for the first time that infection of cotton by a nematode can elicit SAR to another nematode species.
Cotton; induced resistance; Meloidogyne incognita, reniform nematode; root-knot nematode; Rotylenchulus reniformis; split-root system; systemic acquired resistance
Four bean genotypes (IPA-1, A-107, A-211, and Calima), representing all possible combinations of resistance and susceptibility to Fusarium oxysporum f. sp. phaseoli (Fop) and Meloidogyne incognita, were each inoculated with three population densities of these pathogens. Calima and A-107 were resistant to Fop; A-107 and A-211 were resistant to M. incognita; and IPA-1 was susceptible to both pathogens. In Fop-susceptible lines (IPA-1 and A-211), the presence of M. incognita contributed to an earlier onset and increased severity of Fusarium wilt symptoms and plant stunting. However, the Fop-resistant Calima developed symptoms of Fusarium wilt only in the presence of M. incognita. Genotype A-107 (resistant to both M. incognita and Fop) exhibited Fusarium wilt symptoms and a moderately susceptible reaction to Fop only after the breakdown of its M. incognita resistance by elevated incubation temperatures (27 C). Root galling and reproduction of M. incognita was generally increased as inoculum density of M. incognita was increased on the M. incognita susceptible cultivars. However, these factors were decreased as the inoculum density of Fop was increased. It was concluded that severe infections of bean roots by M. incognita increase the severity of Fusarium wilt on Fop-susceptible genotypes and may modify the resistant reaction to Fop.
bean; Fusarium oxysporum f. sp. phaseoli; fusarium wilt; host resistance; interaction; Meloidogyne incognita; nematode; Phaseolus vulgaris; root galling; temperature