Genetics of resistance to Fusarium oxysporum f.sp. cucumerinum races 1 and 2 in cucumber line Wisconsin-2757

The mode of inheritance of resistance to Fusarium oxysporum f.sp. cucumerinum races 1 and 2 in Wisconsin-2757 (WI-2757), a gynoecious cucumber (Cucumis sativus L.), was determined by analysing segregation of F₁, F₂ and BC₁ populations of crosses with susceptible cultivar Straight-8. Resistance to either race 1 or race 2 in WI-2757 was conferred by a single dominant gene. In allelism tests, resistance to either race in WI-2757 was determined by the gene Fcu-1, which also confers resistance in line SMR-18.     

Fine genetic mapping localizes cucumber scab resistance gene <Emphasis Type="Italic">Ccu</Emphasis> into an <Emphasis Type="Italic">R</Emphasis> gene cluster

Scab, caused by Cladosporium cucumerinum, is an important disease of cucumber, Cucumis sativus. In this study, we conducted fine genetic mapping of the single dominant scab resistance gene, Ccu, with 148 F₉ recombinant inbred lines (RILs) and 1,944 F₂ plants derived from the resistant cucumber inbred line 9110Gt and the susceptible line 9930, whose draft genome sequence is now available. A framework linkage map was first constructed with simple sequence repeat markers placing Ccu into the terminal 670 kb region of cucumber Chromosome 2. The 9110Gt genome was sequenced at 5× genome coverage with the Solexa next-generation sequencing technology. Sequence analysis of the assembled 9110Gt contigs and the Ccu region of the 9930 genome identified three insertion/deletion (Indel) markers, Indel01, Indel02, and Indel03 that were closely linked with the Ccu locus. On the high-resolution map developed with the F₂ population, the two closest flanking markers, Indel01 and Indel02, were 0.14 and 0.15 cM away from the target gene Ccu, respectively, and the physical distance between the two markers was approximately 140 kb. Detailed annotation of the 180 kb region harboring the Ccu locus identified a cluster of six resistance gene analogs (RGAs) that belong to the nucleotide binding site (NBS) type R genes. Four RGAs were in the region delimited by markers Indel01 and Indel02, and thus were possible candidates of Ccu. Comparative DNA analysis of this cucumber Ccu gene region with a melon (C. melo) bacterial artificial chromosome (BAC) clone revealed a high degree of micro-synteny and conservation of the RGA tandem repeats in this region.     

Spectrum of resistance to root-knot nematodes and inheritance of heat-stable resistance in in pepper (Capsicum annuum L.)

Capsicum annuum L. has resistance to root-knot nematodes (RKN) (Meloidogyne spp.), severe polyphagous pests that occur world-wide. Several single dominant genes confer this resistance. Some are highly specific, whereas others are effective against a wide range of species. The spectrum of resistance to eight clonal RKN populations of the major Meloidogyne species, M. arenaria (2 populations), M. incognita (2 populations), M. javanica (1 population), and M. hapla (3 populations) was studied using eight lines of Capsicum annuum. Host susceptibility was determined by counting the egg masses (EM) on the roots. Plants were classified into resistant (R; EM ≤ 5) or susceptible (H; EM >5) classes. The french cultivar Doux Long des Landes was susceptible to all nematodes tested. The other seven pepper lines were highly resistant to M. arenaria, M. javanica and one population of M. hapla. Variability in resistance was observed for the other two populations of M. hapla. Only lines PM687, PM217, Criollo de Morelos 334 and Yolo NR were resistant to M. incognita. To investigate the genetic basis of resistance in the highly resistant line PM687, the resistance of two progenies was tested with the two populations of M. incognita: 118 doubled-haploid (DH) lines obtained by androgenesis from F₁ hybrids of the cross between PM687 and the susceptible cultivar Yolo Wonder, and 163 F₂ progenies. For both nematodes populations, the segregation patterns 69 R / 49 S for DH lines and 163 R / 45 S for F₂ progenies were obtained at 22°C and at high temperatures (32°C and 42°C). The presence of a single dominant gene that totally prevented multiplication of M. incognita was thus confirmed and its stability at high temperature was demonstrated. This study confirmed the value of C. annuum as a source of complete spectrum resistance to the major RKN. Received: 2 July 1998 / Accepted: 11 March 1999     

Transgenic cucumbers harboring the 54-kDa putative gene of Cucumber fruit mottle mosaic tobamovirus are highly resistant to viral infection and protect non-transgenic scions from soil infection

Cucumber fruit mottle mosaic tobamovirus (CFMMV) causes severe mosaic symptoms and yellow mottling on leaves and fruits and, occasionally, severe wilting of cucumber (Cucumis sativus L.) plants. No genetic source of resistance against this virus has been identified in cucumber. The gene coding for the putative 54-kDa replicase gene of CFMMV was cloned into an Agrobacterium tumefaciens binary vector, and transformation was performed on cotyledon explants of a parthenocarpic cucumber cultivar. R1 seedlings were screened for resistance to CFMMV by symptom expression, back inoculation on an alternative host and ELISA. From a total of 14 replicase-containing R1 lines, eight resistant lines were identified. Line I44 – homozygous for the putative 54-kDa replicase gene – was immune to CFMMV infection by mechanical and graft inoculation, and to root infection following planting in CFMMV-infested soil. A substantial delay of symptom appearance was observed following infection by three additional cucurbit-infecting tobamoviruses. When used as a rootstock, line I44 protected susceptible cucumber scions from soil infection by CFMMV. This paper is the first report on protection of a susceptible cultivar against a soil-borne viral pathogen, by grafting onto a transgenic rootstock.     

Mapping novel sources of leaf rust and stripe rust resistance introgressed from Triticum dicoccoides in cultivated tetraploid wheat background

Wild emmer wheat, Triticum dicoccoides, the progenitor of modern tetraploid and hexaploid wheats, is an important resource for new variability for disease resistance genes. T. dicoccoides accession pau4656 showed resistance against prevailing leaf rust and stripe rust races in India and was used for developing stable introgression lines (IL) in T. durum cv Bijaga yellow and named as IL pau16068. F₅ Recombinant inbred lines (F₅ RILs) were developed by crossing IL pau16068 with T. durum cultivar PBW114 and RIL population was screened against highly virulent Pt and Pst pathotypes at the seedling and adult plant stages. Inheritance analyses revealed that population segregated for two genes for all stage resistance (ASR) against leaf rust, one ASR gene against stripe rust and three adult plant resistance (APR) genes for stripe rust resistance. For mapping these genes a set of 483 SSR marker was used for bulked segregant analysis. The markers showing diagnostic polymorphism in the resistant and susceptible bulks were amplified on all RILs. Single marker analysis placed all stage leaf rust resistance genes on chromosome 6A and 2A linked to the SSR markers Xwmc256 and Wpaus268, respectively. Likewise one all stage stripe rust resistance gene were mapped on long arm of chromosome 6A linked to markers 6AL-5833645 and 6AL-5824654 and two APR genes mapped on chromosomes 2A and 2B close to the SSR marker Wpaus268 and Xbarc70, respectively. The current study identified valuable leaf rust and stripe rust resistance genes effective against multiple rust races for deployment in the wheat breeding programme.

     

Inheritance of resistance to watermelon mosaic virus in the cucumber line TMG-1: tissue-specific expression and relationship to zucchini yellow mosaic virus resistance

The inbred cucumber (Cucumis sativus L.) line TMG-1 is resistant to three potyviruses:zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and the watermelon strain of papaya ringspot virus (PRSV-W). The genetics of resistance to WMV and the relationship of WMV resistance to ZYMV resistance were examined. TMG-1 was crossed with WI-2757, a susceptible inbred line. F₁, F₂ and backcross progeny populations were screened for resistance to WMV and/or ZYMV. Two independently assorting factors conferred resistance to WMV. One resistance was conferred by a single recessive gene from TMG-1 (wmv-2). The second resistance was conferred by an epistatic interaction between a second recessive gene from TMG-1 (wmv-3) and either a dominant gene from WI-2757 (Wmv-4) or a third recessive gene from TMG-1 (wmv-4) located 20–30 cM from wmv-3. The two resistances exhibited tissue-specific expression. Resistance conferred by wmv-2 was expressed in the cotyledons and throughout the plant. Resistance conferred by wmv-3 + Wmv-4 (or wmv-4) was expressed only in true leaves. The gene conferring resistance to ZYMV appeared to be the same as, or tightly linked to one of the WMV resistance genes, wmv-3.     

Influence of vermicompost and cucumber cultivar on population growth of Aphis gossypii Glover

The melon aphid, Aphis gossypii Glover (Hem., Aphididae), is one of the most important pests of cucumber throughout the world. This aphid has a short generation time and high fecundity that result in an enormous reproductive potential, especially in cucumber‐growing greenhouses. Vermicomposts, which are produced by exploiting interactions between earthworms and microorganisms, may enhance plant growth and plant resistance against some pests and disease. In this study, the effects of vermicompost and cucumber cultivar (Cucumis sativus L.) on infestation levels with A. gossypii were evaluated. We conducted a factorial experiment with two cucumber cultivars (Royal and Storm) and five concentrations of vermicompost in the soil, including 0% (control), 10%, 20%, 30% and 50%, employing a randomized complete block design with four replicates. The experiment was conducted in a growth chamber at 25 ± 2°C, 65 ± 10% RH and a photoperiod of 14 L: 10 D h. The number of aphids was counted 3, 5, 7, 9, 12, 15, 18 and 21 days after infestation of cucumber seedlings by aphids. We found that in all vermicompost‐amended treatments, aphid numbers were lower than when plants were grown in soil without any vermicompost. The highest and lowest aphid counts occurred in the control treatment on cucumbers of the Royal cultivar and in the 30% and 50% vermicompost treatments on the storm cultivar, respectively. Overall, our study showed that the application of vermicompost has a high potential for reducing A. gossypii populations in cucumber cultures.     

QTL Mapping of Downy Mildew Resistance in an Introgression Line Derived from Interspecific Hybridization Between Cucumber and Cucumis hystrix

Downy mildew (DM), caused by Pseudoperonospora cubensis (Berk. & M.A. Curtis) Rostovzev, is a worldwide major disease of cucumbers (Cucumis sativus L.). By screening 10 introgression lines (ILs) derived from interspecific hybridization between cucumber and the wild Cucumis, C. hystrix, through a whole plant assay, one introgression line (IL52) was identified with high DM‐resistance. IL52 was further used as a resistant parent to make an F₂ population with ‘changchunmici’ (susceptible parent). The F₂ population (300 plants) was investigated for DM‐yellowing, DM‐necrosis and DM‐resistance in the adult stage. A genetic map spanning 642.5 cM with 104 markers was constructed and used for QTL analysis from the population. Three QTL regions were identified on chromosome 5 and chromosome 6. By interval mapping analysis, two QTLs for DM‐resistance were determined on chromosome 5 (DM_5.1 and DM_5.2), which explained 17.9% and 14.2% of the variation, respectively. QTLs for DM‐yellowing were in the same regions as DM‐resistance. For DM‐necrosis, by interval mapping analysis, one QTL was determined on chromosome 5 (Necr_5.1) that explained 18.3% of the variation and one on chromosome 6 (Necr_6.1) that explained 13.9% of the variation. Our results indicated that the identification of molecular markers linked to the QTLs could be further applied for marker‐assisted selection (MAS) of downy mildew resistance in cucumber.     

Comparative mapping of ZYMV resistances in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.)

Zucchini yellow mosaic virus (ZYMV) routinely causes significant losses in cucumber (Cucumis sativus L.) and melon (Cucumis melo L.). ZYMV resistances from the cucumber population TMG1 and the melon plant introduction (PI) 414723 show different modes of inheritance and their genetic relationships are unknown. We used molecular markers tightly linked to ZYMV resistances from cucumber and melon for comparative mapping. A 5-kb genomic region (YCZ-5) cosegregating with the zym locus of cucumber was cloned and sequenced to reveal single nucleotide polymorphisms and indels distinguishing alleles from ZYMV-resistant (TMG1) and susceptible (Straight 8) cucumbers. A low-copy region of the YCZ-5 clone was hybridized to bacterial artificial chromosome (BAC) clones of melon and a 180-kb contig assembled. One end of this melon contig was mapped in cucumber and cosegregated with ZYMV resistance, demonstrating that physically linked regions in melon show genetic linkage in cucumber. However the YCZ-5 region segregated independently of ZYMV resistance loci in two melon families. These results establish that these sources of ZYMV resistances from cucumber TMG1 and melon PI414723 are likely non-syntenic.     

SSR markers closely associated with genes for resistance to root-knot nematode on chromosomes 11 and 14 of Upland cotton

Molecular markers closely linked to genes that confer a high level of resistance to root-knot nematode (RKN) [Meloidogyne incognita (Kofoid & White) Chitwood] in cotton (Gossypium hirsutum L.) germplasm derived from Auburn 623 RNR would greatly facilitate cotton breeding programs. Our objectives were to identify simple sequence repeat (SSR) markers linked to RKN resistance quantitative trait loci (QTL) and map these markers to specific chromosomes. We developed three recombinant inbred line (RIL) populations by single seed descent from the crosses of RKN-resistant parents M-240 RNR (M240), developed from the Auburn 623 RNR source, moderately resistant Clevewilt 6 (CLW6), one of the parents of Auburn 623 RNR, and susceptible parent Stoneville 213 (ST213). These crosses were CLW6 × ST213, M240 × CLW6, and M240 × ST213. RILs from these populations were grown under greenhouse conditions, inoculated with RKN eggs, scored for root gall index, eggs plant⁻¹, and eggs g⁻¹ root. Plants were also genotyped with SSR markers. Results indicated that a minimum of two major genes were involved in the RKN resistance of M240. One gene was localized to chromosome 11 and linked to the marker CIR 316-201. This CIR 316-201 allele was also present in CLW6 but not in Mexico Wild (MW) (PI593649), both of which are parents of Auburn 623 RNR. A second RKN resistance gene was localized to the short arm of chromosome 14 and was linked to the SSR markers BNL3545-118 and BNL3661-185. These two marker alleles were not present in CLW6 but were present in MW. Our data also suggest that the chromosome 11 resistance QTL primarily affects root galling while the QTL on chromosome 14 mediates reduced RKN egg production. The SSRs identified in this study should be useful to select plants with high levels of RKN resistance in segregating populations derived from Auburn 623 RNR.     

Multiple alleles for zucchini yellow mosaic virus resistance at the zym locus in cucumber

 Sources of resistance to several potyviruses have been identified and characterized within the cucumber (Cucumis sativus L.) germplasm. Resistance to zucchini yellow mosaic virus (ZYMV) is present in inbred lines derived from the Dutch hybrid Dina (Dina-1) and from the Chinese cultivar ‘Taichung Mou Gua’ (TMG-1). Tests of allelism indicated that the genes for resistance to ZYMV in TMG-1 and Dina-1 are at the same locus; however, the two genotypes exhibited different phenotypes in response to cotyledon inoculation with ZYMV. Dina-1 exhibited a distinct veinal chlorosis and accumulation of virus limited to the first and/or second true leaves, while TMG-1 remained symptom-free and did not accumulate virus. The distinct veinal chlorosis phenotype in Dina-1 was dominant to the symptom-free phenotype in TMG-1 and was shown not to be due to a separate gene. These results indicate that a series of alleles differing in effectiveness and dominance relationships occurs at the zym locus such that Zym>zym ^Dina>zym ^TMG-1. In addition to ZYMV resistance, TMG-1 is also resistant to watermelon mosaic virus (WMV), the watermelon strain of papaya ringspot virus (PRSV-W) and the Moroccan watermelon mosaic virus (MWMV); the WMV and MWMV resistances are at the same locus, or tightly linked to the zym locus. Dina-1 also was found to be resistant to PRSV-W and MWMV. The gene for MWMV resistance in Dina-1 appeared to be at the same locus or tightly linked (<1% recombination) to the gene for ZYMV resistance. In contrast to the response to ZYMV inoculation, Dina-1 does not exhibit distinct veinal chlorosis when inoculated with PRSV-W or MWMV. Collectively, these observations suggest that the gene(s) conferring resistance to ZYMV, WMV, and MWMV may be part of a gene cluster for potyvirus resistance in cucumber. Received: 12 November 1996 / Accepted: 25 April 1997     

Identification of peanut (Arachis hypogaea L.) RAPD markers diagnostic of root-knot nematode (Meloidogyne arenaria (Neal) Chitwood) resistance

DNA markers linked to a root-knot nematode resistance gene derived from wild peanut species have been identified. The wild diploid peanut accessions K9484 (Arachis batizocoi Krapov. & W. C. Gregory), GKP10017, (A. cardenasii Krapov & W. C. Gregory), and GKP10602 (A. diogoi Hoehne) possess genes for ressitance to Meloidogyne arenaria. These three accessions and A. hypogaea cv. Florunner were crossed to generate the hybrid resistant breeding line TxAg-7. This line was used as donor parent to develop a BC₄F₂ population segregating for resistance. Three RAPD markers associated with nematode resistance were identified in this population by bulked segregant analysis. Linkage was confirmed by screening 21 segregatingh BC₄F₂ and 63 BC₅F₂ single plants. Recombination between marker RKN410 and resistance, and between marker RKN440 and resistance, was estimated to be 5.4±1.9% and 5.8±2.1%, respectively, on a per-generation basis. These two markers identified a resistance gene derived from either A. cardenasii or A. diogoi, and were closely linked to each other. Recombination between a third marker, RKN229, inherited from A. cardenasii or A. diogoi, and resistance was 9.0±3.2% per generation. Markers RKN410 and RKN229 appeared to be linked genetically and flank the same resistance gene. All markers were confirmed by hybridization of cloned or gel-purified marker DNA to blots of PCR-amplified DNA. Pooled data on the segregation of BC₅F₂ plants was consistent with the presence of one resistance gene in the advanced breeding lines. Different distributions of resistance in the BC₅F₂ progeny and TxAG-7 suggest the presence of additional resistance genes in TxAG-7.     

Characterization of sources of resistance to the watermelon strain of Papaya ringspot virus in cucumber: allelism and co-segregation with other potyvirus resistances

At least three sources of resistance to the watermelon strain of Papaya ringspot virus (PRSV-W) have been identified in cucumber (Cucumis sativus L.) including: ’TMG-1’, an inbred line derived from the Taiwanese cultivar, ’Taichung Mou Gua’; ’Dina-1’, an inbred line derived from the Dutch hybrid ’Dina’; and the South American cultivar ’Surinam’. In this investigation we sought to determine the inheritance of resistance to PRSV-W in ’Dina-1’, the allelic relationships among the three sources of PRSV-W resistance, and the relationship between PRSV-W resistance and known resistances to other cucurbit potyviruses. Like ’Surinam’ and ’TMG-1’, resistance in ’Dina-1’ is controlled by a single gene. Despite differences in dominance vs recessive performance and patterns of virus accumulation, all three sources of resistance complemented each other. ’TMG-1’ and ’Dina-1’ also possess co-segregating, single-gene resistances to Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus and Moroccan watermelon mosaic virus. Sequential inoculations and F₃ family analysis indicated that resistance to PRSV-W completely co- segregated with resistance to ZYMV in ’TMG-1’. Although PRSV-W resistances are at the same locus in both ’TMG-1’ and ’Surinam’, ’Surinam’ is only resistant to PRSV-W, and progeny of ’TMG-1’×’Surinam’ were resistant to PRSV-W but susceptible to ZYMV. Susceptibility to ZYMV and resistance to PRSV-W in ’Surinam’ was not influenced by co-inoculation or sequential in- oculations of the two viruses. Collectively, the co- segregation of resistances to PRSV-W, ZYMV, WMV and MWMV in ’TMG-1’ (within 1 cM), allelism of PRSV-W resistances in ’TMG-1’ and ’Surinam’, and resistance to only PRSV-W in ’Surinam’, suggest that multiple potyvirus resistance in cucumber may be due to different alleles of a single potyvirus resistance gene with differing viral specificities, or that the multiple resistances are conferred by a tightly linked cluster of resistance genes, of which ’Surinam’ only possesses one member. Received: 22 July 1999 / Accepted: 2 December 1999     

Inheritance and mapping of the ore gene controlling the quantity of β-carotene in cucumber (Cucumis sativus L.) endocarp

The metabolic precursor of vitamin A, ??-carotene, is essential for human health. The gene(s) controlling ??-carotene quantity (Q??C) has been introgressed from Xishuangbanna gourd (XIS, possessing ??-carotene; Cucumis sativus L. var. xishuangbannanesis Qi et Yuan; 2n?=?2x?=?14) into cultivated cucumber (no ??-carotene; Cucumis sativus L.). To determine the inheritance of Q??C in cucumber fruit endocarp, F1 progeny and a set of 124 F7 recombinant inbred lines (RILs) derived from the cultivated cucumber line CC3 and XIS line SWCC8 were evaluated for Q??C during 2009 and 2010 in Nanjing, China. Segregation analysis revealed that endocarp Q??C of greenhouse-grown fruit was controlled by a single recessive gene. Further, marker analysis indicated the gene controlling Q??C was linked to seven SSR markers on linkage group 3, where their order was SSR20710?CSSR19511?CSSR15419?CSSR07706?Core?CSSR23231?CSSR11633?CSSR20270. These markers and the putative candidate gene were mapped to cucumber chromosome 3DS. An evaluation of 30 genetically diverse cucumber lines indicated that marker SSR07706 has utility in further genetic analyses of the Q??C orange endocarp gene, designated ore. Moreover, the markers defined herein may have utility for marker-assisted selection directed towards the development of cucumber germplasm with high fruit ??-carotene content.     

Management of Fusarium oxysporum f. sp. lycopersici and root-knot nematode disease complex in tomato by use of antagonistic fungi,plant resistance and neem

Simultaneous infestation with root-knot nematodes (RKN) and Fusarium oxysporum f. sp. lycopersici (FOL) leads to formation of a disease complex that increases crop losses than effect of either RKN or FOL. In this study a management programme involving plant resistance, biological control agents, and neem was carried out to manage RKN and fusarium wilt disease complex. The biological control agents were Purpureocillium lilacinum (PL) and Trichoderma harzianum (TH) while the RKN was Meloidogyne javanica. In vitro dual culture plates were set up to test the interaction of biological control agents and FOL. Greenhouse experiments were conducted using two tomato cultivars Rambo F1 and Prostar F1. The treatments were; PL, TH, PL–TH, neem, PL neem, TH neem, and PL–TH neem. Each treatment was replicated four times and the treatments set up in a randomised complete block design in the greenhouse. Inhibition of FOL mycelial growth by TH and PL was 51.9%, and 44% respectively by the ninth day in vitro culture plates. In the cultivar, Prostar F1, the treatments PL–TH, PL, and TH in the presence or absence of neem had a FOL disease severity score significantly lower than the untreated control. Host resistance sufficed to prevent infection of Rambo F1 with FOL. The treatments PL–TH, PL and TH reduced FOL propagules and M. javanica juveniles in the roots and performed even better when combined with neem in both tomato cultivars. Therefore, a host that is resistant combined with biological control agents and organic amendments can be used in the management of RKN and FOL in tomato production.     

EFFECTS OF ULTRAVIOLET-B RADIATION ON FUNGAL DISEASE DEVELOPMENT IN CUCUMIS SATIVUS

Three cucumber (Cucumis sativus L.) cultivars were exposed to a daily dose of 11.6 kJ m^-2biologically effective ultraviolet-B (UV-B_Be) radiation in an unshaded greenhouse before and/ or after infection by Colletotrichum lagenarium (Pass.) Ell. and Halst. or Cladosporium cucumerinum Ell. and Arth. and analyzed for disease development. Two of these cultivars, Poinsette and Calypso Hybrid, were disease resistant, while the third cultivar, Straight-8, was disease susceptible. Preinfectional treatment of 1 to 7 days with UV-B_BE in Straight-8 led to greater severity of both diseases. Postinfectional UV treatment did not lead to increased disease severity caused by C. lagenarium, while preinfectional UV treatment in both Straight-8 and Poinsette substantially increased disease severity. Although resistant cultivars Poinsette and Calypso Hybrid showed increased anthracnose disease severity when exposed to UV-B, this effect was apparent only on the cotyledons. Both higher spore concentration and exposure to UV-B radiation resulted in greater disease severity. Of the cucumber cultivars tested for UV-B sensitivity, growth in Poinsette was most sensitive and Calypso Hybrid was least sensitive. These preliminary results indicate that the effects of UV-B radiation on disease development in cucumber vary depending on cultivar, timing and duration of UV-B exposure, inoculation level, and plant age.     

Strain-specific and recessive QTLs involved in the control of partial resistance to Fusarium oxysporum f. sp. melonis race 1.2 in a recombinant inbred line population of melon

Fusarium oxysporum f. sp. melonis (FOM) causes serious economic losses in melon (Cucumis melo L.). Two dominant resistance genes have been identified, Fom-1 and Fom-2, which provide resistance to races 0 and 2 and races 0 and 1, respectively, however FOM race 1.2 overcomes these resistance genes. A partial resistance to FOM race 1.2 that has been found in some Far East accessions is under polygenic control. A genetic map of melon was constructed to tag FOM race 1.2 resistance with DNA markers on a recombinant inbred line population derived from a cross between resistant (Isabelle) and susceptible (cv. Védrantais) lines. Artificial root inoculations on plantlets of this population using two strains, one that causes wilting (FOM 1.2w) and one that causes yellowing (FOM 1.2y), resulted in phenotypic and genotypic data that enabled the identification of nine quantitative trait loci (QTLs). These QTLs were detected on five linkage groups by composite interval mapping and explained between 41.9% and 66.4% of the total variation. Four digenic epistatic interactions involving seven loci were detected and increased the total phenotypic variation that was explained. Co-localizations between QTLs and resistance gene homologs or resistance genes, such as Fom-2 and Vat, were observed. A strain-specific QTL was detected, and some QTLs appeared to be recessive.     

黄瓜转新型抗菌蛋白基因GNK2-1及其抗枯萎病的研究

GNK2-1为一种来自银杏(Ginkgo biloba)种仁的新型抗真菌蛋白, 具有较强的真菌抗性且性质稳定。序列分析表明,其结构与所有已知的抗真菌蛋白不同, 而与富含半胱氨酸的植物类受体激酶的胞外结构域相似。为探索GNK2-1基因在黄瓜(Cucumis sativus)抗病反应中的作用, 利用基因重组技术构建了GNK2-1的高效组成型表达载体, 并利用根癌农杆菌(Agrobacterium tumefaciens)介导转入黄瓜栽培品种农城3号(Cucumis sativus ‘Nongcheng No.3’)基因组中。通过对获得的抗性植株进行PCR、RT-PCR和Western blot检测分析, 结果表明GNK2-1基因可在T₀代转基因植株中转录表达, 并能在T₁代转基因黄瓜中稳定遗传。离体枯萎病抗性鉴定结果表明, 转GNK2-1基因的黄瓜对枯萎病的抗性增强, GNK2-1可以作为黄瓜抗病性改良的潜在基因资源。     

Inheritance and genetic linkage of fusarium wilt {Fusarium oxysporum f.sp. cucumerinum race 1) and scab {Cladosporium cucumerinum) resistance genes in cucumber (Cucumis sativus)

The inheritance of resistance of the cucumber cv. SMR 18 to the race 1 of Fusarium oxysporum f.sp. cucumerinum, the linkage relationship between resistance to race 1 of F. oxysporum f.sp. cucumerinum, resistance to Cladosporium cucumerinum and fruit spine colour, and the reactions of several cucumber cultivars to inoculations with race 1 of F. oxysporum f.sp. cucumerinum and C. cucumerinum were examined. The inbred line Straight 8 (P,), which has white fruit spines and is susceptible to both fusarium wilt and scab was crossed with the inbred line SMR 18 (P₂), which has black fruit spines and resistance to both diseases. When F, F₂, F₃, BC₁P₁ BC₁P₂ and BC₁P₁ selfed progenies were inoculated at the cotyledon stage with a suspension of spores of race 1 of F. oxysporum f.sp. cucumerinum, the ratios of resistant to susceptible plants indicated that resistance was conferred by a single dominant gene, designated Fcu-1. When 171 BC^! plants were selfed and from each resulting F₂ family different groups of 15–25 seedlings each were tested for resistance to either disease, segregation data indicated that the Fcu-1 locus and the Ccu locus for C. cucumerinum resistance were completely linked. No evidence for linkage was found between the Fcu-1 (Ccu) locus and the B locus for fruit spine colour. Among the 59 cultivars tested at the seedling stage, 15 were susceptible, while the remainder were highly resistant to inoculations with both pathogens.