Evaluation of Cucurbita pepo Accessions for Crown Rot Resistance to Isolates of Phytophthora capsici

in HortScience

Phytophthora capsici causes several disease syndromes on Cucurbita pepo L. (squash, pumpkin, and gourd), including crown rot, foliar blight, and fruit rot, which can lead up to 100% crop loss. Currently, there are no C. pepo cultivars resistant or tolerant to this pathogen, which can aid in disease management strategies. The objective of this study was to evaluate a select group of C. pepo accessions for resistance to the crown rot syndrome of P. capsici. One hundred fifteen C. pepo accessions, from 24 countries, were evaluated for their disease response to inoculation with a suspension of three highly virulent P. capsici isolates from Florida. Replications of each accession, including susceptible controls, were planted in the greenhouse using a randomized complete block design. At the second to third true leaf stage, each seedling was inoculated at their crown with a 5-mL P. capsici suspension of 2 × 104 zoospores/mL. Fourteen days after inoculation, the plants were visually rated on a scale ranging from 0 (no symptoms) to 5 (plant death). Mean disease rating scores (DRS) and sds were calculated for each accession and ranged from 1.3 to 5.0 and 0 to 2.0, respectively. Eight accessions with the lowest mean DRS were rescreened. Results paralleled those of the initial study with one accession, PI 181761, exhibiting the lowest mean DRS at 0.5. Further screening and selection of accessions from the C. pepo germplasm collection should aid in the development of breeding lines and cultivars with resistance to crown rot caused by P. capsici.

Abstract

Phytophthora capsici causes several disease syndromes on Cucurbita pepo L. (squash, pumpkin, and gourd), including crown rot, foliar blight, and fruit rot, which can lead up to 100% crop loss. Currently, there are no C. pepo cultivars resistant or tolerant to this pathogen, which can aid in disease management strategies. The objective of this study was to evaluate a select group of C. pepo accessions for resistance to the crown rot syndrome of P. capsici. One hundred fifteen C. pepo accessions, from 24 countries, were evaluated for their disease response to inoculation with a suspension of three highly virulent P. capsici isolates from Florida. Replications of each accession, including susceptible controls, were planted in the greenhouse using a randomized complete block design. At the second to third true leaf stage, each seedling was inoculated at their crown with a 5-mL P. capsici suspension of 2 × 104 zoospores/mL. Fourteen days after inoculation, the plants were visually rated on a scale ranging from 0 (no symptoms) to 5 (plant death). Mean disease rating scores (DRS) and sds were calculated for each accession and ranged from 1.3 to 5.0 and 0 to 2.0, respectively. Eight accessions with the lowest mean DRS were rescreened. Results paralleled those of the initial study with one accession, PI 181761, exhibiting the lowest mean DRS at 0.5. Further screening and selection of accessions from the C. pepo germplasm collection should aid in the development of breeding lines and cultivars with resistance to crown rot caused by P. capsici.

The oomycetous pathogen, Phytophthora capsici Leonian, infects a wide range of plant taxa involving more than 49 species (Erwin and Ribeiro, 1996). Oospores, the sexual stage of P. capsici, can survive in the soil, in crop debris, and in certain weeds for long periods of time (French-Monar et al., 2006; Hausbeck and Lamour, 2004; Zitter et al., 1996). The asexual zoospores of P. capsici contained in sporangia can be dispersed across a field by rain drops and irrigation water in a relatively short period of time. Given optimal conditions, an entire field of crops can be devastated by P. capsici in a matter of days (Roberts et al., 2001; Zitter et al., 1996).

The incidence of disease caused by P. capsici on cucurbits has increased in vegetable production regions of the United States with reported yield loss as high as 100% (Hausbeck and Lamour, 2004; Tian and Babadoost, 2004). The increased occurrence and severity of P. capsici has prompted research for fungicide management alternatives and interest in breeding cucurbits for resistance or tolerance (Babadoost, 2000; French-Monar et al., 2005; Hausbeck and Lamour, 2004; Keinath, 2007; McGrath, 2004; Seebold and Horten, 2003; Stevenson et al., 2000, 2001; Tian and Babadoost, 2004; Waldenmaier, 2004).

Cucurbita pepo L. (pumpkin, squash, gourd) is an economically important group of the Cucurbitaceae (Paris et al., 2003). Eight cultivar groups of edible-fruited domesticates of C. pepo have been described (Paris, 1986), which includes pumpkin, cocozelle, vegetable marrow, zucchini, acorn, scallop, crookneck, and straightneck. Phytophthora capsici can infect C. pepo at any growth stage and is capable of causing crown rot, foliar blight, and fruit rot (Roberts et al., 2001; Zitter et al., 1996). Crown rot appears at the soil line causing stems to turn dark brown, become water-soaked, and quickly collapse causing plant death. Foliar symptoms appear as rapidly expanding, water-soaked lesions. Dieback of shoot tips, wilting, shoot rot, and plant death quickly follows initial infection. Fruit, which can be infected at any stage of maturity, may exhibit sunken, brown, water-soaked areas, which are rapidly covered by white sporangial growth under moist environmental conditions. Currently, there are no C. pepo cultivars resistant or tolerant to P. capsici (Hausbeck and Lamour, 2004).

Germplasm collections are valuable sources of beneficial genes, including resistance or tolerance to numerous plant pathogens. The C. pepo germplasm collection maintained at the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), Ames, IA, has more than 900 C. pepo accessions available for evaluation. Although P. capsici causes several disease syndromes on C. pepo, the objective of this study was to evaluate a select group of C. pepo accessions for resistance to the crown rot syndrome of P. capsici.

Materials and Methods

Plant material.

Because no core collection representing C. pepo has been established to date, accessions selected for this study were based on two criteria, fruit type and geographic location. Based on NCRPIS descriptors, accessions with oblong yellow fruit were chosen. In addition, randomly chosen representatives from each geographic location of the collection with at least two accessions were selected. Overall, the 115 accessions selected represented 24 countries. Susceptible controls used in this study were C. pepo ‘Early Prolific Straightneck’ and ‘Yellow Summer Squash’.

Phytophthora capsici isolates and inoculum preparation.

Three highly virulent P. capsici mating type A1 isolates (01-1938A, RJM98-730, and RJM98-805) collected from squash were obtained from Dr. P. Roberts (SWREC, Immokalee, FL). Inoculum was prepared using a modified procedure based on Mitchell et al. (1978), Mitchell (1978), and Mitchell and Kannwischer-Mitchell (1992). For each P. capsici isolate, one 5-mm mycelial plug from cornmeal agar was transferred to a 20% clarified V8 agar plate. After 7 d of growth at room temperature, 10 5-mmV8 agar mycelial plugs from each plate were placed into a 20% clarified V8 broth plate to grow for an additional 7 d in a 28 °C incubator. The V8 broth was then drained and each plate was washed two times with sterilized distilled water. Sterilized distilled water was added to cover mycelial growth in all plates, which were then placed under incandescent lights at 28 to 30 °C to induce sporangial development. After 24 h, sporangia were chilled at 4 °C for 45 min to induce zoospore release. The mycelia from each plate were strained through cheesecloth and a 1-ml encysted zoospore sample was counted using a hemacytometer. A suspension of the three isolates, containing equal portions of each, was prepared at a concentration of 2 × 104 zoospores/mL.

Greenhouse studies, inoculation, and scoring for response to inoculation.

The selected C. pepo accessions were evaluated in two separate studies. The first study evaluated accessions based on fruit type (71 accessions). The second study evaluated accessions based on geographic location (44 accessions). For each study, a randomized complete block design was used. Eight blocks containing a single seed of each accession and the two susceptible controls were sown in standard 18-cell flats containing Fafard #3S potting mix (Fafard Inc., Agawam, MA). Not all of the 115 accessions germinated in all eight replications. Greenhouse temperatures were maintained between 19 to 34 °C. Seedlings were watered daily and at the cotyledon stage, each received 1 g of slow-release fertilizer (Osmocote 14N–14P–14K; Grace Sierra Horticulture Products, Milpitas, CA). At the second to third true leaf stage, each seedling was inoculated at its crown with 5 mL of the 2 × 104 zoospores/mL suspension of P. capsici. Before inoculation, the potting mix was watered and remained saturated for 24 to 36 h to optimize the zoospore infection process. Fourteen days after inoculation, the plants were visually rated based on a scale ranging from 0 to 5 in which 0 = no symptoms, 1 = small brown lesion at base of stem, 2 = lesion has progressed up to the cotyledons causing constriction at the base, 3 = plant has partially collapsed with apparent wilting of leaves, 4 = plant has completely collapsed with severe wilting present, and 5 = plant death. A mean disease rating score (DRS), calculated as a weighted average, and sds were calculated for each accession and the susceptible controls. A third test was performed to rescreen accessions from the first two studies exhibiting a mean DRS of less than 2. Eight replications consisting of one plant of each of these accessions and the susceptible control ‘Yellow Summer Squash’ were planted in a randomized complete block design, inoculated, and visually rated for their response to P. capsici as described previously. Mean DRSs and sds were calculated for each of the rescreened accessions and the susceptible control.

Results and Discussion

Mean DRSs to crown inoculation with P. capsici among the 115 accessions ranged from 1.3 to 5 (Table 1). Average standard deviation of DRSs within accessions was 1.1 and ranged from 0 to 2. Thirteen accessions (11.3%) had at least 50% of their replicates with disease ratings of 0 or 1. Eight of these had a mean DRS of less than 2. These eight accessions were chosen for rescreening (Table 2). Results of the rescreen study paralleled those of the initial study in that the mean DRSs among the accessions remained less than 2 and the average sd was 1.4. PI 181761 exhibited the lowest mean DRS at 0.5 with all plants in this accession rated as either 0 or 1. These findings suggest that accessions within the C. pepo collection are worth considering as potential sources of resistance to P. capsici.

Table 1.

Response of Cucurbita pepo accessions to a suspension of Phytophthora capsici isolates from Floridaz.

Table 1.Table 1.
Table 2.

Response of eight selected accessions of Cucurbita pepo to a suspension of Phytophthora capsici isolates from Florida.

Table 2.

In this study, all accessions collected in the United States were susceptible to the suspension of P. capsici isolates from Florida. Based on the origin of the eight accessions chosen for rescreening, four were obtained from Germany and Turkey. Evaluating additional accessions from Asia, Europe, and Mexico in the future might be worthwhile.

The findings from these tests suggest that heterogeneity for resistance to P. capsici crown rot may be present within the C. pepo accessions evaluated. Many cucurbit accessions are maintained by open or sib pollination; therefore, heterogeneity for a particular trait among its individuals may exist. Screening and continuous selection of individuals originating from cucurbit accessions can lead to breeding lines homogeneous for particular trait(s). This approach was used to develop the melon race one powdery mildew [Podosphaera xanthii (syn. Sphaerotheca fuliginea auct. p.p.)] resistant watermelon (Citrullus lanatus var. lanatus) line, PI 525088-PMR (Davis et al., 2006).

Phytophthora capsici can cause disease on all plant tissue of susceptible hosts. Disease on each of these tissues can be considered a separate disease syndrome, i.e., crown rot, root rot, foliar blight, and fruit rot. Different genetic mechanisms may be responsible for host resistance to the various syndromes. This is the case with root rot and foliar blight resistance in pepper (Capsicum annuum var. annuum) (Walker and Bosland, 1999). A similar situation exists in the host–pathogen interaction of P. infestans and potato (Solanum tuberosum L.). Different genes are responsible for the resistances in tubers, vines, and foliage of the potato plant (Budin et al., 1978; Howard, 1978).

Physiological races within the P. capsici–C. annuum interaction have been identified (Glosier et al., 2008; Oelke et al., 2003). Pathogen races are important in pepper breeding as cultivars resistant to P. capsici isolates found in specific growing regions continue to be developed. Although we have tentatively identified resistance to isolates of P. capsici from Florida in C. pepo, additional studies will be performed to evaluate the Phytophthora crown rot-resistant lines against isolates from around the world. If physiological races within the P. capsiciC. pepo interaction are identified, it will play an important role in breeding for Phytophthora resistance of the edible-fruited domesticates of C. pepo.

Results from this study indicate that there is potential resistance to P. capsici crown rot within C. pepo accessions. Through screening and selection, the development of C. pepo lines homozygous for P. capsici resistance will allow us to study the inheritance of resistance, evaluate the P. capsiciC. pepo interaction, and create Phytophthora crown rot resistant cultivars to aid in disease management of this pathogen. Further studies are also necessary to evaluate the Phytophthora crown rot-resistant C. pepo breeding lines developed from this study for their response to Phytophthora foliar blight and fruit rot.

Literature Cited

  • BabadoostM.2000Outbreak of Phytophthora foliar blight and fruit rot in processing pumpkin field in IllinoisPlant Dis.841345

  • BudinK.Z.BrokshV.L.KhromtsovaM.M.1978Resistance to Phytophthora infection in hybrids obtained from crosses of the dihaploid S. tuberosum L. with wild and cultivated forms of Solanum168177KamerazA.Y.Systemics breeding and seed production of potatoesAmerind Publishing Co. Pvt. LtdNew Delhi, India

    • Search Google Scholar
    • Export Citation
  • DavisA.R.LeviA.WehnerT.PitratM.2006PI 525088-PRM, a melon race 1 powdery mildew-resistant watermelon lineHortScience4115271528

  • ErwinD.C.RibeiroO.K.1996Phytophthora diseases worldwideAPS PressSt. Paul, MN

    • Export Citation
  • French-MonarR.JonesJ.RobertsP.2006Characterization of Phytophthora capsici associated with roots of weeds on Florida vegetable farmsPlant Dis.90345350

    • Search Google Scholar
    • Export Citation
  • French-MonarR.RobertsP.JonesJ.2005Insensitivity of isolates of Phytophthora capsici to mefanoxam in southeast FloridaPhytopathology.95S31S32

    • Search Google Scholar
    • Export Citation
  • GlosierB.R.OgundiwinE.A.SidhuG.S.SischoD.R.PrinceJ.P.2008A differential series of pepper (Capsicum annuum) lines delineates fourteen physiological races of Phytophthora capsici Euphytica1622330

    • Search Google Scholar
    • Export Citation
  • HausbeckM.K.LamourK.H.2004 Phytophthora capsici on vegetable crops: Research progress and management challengesPlant Dis.8812921303

  • HowardH.W.1978The production of new varieties607646HarrisP.M.The potato cropChapman & HallLondon, UK

  • KeinathA.P.2007Sensitivity of isolates of Phytophthora capsici from South Carolina to mefenoxam, dimethomorph, zoxamide and cymoxanilPlant Dis.91743748

    • Search Google Scholar
    • Export Citation
  • McGrathM.T.2004Evaluation of fungicides for managing Phytophthora blight of squash, 2003. Fungicide nematicide tests 59:V0547 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2004/V054.pdf>.

    • Export Citation
  • MitchellD.J.1978Relationships of inoculum levels of several soilborne species of Phytophthora and Phythium to infection of several hostsPhtyopathology6817541759

    • Search Google Scholar
    • Export Citation
  • MitchellD.J.Kannwischer-MitchellM.E.1992 Phytophthora 3138SingletonL.L.MihailJ.D.RushC.M.Methods for research on soilborne phytopathogenic fungiAmerican Phytopathological SocietySt. Paul, MN

    • Export Citation
  • MitchellD.J.Kannwischer-MitchellM.E.MooreE.S.1978Relationship of numbers of Phytophthora cryptogea zoospores to infection and mortality of watercressPhytopathology6814461448

    • Search Google Scholar
    • Export Citation
  • OelkeL.M.BoslandP.W.SteinerR.2003Differentiation of race specific resistance to phytophthora root rot and foliar blight in Capsicum annuum J. Amer. Soc. Hort. Sci.128213218

    • Search Google Scholar
    • Export Citation
  • ParisH.S.1986A proposed subspecific classification for Cucurbita pepo Phytologia61133138

  • ParisH.S.YonashN.PortnoyV.Mozes-DaubeN.TzuriG.KatzirN.2003Assessment of genetic relationships in Cucurbita pepo (Cucurbitaceae) using DNA markersTheor. Appl. Genet.106971978

    • Search Google Scholar
    • Export Citation
  • RobertsP.D.McGovernR.J.KucharekT.A.MitchellD.J.2001Vegetable diseases caused by Phytophthora capsici in Florida. UF/IFAS EDIS publication10 Dec. 2007.<http://edis.ufl.edu>.

    • Export Citation
  • SeeboldK.W.HortenT.B.2003Evaluation of fungicides for control of Phytophthora crown and fruit rot of summer squash, 2002. Fungicide nematicide tests. 58:V0989 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2003/V098.pdf>.

    • Export Citation
  • StevensonW.R.JamesR.V.RandR.E.2000Evaluation of selected fungicides to control Phytophthora blight and fruit rot of cucumber. Fungicide nematacide tests. 55:1637 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2001/V16.pdf>.

    • Export Citation
  • StevensonW.R.JamesR.V.RandR.E.2001Evaluation of selected fungicides to control Phytophthora blight and fruit rot of cucumber. Fungicide nematacide tests. 56:V167 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2001/V16.pdf>

    • Export Citation
  • TianD.BabadoostM.2004Host range of Phytopthora capsici from pumpkin and pathogenicity of isolatesPlant Dis.88485489

  • WaldenmaierC.M.2004Evaluation of fungicides for control of pumpkin diseases, 2003. Fungicide nematicide tests, 59:V0649 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2004/V064.pdf>.

    • Export Citation
  • WalkerS.J.BoslandP.W.1999Inheritance of Phytophthora root rot and foliar blight resistance in pepperJ. Amer. Soc. Hort. Sci.1241418

  • ZitterT.A.HopkinsD.L.ThomasC.E.1996Compendium of cucurbit diseasesAPS PressSt. Paul, MN

If the inline PDF is not rendering correctly, you can download the PDF file here.

Contributor Notes

To whom reprint requests should be addressed; e-mail ekabelka@ufl.edu

  • BabadoostM.2000Outbreak of Phytophthora foliar blight and fruit rot in processing pumpkin field in IllinoisPlant Dis.841345

  • BudinK.Z.BrokshV.L.KhromtsovaM.M.1978Resistance to Phytophthora infection in hybrids obtained from crosses of the dihaploid S. tuberosum L. with wild and cultivated forms of Solanum168177KamerazA.Y.Systemics breeding and seed production of potatoesAmerind Publishing Co. Pvt. LtdNew Delhi, India

    • Search Google Scholar
    • Export Citation
  • DavisA.R.LeviA.WehnerT.PitratM.2006PI 525088-PRM, a melon race 1 powdery mildew-resistant watermelon lineHortScience4115271528

  • ErwinD.C.RibeiroO.K.1996Phytophthora diseases worldwideAPS PressSt. Paul, MN

    • Export Citation
  • French-MonarR.JonesJ.RobertsP.2006Characterization of Phytophthora capsici associated with roots of weeds on Florida vegetable farmsPlant Dis.90345350

    • Search Google Scholar
    • Export Citation
  • French-MonarR.RobertsP.JonesJ.2005Insensitivity of isolates of Phytophthora capsici to mefanoxam in southeast FloridaPhytopathology.95S31S32

    • Search Google Scholar
    • Export Citation
  • GlosierB.R.OgundiwinE.A.SidhuG.S.SischoD.R.PrinceJ.P.2008A differential series of pepper (Capsicum annuum) lines delineates fourteen physiological races of Phytophthora capsici Euphytica1622330

    • Search Google Scholar
    • Export Citation
  • HausbeckM.K.LamourK.H.2004 Phytophthora capsici on vegetable crops: Research progress and management challengesPlant Dis.8812921303

  • HowardH.W.1978The production of new varieties607646HarrisP.M.The potato cropChapman & HallLondon, UK

  • KeinathA.P.2007Sensitivity of isolates of Phytophthora capsici from South Carolina to mefenoxam, dimethomorph, zoxamide and cymoxanilPlant Dis.91743748

    • Search Google Scholar
    • Export Citation
  • McGrathM.T.2004Evaluation of fungicides for managing Phytophthora blight of squash, 2003. Fungicide nematicide tests 59:V0547 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2004/V054.pdf>.

    • Export Citation
  • MitchellD.J.1978Relationships of inoculum levels of several soilborne species of Phytophthora and Phythium to infection of several hostsPhtyopathology6817541759

    • Search Google Scholar
    • Export Citation
  • MitchellD.J.Kannwischer-MitchellM.E.1992 Phytophthora 3138SingletonL.L.MihailJ.D.RushC.M.Methods for research on soilborne phytopathogenic fungiAmerican Phytopathological SocietySt. Paul, MN

    • Export Citation
  • MitchellD.J.Kannwischer-MitchellM.E.MooreE.S.1978Relationship of numbers of Phytophthora cryptogea zoospores to infection and mortality of watercressPhytopathology6814461448

    • Search Google Scholar
    • Export Citation
  • OelkeL.M.BoslandP.W.SteinerR.2003Differentiation of race specific resistance to phytophthora root rot and foliar blight in Capsicum annuum J. Amer. Soc. Hort. Sci.128213218

    • Search Google Scholar
    • Export Citation
  • ParisH.S.1986A proposed subspecific classification for Cucurbita pepo Phytologia61133138

  • ParisH.S.YonashN.PortnoyV.Mozes-DaubeN.TzuriG.KatzirN.2003Assessment of genetic relationships in Cucurbita pepo (Cucurbitaceae) using DNA markersTheor. Appl. Genet.106971978

    • Search Google Scholar
    • Export Citation
  • RobertsP.D.McGovernR.J.KucharekT.A.MitchellD.J.2001Vegetable diseases caused by Phytophthora capsici in Florida. UF/IFAS EDIS publication10 Dec. 2007.<http://edis.ufl.edu>.

    • Export Citation
  • SeeboldK.W.HortenT.B.2003Evaluation of fungicides for control of Phytophthora crown and fruit rot of summer squash, 2002. Fungicide nematicide tests. 58:V0989 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2003/V098.pdf>.

    • Export Citation
  • StevensonW.R.JamesR.V.RandR.E.2000Evaluation of selected fungicides to control Phytophthora blight and fruit rot of cucumber. Fungicide nematacide tests. 55:1637 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2001/V16.pdf>.

    • Export Citation
  • StevensonW.R.JamesR.V.RandR.E.2001Evaluation of selected fungicides to control Phytophthora blight and fruit rot of cucumber. Fungicide nematacide tests. 56:V167 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2001/V16.pdf>

    • Export Citation
  • TianD.BabadoostM.2004Host range of Phytopthora capsici from pumpkin and pathogenicity of isolatesPlant Dis.88485489

  • WaldenmaierC.M.2004Evaluation of fungicides for control of pumpkin diseases, 2003. Fungicide nematicide tests, 59:V0649 Jan. 2008.<http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2004/V064.pdf>.

    • Export Citation
  • WalkerS.J.BoslandP.W.1999Inheritance of Phytophthora root rot and foliar blight resistance in pepperJ. Amer. Soc. Hort. Sci.1241418

  • ZitterT.A.HopkinsD.L.ThomasC.E.1996Compendium of cucurbit diseasesAPS PressSt. Paul, MN

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 191 111 13
PDF Downloads 60 46 7