Effect of tissue wounding and time of soil inoculation on pepper root rot development

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  • This article was downloaded by: [University of North Carolina]On: 12 November 2014, At: 14:58Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

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    Effect of tissue wounding and timeof soil inoculation on pepper root rotdevelopmentS. E.L. Alao a , O. Alabi a , A. D. Akpa a , M. D. Alegbejo a & P. S.Marley aa Department of Crop Protection , Institute for AgriculturalResearch, Ahmadu Bello University , P.M.B. 1044, Zaria , NigeriaPublished online: 11 Jul 2011.

    To cite this article: S. E.L. Alao , O. Alabi , A. D. Akpa , M. D. Alegbejo & P. S. Marley (2012)Effect of tissue wounding and time of soil inoculation on pepper root rot development, Archives OfPhytopathology And Plant Protection, 45:4, 468-474, DOI: 10.1080/03235408.2011.587985

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  • Effect of tissue wounding and time of soil inoculation on pepper rootrot development

    S.E.L. Alao*, O. Alabi, A.D. Akpa, M.D. Alegbejo and P.S. Marley

    Department of Crop Protection, Institute for Agricultural Research, Ahmadu Bello University,P.M.B. 1044, Zaria, Nigeria

    (Received 16 January 2011; final version received 5 March 2011)

    Five-week-old pepper plants with wounds created on stems and roots weretransplanted to soils having inoculum of Phytophthora capsici incorporated fordifferent lengths of time. Disease severity (39.99%) on root trimmed seedlings wasnot significantly different (P 0.05) from the severity (36.24%) obtained on stemlacerated seedlings. The wound treatments did not result in significantly differentrates of lesion extension per day; stem lacerated seedling had the fastest, 1.99 mm/day lesion extension rate, followed by 1.90 and 1.89 mm/day extension ratesobtained on root trimmed and unwounded treatments, respectively. However,time of soil inoculation had significant effect on severity; root trimmed and stemlacerated treatments had 46.3% and 39.8% severities, respectively. Tissuewounding 6 time of soil inoculation interaction did not have significant effecton disease severity; stem lacerated seedlings transplanted to 1-day and 3-dayinoculated soils gave highest severity (49.9%), followed by seedlings inoculated atthe time of transplantation. Root trimmed seedlings inoculated at the time oftransplantation had highest severity (61.1%), while the lowest severity wasobtained on seedlings transplanted to 5-day inoculated soil.

    Keywords: stem laceration; root trimmed; disease severity; Phytophthora capsici;Capsicum annuum

    Introduction

    The peppers, Capsicum annuum (L.) and Capsicum frutescens (L.), are importantcrops grown as annual or biennial shrubs in all parts of Nigeria; large scaleproduction is, however, from the northern parts (Olarewaju and Mohammed 1990).Despite being Africas leading producer, 723,000 tonnes produced per annum (FAO2007), the 793 kg/ha yield is very low due to a plethora of pests and diseases (Boslandand Votava 1999). The incompetent method of transplanting pepper seedlings withvery high percentage of either immature or injured seedlings also contributes to thelow yield (Adedoyin 1990).

    Kim et al. (1990) observed that disease severity was increased on fields infectedwith Phytophthora capsici, cultivated in Southern provinces of Korea, when injurieswere present on pepper roots, stems, fruits and foliage. Biles et al. (1992) reportedthat although P. capsici does not require wounding of host tissues for diseasedevelopment, severity of disease significantly increased whenever wounds

    *Corresponding author. Email: alaoemma@gmail.com

    Archives of Phytopathology and Plant Protection

    Vol. 45, No. 4, February 2012, 468474

    ISSN 0323-5408 print/ISSN 1477-2906 online

    2012 Taylor & Francishttp://dx.doi.org/10.1080/03235408.2011.587985

    http://www.tandfonline.com

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  • (mechanical injuries) occurred. Of recent, an identified disincentive to pepperproduction in northern Nigeria is the pepper root rot pathogen, Phytophthora capsici(Leon.), whose post-harvest survival in soil is accomplished by oospores with cellwall composed of multilayered b-glucan and cellulose (Alegbejo et al., 2006). Theoospores are hyaline, slightly wrinkled, spherical (between 25 and 35 mm in diameter)with 2.02.5 mm thick walls (Waterhouse 1963), and they remain infective in fallowsoils up to 10 years (Lamour and Hausbeck 2002), although germination can occuronly after a month of dormancy (Hausbeck and Lamour 2004). The produced germtubes can penetrate fresh plant tissues and the successful infection results in therelease of biflagellate zoospores that swim briefly before encysting. The duration offree water in soil, on foliage and on fruit is important in the development of pepperroot rot because the zoospores of P. capsici can only proliferate and cause infectionin the presence of free water (Wilcox and Mirecetich 1985).

    Manohara et al. (2002) reported that P. capsici infected propagules survivedmore than 20 weeks in latosol soil at 100% field capacity, with some Phytophthoraspp. surviving saprophytically on pepper leaves for 11 weeks in soils held at 60100% field capacity. This study was conducted at Samaru (118 110N 078 380E, at686 m above sea level) to determine the effect of transplanting injured seedlings tosoils contaminated with P. capsici on disease severity.

    Materials and methods

    Five-week-old seedlings of local variety SAMPEP 4 sown in sterilised soil(loam washed river sand in a 1:3 ratio) were transplanted to earthen pots(20 cm diameter) which had N:P:K (15:15:15) at 135 kg/ha thoroughly mixed in. Thethree wound treatments, namely root trimmed, stem laceration and not woundedwere made as described.

    Seedling roots were 5 mm trimmed using flame sterilised scissors; while fivelacerations (each approximately 5 mm long) were made at collar region with flamedrazor blade before transplantation. The wounds were made with stems of seedlingsplaced in sterile water. Seedlings that had no wound made were inoculated with P.capsici. Check plants had appropriate wounds made and were inoculated with steriledistilled water (SDW).

    An isolate of P. capsici obtained from the Department of Crop Protection,Ahmadu Bello University, Zaria, Nigeria was grown on oatmeal agar in Petri dishesincubated at 28 + 0.58C for 5 to 7 days. The culture of P. capsici was flooded with10 ml of SDW and chilled for 2 h at 48C to induce the release of zoospores. Myceliawere harvested, macerated using low speed Warren blender and decanted throughdouble layer cheesecloth. Released zoospores were counted using haemocytometerand final concentration was adjusted to 2.5 6 105 zoospores/ml. Twenty millilitresof the suspension of motile zoospores were used to drench soil contained in each pot.SDW (250 ml) was used to flood each pot prior to transplanting seedlings. Inoculumof P. capsici was applied to drench sterilised soil 0, 1, 2, 3, 4, and 5 days beforetransplanting a five-week-old seedling. Treatment where P. capsici inoculum wasapplied at transplanting time represented the 0-day treatment (T1). Check wasinoculated with only SDW before seedling was transplanted.

    One hundred and eighty earth pots were arranged in a completely randomiseddesign (CRD) on the screen house bench. Each treatment was replicated five times.

    Archives of Phytopathology and Plant Protection 469

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  • Parameters taken include incubation period, l

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