A solar collector was used to disinfest potting medium inoculated with Ralstonia solanacearum. Tomato plantlets grown in the potting medium treated in the solar collector for one full day had no symptoms of bacterial wilt

ALMEIDA, I. M. G.

GHINI, R.

PATRÍCIO, F. R. A.

PATRÍCIO, F.R.A.

ALMEIDA, I.M.G.

RCAAP - Repositório Científico de Acesso Aberto de Portugal

Control of Ralstonia solanacearum in tomato potting medium by the use of a solar collector.

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CSIRO PUBLISHINGwww.publish.csiro.au/journals/apdn Australasian Plant Disease Notes, 2007, 2, 77–78Control of Ralstonia solanacearum in tomato potting mediumby the use of a solar collectorR. GhiniA,C, F. R. A. PatricioB and I. M. G. AlmeidaBAEmbrapa Environment, Caixa Postal 69, Jaguariu´na, SP 13820-000, Brazil.BInstituto Biolo´gico, Caixa Postal 70, Campinas, SP 13001-970, Brazil.CCorresponding author. Email: raquel@cnpma.embrapa.brAbstract. A solar collector was used to disinfest potting medium inoculated with Ralstonia solanacearum. Tomatoplantlets grown in the potting medium treated in the solar collector for one full day had no symptoms of bacterial wilt.Ralstonia solanacearum, a widespread and destructive bacterialplant pathogen, limits production of many important crops,including the solanaceous species potato, tomato and pepper.This pathogen can also infect other herbaceous and woodyplants and its control is difﬁcult (Hayward 1994). Disinfestationof container medium is particularly important for thegrowth of disease-free seedlings and prevention of pathogendissemination.A solar collector was developed by Ghini (1993) with theaim of disinfesting container medium using solar radiation.This equipment was shown to be very efﬁcient in controllingseveral fungal soilborne plant pathogens, including species ofFusarium, Pythium, Rhizoctonia, Sclerotium, Sclerotinia andPhytophthora, as well as nematodes such asMeloydogyne (Ghini1993; Ghini et al. 1998). The purpose of this work was toFig. 1. Solar collector for substrate disinfestations.determine the efﬁcacy of the solar collector for the control ofbacterial wilt caused by R. solanacearum.As previously described (Ghini 1993), the solar collectorcomprises six aluminum tubes (15-cm diameter) placed inparallel rows in a wooden box (1.5m× 1.0m× 0.3m), coveredwith transparent plastic (Fig. 1). Pottingmedium is placed insidethe tubes for solar treatment.In the experiments, which were conducted during autumnand spring (April and December 2005) in Jaguariu´na, Sa˜o Paulo(22◦42′S, 46◦59′W), 2 kg of potting medium (moisture contentof ∼70% of ﬁeld capacity) was mixed with 7mL of a bacterialsuspension (∼8× 106 cfu/mL) of Ralstonia solanacearum(biovar I) strain IBSBF 32 (IBSBF= Phytobacteria CultureCollection of Instituto Biologico, Caixa Postal 70, Campinas,SP 13001-970, Brazil), isolated from tomato. Inoculum was© Australasian Plant Pathology Society 2007 10.1071/DN07031 1833-928X/07/01007778 Australasian Plant Disease Notes R. Ghini et al.prepared from the virulent ﬂuidal wild-type colonies selectedon TZC medium (Kelman 1954).The mixture was placed in the solar collector and treated for1, 2, 3 and 4 days under full sunlight. Average day temperaturesover the treatment period were 23◦C in April and 25◦C inDecember. Temperatures of the potting medium inside the solarcollector weremeasured with a digital temperature multi-sensor,at intervals of 1 h. The sensor was placed along the middle of thetubes. Controls with infested and non-infested potting mediumwere kept at room temperature during the solarisation treatment.Subsequently, potting medium from all the differenttreatments was placed in 2-L pots and ﬁve 30-day-old tomatoseedlings, cv. Santa Clara, were transplanted to each pot, witheight replications per treatment. The plants were maintained in agreenhouse (25–30◦C) and examined daily for the developmentofwilt symptoms.Reisolationsweremade onTZCmedium fromvascular tissues showing bacterial exudates.Potting medium temperature inside the solar collector washigher than 60◦C for at least 5 h during the day. Maximumtemperature reached was 78.8◦C. There were no wilted plantsin the treatments solarised for 1–4 days, as well as in thecontrol without the pathogen in both trials, while 60 and 70%of tomato plants showed wilt symptoms in the non-solarisedinfested potting medium from the experiments carried out inApril and December, respectively (Fig. 2). The control of thedisease was observed in two different periods of the year, asveriﬁed for other pathosystems (May-de Mio et al. 2002).The results described by Ghini (1993) demonstrated thattemperatures obtained in the solar collectors are sufﬁcient tocontrol soilborne plant pathogens but do not completely sterilisethe potting medium, even after a prolonged treatment of 7 days.It does not create a ‘biological vacuum’ to the same extent asdo other disinfestation methods, such as treatment with methylbromide, soil steaming or autoclaving. Reinfestation is morelikely to occur in a soil with a ‘biological vacuum’ becauseFig. 2. Tomato plants growing on substrate infested with Ralstoniasolanacearum and (1) not treated; (2) treated for 1 day, (3) 2 days, (4) 3 days,and (5) 4 days with solar radiation from a collector; (6) not infested and nottreated; and (7) not infested and treated on solar collector.antagonistic organisms are also removed. A prolonged solartreatment of 7 days also did not alter the nutrient contents of thesoil (Ghini 1993). Randig et al. (2002) observed a decrease inan indigenous community of arbuscular mycorrhizal fungi, buta higher weight of dry plants of maize was veriﬁed on treatedsubstrate.A comparative economic evaluation was performed for solarand methyl bromide soil disinfestation, based on actual costdata from a commercial nursery (Ghini et al. 2000). The yearlycost per cubic meter of soil ranged from US$0.42 to US$0.52in favour of methyl bromide disinfestations. However, theevaluation does not take into consideration the occupationalhealth and environmental beneﬁts, which greatly favour solarover chemical control. Moreover, methyl bromide is beingprohibited worldwide for soil and potting medium treatment.This study showed that the solar collector is an efﬁcientmethod to treat potting medium infested with R. solanacearum.This equipment has started to be used bymanygrowers, nurseriesand research institutions in Brazil as an alternative method ofcontrol in view of the methyl bromide crisis. It can be usedduring the whole year and over the entire country. The ease ofconstruction and operation of the solar collector offers a low-cost, efﬁcient and safe system for the production of healthyseedlings.ReferencesGhini R (1993) A solar collector for soil disinfestation. Netherlands Journalof Plant Pathology 99, 45–50. doi: 10.1007/BF01974784Ghini R, Inomoto MM, Saito ES (1998) Coletor solar no controlede Meloidogyne arenaria em substratos para produc¸a˜o de mudas.Fitopatologia Brasileira 23, 65–67.Ghini R, Marques JF, Tokunaga T, Bueno SCS (2000) Controle dePhytophthora sp. e avaliac¸a˜o econoˆmica do coletor solar paradesinfestac¸a˜o de substratos. Fitopatologia Venezolana 13, 11–14.Hayward AC (1994) The hosts of Pseudomonas solanacearum. In ‘Bacterialwilt: the disease and its causative agent, Pseudomonas solanacearum’.(Eds AC Hayward, GL Hartman) pp. 9–24. (CABI: Taiwan)Kelman A (1954) The relationship of pathogenicity in Pseudomonassolanacearum to colony appearance on a tetrazolium medium.Phytopathology 44, 693–695.May-de Mio LL, Ghini R, Kimati H (2002) Solarizac¸a˜o para controle dePhytophthora parasitica em mudas de citros. Fitopatologia Brasileira27, 254–258. doi: 10.1590/S0100-41582002000300003Randig O, Medeiros CAB, Sperandio CA (2002) Efeito da desinfestac¸a˜o dosolo pelo uso de energia solar sobre fungos micorrı´zicos arbusculares.Revista Brasileira de Cieˆncia do Solo 26, 135–140.Manuscript received 20 March 2007, accepted 26 April 2007http://www.publish.csiro.au/journals/apdn

Control of Ralstonia solanacearum in tomato potting medium by the use of a solar collector.

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