Evaluation of new postharvest fungicides for the control of Phytophthora brown rot
| dc.contributor.advisor | Van Niekerk, Jan | en_ZA |
| dc.contributor.advisor | Lennox, Cheryl L. | en_ZA |
| dc.contributor.author | Van der Merwe, Elizabeth | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology. | en_ZA |
| dc.date.accessioned | 2020-02-20T12:37:25Z | |
| dc.date.accessioned | 2020-04-28T15:11:48Z | |
| dc.date.available | 2020-02-20T12:37:25Z | |
| dc.date.available | 2020-04-28T15:11:48Z | |
| dc.date.issued | 2020-03 | |
| dc.description | Thesis (MScAgric)--Stellenbosch University, 2020. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Brown rot is a citrus postharvest disease caused by Phytophthora spp. during continuous wet conditions. Fruit closest to the soil surface in the orchard are usually infected when the infecting propagules present are splashed upward during irrigation or rain. When infections on fruit are still in early development, it may go unnoticed when fruit are harvested. Infections develop further after harvest and can infect other fruit while in storage or transit. In the current study, the efficacy of actives azoxystrobin, fludioxonil and potassium phosphite was tested for the control of postharvest Phytophthora brown rot on citrus, as there is currently nothing registered for the management of this disease in South Africa. The fungicide sensitivities of 121 Phytophthora nicotianae isolates belonging to either a previously unexposed population or previously possibly exposed population, were tested for against the strobilurin azoxystrobin, based on the growth of mycelium. The mycelial growth on corn meal agar (CMA) amended with azoxystrobin at 0-, 0.25-, 0.5-, 1-, 10-, 100-, and 2000 µg/ml with the addition of 100 µg/ml salicylhydroxamic acid (SHAM), to inhibit the alternative respiration route, was measured after 7 days. The addition of SHAM did not have a significant effect on the growth of mycelia. CMA was also amended with the phenylpyrrole fludioxonil at 0-, 1-, 100-, 1000-, and 10 000 µg/ml. The effective concentration for 50% reduction of mycelial growth (EC50) for azoxystrobin ranged from 0.01 to 0.46 µg/ml for both populations and the EC90 ranged from 4.28 to 84.85 µg/ml for both populations. Fludioxonil sensitivity had a much wider range and higher EC values. The EC50 for both populations ranged from 3.10 to 1613.52 µg/ml and the EC90 values were 1090.50 to 9929 µg/ml. Subsequently, curative and protective actions of aqueous postharvest dip treatments, were carried out with the use of azoxystrobin at 1125 µg/ml and fludioxonil at 598 µg/ml. With the in vivo trials, potassium phosphite was added as an additional treatment at 1500 µg/ml. These trials were repeated on three fruit types namely lemons, oranges and mandarins and at four time intervals. The data clearly showed that with all three fungicides, the curative efficacy is excellent when treatments occurred up to 12 hrs after inoculation. Azoxystrobin and potassium phosphite exhibited excellent protective activity up to 48 hrs between treatment and inoculation. An overall trend that was seen with all three fruit types, was that the longer the fungicide was present on the fruit, the better the protective activity. The nesting data clearly demonstrated that only azoxystrobin amended wax significantly reduced brown rot from spreading to the healthy fruit, when compared to the control. With this study, it could be seen that all three fungicides, with their different actives, have the potential to effectively manage postharvest brown rot. Considering that azoxystrobin and fludioxonil are already registered on citrus for the postharvest use of Penicillium management, and potassium phosphite that are registered as a preharvest Phytophthora treatment, this study indicate that they will also provide added protection against Phytophthora brown rot. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Bruin vrot is ‘n sitrus na-oes siekte wat veroorsaak word deur Phytophthora spesies gedurende aanhoudende nat toestande. Die vrugte naaste aan die grond oppervlakte in boorde word gewoonlik geïnfekteer wanneer die infekterende propagules opwaarts gespat word tydens besproeiing of wanneer dit reën. Wanneer infeksie op vrugte nog in vroeë ontwikkeling is, kan dié vrugte ongesiens geoes word en ander vrugte tydens die stoor daarvan, of tydens vervoer, infekteer. Die huidige studie toets die effektiwiteit van aktiewes asoksistrobien, fludioxonil en kaliumfosfiet vir die beheer van na-oes Phytophthora bruin vrot op sitrus, aangesien daar tans niks geregistreer is vir die beheer van hierdie siekte in Suid-Afrika nie. Die swamdoder sensitiwiteit van 121 Phytophthora nicotianae isolate wat behoort aan nie-blootgestelde- en moontlik blootgestelde populasies, was gebaseer op die groei van die miselium. Die miselium groei op mieliemeel agar (MMA) met die byvoeging van die strobilurien asoksistrobien teen 0-, 0.25-, 0.5-, 1-, 10-, 100-, en 2000 μg/ml en addisioneel 100 μg/ml salisielhidroksamiensuur (SHAM), om alternatiewe respirasie roetes the inhibeer, was gemeet na sewe dae. Die byvoeging van SHAM het geen betekenisvolle effek gehad op die miselium se groei nie. KMA was ook bygevoeg met die finielpirool fludioxonil teen 0-, 1-, 100-, 1000-, en 10 000 μg/ml. Die effektiewe konsentrasie om die miselium se groei met 50% te verminder (EC50) was vir asoksiestrobien tussen 0.01 en 0.46 μg/ml vir beide populasies en die EC90 was tussen 4.28 en 84.85 μg/ml vir beide populasies. Fludioxonil sensitiwiteit het ‘n veel wyer reeks en hoër EC waardes gehad. Die EC50 vir beide populasies was tussen 3.10 en 1613.52 μg/ml en die EC90 waardes was tussen 1090.50 en 9929 μg/ml. Gevolglik was die genesende en beskermde aksies getoets met die gebruik van ‘n na-oes doop en was uitgevoer met asoksiestrobien teen 1125 μg/ml en fludioxonil teen 598 μg/ml. Met die in vivo proewe was kalium fosfiet teen 1500 μg/ml bygevoeg. Hierdie proewe was getoets op drie vrug tipes, naamlik suurlemoene, lemoene en mandaryne en teen vier tyd intervalle. Die data wys duidelik dat al drie swamdoders goeie genesende aksies het wanneer behandeling plaasvind tot en met 12 ure na inokulasie. Asoksietrobien en kalium fosfiet het goeie beskermende effektiwiteit gewys tot en met 48 uur tussen behandeling en inokulasie. ‘n Algehele tendens wat opgemerk was met al drie vrug tipes, was dat hoe langer die swamdoder teenwoordig was op die vrug voor inokulasie, hoe beter was die beskermende effek van die swamdoder. Die voorkoming van oordrag data het gedemonstreer dat net asoksiestrobien wat in waks bygevoeg was, het die verspreiding van bruin vrot na gesonde vrugte betekenisvol verminder het, as dit met die kontrole vergelyk was. Met hierdie studie, kan daar gesien word dat al drie van die swamdoders, met hul verskillende aktiewes, effektief aangewend kan word vir na-oes bruin vrot beheer. Aangesien asoksiestrobien en fludioxonil klaar in Suid-Afrika geregistreer is vir na-oes Penicillium beheer op sitrus, en kalium fosfiet vir voor-oes Phytophthora beheer, kan hierdie studie aandui dat die swamdoders addisionele beskerming bied teen na-oes Phytophthora bruin vrot. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.embargo.terms | 2021-02-19 | |
| dc.format.extent | x, 71 pages | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/108389 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Citrus fruits -- Postharvest diseases and injuries -- Biological control | en_ZA |
| dc.subject | Brown rot | en_ZA |
| dc.subject | Postharvest fungicides | en_ZA |
| dc.subject | Phytophthora -- Treatment | en_ZA |
| dc.subject | Crops -- Postharvest losses -- Prevention | en_ZA |
| dc.subject | Fungicides -- Fungal diseases of plants | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Evaluation of new postharvest fungicides for the control of Phytophthora brown rot | en_ZA |
| dc.type | Thesis | en_ZA |