Improving pruning wound protection against grapevine trunk disease pathogens

Mutawila, Cheusi (2014-03)

Thesis (PhD)--Stellenbosch University, 2014.


ENGLISH ABSTRACT: Grapevine trunk diseases are a cause of decline and loss of productivity in grapevines at all stages of growth. These diseases are caused by a complex of wood-inhabiting fungi that infect mainly through pruning wounds. The management of these diseases relies on wound protection to prevent infection since there are no eradicative control measures to cure infected vines. There are few or no fungicides registered for grapevine pruning wound protection in most countries, while Trichoderma biocontrol agents are often available. This study aimed at improving grapevine wound protection by Trichoderma (T.) spp. and to gain a better understanding of the factors and mechanisms involved in biocontrol. The effect of pruning time (early or late) and five timings of application of the biocontrol agent after pruning on pruning wound colonisation by T. atroviride and T. harzianum were determined. Chenin blanc and Cabernet Sauvignon vineyards were pruned in July (early) and August (late) of 2011 and 2012, and pruning wounds were treated with suspensions of the Trichoderma spp. at various times (0, 6, 24, 48 and 96 hours) after pruning. Wound colonisation was depended on the physiological state of the vine at pruning for both cultivars. However, for the 2012 season in Chenin blanc, wound colonisation was similarly high for both pruning times, which was attributed to high rainfall and humidity. Application of the biocontrol agents 6 hours after pruning consistently resulted in high wound colonisation by the Trichoderma spp. in both cultivars and pruning times. In both cultivars, pruning wound infection due to natural inoculum was higher in wounds made in late winter than those made earlier. The effect of conidial formulation in nutritional (glucose, yeast extract and urea) and bio-enhancing (chitin and cell free culture filtrates) additives, on pruning wound colonisation by T. atroviride was also investigated. Nutritional additives increased the extent of pruning wound colonisation by T. atroviride compared to the un-amended conidial suspensions in a glass house study. The additives as well as Garrison, a fungicide containing pruning wound paint, and Eco77®, a registered T. harzianum biocontrol product, were tested in field trials for wound protection from infection by Phaeomoniella (Pa.) chlamydospora. In 2011, the pathogen was inoculated a day after pruning and all the Trichoderma spp. treatments similarly reduced Pa. chlamydospora infection by 75% to 90% in Thompson Seedless, while control was less in Chenin blanc and ranged from 40% to 74%. In 2012, the trial was carried out on Chenin blanc only and the pathogen was inoculated at intervals of 1, 3 and 7 days after pruning. Wound protection by the Trichoderma treatments was highest when wounds were inoculated with Pa. chlamydospora seven days after pruning. Two conidial formulations, a culture filtrate made from a chitin based medium and a combination of yeast extract, urea and glucose, consistently enhanced biocontrol efficacy. These formulations reduced Pa. chlamydospora infection to levels similar to those of Garrison. The integration of chemical and biological wound protection could provide both immediate and long term wound protection, but is limited by the sensitivity of the biocontrol agent to fungicides. Benzimidazole resistant Trichoderma strains were generated by gamma irradiation from the wild type isolates of T. atroviride (UST1 and UST2) and T. harzianum (T77). Mutants from UST1 and UST2 were of similar biological fitness as the wild type isolates and retained their in vitro antagonistic activity against grapevine trunk pathogens, while the mutant from T77 had reduced fitness and was not antagonistic to the pathogens. The wild type, UST1, and its mutant were tested alone and in combination with thiophanate methyl and carbendazim, respectively, for their ability to prevent pruning wound infection by Pa. chlamydospora. The combination of the UST1 mutant and carbendazim was the most effective treatment and gave the highest reduction in Pa. chlamydospora infection (70% to 93% control). Grapevine cell cultures were used to compare the response of grapevines to T. atroviride and Eutypa (E.) lata as a first step to determining the importance of Trichoderma-grapevine interactions in pruning wound bio-protection. The expression of genes coding for enzymes of the phenylpropanoid pathway and pathogenesis related (PR) proteins was profiled over a 48-hour period using quantitative reverse transcriptase PCR. The cell cultures responded to fungal elicitors in a hypersensitive-like response that lead to a decrease in cell viability. Fungal elicitors from both fungi triggered the same genes and caused up-regulation of phenylalanine ammonia-lyase (PAL), 4 coumaroyl Co-A ligase (CCo-A), stilbene synthase (STS), chitinase class IV (CHIT IV), PR 3 and PR 4, and a down regulation of chalcone synthase (CHS) genes. Higher expression of PAL and CHIT IV in cell cultures treated with the T. atroviride elicitor led to a significantly higher (P < 0.05) total phenolic content and chitinolytic enzyme activity of the cell cultures compared to cell cultures treated with the E. lata elicitor. The response of the cell cultures to the T. atroviride elicitor signifies that the induction of grapevine resistance may be involved in wound bio-protection. The role of secondary metabolites produced by Trichoderma spp. used in pruning wound protection was also investigated. A volatile antimicrobial compound, 6-pentyl α-pyrone (6PP), was isolated and found to be the major secondary metabolite from the T. atroviride (UST1 and UST2) and T. harzianum (T77) isolates. This metabolite was found to inhibit mycelial growth, spore and conidia germination of E. lata, Neofussicocum (N.) australe, N. parvum and Pa. chlamydospora. The production of 6PP was induced when the T. atroviride isolates were grown in a grapevine wood extract medium while for UST1, the 6PP concentration was further doubled when it was co-cultured with N. parvum. Results therefore, indicate that 6PP is involved in the Trichoderma-pathogen interactions on pruning wounds. The results of this study have provided new information in regards to the application of Trichoderma-based pruning wound products. The best time of application proved to be 6 hours post pruning. The formulation of conidial suspensions of Trichoderma spp. with nutritional additives and in protein extracts of the biocontrol agent showed potential in reducing variability of wound bio-protection. However, further research would be necessary to develop commercial products. The application of a fungicide together with Trichoderma spp. in the field holds promise to improve control, but would require further trials for possible commercialisation. This study is the first to report on grapevine host defence genes that are activated by the Trichoderma spp. used in pruning wound protection. Together with the characterisation of the major secondary metabolite produced by these Trichoderma spp., this information aids in understanding the mechanisms involved in the complex interaction between the biocontrol agent, the host and the pathogen.

AFRIKAANSE OPSOMMING: Wingerdstamsiektes veroorsaak terugsterwing en verlies aan produktiwiteit in wingerdstokke gedurende alle groeifases. Hierdie siektes word veroorsaak deur „n verskeidenheid van hout-koloniserende swamme wat die wingerdstok meestal deur snoeiwonde infekteer. Die bestuur van hierdie siektes is afhanklik van wondbeskerming om infeksie te verhoed, omdat daar geen uitwissende beheermetodes na infeksie bestaan nie. In meeste lande is daar min of geen swamdoders geregistreer vir snoeiwond beskerming, terwyl Trichoderma biobeheer agente gereëld beskikbaar is. Hierdie studie poog om wingerd wondbeskerming deur Trichoderma (T.) spp. te verbeter en „n meer volledige begrip van die faktore en meganismes betrokke by biologiese beheer te ontwikkel. Die effek van die tydsberekening van snoei (vroeg of laat) en vyf behandelingstye van die biobeheer agent na snoei op die kolonisering van snoeiwonde deur T. atroviride en T. harzianum is bepaal. Chenin blanc en Cabernet Sauvignon wingerde is gesnoei gedurende Julie (vroeg) en Augustus (laat) in 2011 en 2012, en snoeiwonde is behandel met Trichoderma spp. suspensies op verskillende tydspunte (0, 6, 24, 48 en 96 ure) na snoei. Wond-kolonisering was afhanklik van die fisiologiese toestand van die wingerdstok gedurende snoei vir albei kultivars. Gedurende die 2012 seisoen was wond-kolonisering ewe hoog vir albei snoeitye op Chenin blanc. Dit is verklaar deur hoë reënval en humiditeit gedurende daardie seisoen. Die aanwending van biobeheer agente 6 ure na snoei het konsekwent hoë kolonisering deur Trichoderma spp. tot gevolg gehad op albei kultivars en albei snoeitye. In albei kultivars is wondinfeksie as gevolg van natuurlike inokulum hoër gewees in wonde gemaak gedurende laat winter as in wonde wat vroeër in die seisoen gemaak is. Die effek van konidia formulasie in voeding (glukose, gisekstrak en urea) en bioverbetering (chitien en sel-vrye kultuurfiltraat) toevoegings op snoeiwond-kolonisering deur T. atroviride is ook ondersoek. Voeding toevoegings het die omvangs van snoeiwond-kolonisering deur T. atroviride vergroot in vergelyking met ongewysigde konidia suspensies gedurende „n glashuis studie. Die toevoegings, sowel as Garrison, „n snoeiwond verf wat „n swamdoder bevat, en Eco77®, „n geregistreerde T. harzianum biobeheer produk, is getoets in veldproewe vir wondbeskerming teen infeksie deur Phaeomoniella (Pa.) chlamydospora. In 2011 is die patogeen geïnokuleer „n dag na snoei en al die Trichoderma spp. behandelings het infeksie verminder met 75% tot 90% op Thompson Seedless. Beheer was minder suksesvol op Chenin blanc, waar slegs 40% tot 74% beheer behaal is. In 2012 is die proef uitgevoer slegs op Chenin blanc en die patogeen is geïnokuleer teen intervalle van 1, 3 en 7 dae na snoei. Wondbeskerming by die Trichoderma behandelinge was die hoogste wanneer wonde sewe dae na snoei geïnokuleer is met Pa. chlamydospora. Twee konidia formulasies, „n kultuurfiltraat wat bestaan het uit „n chitien-gebaseerde medium en „n kombinasie van gisekstrak, urea en glukose het deurlopend die effektiwiteit van biobeheer verbeter. Hierdie formulasies het Pa. chlamydospora infeksie verminder tot soortgelyke vlakke behaal deur Garrison. Die integrasie van chemiese- en biobeheer in wondbeskerming kan onmiddelike en langtermyn wondbeskerming bied, maar is beperk deur die sensitiwiteit van die biobeheer agent teen swamdoders. Benzimidazole-weerstandbiedende Trichoderma isolate is ontwikkel deur gamma-bestraling van die wilde-tipe isolate van T. atroviride (UST1 en UST2) en T. harzianum (T77). Mutante van UST1 en UST2 het soortgelyke biologiese fiksheid getoon as die wilde-tipe en het hul in vitro antagonistiese aktiwiteit teen wingerd stampatogene behou, terwyl die mutant van T77 verminderde fiksheid getoon het en nie meer antagonisties teen patogene was nie. Die wilde-tipe, UST1, en sy mutant is apart en in kombinasie met thiofanaatmetiel en carbendazim, respektiewelik, getoets vir die vermoë om snoeiwonde te beskerm teen Pa. chlamydospora. Die kombinasie van die UST1 mutant met carbendazim was die mees effektiewe behandeling en het die hoogste vermindering in Pa. chlamydospora infeksie gelewer (70 tot 93% beheer). As „n beginpunt om die belang van Trichoderma-wingerd interaksies in snoiewondbeheer te bepaal, is die invloed van T. atroviride en Eutypa (E.) lata op somatiese selkulture van wingerd vergelyk. Die effek van dié behandelings op ensieme in die fenielpropanoïedweg en patogenese-verwante (PR) proteïene is bepaal deur intydse PKR (real time PCR) van die korresponderende gene oor „n 48 uur tydperk. Die swam-afkomstige ontlokkers het „n hipersensitiewe-tipe reaksie in die selkulture ontlok, wat tot „n afname in sellewensvatbaarheid gelei het. Ontlokkers afkomstig van beide swamme het dieselfde gene aangeskakel en het induksie van fenielalanien ammoniak-liase (PAL), 4 kumaroïel Ko-A ligase (CCo-A), stilbeen sintase (STS), chitienase klas IV (CHIT IV), PR 3 en PR 4 veroorsaak en „n onderdrukking in chalkoon sintase (CHS) gene tot gevolg gehad. Hoër uitdrukking van PAL en CHIT IV in selkulture behandel met die T. atroviride ontlokker het gelei tot „n beduidende hoër (P < 0.05) totale fenoolinhoud en chitienolitiese aktiwiteit in selkulture in vergelyking met selkulture wat behandel is met die E. lata ontlokker. Die reaksie van die selkulture op die T. atroviride ontlokker dui daarop dat die induksie van wingerd weerstandbiedenheid betrokke mag wees in wond biobeheer. Die rol van sekondêre metaboliete geproduseer deur Trichoderma spp. wat gebruik word in snoeiwond beheer is ook ondersoek. „n Vlugtige antimikrobiese verbinding, 6-pentiel α-pyroon (6PP) is geïsoleer en bepaal om die hoof sekondêre metaboliet afkomstig vanuit die T. atroviride (UST1 en UST2) en T. harzianum (T77) isolate te wees. Hierdie metaboliet is betrokke by inhibisie van miselium groei, spoor en konidium ontkieming van E. lata, Neofusicoccum (N.) australe, N. parvum en Pa. chlamydospora. Die produksie van 6PP is geïnduseer deur die T. atroviride in wingerd hout ekstrak te kweek. In die geval van UST1, is die 6PP konsenstrasie verdubbel deur die isolaat met saam met N. parvum te kweek. Hierdie resultaat is „n aanduiding dat 6PP betrokke is in die Trichoderma-patogeen interaksie op snoeiwonde. Die resultate van hierdie studie het nuwe inligting met betrekking tot die aanwending van Trichoderma-gebaseerde snoeiwond produkte verskaf. Die beste tyd vir aanwending van sulke produkte was 6 ure na snoei. Die formulasie van konidia suspensies van Trichoderma spp. met voeding toevoegings en in proteïen ekstrakte van die biobeheer agent het potensiaal getoon in die vermindering van variasie in wondbeskerming deur biobeheer agente. Verdere navorsing sal nodig wees om kommersiële produkte te ontwikkel. Die aanwending van „n swamdoder saam met Trichoderma spp. in die wingerd is belowend om beheer te verbeter, maar het meer proewe nodig voor kommersialisering. Hierdie studie is die eerste om wingerd beskerming gene wat deur Trichoderma spp. geaktiveer word aan te meld. Laasgenoemde, saam met die beskrywing van die hoof sekondêre metaboliete wat deur hierdie Trichoderma spp. geproduseer word, dra by tot „n meer volledige begrip van die meganismes betrokke by die komplekse interaksie tussen die biobeheer agent, die gasheer en die patogeen.

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