Occurrence of canker and wood rot pathogens on stone fruit propagation material and young stone fruit trees

Van der Merwe, Rhona (2019-03)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The phytosanitary status of stone fruit propagation material and nursery trees in South Africa are not known. Canker and wood rot pathogens can be present in visibly clean material. Due to stress and other improper cultural practices, symptoms will be expressed and cankers, dieback of parts of the tree and possible death of the trees can be seen. Therefore, the aim of this study was to identify the fungal canker and wood rot pathogens present in propagation material and nursery stone fruit trees. Green scion shoots were collected from three plum and one nectarine cultivars and dormant scion shoots were collected from three plum cultivars. The rootstock cultivars included three plum and one nectarine cultivar for the dormant rootstock shoots and three plum and two nectarine cultivars for the ungrafted rooted, rootstock plants. Nursery trees, made with the same combinations of scion and rootstock cultivars were also sampled. All the plant material were surface sterilised and isolations were made from the different plant material types. The fungal cultures were identified to species level with DNA sequencing and phylogenetic analyses of either ITS, β-tubulin, EF1α and histone gene regions. From the green scion shoots, low levels of bud infection were observed. In total 0.4% buds were infected with canker pathogens with one bud infected with “Cylindrocarpon”-like fungi. The most abundant species isolated were Coniochaeta prunicola followed by Biscogniauxia sp. Buds from dormant scion shoots had a higher total infection of 1.2% with canker pathogens. Truncatella angustata followed by Didymella pomorum were the species isolated the most. Dormant rootstock shoots had 6.2% of shoots infected with canker pathogens. The pathogens that were isolated most often include Cytospora leucostoma, Diplodia seriata and Didymella pomorum. From the total ungrafted, rooted rootstock plants (378), 10.6% were infected with canker and wood rot pathogens and 6.4% were infected with “Cylindrocarpon”- like fungi. The nectarine rootstock which had a low level of infection (1.3%) can be explained by the fact that these plants were made from seeds. Cadophora and Dactylonectria species were the most abundant. Rootstock plants were mainly infected at the crown, but also below the pruning wound at the tip of the main shoot. Out of 1080 nursery trees that were sampled, 235 trees (21.8%) had infection with canker or wood rot pathogens and 255 trees (23.6%) had infection with “Cylindrocarpon”-like fungi. Cadophora luteo-olivacea, Diplodia seriata and Truncatella angustata were the most abundant canker species isolated from the nursery trees. There were clear differences between the infection percentages of the trees being propagated by using hardwood rootstock cuttings in comparison with the seedling rootstock trees. The propagation material investigated had infections with canker pathogens. Buds from scion shoots had very low levels of infection. Ungrafted, rooted rootstock plants had higher levels of infection than the dormant rootstock shoots, although there were already pathogens that occur inside the dormant rootstock shoots before it was planted in the field. Infections were more often at the crown area of the rootstock plants and accompanied with dark brown streaking originating from the base. It is evident that rootstock cuttings that are pushed into the soil have an open wound that can easily be infected. Fifty-five fungal species associated with canker or wood rot were isolated in this study. Nineteen have been reported on stone fruit trees in South Africa and 26 are first reports on stone fruit trees in South Africa, which include species of the genera Biscogniauxia, Cadophora, Coniochaeta, Coprinellus, Cytospora, Diaporthe, Didymella, Dothiorella, Eutypa, Lasiodiplodia, Neopestalotiopsis, Paraphaeosphaeria, Paraphoma, Pleurostoma, Truncatella and Valsa. Four of these species have been reported on stone fruit trees in other countries, thus, 22 species have been reported for the first time on stone fruit trees worldwide. Ten putative new species were found which include species of Peniophora, Cadophora, Coniochaeta, Eutypella, Cytospora and Biscogniauxia, however, these species needs to be described. A pathogenicity trial done on field grown plum trees confirmed the pathogenic status of 38 of the canker and wood rot species to be pathogenic to plum trees four months after inoculation. None of the 14 “Cylindrocarpon”-like species have been reported on stone fruit trees in South Africa. Only Ilyonectria robusta have been reported on stone fruit in Canada. The pathogen status and relevance of the “Cylindrocarpon”-like fungi needs to be determined with pathogenicity trials. This study has found that seemingly healthy, certified nursery trees with latent canker and wood rot pathogens and “Cylindrocarpon”-like fungi present inside the plant tissue, are distributed to producers. This fungal infection could have occurred from the propagation process with infected scion and rootstock material or from aerial inoculum present when wounds were made. These findings will aid to identify areas where management practices can be implemented to improve nursery plant health.

AFRIKAANSE OPSOMMING: Die fitosanitêre status van steenvrug entmateriaal en kwekery bome is nie bekend in SuidAfrika nie. Kanker en houtverrottingspatogene kan voorkom in ooglopende skoon materiaal. As gevolg van stres toestande en ander verkeerde landbou praktyke, kan simptome soos kankers, terugsterwing van gedeeltes van die boom en die moontlike sterwing van die hele boom waargemeem word. Die doel van die studie was dus om die kanker en houtverrottings patogene te identifiseer wat voorkom in steenvrug entmateriaal en kwekery bome. Groen bo-stok lote was ingesamel van drie pruim kultivars en een nektarien kultivar en dormante bo-stok lote was ingesamel van drie pruim kultivars. Die onderstok kultivars sluit drie pruim kultivars en een nektarien kultivar in vir die dormante onderstok lote en drie pruim en twee nektarien kultivars vir die ongeënte, gewortelde onderstok plante. Kwekery bome, wat gemaak is met dieselfde bo-stok en onderstok kultivars, was ook ingesamel. Al die plantmateriaal was oppervlak gesteriliseer en isolasies was gemaak van die verskillende plantmateriaal tipes. Die swam kulture was identifiseer tot op spesie vlak met DNS volgorde bepaling en filogenetiese analise van die ITS, β-tubulin, EF1α en histone geen areas. Lae infeksie vlakke was gesien vir die groen bo-stok lote. In totaal was 0.4% van die ogies infekteer met kanker patogene en een ogie infekteer met `n “Cylindrocarpon”- assossieerde swam. Die spesies wat die meeste isoleer was, was Coniochaeta prunicola gevolg deur Biscogniauxia sp. Ogies van die dormante bostok lote het `n hoër totale infeksie gehad van 1.2% met kanker patogene. Truncatella angustata gevolg deur Didymella pomorum was die spesies wat die meeste isoleer was. Die dormante onderstok lote het 6.2% infeksie met kanker patogene gehad. Die patogene wat die meeste isoleer was, sluit Cytospora leucostoma, Diplodia seriata en Didymella pomorum in. Van die totale ongeënte, gewortelde onderstok plante (378), was 10.6% infekteer met kanker en houtverrottings swamme en 6.4% infekteer met “Cylindrocarpon”-assossieerde swamme. Die nektarien onderstok met die lae infeksie (1.3%), kan verduidelik word deurdat hierdie plante saailinge is. Cadophora spesies en Dactylonectria spesies was die meeste gevind. Die onderstok plante was hoofsaaklik infekteer by die kroon, maar ook onder die snoeiwond by die tip van die hoof loot. Uit die 1080 kwekery bome wat ingesamel is, was 235 bome (21.8%) infekteer met kanker en houtverrottings patogene en 255 bome (23.6%) infekteer met “Cylindrocarpon”- assossieerde swamme. Cadophora luteo-olivacea, Diplodia seriata en Truncatella angustata was die spesies wat die meeste isoleer was van die kanker swamme vanaf die kwekery bome. Daar was duidelike verskille in die infeksie persentasies tussen die bome gemaak van hardehout onderstok steggies in vergelyking met saailing onderstok plante. Die entmateriaal wat ondersoek was, het infeksies gehad met kanker patogene. Ogies van die bostok lote het baie lae infeksie gehad. Ongeënte, gewortelde onderstok plante het hoër infeksie gehad as die dormante onderstok lote, alhoewel daar alreeds patogene in die dormante onderstok lote was nog voor dit in die veld uitgeplant was. Infeksie was meer gereeld by die kroon gedeelte van die onderstok plante tesame met donker bruin verkleuring vanaf die basis. Dit is duidelik dat onderstok steggies wat in die grond gedruk word `n oop wond het wat maklik infekteer kan word. Vyf-en-vyftig spesies wat assosieer word met kanker en houtverrotting was isoleer in hierdie studie. Negentien is reeds rapporteer op steenvrugte in Suid-Afrika en 26 is eerste rapporterings op steenvrugte in Suid-Afrika, wat spesies van die genera Biscogniauxia, Cadophora, Coniochaeta, Coprinellus, Cytospora, Diaporthe, Didymella, Dothiorella, Eutypa, Lasiodiplodia, Neopestalotiopsis, Paraphaeosphaeria, Paraphoma, Pleurostoma, Truncatella en Valsa in sluit. Vier van hierdie spesies was al rapporteer op steenvrugte in ander lande, dus 22 spesies was vir die eerste keer op steenvrugte wêreldwyd rapporteer. Tien vermeende nuwe spesies was gevind wat Peniophora, Cadophora, Coniochaeta, Eutypella, Cytospora en Biscogniauxia in sluit, maar hierdie spesies moet nog beskryf word. `n Patogenesiteitstoets wat gedoen was op pruim bome in die veld het die patogeen status van 38 van die kanker en houtverrottings spesies bevestig vier maande na inokulasie. Geen van die “Cylindrocarpon”- assossieerde swamme was al rapporteer op steenvrugte in Suid-Afrika nie. Slegs Ilyonectria robusta was rapporteer op steenvrugte in Canada. Die patogeen status en relevansie van die “Cylindrocarpon”-assossieerde swamme moet nog bepaal word met patogenesiteitstoetse. Die studie het gevind dat oënskynlik gesonde, gesertifiseerde kwekery bome met latente kanker en houtverrotting patogene en “Cylindrocarpon”-assossieerde swamme teenwoordig binne die plantweefsel, versprei word aan produsente. Hierdie swam infeksie kon ontstaan vanaf die ent prosses met infekteerde bostok en onderstok materiaal of van luggedraagde inokulum teenwoordig wanneer wonde gemaak was. Hierdie bevindinge sal toevoeg om areas te identifiseer waar bestuurspraktyke implimenteer kan word om kwekery plante se gesondheid te verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105708
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