Determining the resistance or susceptibility of grapevine rootstocks used in South Africa towards fungal trunk disease pathogens

Sieberhagen, Madeleine (2017-03)

Thesis (MScAgric)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Grapevine fungal trunk diseases are responsible for reduced grapevine production world-wide. Trunk diseases are caused by endophytic, xylem-inhabiting pathogens associated with a wide range of symptoms. Currently the largest concern is the presence of pathogens in rootstock mother vines and propagation material. Very little information is available on the susceptibility of grapevine rootstocks used in the South African industry. The susceptibility of the most popular grapevine rootstocks in South Africa to Petri disease (Phaeomoniella chlamydospora, Phaeoacremonium minimum, Pm. parasiticum, Cadophora luteo-olivacea and Pleurostoma richardsiae), black-foot disease (Ilyonectria liriodendri, Dactylonectria macrodidyma, Campylocarpon fasciculare and C. pseudofasciculare) and Botryosphaeria dieback (Neofusicoccum australe and N. parvum) pathogens were evaluated. Firstly, virulence screenings were conducted by plug inoculating dormant Paulsen 1103 cuttings with 10 isolates of each pathogen. The two most virulent isolates were identified according to lesion lengths that developed after six weeks of incubation at 22 °C. There was significant variability between the isolates of all the pathogens, except Pleurostoma richardsiae. Dormant rootstock cuttings of Ramsey, Ruggeri 140, Paulsen 1103, Richter 99, Richter 110, US 8-7, 101-14 Mgt and SO4 were vacuum inoculated with conidial suspensions (1 x 106 conidia mL) of the two most virulent isolates of each pathogen. After eight months in nursery fields, the dormant plants were uprooted and assessed for un-dried shoot and root weight. The percentage disease severity was determined by cutting the plant 10 cm from the base and assessing the internal vascular discolouration. All of the rootstocks inoculated with Petri disease, black-foot disease and Botryosphaeria dieback pathogens showed a significant reduction in root mass, shoot mass and a significant increase in percentage disease severity. None of the rootstocks were completely resistant to fungal trunk disease pathogens, but differential levels of tolerance did exist. The reduction in shoot and root mass did not show consistent results between the rootstock cultivars, but rootstocks 101-14 Mgt and SO4 were the most susceptible and Ramsey the most tolerant, in terms of percentage disease severity. In an attempt to explain the variable tolerance of rootstocks to infection, suberin production and xylem morphology was investigated. Transversal cuts of Ramsey and 101-14 Mgt were made and stained using two suberin staining techniques. The important role suberin plays in the compartmentalization of a pathogen in grapevine wood was confirmed. Suberin was located around vessels filled with tyloses, tyloses itself was also suberized, ray parenchyma cells and cells located on the growth boundary ring. The suberized zones form impermeable barriers that restrict pathogen spread to uninfected and newly developed vascular tissue. The mean vessel diameters were determined for each cultivar using 40 μm thick transversal cuts stained with toluidine O. A strong correlation between mean vessel diameter and rootstock tolerance to fungal trunk pathogens was established. Ramsey had the smallest mean vessel diameter and 101-14 Mg the largest. The quality of plant material is crucial in the success and longevity of newly established vineyards. By combining existing knowledge of disease management in the propagation process with knowledge obtained from this research, can the quality of plant material be optimized to ensure the sustainability of the South African grapevine industry.

AFRIKAANSE OPSOMMING: Wingerd stamsiektes veroorsaak afname in wingerdproduksie wêreldwyd. Hierdie stamsiektes word veroorsaak deur endofitiese swamme en word geassosieer met ‘n wye reeks simptome. Tans skep die teenwoordigheid van patogene in onderstok moederplante en kwekery materiaal groot bekommernisse. Beperkte inligting is beskikbaar oor die vatbaarheid van onderstokke wat algemeen in Suid-Afrika gebruik word. Die vatbaarheid van die gewildste onderstok kultivars in Suid-Afrika teenoor Petri-siekte (Phaeomoniella chlamydospora, Phaeoacremonium minimum, Pm. parasiticum, Cadophora luteo-olivacea en Pleurostoma richardsiae), swartvoet (Ilyonectria liriodendri, Dactylonectria macrodidyma, Campylocarpon fasciculare en C. pseudofasciculare) en Botryosphaeria terugsterwing (Neofusicoccum australe en N. parvum) patogene is geëvalueer. Die virulensie van tien isolate per patogeen is bepaal deur dormante Paulsen 1103 stokkies te inokuleer met miselium skyfies. Die letsels wat die isolate veroorsaak het na ses weke teen 22 °C is gemeet en die twee virulentste isolate geïdentifiseer. Behalwe vir Pleurostoma richardsiae, was daar beduidende verskille tussen die isolate van elke patogeen. Dormante stokkies van Ramsey, Ruggeri 140, Paulsen 1103, Richter 99, Richter 110, US 8-7, 101-14 Mgt en SO4 is geïnokuleer deur spoor suspensies (1x106 spore mL) van elke isolaat met behulp van ‘n vakuumpomp deur die stokkies te suig. Nadat die stokkies vir agt maande in kwekery gronde gegroei het, is hulle gelig en ongedroogde loot- en wortelmassas bepaal. Die persentasie infeksie is ook vasgestel deur die stokkies 10 cm van die basis af deur te sny en die interne vaskulêre verkleuring te evalueer. Al die onderstokke wat met die Petri-siekte, swartvoet en Botryosphaeria terugsterwing patogene infekteer was, het ‘n beduidende afname in wortel- en lootmassa en ‘n toename in persentasie infeksie getoon. Die onderstokke was nie een totaal weerstandbiedend teen swaminfeksie nie, maar verskillende vlakke van toleransie is waargeneem. Die afname in loot- en wortelmassas was nie konsekwent tussen die kultivars nie, maar in terme van persentasie infeksie was 101-14 Mgt en SO4 die mees vatbaar en Ramsey die mees tolerant. Om meer insig omtrent die verskillende vlakke van toleransie tussen die kultivars te bekom, is die suberien produksie en gemiddelde xileem vat deursnit bepaal. Deursnitte is gemaak van Ramsey en 101-14 Mgt en die snitte het twee suberien verkleuringstegnieke ondergaan. Die belangrike rol wat suberien speel in die kompartimentering van patogene in wingerdhout is bevestig. Suberien was geleë rondom xileem vate gevul met tilose (die tilose was ook gesuberiseer), in straalselle en selle geleë op die jaarring. Die zones met suberien vorm ondeurlaatbare versperrings wat die beweging van patogene na gesonde materiaal beperk. Die gemiddelde vat deursnitte is bepaal vir elke kultivar deur 40 μm deursnitte te kleur met toluidine O en te evalueer onder ‘n ligmikroskoop. Daar is ‘n sterk korrelasie tussen ‘n kultivar se gemiddelde vaat deursnit en sy vatbaarheid vir stamsiektes gevind. Ramsey het die kleinste en 101-14 Mgt die grootste gemiddelde vat deursnit gehad Die kwaliteit van plant materiaal is krities vir die sukses en langslewendheid van nuut gevestigde wingerde. Deur die bestaande kennis, met betrekking tot siekte-beheer in die kwekery prosesse, te kombineer met kennis wat verkry is in die huidige studie kan daar voortgegaan word om die kwaliteit van plantmateriaal te verhoog om die volhoubaarheid van die Suid-Afrikaanse wingerd industrie te verseker.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101450
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