Resistance to Botrytis cinerea in parts of leaves and bunches of grapevine

Gutschow, Minique (2001-03)

Thesis (MScAgric)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: Knowledge of the presence of Botrytis cinerea in morphological parts of bunches and leaves of grapevine would help to find a reliable, sensitive, and specific assay to verify the actual occurrence of latent infection, and to plan strategies for the effective control of B. cinerea bunch rot. The aim of this study was (i) to determine natural B. cinerea infection at specific sites in leaves and bunches of grapevine at different phenological stages, and (ii) to determine resistance in the morphological parts to disease expression. Bunches and leaves of the wine grape cultivar Merlot and the table grape cultivar Dauphine, were collected at pea size, bunch closure and harvest from five vineyards in the Stellenbosch and De Dooms regions respectively. The material was divided into two groups and sealed in polythene bags. The bags were lined with wet paper towels to establish high relative humidity. Leaves and bunches incubated in one group of bags were first treated with paraquat in order to terminate active host responses. These treatments provided conditions that facilitated disease expression under two host resistance levels by different inocula during the period of moist incubation. Disease expression was positively identified by lesion development, and the formation of sporulating colonies of B. cinerea at a potential infection site. Sites in leaves were the blades and petioles. Sites in bunch parts were rachises, laterals and pedicels, and on berries sites were the pedicel-end, cheek and style-end. In Dauphine, the various sites were at all stages classified as resistant to moderately resistant. However, at pea size and bunch closure, in spite of their resistance, nearly all the sites carried high to very high inoculum levels. The only exception was the berry cheek, which carried intermediate inoculum levels at pea size, and low inoculum levels at bunch closure. In nearly all sites, inoculum levels were lower at harvest. The decrease was the most prominent in petioles, rachises, laterals, pedicels and the pedicel-end of the berry. All these sites carried intermediate to low inoculum levels at harvest. In Merlot, sites constantly exibited a resistant reaction, except for the pedicel and pedicel-end of the berry, which changed from resistant at the early developmental stages to susceptible at harvest. Inoculum levels decreased during the season in the rachises and laterals, but were constantly high during the season in the pedicel and pedicel-end of the berry. According to this pattern of natural occurrence, B. cinerea fruit rot in these vineyards was not caused by colonisation of the pistil, and subsequent latency in the style end of grape berries. However, fruit rot was primarily caused by colonisation of the pedicel, and subsequent latency in the pedicel or pedicel-end of the berry. These findings furthermore support the hypothesis of increased host resistance during development, but also indicate that in the Western Cape province, inoculum in vineyards is abundant during the early part of the season, and less abundant later in the season. More information is therefore needed on the behaviour of the different types of B. cinerea inocula on the different morphological parts of grapevine to validate the pathway described for natural B. cinerea infection in vineyards. The penetration and disease expression at the different morphological parts of bunches of two grape cultivars (Dauphine and Merlot) under conditions simulating natural infection by airborne conidia was therefore investigated. The two cultivars did not differ in resistance of the berry cheek, which was at all stages classified as resistant. However, in Dauphine, latent inoculum levels in berry cheeks declined from intermediate at pea size to low at the following stages, whereas in Merlot, levels were intermediate during pea size and at harvest. Some differences between cultivars were found in the resistance of the structural bunch parts, and of their latent inoculum levels. In Dauphine, the rachis reacted susceptible at pea size, and was classified moderately resistant later in the season. Laterals and pedicels were moderate resistant at pea size, and resistant at later stages. Inoculum levels in rachises, laterals and pedicels were high at pea size, but intermediate at bunch closure and at harvest. The finding that B. cinerea infected and naturally occurred more commonly in the tissues of immature than mature bunches, that the structural parts of the bunch carried more B. cinerea than the berry cheek, and that these infections may be more important in B. cinerea bunch rot than infection of the cheek or the style end, suggest that emphasis should be placed on the disease reaction of the pedicel and related parts of immature bunches rather than on the berry. The resistanc-e reaction of leaf blades, petioles, internodes and inflorescences on cuttings, compared to those on older shoots from the vineyard were therefore investigated. In the case of vinelets, leaf blades, petioles, internodes and inflorescences were all classified susceptible to highly susceptible. The different parts furthermore all carried very high latent inoculum levels. In vineyard shoots the petioles and inflorescences showed resistance, and carried intermediate to latent inoculum levels. This finding suggests that leaf blades are not appropriate parts for studying the behaviour of inoculum of B. cinerea and host responses in grape bunches. In stead, petioles and inflorescences of vineyard shoots should be used for this purpose.

AFRIKAANSE OPSOMMING: WEERSTAND TEEN BOTRYTIS CINEREA IN MORFOLOGIESE DELE VAN BLARE EN TROSSE VAN WINGERD Kennis oor die teenwoordigheid van Botrytis cinerea in morfologiese dele van wingerd word benodig vir die ontwerp van 'n betroubare, sensitiewe en spesifieke toets vir die bevestiging van latente infeksies, en vir die implementering van strategieë vir die effektiewe beheer van B. cinerea-vrot. Die doel van hierdie studie was om (i) natuurlike B. cinerea infeksie by spesifieke areas in blare en trosse van wingerd te bepaal, en (ii) om weerstand teen siekte-uitdrukking in hierdie morfologiese dele vas te stel. Trosse en blare van die wyndruif kultivar Merlot en die tafeldruif kultivar Dauphine, is by ertjiekorrel, tros-toemaak en oes in vyf wingerde in die Stellenbosch- en De Doomsomgewing, onderskeidelik, versamel. Die materiaal is in twee groepe verdeel en in polietileen sakkies verseël. Die sakkies is met klam papierdoekies uitgevoer om sodoende hoë relatiewe humiditeit te verseker. Blare en trosse wat in die een groep geïnkubeer is, is eers met paraquat behandel om aktiewe gasheerreaksies te beëindig. Hierdie behandelings het toestande geskep wat gedurende die periode van vogtige inkubasie gunstig was vir siekteontwikkeling deur verskillende inokula by twee gasheer-weerstandsvlakke. Siekteuitdrukking is positief geïdentifiseer deur letsel-ontwikkeling en die vorming van sporuierende kolonies van B. cinerea by 'n potensiële infeksie-area. Dele waarop in die blare gekonsentreer is, was die blaarskyf en -steel. In die trosse was die dele die rachis, lateraal en korrelsteel, en op korrels was dit die korrelsteel-end, wang en styl-end. In Dauphine is die verskillende dele tydens al die fenologiese stadia as weerstandbiedend tot matig weerstandbiedend geklassifiseer. Die verskillende dele her egter, ten spyte van hul weerstandbiedendheid, hoë tot baie hoë inokulumvlakke by ertjiekorrel- en tros-toemaakstadium gedra. Die enigste uitsondering was die korrelwang, wat 'n middelmatige inokulumvlak by ertjiekorrel, en 'n lae inokulumvlak by tros-toemaak, gedra het. Die inokulumvlakke was in byna al die dele laer by oes. Die afname in inokulumvlakke was die prominentste in die blaarstele, rachi, laterale, korreisteie en die korrelsteel-end van die korrel. Al hierdie dele het 'n middelmatige tot lae inokulumvlak by oes gehad. In Merlot was die dele konstant weerstandbiedend, behalwe vir die korrelsteel en die korrelsteel-end van die korrel, wat gewissel het van weerstandbiedend by die vroeë ontwikkelingstadia, tot vatbaar by oes. lnokulumvlakke in die rachis en lateraal het gedurende die seisoen afgeneem; maar was deur die seisoen konstant hoog in die korrelsteel en korrelsteel-end van die korrel. Volgens die patroon van natuurlike voorkoms, word B. cinerea-vrot in hierdie wingerde nie deur kolonisasie van die stamper, en die daaropvolgende latensie in die styl-end van die korrels, veroorsaak nie. Vrot word egter primêr deur kolonisasie van die korrelsteel, en die daaropvolgende latensie in die korrelsteel of korrelsteel-end van die korrel, veroorsaak. Hierdie bevindinge ondersteun die hipotese van toenemende gasheerweerstand gedurende ontwikkeling, en dui ook daarop dat inokulumvlakke in wingerde in die Wes-Kaap provinsie volop is gedurende die eerste deel van die seisoen, en minder volop is later in die seisoen. Meer inligting word dus benodig aangaande die gedrag van die verskillende inokulum tipes van B. cinerea op die verskillende morfologiese dele van wingerd, ten einde die infeksieweg vir natuurlike B. cinerea infeksie in wingerde te bevestig. Die vestiging van latente infeksies in die verskillende morfologiese dele van trosse van twee kultivars (Dauphine en Merlot), onder toestande wat natuurlike infeksie deur luggedraagde konidia simuleer, is dus ondersoek. Die twee kultivars se weerstand in die korrelwang het nie verskil nie en is by alle fenologiese stadia as weerstandbiedend geklassifiseer. Die latente inokulumvlakke in die korrelwang van Dauphine het egter van middelmatig by ertjiekorrel, tot laag in die daaropvolgende stadia afgeneem, terwyl die vlakke in Merlot middelmatig by ertjiekorrel en oes was. Verskille tussen die twee kultivars is gevind ten opsigte van die weerstand in die trosdele, asook hulle latente inokulumvlakke. Die rachis van Dauphine was by ertjiekorrel vatbaar, en matig weerstandbiedend later in die seisoen. Die lateraal en korrelsteel was matig weerstandbiedend by ertjiekorrel en weerstandbiedend by latere stadia. lnokulumvlakke in rachi, laterale en korreisteie was hoog by ertjiekorrel, maar middelmatig by tros-toemaak en oes. Die bevindinge dat B. cinerea natuurlik meer algemeen in die weefsel van onvolwasse trosse voorgekom en laasgenoemde meer algemeen geïnfekteer het, dat B. cinerea se voorkoms hoër was in die morfologiese dele van die tros as in die korrelwang, en dat hierdie infeksies van groter belang in B. cinerea-vrot mag wees as infeksie van die wang of styl-end, dui daarop dat klem gelê moet word op die siektereaksie van die strukturele dele van onvolwasse trosse, eerder as van die korrel. Die weerstand van blaarskywe, blaarstele, internodes en blomtrossies van steggies, in vergelyking met die op ouer lote in wingerde, is dus ondersoek. Blaarskywe, blaarstele, internodes en blomtrossies van steggies is almal as vatbaar tot hoogs vatbaar geklassifiseer. Die verskillende dele het verder ook almal baie hoë latente inokulumvlakke gedra. By die ouer lote van wingerde het die blaarstele en blomtrossies weerstandbiedend vertoon, en middelmatige latente inokulumvlakke gedra. Hierdie bevindinge dui daarop dat blaarskywe nie die ideale morfologiese deel is vir gedragstudies van B. cinerea in druiwetrosse nie. Blaarstele en blomtrossies van ouer lote moet eerder vir die doel gebruik word.

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