WINETECH Technical Yearbook 2021

viii) HWT at 50°C for 30 minutes. ix) HWT at 50°C for 45 minutes. x) An untreated control.

ous trials low Trichoderma re-isolations were obtained, indicating that the BCA did not establish well. Currently, there are no Trichoderma products registered for root application on grapevine in South Africa. FIELD TRIALS Sauvignon blanc clone SB316G grafted onto rootstock variety Ramsey clone SC18AB were used for both trials. For the trial evaluating different methods of application of Trichoderma to nursery vines post callusing, treatments consisted of: i) Coating the basal ends with dry product as depicted in figure 1. ii) Coating the basal ends with dry product followed by one soil drench per month for six months. iii) HWT (of dormant rootstock and scion shoots) at 50°C for 30 minutes and coating the basal ends with dry product. iv) Soil drenching directly after planting followed by one soil drench per month for six months. v) Soaking for one hour in conidial suspension. vi) HWT at 50°C for 30 minutes and soaking for one hour in conidial suspension. vii) HWT at 50°C for 45 minutes and soaking for one hour in conidial suspension.

of water as USPP-MT1 is a benzimidazole resistant mutant obtained through gamma irradiation. The root zones of the treated plots were drenched with 10 L of conidial suspension of the respective Trichoderma products at monthly intervals for the first three months after planting. Each treatment consisted of 100 graftlings, replicated four times and repeated over two seasons. Following on site treatment the trials were planted in a commercial grapevine nursery located in the Wellington region and allowed to root for one season according to standard nursery practice. After seven months the vines were uprooted and fungal incidences determined from 25 vines per replicate. Isolations were made from 1) the xylem and pith in the basal end, and 2) three sections of the roots, namely the rootstock attachment, central part and root tips. Fungal isolates representing any of the BFD pathogens or Trichoderma isolates were grouped and identified according to standard protocols. RESULTS AND DISCUSSION The two field trials showed that Tricho­ derma species, even after more effective colonisation, were not sufficient to prevent all infections by BFD pathogens. The efficacy of Trichoderma is influenced by the specific pathogen complex. In the current study the majority of the BFD pathogens were found to be of the genus

Campylocarpon , that are less sensitive to secondary metabolites produced by Trichoderma in vitro (data not shown). Analyses of the different tissue types revealed that in both trials BFD infections of the roots were significantly higher than in the basal ends of the rootstocks, while the opposite was true for Trichoderma as demonstrated with the different products trial in figure 2. This effect was, however, variable over the two years. It appears as if Trichoderma was able to prevent pathogen infection of the basal ends where its colonisation was higher. When taking the results of the trial evaluating the methods of application of both seasons into account the highest re- isolation percentages of Trichoderma were obtained with the dry product application in combinat ion wi th monthly soi l drenches, or with 30 minutes HWT prior to grafting. In contrast, one hour soaking in a Trichoderma conidial suspension prior to planting, and combinations thereof, were mostly ineffective and resulted in an outcome not different from the untreated control in either of the seasons (figure 3). Different from the standard methods of ap - plication, the dry product application places high inoculum loads at the basal end of the graftlings before planting. At the time of planting the basal ends are often not com- pletely healed or covered by callus tissue, and

For the respective treatments that received dry product applications (i, ii and iii) approximately 30 mm of the basal ends of the rootstock material were dipped in water and then in one kg dry product formulation, while for soaking (v, vi and vii) approximately 150 mm of the basal ends of the rootstock material were soaked in a Trichoderma conidial suspension for one hour. For treatments receiving soil drenches (ii and iv) the root zones of the respective plots were drenched with 10 L of conidial suspension at monthly intervals for six months after planting. Each treatment consisted of 100 graftlings, replicated five times and repeated over two seasons. Some treatments were adjusted in the second season and were, therefore, not repeated. For the trial evaluating different Tricho­ derma-based products to nursery vines post callusing, treatments included six commercial products, of which two are registered for pruning wound application on grapevines, and two isolates that are in the process of commercialisation USPP-MT1 and USPP-T1 (Stellenbosch University), as well as an untreated control. All treatments were done as described for the dry product application above, except for USPP-MT1 that was dipped in Bendazid ® 500 SC instead

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