Arbuscular mycorrhizal root colonisation and the subsequent host plant response in young grapevines in a South African commercial vineyard

[摘要] ENGLISH SUMMARY: Arbuscular mycorrhizal (AM) fungi facilitate the uptake of nutrients, improve growth and alleviatedrought stress in grapevines. Consequently, AM fungal root colonisation contributes to theoptimum performance of grapevines. It is for this reason that young grapevines are sometimesinoculated with commercial AM fungal strains to reduce environmental stresses during transplant.In the past, soil fumigation has often been considered as a prerequisite for soil conditioning withcommercial AM fungal strains. However, grape growers opting to inoculate with these fungalstrains will have to do so in unfumigated soils, since the use of fumigants in South Africanagricultural soils is currently being phased out. Since little is known about the nature and scope ofindigenous AM fungi that may be present in SA vineyard soils, it is difficult to predict the grapevine'sresponse to artificial inoculation in soils already containing adequate concentrations of these fungi.In the first part of the study, commercially available AM inocula were tested under field conditionsthat would prevail on a typical farm. This entailed measuring vine growth, nutrition, drought stressresistance and percentage root colonisation, over two consecutive seasons, from the onset ofplanting new commercial grapevines. The field trial carried out at Groenland, a commercial farm inthe Stellenbosch Region. Merlot grafted onto 101-14 Mgt, 110 Richter (110 R) and 99 Richter (99R), was planted in December 1998. These rootstocks were selected to accommodate different soilforms: 101-14 Mgt and 110 R on a Westleigh soil form, which was ridged and 99 R on anunridged Fernwood soil form. Vine roots were inoculated during planting with different AM inocula,i.e. Biocult®, Vaminoc and Glomus sp. 1054. One treatment was left uninoculated and treatedwith a combination of the fungicides Benlate (active ingredient: benomyl) and Rovral Flo® (activeingredient: iprodione). The control received neither fungicides nor inocula.Microscopic examination of the vine roots revealed that, apart from a significantly higher level ofroot colonisation observed in Biocult-treated 99 R vines during the first season, the level of AMroot colonisation was similar in both the uninoculated (control) and inoculated vines. Infectedcontrol vines indicated that indigenous AM fungi were present in the vineyard soil. This levelranged between 40% and 85%, and 70% and 90% in the first and second season, respectively.Apart from the significant growth improvement observed in 110 R vines inoculated with Glomus sp.1054 during the first season, no growth improvement was observed for the other rootstocks ortreatments. Furthermore, generally no alleviation of water stress and nutritional benefits could bedetected for both the seasons. Despite this, less than 1% dieback was recorded for the vines.In the second part of the study, additional information on the diversity of indigenous AM fungalspecies was obtained, which included the quantification and identification of these fungi present inthe soil. The AM fungal spore numbers in the vineyard soil ranged from 1000 to 3779 spores/100 gdry soil. The results confirmed that the majority of AM fungal species found in the soil was not partof the commercial inocula, but originated either from the vineyard and/or the nursery where thevines were obtained. The uncovered AM fungal species belong to the genera Acaulospora, Gigaspora, Glomus, Sclerocystis and Scutellospora. This is similar to the AM fungal generarecorded in vineyards by other workers.To the best of our knowledge, this study provided the first documented evidence on the diversity ofindigenous AM fungi present in SA vineyard soils. Although it may be preliminary in nature, theresults clearly showed that a wide diversity and abundance of indigenous AM fungal populationsmay occur in a typical SA vineyard. Depending on the superiority and possible masking effects onthe part of the indigenous AM fungal populations, positive responses to inoculation with commercialAM fungal strains in grapevines grown in such vineyard soils may consequently be unlikely. Thus,before reconditioning of vineyard soils with these fungi can commence, it is essential for farmers tofirst assess the mycorrhizal status of their soils and nursery vines. Since the majority of SA farmersare not yet familiar with inoculation practices and are still unacquainted with the mycorrhizal statusof their soils, the findings from this study could be of great benefit to particularly wine grape growersopting to inoculate with commercial AM fungal strains on a large-scale.

[发布机构] Stellenbosch University