Browsing by Author "Van Zyl, Sonet"

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    Inheritance and genetic mapping of Xiphinema index resistance derived from Vitis arizonica
    (Stellenbosch : Stellenbosch University, 2012-12) Van Zyl, Sonet; Walker, M. A.; Vivier, Melane A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Grapevines are one of the most important and diverse crops in the world, but tend to be susceptible for numerous pests and diseases. The dagger nematode, Xiphinema index (X. index) is a well-known soil-borne pest of grapevine and vector of grapevine fanleaf virus. Several Vitis species showed resistance to this pest. Breeding efforts have been underway for several decades to create resistant rootstocks. However, conventional breeding efforts are time consuming due to grapevines being a perennial crop, its heterozygosity, as well as its long growth cycle. Breeding new grapevine varieties are also expensive and work intensive. The development of marker-assisted selection introduced a way to overcome some of the abovementioned problems. The aim of this study was to broaden the genetic evaluation and breeding efforts for improved X. index resistance in grapevine rootstocks. In 2007 several crosses were made in the University of California, Davis vineyards. The background for all these crosses consisted of V. arizonica. These V. arizonica plants are part of a collection obtained by H.P. Olmo during the 1960’s. In recent studies it was established that X. index resistance is controlled by a single dominant gene. The 0701 (R8916-07 (Wichita Refuge x b40-14) x R8916-32), 0704 (161-49C x b40-14) and 0705 (161-49C x R8916-22) populations were created to confirm the homozygous nature of b40-14, a V. arizonica accession. In addition, several V. arizonica species were screened to confirm their resistance or susceptibility towards X. index feeding. The 0705 population was also used to create a genetic map for X. index resistance. In this study a new and improved screening method was developed to inoculate vines under greenhouse conditions. This screening method proved to be quicker and less damaging on the nematodes than traditional systems. Control varieties were used and O39-16, a commercial rootstock showed no damage, even with high nematode pressure, whereas V. rupestris Saint George had severe root damage and decline after eight weeks of exposure. A range of V. arizonica accessions was tested for their resistance to X. index feeding. Of the 18 genotypes tested, half showed resistance and the rest were susceptible. It is possible that these genotypes are not pure V. arizonica genotypes. Genotypes with V. arizonica in the background were also tested. Wichita Refuge was used as a susceptible female parent and the progeny were expected to be heterozygous resistant. Some of the progeny allowed low levels of feeding damage, which may have been the result of the more effective inoculation method described above. The 0701 population confirmed the hypothesized model of 3:1 (Resistance (R):Susceptible (S)) segregation although 13 of the genotypes showed significantly higher gall numbers than the susceptible female parent. The possibility of transgressive segregation exists, but needs to be confirmed. All progeny from the 0704 population should be heterozygous resistant, but a 1:1 (R:S) segregation pattern was observed. The 0705 population was created as a mapping population to study X. index resistance. This population was also tested in the greenhouse for its X. index resistance and was expected to segregate 1:1 (R:S). The X2 analysis did not fully support this model. A genetic map covering all 19 linkage groups, and positioning 175 polymorphic SSR markers was created for the 164 progeny in the 0705 population. MapQTL analysis revealed a major QTL on linkage group 9 and two minor QTL’s on groups 13 and 19. The major QTL placed between markers VMC1c10 and CTG1032918 with a LOD score of 33.4 explaining 70.5% of the phenotypic variance for X. index. This QTL is the second major QTL discovered for X. index resistance. With the discovery of a second major QTL, the two types of resistance can be pyramided. Work is underway to saturate the area around the major QTL on linkage group 9 and to move towards physical mapping of X. index resistance. The b40-14 V. arizonica accession is also known for its resistance to Pierce’s disease and the possibility of simultaneous expression of two types of resistance is created. The 0705 population can also be used to evaluate phenotypical characteristics in the field to determine if useful rootstocks can be selected. Taken together, the results obtained in this study provide improved methods and highly characterized plant populations to support the efforts in obtaining improved X. index resistance in grapevine rootstocks.
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    Open hydroponic systems in table grape production : a case study
    (Stellenbosch : Stellenbosch University, 2003-12) Van Zyl, Sonet; Vivier, Melane A.; Stassen, P. J. C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: An open air hydroponic production system (OHS) is based on classic hydroponic principles, with the difference that it lacks climatological control because the plants are not produced in greenhouses and are cultivated in the outside environment. In these systems the plant is provided with all the essential nutrients through the irrigation system, which is scheduled according to accurate measurements of the available soil water, in three to seven pulses a day. The rationale is that, by delivering nutrients each day, the mixes can be representative of what the plant actually requires for that specific phenological stage. The aim of this study was to monitor the usefulness and impact of OHS on table grape production within the framework of a case study. For this purpose, it was necessary that all factors involved in the development and growth of the plant should be studied and integrated in a multidisciplinary approach. Currently very limited information exists on basic guidelines for the effective implementation of these systems for table grape production, particularly with regard to local conditions. As a start, and to establish some guidelines and measurable parameters for the implementation of these systems, vegetative growth parameters were analysed within the framework of yield and fruit quality. The experiments were performed in a commercial vineyard in the Paarl region and the cultivars used were Dan ben Hannah (DBH) and Waltham Cross (WC). Relevant soil and climatic conditions, irrigation scheduling, fertiliser application, as well as cultivation practices, were taken into account. The soil maps provided information on the soil types identified in the blocks prior to the establishment of the two cultivars. The conventionally treated vines were irrigated and fertilised according to historical block data, and the OHS-treated vines according to programmes established by two different consultants. The experimental layout included a comparison of conventional cultivation methods and vines that had been switched over from conventional methods to OHS in the middle of 2000. All measurements within the different treatments were done at specific measuring points laid out statistically. Ten phenological stages were chosen to monitor the various aspects throughout the season for both cultivars treated conventionally and hydroponically. All relevant climatic parameters were collected for this specific production unit. The growth, fertility and quality indicators of these cultivars under the mentioned cultivation practices are discussed and established through quantitative analysis One of the aims, namely to show that established table grape vines could adapt from micro-irrigation to drip irrigation within two seasons in terms of root adaptation, was proven in this study. Initially the soil types were identified as Cartref, Clovellyand Glenrosa for both cultivars. The WC block contained an Avalon and the DBH a Westleigh soil type as well. The soil pits in all four treatments revealed the soil type to be a Tukulu form with differences in the clay content. Active roots developed underneath the drip lines for the OHS-treated cultivars, while the roots were still evenly distributed over the entire soil profile for the conventionally treated vines. Also, both cultivars adapted to OHS in terms of yield and production within two seasons, especially WC, which produced a higher yield in the 2001/2002 season than in the previous four seasons. DBH showed a strong vegetative reaction to OHS in terms of excessive vegetative growth, which had an indirect effect on fruit quality and bud fertility. A higher rate of bud mite infection in the OHS-treated vines also had a negative influence on bud fertility. The excessive vegetative growth was due to a rainy 2001/2002 growth season, in combination with the irrigation and fertiliser programmes. The irrigation and fertiliser programmes were changed from the 2000/2001 to the 2001/2002 season because of the change in consultants. As a result of this change, the OHS-treated vines were given very high nitrogen, phosphorus, potassium and micronutrient applications in the 2001/2002 season. The penetration of light in the canopy of the OHS-treated DBH was lower than in the conventionally treated DBH as a result of the above-mentioned factors, but the situation in Waltham Cross was the opposite. In the winter season of 2001, both OHS-treated cultivars were not fully adapted to the new system, as their pruning mass was lower than in the conventionally treated cultivars. No significant differences were determined for the winter cane starch content of both cultivars under conventional and OHS treatments. Effective fertiliser uptake proved to be suboptimal, especially in the case of calcium. Fruit analyses showed a lower calcium content in the OHS-treated fruit, which led to a poor skin cell structure and higher Botrytis infection during cold storage. The OHStreated cultivars showed more compact bunches, with an overall smaller rachis structure, which was another reason for the higher Botrytis infection during cold storage. However, the more compact rachis structure could not be explained on the basis of the elemental analyses. The OHS-treated DBH showed a more intense red berry colour, while the OHS-treated WC had a higher Fosscan Brix value. Both OHS-treated cultivars therefore ripened earlier than the conventional treatments. One of the advantages of the use of OHS in table grape production shown in this study was the ability to manipulate the phenology of the grapevine to provide fully ripened grapes a few days earlier than the conventionally treated grapes. This kind of advantage could be used to manipulate the production of table grapes for a better market window. Despite its limitations, this study concluded that the use of OHS for table grape production might be a useful tool for future production management, but that accurate management regarding irrigation and nutrient applications is a prerequisite. This will have to be developed systematically through experimentation to fully unlock the potential of the OHS management system for table grape production. This study provides a starting point for future research to elucidate these aspects and has clearly shown that even established vineyards can be switched to OHS in a relatively short period of time. It is envisaged that the advantages of this system, as long as the correct management protocols are in place, could have a positive effect on the production of high quality fruit for the international market.