Abstract
In a South African wine industry-funded study (IWBT B 14-01), researchers focused on selecting and screening ‘untested/poorly tested’ rootstock material for abiotic stress-resistance phenotypes. The study also evaluated disease-resistance phenotypes of potentially valuable grapevine material. The findings shed light on the importance of waxiness in protecting grape berries against fungal pathogen infection, providing useful insights for future breeding and evaluation programs.
Introduction
Several grapevine lines developed through breeding programs, i.e., the South African rootstock breeding program and clonal selection programs by various industry role players, hold a wealth of potentially valuable characteristics yet to be thoroughly analysed. The challenge lies in the time and costs associated with field studies. However, the prospect of quicker, informative pre-screens of potentially important material, leading to the selection of specific lines for more comprehensive field testing, holds promise for the future of grapevine production.
The study’s first aim was to develop and evaluate lab-based (in vitro) screens for abiotic (environmental) and biotic (infection) stresses to provide alternatives or supplementary methods for classical field-based methods. The study’s second aim was to screen and select potentially valuable grapevine resources to support the industry’s current and future aims, specifically focusing on sustainable and environmentally friendly production. This aim had two objectives: Selecting and screening rootstock material with lab-based tests to profile their abiotic resistance phenotypes, particularly water and salt sensitivities, and evaluating disease resistance phenotypes of potentially valuable grapevine material.
Experimental layout
Rootstock cultivars (Dog Ridge, Vitis Berlandierii, 143-B MGT, Ramsey, 1103 Paulsen, Paulsen 775, Gravsac, SO4, 101-14, RUG 140, R1012 and 44-53 Malegue) were selected for in vitro testing to analyse abiotic and biotic stress resistance phenotypes using non-field-based methods. The buds and growth points of the winter canes of the above-mentioned rootstock cultivars were used for in vitro initiation to provide source materials for in vitro grafting and water and salt-stress screening.
The parents and progeny of a breeding experiment (targeting disease resistance) have also been screened for a possible correlation between the waxiness of the berries and pathogen resistance. This screening occurred with berry infections with Botrytis cinerea under controlled conditions.
Screening of rootstock cultivars against simulated drought conditions
Many cultures were established and maintained to screen for osmotic stress tolerance in vitro. A test system was implemented to evaluate the stress levels perceived by the plantlets and compare the different materials for their stress resistance levels. Scoring of axillary bud outgrowth and the delay thereof under induced stress conditions, as well as root formation and biochemical stains for stress indication, correlated very well with stress levels.
The following cultivars were screened successfully: Dog Ridge, Gravsac, Vitis Berlandierii, 143-B MGT, SO4, Ramsey, 1103 Paulsen and Paulsen 775. The rootstocks 101-14, RUG 140, R1012 and 44-53 Malegue were not screened for phenotypic and biochemical profiles due to slow growth and/or low population sizes.
1103 Paulsen and Paulsen 775 displayed the most favourable phenotypic traits and exhibited the lowest stress under simulated drought conditions in vitro. The data generated under tissue culture conditions correlated well with the known data sets based on field trial experiments for all the screened rootstocks.
These methods were successful in categorising the rootstocks according to their known sensitivities. They proved to be sensitive, and since the screens were completed within five weeks, they hold great promise for screening materials before lengthy field trials.
Botrytis and waxiness
To investigate the role of waxiness in grape berry infection, the researchers performed Botrytis cinerea inoculations on berries from the selected populations. The screening of the berries from the parents and some of the progenies that displayed different levels of waxiness in terms of their Botrytis infection susceptibility provided clear evidence that the waxy layers are essential for protecting the berries against successful infection. The presence of wax layers was found to delay or inhibit the infection take rate and level of infection. On average, berries considered ‘waxy’ had a 20% rate of establishing an effective infection, compared to 55% in ‘non-waxy’ berries. When the waxes were chemically removed before infection, the take rate increased to 37.5% for intact waxes and 88% when the waxes were removed. These results indicate that a waxier phenotype reduced infection rates when the berries were infected with B. cinerea.
Conclusions
The in vitro screening methods and laboratory-based infection analyses implemented in this study were successful in characterising the materials targeted. The protocol for screening the rootstock materials was optimised to be completed in four to five weeks, making it potentially very useful to pre-screen potential materials under controlled conditions in a reasonable timeframe before proceeding with more comprehensive analyses under field conditions.
Similarly, a laboratory-based infection strategy of grapevine berries to characterise the berries in terms of the possible link between waxes and diminished Botrytis infection was very successful and contributed to the phenotyping of a breeding and mapping population targeting disease resistance. The results also show that the waxiness trait would be an excellent trait to incorporate when looking for disease resistance in grapevines.
The major benefit is potential technology/workflow optimisation that could become part of a ‘toolbox’ of methods available for viticultural applications, specifically the phenotypic characterisation of grapevine material.
For more information, contact Melané Vivier at mav@sun.ac.za.
Click here to get your copy of WineLand Magazine.
