In its current fifth phase (PHI-5), the PHI Programme and the South African Table Grape Industry (SATI) initiated and co-funded a project in 2023. This is one of three such collaborative projects between the two entities.
The project was dubbed “Generation of a berry cracking index for the South African table-grape gene bank”. This article is a precursor for the one on page 56 that elaborates further on the technical aspects of the project.
A problem to solve
The project was focused on berry cracking, which demands a robust mitigation strategy. From it, emanated the development of an index that can offer vital insights to breeders when selecting parents and when evaluating cultivars.
Berry cracking typically occurs due to the physical failure of the waxy layer of the skin of the grape berry. This is a major concern for table-grape growers worldwide, and certainly those in the South African export-oriented table-grape industry.
This physiological disorder, which is intersectional in nature, has its origins in a complex junction of environmental, physiological and genetic factors. The physical failure of the berry cuticle is triggered by a combination of factors, including the structure and composition of the fruit surface, turgor, Abscisic acid (ABA) levels, and water absorption. Turgor is the pressure exerted by fluid against the cell wall, which reflects in the sugar content of the berry flesh.
Getting to work
To commence the co-funded project, Dr Justin Lashbrooke of Stellenbosch University’s Department of Genetics headed up a team, including PhD student Robin Bosman, who was tasked with implementing an optimised assay.
The successful implementation of the harvesting and data acquisition work was vital to the success of the task at hand.
The laboratory procedure was implemented across the South African table-grape gene bank, resulting in the developed index for cracking resistance or susceptibility. The team could measure up to 220 different table-grape cultivars for their skin elasticity, which was then used as a proxy for measuring their susceptibility to cracking. The objective findings from this exercise allowed the researchers to rank cultivars based on cracking resistance.
Pre-harvest vigilance
The rationale behind the co-funded project was to gain an understanding of berry cracking at field level.
Long before table grapes are harvested, opportunistic pathogens can enter the berries through surface cracks and, under specific conditions, latent infections may become active. In some instances, this manifests as berry cracking. So, the reality is that observable post-harvest berry cracking can originate in pre-harvest conditions.
Cultivar choice
To breed the next generation of cultivars, breeders must select the correct parent material. Therefore, the referenced index is a useful tool in objectively scoring cultivars for their resistance to cracking.
Berry cracking is also under genetic control, as it has been established that some cultivars are more susceptible to cracking than others. Plus, it has become evident that there is a clear correlation between skin elasticity and crack resistance.
The research outcome provides growers with concrete knowledge of the extent of cultivar susceptibility to cracking, as well as a uniform point of reference. This is a breakthrough in providing the right tools for growers’ planning around cultivation and breeding programmes.
Waste not, want not
Table-grape growers can ill afford the fruit loss related to berry cracking – not to mention the potential related economic losses.
Quality being a key focus in the production of South African table grapes, effective mitigation of cracking improves the export potential and possibly even the shelf-life of table grapes. Down the line, the findings of this research project can be instrumental in bringing about significant savings for proactive growers. In turn, this will help ensure financial stability at farm level and enable these growers to continue to provide much needed jobs.
And the pre-harvest component of the research can help table-grape growers manage their vineyards more effectively, to avoid berry cracking later on.
Out with the old
In an ever-evolving industry, producing different results demands a new way of thinking. This places immense pressure on growers for a paradigm shift.
They face an increasingly competitive global market landscape. And research such as this, which presents new approaches to address long-standing challenges, plays a key role in ensuring industry sustainability.
The outcomes of this co-funded project align with industry disease mitigation objectives and signal a promising future. However, further research is required to fully maximise this significant groundwork.
