2024 Chenin Blanc and SAD: Part Three

This is the final blog detailing the problem we had with our 2024 Chenin Blanc experiencing a sugar accumulation disorder (SAD) and suppression of uniform ripening (SOUR) problem.
The first blog 2024 Chenin Blanc and SAD: Part One was an overview of the grape ripening disorders that can occur.
2024 Chenin Blanc and SAD: Part Two focussed on sugar accumulation disorder (SAD) and suppression of uniform ripening (SOUR) both classified as grape ripening disorders that occur shortly after the resumption of ripening in stage 3.
In order to discover why the grape berries stopped accumulating sugar, the authors of the article noticed that:¹

• Once initiated, the impaired sugar import into the berries triggers downstream effects on primary and secondary metabolism before the visible symptoms of berry shrivel (BS) appear
• BS berries remained low in K+ (which, like sucrose, is imported via the phloem) and pH
• BS berries showed a higher total acidity in BS berry juice, possibly due to a concentration effect of less turgescent berries
• There may be a genotype that succumb to BS, which includes varieties such as Cabernet Sauvignon, Blauer Zweigelt, Pinot noir, Pinot blanc, Durif, Sémillon, Sauvignon blanc, Grüner Veltliner, Nebbiolo, Chasselas, Humagne rouge, Gewürztraminer, Melon, Merlot, and Cornalin

BS is associated with major shifts in primary and secondary metabolism at the transcriptional level, resulting in distinct metabolic profiles. The authors made the following observations between healthy and BS affected berries:

• The brush, an opaque flesh consisting of vascular tissues in healthy berries, remains attached to the pedicel when the berry and pedicel are pulled apart; in contrast, the brush lacks flesh when BS berries are removed
• In BS berries, a higher percentage of cell death is observed near the seeds in the inner mesocarp
• In BS-afflicted clusters, the extent of the plugging of sieve tubs is much greater than in healthy berries

While the authors made all of these observations, they were uncertain as to the cause of the BS in the grape berries, they could only point to a disturbance in the onset of ripening.
I still found this an interesting review article to read. We will certainly be on the look out for SAD and SOUR in our grapes during the coming season.

References:
1. Griesser M, Savoi S, Bondada B, Forneck A, Keller M. Berry shrivel in grapevine: a review considering multiple approaches. J Exp Bot. 2024 Apr 15;75(8):2196-2213. doi: 10.1093/jxb/erae001. PMID: 38174592; PMCID: PMC11016843.