The Microbial Community of Grape Berry

During the 2022 growing season, we did a really good job of taking care of our canopy and keeping diseases out of the vineyard until.....the disastrous rains came.
We were able to harvest the Auxerrois on September 25 and the Chardonnay on October 2 which came in free of rot and later the Cabernet Sauvignon, Cabernet Franc and Barbera on October 21 which were also clean.
However, in the middle, the Chenin Blanc harvested on October 16 and 17 was doing very well until the rains came on October 6, 8, and 13 and each time it rained, we lost a little more of our crop to rot.
Now is the time to look back and figure out what we can do so that we are not repeating this unfortunate scenario in the future.
Fortunately, I came across "The Microbial Community of Grape Berry", a chapter in the book called The Biochemistry of the Grape Berry.¹ The book was published in 2012 and this chapter is a very comprehensive look at what kinds of microbes are present on a grape berry at any given time.
It is a very long chapter so I'm going to break it up into digestible bites which will be written up in subsequent blogposts. The one big takeaway from this report is that there are 4 distinct groups of microorganisms that can be present on the grape berry.
This is a summary of these various groups from a table provided in the chapter:

The residents are microorganisms on the undamaged grape, from berry set to harvest, that use nutrients available on the surface of immature or mature berries.
The adventitious are those detected on berry surfaces, at any phase of berry development, but without the ability to grow and whose presence derives from mere contamination by both biotic and abiotic vectors.
The invaders are those which manage to penetrate through the intact skin tissue by their own means to gain access to grape pulp (or leaf) nutrients. They thrive from berry set to veraison and do not require the existence of skin lesions.
The opportunists, also called copiotrophic residents, are those able to grow, typically after veraison, at the expense of grape pulp nutrients as a consequence of microfractures or wounds in the berry skin.
It is not enough to know what types of microbes are present, it is also important to know when they are resident on the grape berry and what impact it has on the condition of the berry. These are some topics I will cover in the next blogposts. Stay tuned!
References:
1. V. Loureiro, M. M. Ferreira1, S. Monteiro1 and R. B. Ferreira, "The Microbial Community of Grape Berry", The Biochemistry of the Grape Berry, Chapter 12, 2012, 241-268.