Disease Resistant Apple

Have you ever purchased an apple tree, based on the wonderful description of the fruit-to-come on the tag/website, and poured time, energy, and love into it?
And several years later found that it is struggling due to a disease?

What novice I recently learned is that apples are typically grafted onto rootstocks.
Very oversimplified, these rootstocks will then essentially determine the foundational characteristics (hardiness, size, disease/pest resistance, etc.).

There is a post on the North American Fruit Explorers (NAFEX) group on Facebook and it appears that the following experts have the top recommendations in terms of disease resistant apples.
Would you agree, or would you happen to know of other(s) whom would be knowledgeable?

Larry Stephenson
Mike Biltonen
Cummins family of Cummins Nursery
Eliza Greenman
Jules Janick
Amy Christel Miller
Guy King Ames
Gennaro Fazio
Joseph Lofthouse
Michael McConkey
Dan Bussey
David Vernon
Doug Crouch

Lastly, what would you happen to know about the Marssonina Leaf Spot?
Any recommended expert who is versed on this topic?

akira hirose wrote:, these rootstocks will then essentially determine the foundational characteristics (hardiness, size, disease/pest resistance, etc.).

I hadn't realised that the rootstock had that much effect. In the UK they are mainly for controlling the vigour of the tree. You can chose the top graft for better disease resistance though. Many of the apple tree suppliers will give information on the relative disease resistance of the varieties.