In practice, how does industry marketing and solutions marketing look different from product marketing? Doesn't product marketing have to message to industries and solutions already?

First off, I think of both industry and solution marketing as specializations within product marketing; and there are cetainly successful companies that don't divide out their product marketing organization this way. The key distinction is the focus, and what the marketer needs to be a true expert in. 

All product marketers, of course, need to "know" their products, solutions, buyers, and market and the key messages and value propositions of the union between each of those things. But in companies with mature industry marketing functions, part of the product marketing organization focuses on the way to message and create value for specific industries and aligns closely with demand generation, sales, and (often) customer success functions also orientated towards those industries.

This create the opportunity to become deep experts into that component of the addressable market. 

Most organizations do not properly understand solution and industry marketing - mainly because it is different from how the company currently operates. Industry marketing requires a different GTM approach than a product focused company. Some companies may benefit from having a product, solution, and industry team that is part of product marketing while in other companies, especially if you have multiple products and solutions encompassing different target customers, industry and solution marketing is its own discipline and a bigger priority.  

Solution marketing (customer centric) will encompass the entire breadth of products, services, and whatever else is needed (partners) to solve the customers pain. A major value for solution marketing is that you put yourself in the shoes of the customer, understand their POV, and give them solutions that solve their problem. 

Product Marketing (product centric) is complimentary to solution marketing ie product centrict vs customer problem centric. Product Marketing focuses more on the benefits of the product and features. There are instances where customers need a single product, that is where product marketing is a fit. Even in a company with multilple products and solution marketing is the norm, customers often want to buy single products, that's product marketing.

Industry marketing is customer-segment centric (oil & gas, construction, food & beverage, etc) ie how do you message and segment each vertical in order to derive product market fit. Solution marketing is the stem and message that solves the customer problem that intertwines with industry marketing. 

To increase marketing effectiveness, companies must establish teams of industry marketers to solve customer problems. 

When a company has a broad portfolio of products and serves multiple vertical markets, it is useful to have product marketers dedicated to reaching those audiences. This helps ensure resources are focused on under-represented audiences and that messaging is relevant to them so they clearly understand product benefits for their needs