Or, perhaps, prospect of cultivation success?

i.e. ability to survive and mature; resistance to weather conditions, blight, insects etc

I am sure that Andrew's interpretation is the right one (and I say that by analogy with the concept of Nahrungssicherheit or food security, which is much talked about in the context of agriculture and development) - it is whether the plant can be relied upon to grow if you have a year that is particularly cold/wet/hot/dry or whatever - it is therefore in some cases the very opposite of "ease of cultivation", which means that the plant might grow readily in normal conditions but would pack up completely if, for example, it didn't rain. So I wouldn't quibble with "robustness" as a translation, except that I think you need to work the "Anbau- " in there somewhere, to make it clear that we are not talking about robust flavour, nor about robustness as resistance to damage during picking or handling.