I regard the diversity analysis in this paper as wishful thinking, but the isolation of the candidate gene is excellent work.
Species and their cultivars are defined by physical (and occasionally biochemical) characteristics. True “genetic ID” of a specimen therefore depends on knowing the genes responsible for these characteristics. Present-day methods rely on error-prone extrapolation.
In the case of Guava, my guess is that about 60 genes could define a cultivar. At present, one is known for certain and now there is a candidate second. The same is true for nearly all fruits. Perhaps in 20 years we’ll have a true means of “genetic ID”.
(no pay wall)
https://www.mdpi.com/2311-7524/11/10/1194