Not Martin but,
I have a Morus Nigra “Black Beauty” cultivar. Planted in ground spring 2013. I checked it a few days ago seems to have handled 1F this winter without dieback, but will know in a month or so. It did not seem bothered by my southeast heat and humidity last summer which surprised me. I have several other cultivars, but only the one Nigra I believe. Illinois Everbearing, Pakistan and (Geraldi/Gerardi/Girardi dwarf. I have seen it spelled as 3 ways) in ground as well. I think the Pakistan has taken some freeze damage. Going into ground this spring will be Shangri La, Middleton, Kokuso No. 20, and Wassica and 4 I picked up at Just Fruits and Exotics as lost Label mystery trees, so I at least knowing what cultivars they stock I might ID at some time. Expecting some additional cultivar from USDA Davis. If anyone wants to trade some cutting of 'Kaester', 'Noir of Spain', or 'King James' I would be interested, probably have all I listed above at least for a few cuttings, , if they have not broken dormancy in my garage. I did notice some were swelling bud. Some were just cuttings this time last year. Not 100% on Black Beauty as It is small and already promised the cuttings I took there. I know I have Illinois Everbearing, Pakistan cuttings in the fridge.