Hi @nicollas , it is primarily for making strong upright trunks, since sugarcane wood is stiff and has a tendency to grow many upright trunks relative to size of tree. Hj tends to get droopy with fruits, so would rather graft to sugarcane at about 5 feet level, so should the hj budwood start sagging with fruits, the sagging would likely stop at 5 feet, making it easy to harvest. As for vigor, we don’t have much data other than chico, sihong, bok jo, r1t4 being very vigorous as grafts, but of course mere observations and may just be contingent to the workmanship (or lack of) of the grafts, and possible that the sc interstem didn’t even have any positive or negative effects whatsoever apart from holding the grafts up against gravity.
but most certainly sugarcane as interstems minimize hj’s sagging to the ground. We have a 12 ft tall hj(grafted low to the ground with no interstem) that sagged down to 2 feet level due to heavy bearing. So best to use sc budwood and graft it low and let grow to ~5 feet to achieve the desired ergonomics with droopy cultivars(li, hj, silverhill, r1t4). The variety coco seems to have exceptionally stiff wood as well.