Vented vessels affect growth rate of in vitro Vitis vinifera cv. Nebbiolo

Procedures leading to in vitro hardening during the last micropropagation phase generally facilitate plantlet acclimatization. A reduced relative humidity (RH) inside the culture vessels enhanced water loss control from leaves of micropropagated grapevines. We tested commercially available vessels whose lid has a hole covered with a partially permeable membrane, allowing a higher water vapor transpiration. Grapevine shoots were cultivated in LifeGuard(R) vessels on solid medium without plant growth regulators. The vessel lids had membrane-covered holes with 10, 16, 22, or 40 mm diameter, or no hole. After 4 weeks, shoots cultivated in vented vessels were taller than shoots grown in the unvented ones, with the exception of the 40 mm-hole diameter treatment. A similar behaviour was recorded for plantlet fresh and dry weights. Leaf area was larger and chlorophyll content was higher in shoots from vented vessels. The vented vessels with a hole diameter up to 22 mm generally improved grapevine plantlet growth and were suitable for grape culture. The largest holes (40 mm), on the contrary, caused an excessive water stress during the culture: shoots became more resistant to wilting if exposed to 70% RH, but their growth was seriously retarded.