PATTERNS OF STEM WATER POTENTIAL IN-FIELD GROWN POTATOES USING STEM PSYCHROMETERS

The first large scale outdoor measurements of potato (Solanum tuberosu m L.) stem water potential (SWP) using in situ temperature-corrected s tem psychrometers were performed on three cultivars common to Ontario, Canada (Atlantic, Monona and Norchip). Potato plants were examined un der three soil water treatments which included rainfed, irrigated and stressed through the use of rain shelters. Cultivar variations in SWP under both irrigated and rainfed conditions were slight (P>0.05), alth ough some significant (P<0.05) differences in mid-day SWP were evident , especially under conditions conducive to high atmospheric water dema nd. Under these conditions, cv. Atlantic maintained the lowest SWP wit h cv. Monona highest and cv. Norchip was intermediate. Few differences in pre-dawn SWP were detected between the three cultivars under well watered and rainfed conditions. Under low soil water, significant diff erences (P<0.05) were observed. The similar trend of Atlantic maintain ing the lowest SWP with Monona the highest was consistent.