Response of stem diameter variations to water stress in greenhouse-grown vegetable crops

Abstract

SummaryThe ability of indices derived from stem diameter variations (SDV) to detect water stress in vegetable crops grown under greenhouse conditions was evaluated. Two crops, an Autumn-Winter pepper crop and a Spring-Summer melon crop, were grown in soil, in an unheated plastic greenhouse with drip irrigation, in conditions similar to commercial production. A pot study with pepper was also conducted during Autumn-Winter. In each study, two drying cycles were imposed for 7–21 d during the fruit production stage, and un-watered plants were compared with well-watered plants. During each drying cycle, linear variable displacement transducer (LVDT) sensors were used to measure SDV continuously, and daily measurements were made of leaf ( leaf) and stem water potential ( stem). Several indices derived from SDV measurements, including maximum daily shrinkage (MDS) and daily stem diameter growth rate (SGR) were evaluated. In the drying cycles of soil-grown pepper, conducted during Winter, under climatic conditions of low evaporative demand, SDV-derived indices were unaffected by 20-21 d of soil drying, despite both stem and leaf being moderately affected. Pepper plants grown in pots under very similar climatic conditions had appreciable and rapid responses in SDV-derived indices, with MDS increasing and SGR decreasing. In the drying cycles of soil-grown melon, imposed during the relatively higher evaporative demand conditions of Spring and Summer, MDS responded earlier and had larger “signal” values (ratio of values from un-watered to control plants) than leaf or stem. However, there was more variation associated with MDS. In melon, there were strong linear relationships between MDS and both leaf and stem. The present study suggested that SDV-derived indices can be sensitive indicators of plant water status in melon and pepper when grown (a) in pots with a restricted root volume under any climatic conditions, and (b) in soil during periods that do not include climatic conditions of low evaporative demand.