Vol. 81 No: 3

Title:
Response of stem diameter variations to water stress in greenhousegrown vegetable crops

Authors:
M. GALLARDO, R.B. THOMPSON, L.C. VALDEZ and M.D. FERNÁNDEZ

pp: 483-495

Abstract:
The 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 (Ψ_leaf) and stem water potential (Ψ_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 Ψ_stem and Ψ_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 Ψ_leaf or Ψ_stem. However, there was more variation associated with MDS. In melon, there were strong linear relationships between MDS and both Ψ_leaf and Ψ_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.

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