Monitoring salt stress in grapevines: are measures of plant trait variability useful?
Measures of trait variability, in particular fluctuating asymmetry (FA), have been proposed as biological tools for monitoring environmental quality, but relevant data are often collected under artificial conditions and it can be difficult to separate genetic and environmental factors. We considered a number of trait variability measures for potential use as indicators in field grapevines exposed to salt stress. Vine responses to a salt gradient were compared using two measures of developmental stability (DS). DS quantifies an organisms' ability to buffer developmental noise. The two measures of DS tested were leaf FA, representing random deviations from perfect bilateral symmetry, and translational asymmetry (TA), representing deviations in allometric relationships, in this case the relationship between internode distance and node order. Leaf size (measured as centroid size), leaf shape (calculated using the Procrustes method) and maximum internode length were also tested for sensitivity to salinity. We found that both measures of DS, FA and TA, failed to identify salinity stress in grapevines. Other measures, such as maximum internode length, leaf shape and leaf size, were sensitive to salt stress. Synthesis and applications. Often, salinity stress is detected only when the impact is harmful enough to cause severe biological effects. Alternative, more sensitive monitoring techniques would allow earlier intervention and management of the problem. We evaluated a number of techniques and showed that indices of bilateral and TA were not useful in detecting salt stress in grapevines. However, changes in internode length, leaf size and leaf shape proved to be sensitive and are potential tools for monitoring salinity in vineyards.