Varietal differences in leaf functional traits and spider mite susceptibility in almond

Background/Question/Methods

In agroecosystems, higher temperatures due to climate change may increase pressure from some leaf feeding pests, further exacerbating existing water stress in summer-dry Mediterranean-type environments. Leaf functional traits provide insight into how plants will respond to such combined stresses and help in the development of appropriate responses, such as which varieties to choose for planting. Since stomata control photosynthesis and transpiration, leaf traits such as stomatal frequency and size often indicate plant water stress tolerance, while biochemical traits such as δC13 indicate water use efficiency. The interaction between pests and leaf functional traits was assessed, using almonds (Prunus dulcis) and leaf feeding mites (Tetranchus urticae), in a regional variety trial in an orchard near McFarland, California. Varieties examined included Marcona, Nonpareil, Solano, Sweetheart and Winters.

Results/Conclusions

Across all varieties, higher stomatal density was associated with more mites (p=0.04), while stomatal length was negatively associated with both numbers of mites (P=0.01) and eggs (P<0.01). Stomatal length and density were negatively related (P=0.01). Almond varieties differed in leaf traits and mite populations, with Marcona having significantly fewer average stomata than either Solano or Winters (P<0.05), and the lowest populations of mites. Water use efficiency was higher in Marcona than Sweetheart, based on lower δC13 levels. Thus, almond varieties possess substantial differences in leaf traits which can affect their drought tolerance and susceptibility to T. urticae. The variety, Marcona, may be particularly well-adapted to avoiding pest pressure and dry conditions.