Nutritional status, growth, CO2 assimilation, and leaf anatomical responses in two kiwifruit species under boron toxicity

Two Actinidia species [Actinidia deficiosa (A.Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Hayward] and (Actinidia arguta Planch.) were grown in a sand-perlite mixture (1 : 1) in a growth room and irrigated with Hoagland's nutrient solutions containing 20, 50, 100, 200, and 500muM boron (B). Growth, leaf ion concentration, photosynthetic rate and B induced changes in leaf anatomy were investigated. The greatest shoot length of the two species was recorded with 50muM B. Boron concentration was highest in the leaf margin, intermediate in the remaining leaf blade and minimum in petioles. Boron toxicity induced a decrease of photosynthetic rate (Pn), of the volume of mesophyll cells, an increase of the volume of intercellular spaces and cell damage. Inclusion of 500muM of B in the nutrient solution decreased calcium (Ca) and manganese (Mn) concentrations in kiwifruit leaves but did not affect the concentration of other mineral nutrients. Finally, the two species did not differ significantly in leaf B accumulation and sensitivity to B.