Identification of morphological, biochemical and physiological parameters for characterizing nutritional stress status in arboreous species differently tolerant to chlorosis

Abstract

Lime-induced chlorosis is one of the major abiotic stresses affecting fruit tree crops in the Mediterranean area. However, fruit tree species have been the object of only few studies and the results obtained are insufficient to supply parameters for breeding. Here we report the results of a study carried out to identify morphological and biochemical modifications induced by low iron availability and a high level of bicarbonate in the medium in pear (cv Conference; tolerant genotype) and quince rootstocks (MA and BA29; susceptible genotypes) cultured by in vitro and hydroponic culture. Morphological parameters of in vitro plantlets were differently influenced by the two stress conditions depending on plant genotype and parameter analyzed, and suggested that the pear cv carried out an adaptive strategy to warrant sufficient iron supply, whereas the two quince root-stocks failed to adapt to conditions typical of calcareous soil. The strong and generalized reduction in chlorophyll and carotenoid content observed only in quince plantlets suggests a down-regulation of the whole chloroplast machinery in iron-deficient quince. Measurement of Fe(III)-chelate reductase activity (FCR) of rooted cuttings from in vitro culture grown in hydroponic solution suggests the probable involvement of enhanced FCR activity in the major tolerance of cv Conference to iron chlorosis. Cv Conference was also less sensitive to bicarbonate supply than quince rootstocks in terms of reduction of leaf pigment content and activation of the photoprotective xanthophyll cycle. In conclusion, this study shows that the mechanisms of differential Fe efficiency are associated to differences in leaf pigment content and photoprotective process and that in vitro culture could be a valid technique to test rootstock susceptibility to iron chlorosis.