Morphophysiological markers apt to individuate different susceptibility of pear rootstocks cultivated in 'in vitro' iron-deficient conditions

In many deciduous fruit trees species lime-induced chlorosis represents a serious economical damage. It may be overcome by agronomic strategies, as the use of tolerant rootstocks, valid alternative to reduce expensive iron-chelate fertilisation and chemical environmental impact. Since few years in vitro culture technique is applied to test rootstocks for iron chlorosis susceptibility. Micropropagated shoots were used for screening of quince rootstocks MA and BA 29, and pear cv. Conference under stress conditions on MS medium supplemented with different concentrations of FeNaEDTA, 100%=0.1 mM Fe (FeN) and 15%=0.015 mM (Fe15), and/or potassium bicarbonate, 0 mM (FeN) and 1 mM KHCO3 (FeNC and Fe15C). After 24 days, substrate pH, shoot growth markers, total leaf iron and photosynthetic pigment contents were determined. The medium pH reduction resulted similar among genotypes but different among treatments. Iron deficiency and high bicarbonate concentration induced different growth performances among the genotypes, reflecting a different sensibility and plastic adapation to the induced iron chlorosis. Total leaf iron content decreased in all genotypes, when iron deficiency and bicarbonate concentration increasing onto the medium, although pear cultivar showed more slight reduction. Photosynthetic pigments, analysed by HPLC, decreased in all type of stress, and the lowest levels were detected in Fe15C treatment, except for cv. Conference. A similar trend was exhibited by carotenoids, in particular by Violaxanthin. Our preliminary data confirm the potential of in vitro culture as a rapid screening method. The choice of markers and the result interpretation will be deeply discussed in the paper.