Nutritional (Fe-Mn) interactions in 'Big Top' peach plants as influenced by the rootstock and by the soil CaCO3 concentration

Manganese (Mn) toxicity in plant.s is often not a clearly identifiable disorder and it can interfere with the absorption, translocation, and utilization of other elements such as Ca, Mg, Fe, and P. Soil conditions, management factors, and the use of different genotypes of rootstock can determine the degree of Mn toxicity and of interaction with other elements in the orchard. Five plants of the cultivar 'Big top'R grafted onto itself, onto plum root- stock 'Mr.S.2 / 5' and onto hybrid peach Chi almond rootstock 'GF677' were grown in 25-L containers under three treatments, 0, 20, 30% concentration of total lime, obtained by mixing powdered CaCO3 to a sandy soil. Plants were fertilized with manure and a solid fertilizer early in April and irrigated in summer periodically with water rich in manganese. After just 28 d, active lime caused a decrease of chlorophyll SPAD index especially in plants grafted on itself, while those grafted on the tolerant 'GF677' rootstock behaved better than those grafted on 'MrS.2 / 5.' From June to September, irrigation caused increases in soil Mn concentration and Mn concentration in control plants. This caused first a serious defoliation In Big Top / Big Top plants and then a re-greening of cultivar grafted onto 'Mr.S.2 /5' and 'GF677,' probably due to the interaction between iron and manganese at high pH. In particular the 20% CaCO2, addition to the soil preserved the plants of cultivar grafted onto 'Mr.S.2 /5' from Mn toxicity, as shown by their high chlorophyll content and growth and lower Mn leaf concentrations. Plants grafted onto 'GF677' rootstock showed the best behaviour under 30% CaCO3 treatment associated to higher Fe(III)-reducing capacity and photosynthetic activity Rootstocks and soil conditions (lime and waterlogging) influenced mineral status and growth of the peach cultivar 'Big Top,' particularly by interacting together and modifying Fe-Mn availability.