Chemical content in peels of fruits belonging to cultivars of Clementine mandarin (Fino, Loretina and Marisol), Satsume mandarin (Owari), Navel orange (Navelate and Navelina) and Common orange (Valencia Late) groups have been analyzed. The influence of the variety on the content of bioactive constituents at the varietal level is discussed. Rind contents showed similar tendencies for the majority of compounds although Satsume group presented the highest amounts on the flavanone glycosides hesperidin and narirutin, as well as the highest amounts of the carotenoid and β-cryptoxanthin, comparing with the remaining varieties studied. Both mandarin and orange varieties studied showed similar tendencies concerning to other phenolic compounds and total ascorbic acid concentrations. Limonene was the most abundant peel essential oil in all cultivars studied, followed by myrcene. Calcium and potassium were the dominant macronutrients for each cultivar studied, although the proportion of the individual nutrients ranged among different cultivars.

Iron chlorosis is one of the major abiotic stresses affecting fruit trees and other crops in calcareous soils and leads to a reduction in growth and yield. Usual remediation strategies consist of amending iron to soil, which is an expensive practice, or using tolerant cultivars, which are difficult to develop when not available. To understand the mechanisms underlying the associated physiopathy better, and thus develop new strategies to overcome the problems resulting from iron deficiency, the differential gene expression induced by iron deficiency in the susceptible citrus rootstock Poncirus trifoliata (L.) Raf. have been examined. The genes identified are putatively involved in cell wall modification, in determining photosynthesis rate and chlorophyll content, and reducing oxidative stress. Additional studies on cell wall morphology, photosynthesis, and chlorophyll content, as well as peroxidase and catalase activities, support their possible functions in the response to iron deficiency in a susceptible genotype, and the results are discussed.

Citrus crops in the Mediterranean region are often grown in high pH calcareous soils, which promote nutrient imbalances, especially iron deficiency. ‘Navelina’ trees grafted on eight different citrus rootstocks were assessed in terms of their relative tolerance to these soils. To do so, leaf gas exchange and chlorophyll a fluorescence parameters were measured for 2 consecutive years in leaves without visible injury symptoms. Trees were grown on the rootstocks Carrizo citrange, hybrids of Cleopatra mandarin × Poncirus trifoliata no. 5 (F-A 5), 13 (F-A 13), and 16 (030116), Troyer citrange × common mandarin no. 18 (F-A 418), King mandarin × P. trifoliata no. 7 (F-A 517), 020324 (Troyer citrange × Cleopatra mandarin), and Volkamer lemon × P. trifoliata no. 64 (230164). gS and transpiration rate were clearly lower in leaves of shoots grafted on Carrizo citrange than in those on the other rootstocks assayed, but net photosynthetic flux did not differ. However, leaves of shoots on Carrizo citrange displayed a decline in their maximum quantum yield of PSII photochemistry [variable fluorescence/maximum fluorescence (Fv/Fm) ratio] and other chlorophyll parameters in the steady state such as photochemical quenching (qP) and the quantum efficiency of PSII photochemistry (ΦPSII) as well as an increase in nonphotochemical quenching (qN). Other rootstocks such as 030116, F-A 517 and, especially, F-A 5 showed the highest ΦPSII and Fv/Fm values, whereas F-A 5 had the lowest qN in the steady state. The photosynthetic characteristics observed in leaves on Carrizo citrange showed them to be the least tolerant to these calcareous conditions, whereas photosynthesis of ‘Navelina’ trees budded on F-A 5 were the most tolerant.