Screening of citrus rootstocks for lime‐induced chlorosis tolerance

Abstract

Although sour orange (Citrus aurantium L.) is sensitive to tristeza disease, it is the predominant citrus rootstock in the Mediterranean region. However, rootstocks of the Poncirus genus and their intergeneric hybrids ("Troyer”; and “Carrizo”; citrange, “Swingle”; citrumelo) are tolerant. Resistance to lime‐induced chlorosis is also a major consideration in semi‐arid regions. The objective of this study was to evaluate resistance of 12 citrus rootstocks for lime‐induced chlorosis when grown in calcareous soil. Physiological differences of these rootstocks were also evaluated in an equilibrated hydroponic medium. The rootstocks tested were: three Citrus genus, one Poncirus genus, five interspecific and three intergeneric hybrids. None of the rootstocks exhibited chlorosis when grown in a non‐calcareous soil. Four degrees of resistance were observed in the rootstocks when grown in calcareous soils: highly resistant ‐ C. jambhiri and C. macrophylla; moderately resistant ‐ C. volkameriana, C. aurantium, C. reticulata and C. limonia; mildly resistant ‐ C. taiwanica, C. sinensis, “Troyer”; and “Carrizo”; citrange; and non‐resistant (susceptible) ‐ P. trifoliata and “Swingle”; citrumelo. In the hydroponic medium, susceptible rootstocks exhibited greater K uptake, while resistant ones took up more Ca. The K/Ca ratio was inversely proportional to the degree of resistance to lime‐induced chlorosis. Resistant cultivars had higher root cation exchange capacities and a lower degree of root membrane esterification than susceptible rootstocks.

These parameters may help distinguish between resistant and susceptible citrus cultivars.

Key words:

• iron deficiency
• xylem sap analysis
• root cation exchange capacity
• plant K/Ca ratio