© 2003 Heron Publishing—Victoria, Canada
Improvement in growth and salt resistance of lemon (Citrus limon) trees by an interstock-induced mechanism
J. M. Cámara Zapata (1, 2), M. Nieves (1) and A. Cerdá (3)
1. EPSO (Univ. Miguel Hernández), Ctra. Beniel km 3,2 03312 Orihuela (Alicante), Spain / 2. Author to whom correspondence should be addressed (jm.camara@umh.es) / 3. Department of Plant Nutrition and Physiology, CEBAS, CSIC, Apdo. 4195, 30080 Murcia, Spain / Received July 15, 2002; accepted March 1, 2003; published online August 1, 2003
Summary
Interstocks can reduce toxic ion accumulations in leaves of budded citrus trees, but the mechanism is not understood. We grew
sour orange (Citrus aurantium L.; SO) seedlings, budded trees of ‘Salustiano’ orange (Citrus sinensis L. Osbeck; SAO) on SO, ‘Verna’ lemon (Citrus limon L. Burm. f; VL/SO) and interstock trees (VL/SAO/SO) in pots of sand watered with nutrient solution containing 5 (control)
or 50 mM NaCl (saline treatment) for 12 weeks. Plants were harvested in six successive harvests and time trends in relative
growth rate (RGR) and its components were estimated by fitting a Richards function regression to the harvest data. The VL/SAO/SO
trees in saline conditions had higher mean RGR than VL/SO trees in control conditions. Increases in both net assimilation
rate on a leaf mass basis (NARw) and leaf mass fraction (LMF) contributed equally to a twofold increase in RGR of VL/SAO/SO trees in saline conditions. In
control conditions, the increase in RGR caused by the interstock had growth response coefficients of GRCNARw = 0.20 and GRCLMF = 0.80. Structural modifications—specific leaf area, leaf area ratio and LMF—had a slight influence on the salt-induced changes
in RGR, whereas NARw had a large influence. Salinity decreased root mass fraction (RMF) and increased stem mass fraction (SMF). In contrast, the
interstock decreased SMF and increased LMF and RMF. The VL/SAO/SO trees had the highest RMF and proportionally higher Cl– and Na+ allocations in roots than the other plant types. In saline conditions, reductions in leaf ion transport rate and dilution
of imported ions by foliar growth nearly halved ion accumulations in leaves of VL/SAO/SO trees.
Keywords:
allocation, leaf area ratio, net assimilation rate, relative growth rate, Richards function, specific leaf area.
