Growth and physiological response of salt-sensitive and salt-tolerant rootstocks of citrus to paclobutrazol under salt stress

The response of paclobutrazol was studied during 2006-07 on salt-sensitive 'Soh Sarkar' (Citrus karna Raf.) and salt-tolerant 'Rangpur lime' (Citrus limonia Osbeck) under salt stress. One-year-old seedlings of both rootstocks were grown in earthen pots of 10 inches size containing 5 kg soil. Paclobutrazol (0, 125 and 250 ppm) was applied 7 days prior to salinization is a 1 1/2 litre solution/pot. Computed amount of NaCl (1 000 mg/kg soil) was added in solution form to get soil salinity level of 2 dS/m. Paclobutrazol mitigated the salinity stress effects in both the rootstocks. Application of 250 ppm paclobutrazol increased plant height (34.70%), leaves/plant (170.61%), root length (51.83%), shoot fresh weight (51.89%) and dry weight (44.88%), root fresh weight (14.42%) and dry weight (58.06%) under salt stress than salinized control without paclobutrazol application in salt-susceptible 'Soh Sarkar'. While in 'Rangpur lime', application of 125 ppm paclobutrazol increased maximum plant height (10.33%), root length (68.84%), shoot fresh weight (31.38%) and dry weight (41.25%), root fresh weight (95.40%) and dry weight (76.34%) under salt stress as compared to salinized seelings without paclobutrazol. Root to shoot ratio increased maximum in 'Soh Sarkar' (35.30%) and in 'Rangpur lime' (24.32%) with application of 125 ppm paclobutrazol under salt stress. Paclobutrazol-treated plants of the both rootstocks had less defoliation and toxicity symptoms appeared on fewer leaves. Relative water content, chlorophyll a and b, total chlorophyll and chlorophyll a to b ratio in both rootstocks increased by application of paclobutrazol. Membrane injury index reduced by 20.18% in Soh Sarkar and 51.83% in 'Rangpur lime' with application of 250 ppm paclobutrazol under salt stress than salinized seedlings without paclobutrazol treatment. The findings suggested that paclobutrazol promoted salt stress avoidance in both salt-sensitive and salt-tolerant rootstocks of citrus.