Influence of doses and application methods of paclobutrazol in litchi on leaf gaseous exchange and biochemical attributes

The effects of either ring basin (RB) or trunk soil line pore (TSLP) method of application of paclobutrazol (PBZ; 1–4 g per m canopy diameter) on leaf gaseous exchange parameter, biochemical status and fruit quality of two cultivars (China and Shahi) of litchi (Litchi chinensis Sonn.) were investigated during in subtropical climate of northern Bihar. Net photosynthetic rate was found to be non-significant during August and October but reduced during flowering stage (3.3 to 4.2 μmol m² s⁻¹) over control (4.96 μmol m⁻² s⁻¹). Maximum transpiration rate was recorded during February due to 3.0 g PBZ while 2–3 times more stomatal conductance in PBZ applied trees @ 1 or 2.0 g through TSLP, over control. During October-November, the leaf chlorophyll content was found to be improved through RB method over control. Application of PBZ reduced leaf N content during October, which was conducive for flower bud differentiation in litchi trees. Also, 4.0 g PBZ applied through TSLP method assured maximum number of fruit per tree (2567.66), while in control it was only 32140 fruits per tree. The total sugar (15.80% over control had 15.21%), vitamin ‘C’ in pulp was also recorded highest in trees treated with 4.0 g PBZ with any method of PBZ application. However, the same dose of PBZ with TSLP method imparted higher vitamin ‘C’ and total anthocyanin (28.51 mg per 100 g peel). Although, PBZ had only small effect on gas exchange parameters, it improved chlorophyll content, reduced leaf N content (just prior to FBD) after application of PBZ @ 3.0 or 4.0 g through TSLP method which may reduce alternate bearing tendency in litchi trees with high yield and better quality fruits.