Infuence of new generation plant bio-regulators on physio-biochemical alterations in grapes cv. Beauty Seedless

Infuence of benzothiadiazole (BTH) and pro-hexadione calcium (Pro-Ca), abscisic acid (ABA) and ethephon on leaf gas exchange parameters such as net photosynthesis rate (A), stomatal conductivity (g_s), intercellular CO₂ concentration (Ci) and leaf transpiration rate (E), leaf stomatal density, leaf relative water content (RWC) and leaf biochemical parameters along with berry surface colour characteristics such as L*(lightness), a*(greenness to redness), b*(blueness to yellowness), chroma (C*), hue angle (hº) and CIRD (Colour Index for Red Grapes) were examined on grapevine cv. ‘Beauty Seedless' especially under hot subtropical conditions. The highest leaf A(12.20 µmol CO₂ m⁻² s⁻¹) and g_s(0.15 mmol m⁻² s⁻¹) were recorded with Pro-Ca 400 ppm treatment, while the lowest A(7.97 µmol CO₂ m⁻² s⁻¹) and g_s(0.05 mmol m⁻² s⁻¹) were recorded with ABA 400 ppm and ethephon 400 ppm, respectively. Among other physiological parameters, the highest value of Ci was measured with ABA 400 ppm (265.29 mol m⁻² s⁻¹) treated vines followed by ethephon 400 ppm (261.78 mol m⁻² s⁻¹). The vines sprayed with ethephon 400 ppm (3.18 mmol m⁻² s⁻¹) were recorded had the lowest value of leaf E. Similar trends were also recorded for leaf RWC. Treatments ABA (400 ppm) and ethephon (400 ppm) decreased the stomatal density signifcantly. The highest chlorophyll ‘a' content was observed in case of ethephon 400 ppm (2.39 mg g⁻¹) treated leaves having similarity statistically with all the treatments except control, while the highest chlorophyll ‘b' and total chlorophyll contents were noted with ABA 400 ppm. Treatment ethephon 400 ppm (0.89 mg g⁻¹) improved the total carotenoids content, which proved similar statistically with ABA 400 ppm (0.88 mg g⁻¹). The least values of L*, C* and the highest CIRG index were recorded for ABA 400 ppm (19.63, 2.36 and 7.61, respectively) followed by ethephon 400 ppm (20.14, 2.67 and 7.43, respectively).