Foliar application of zinc and boron alleviate deficiency stress in papaya (Carica papaya L.) seedlings

Papaya is among the most important tropical fruits and is cultivated in nearly all Indian states. Micronutrient deficiency at an early stage can lead to poor growth and reduced yield in papaya. The effect of foliar application of zinc and boron on stress metabolism of papaya seedlings has been studied through a pot experiment conducted under greenhouse conditions. The experiment was framed in a completely randomised design with nine treatments that included zinc sulphate @ 0.2%, 0.4% and borax @ 0.2%, 0.4% and their combinations along with a control treatment (distilled water only). Seedlings were grown in polythene bags filled with properly washed sand and sprayed with the above treatment combinations of micronutrients at 15 days interval after germination adjusting neutral pH. The foliar spray of 0.4% zinc sulphate combined with 0.2% borax led to an increase in leaf chlorophyll content (a, b, and total), thereby boosting photosynthesis (soluble sugars) and enhancing the relative water content in leaves available for all metabolic processes. Increased application of zinc and boron also reduced the stress expression of papaya seedlings by reducing proline content, superoxide dismutase enzyme and phenol content. Lipid peroxidation in the leaf was also minimal with higher zinc application and moderate boron application, as indicated by the lower malondialdehyde content. Therefore, foliar application of 0.4% zinc sulphate and 0.2% borax can be recommended for better seedling growth of papaya in terms of less stress and high metabolic activity.