Impact of climate variables on growth and development of Kinnow fruit (Citrus nobilis Lour x Citrus deliciosa Tenora) grown at different ecological zones under climate change scenario

Abstract

Kinnow orchards of uniform age, planting density and vigor were selected in three different ecological zones situated in the districts of Sargodha, Toba Tek Singh (TTS) and Vehari of Pakistan. Climate change has adversely affected plants; particularly perennial fruits cultivated in tropical (banana, mango), subtropical (citrus, olive, grapes) and temperate (apple, apricot, plum) zones owing to their slow adaptability. In this context, the fluctuating effect of agrometeorological indices and energy-use efficiency on Kinnow mandarin's fruit growth and development was evaluated. Each experiment was performed in three biological replicates. Ten fruits were randomly collected at the end of each month (April-December) from a single plant to study fruit growth and development. Similarly, physical fruit parameters were recorded from August to February. More days were passed between fruit-setting till arrival of maturity at Vehari, whereas less number of days was counted in Sargodha. More growing degree days and photothermal index were calculated at Vehari during different phenophases of Kinnow fruit as compared to Sargodha. Hydrothermal units were more recorded in Sargodha than Vehari. More yields were obtained from TTS which had increased energy use efficiency than other two districts. Fruit cell division and cell enlargement stages were commenced afore and had finished earlier in Vehari district, followed by TTS. Fruit diameter, peel and pulp thickness as well as fresh weight were recorded in higher values at TTS and Vehari. Non-significant differences were seen in moisture percentage. More fruit size and shape indices were also recorded in TTS and Vehari. Fruit volume was measured larger at TTS, whereas fruit specific gravity was recorded higher at Sargodha from August to February. More intercellular space was seen in fruit samples collected from Vehari and TTS, which at maturity had reduced fruit firmness. Fruit color was recorded as green in samples from all three districts until the beginning of color-break in October. At the arrival of ripening phase in February, more values of color parameters a, b, C and L were enumerated at Vehari. Hue angle of fruit color was found to be at 1200, depicting green color that was rotated at 600 by portraying deep yellow or orange tinge on Kinnow mandarin. Climate variables have had a substantial effect on fruit growth and development phases as well as physical characteristics. Better physical quality and timely color development of Kinnow fruit was noted at Sargodha due to milder environmental conditions compared to TTS and Vehari.