Research Article Received: 12 November 2019 Revised: 18 January 2020 Accepted article published: 30 January 2020 Published online in Wiley Online Library: 21 February 2020 (wileyonlinelibrary.com) DOI 10.1002/jsfa.10300 Impact of varying agrometeorological indices on peel color and composition of Kinnow fruit (Citrus nobilis Lour x Citrus deliciosa Tenora) grown at different ecological zones Rab Nawaz, a Nadeem A Abbasi, a * Ishfaq A Hafiz a and Azeem Khalid b Abstract Background: Kinnow orchards were selected in different ecological zones in districts Sargodha, Toba Tek Singh (TTS) and Vehari of the Punjab province, Pakistan. Three biological replicates in block form were applied by using analysis of variance techniques to assess varying agrometeorological indices impact on fruit color-development and peel composition. Results: Fruit samples were randomly collected on each month's end starting from August up to February. Chromameter was used for measuring coloring parameters and its values a*, b*, C* and L* were increased from August till February with a rapid elevation started at color-break stage, while hue angle (h*) rotated from 120° to 60° of portraying green to yellow shade. An increasing level of chlorophyll contents were noted in August till color-break at the end of October and then diminished after- wards. Whereas, carotenoids increased rapidly upon yellow tinting peel of Kinnow fruits till fully attained deep orange color at the end of February. Ascorbic acid content and total phenolic content (TPC) showed a decreasing trend whereas anthocyanins and antioxidant activity were increased from August to February, with unchanged flavonoids and flavonols level. Fruit firmness was gradually reduced till color-break with rapid reduction noted subsequently. Maturity index represented internal ripening directly increased with color-development. Conclusion: Color development has directly influenced on maturity index and both were increased rapidly after color-break to afterwards. More color development with rapid reduction in chlorophyll, ascorbic acid and TPC level were seen in warm districts namely TTS and Vehari after color-break stage due to accumulating more agrometeorological indices. © 2020 Society of Chemical Industry Keywords: impact; varying; agrometeorological indices; peel color and composition; Kinnow fruit; ecological zones INTRODUCTION Color is one of main visual traits that can be used to define quality of processed or fresh fruit, 1 despite the fact that intelligent tools in the packaging industry are being popularized in the modern world, 2 color majorly decides acceptance or rejection of fruit, 3 consumer choice 4 and selling of horticultural produces along with online color imaging used are further utilized for distant marketing. 5 Color development is used as an indicator for harvest of non- climacteric fruits including citrus 6 along with checking its external quality. 7 Color is also used for determining maturity index and fruit inner quality attributes. 8 Color-break in Kinnow mandarin changes fruit internal quality parameters 9 and is still used as a tool in judging the maturity and quality of fruit in the domestic market. 10 In advanced countries, color along with citrus fruit's other quality attri- butes are used for fruit harvesting and marketing at domestic and external level. 11,12 Climatic factors unpredictability do effect color-break in citrus. 13,14 In warm regions, color-break is deferred with faded coloration 15 and citrus peel remains green in tropical regions. 16 Color development is also linked with change in peel composition, depending on external environment. Upon color-break to afterwards, chlorophyll contents in peel start to decrease and color imparting contents like caroten- oids and anthocyanins show an increasing predisposition. 10 Simi- larly, polyphenols and antioxidants in peel, along with fruit peel firmness are also changed with color development 9 ; all of them are swayed by external environment. 14 Growing degree days (GDDs) of certain crop in a particular area are solely decided by prevailing mean daily-temperature and rest of agrometeorological indices were directly or indirectly calculated from GDDs. 17 Fluctuating agro- meteorological indices in different citrus phenophases also influ- ences on fruit internal and external quality. 18 Sigmoid growth trend in citrus fruit 19 starts at fruit setting stage 20 to continue till color-break at early ripening time. 21 Citrus * Correspondence to: NA Abbasi, Department of Horticulture, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi, Pakistan. E-mail: nadeemabbasi65@yahoo.com a Department of Horticulture, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi, Pakistan b Department of Environmental Sciences, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi, Pakistan J Sci Food Agric 2020; 100: 2688–2704 www.soci.org © 2020 Society of Chemical Industry 2688