KINNOW MANDARIN (Citrus reticulata Blanco) FRUIT QUALITY IN MAJOR PRODUCTION DISTRICTS AND STRATEGIES FOR COSMETIC IMPROVEMENT

Abstract

The entire doctoral study was conducted during 2007-2011. The main objective of the study was to find out new premium Kinnow (Citrus nobilis Lour × Citrus deliciosa Tenora) growing areas to expand export base and to help reduce fruit rind blemishes in order to improve cosmetic quality and marketing grade of Kinnow mandarin. The study was focused on two main aspects i) comparison of fruit quality and shipping potential of Kinnow fruit produced in four main Kinnow mandarin growing districts of Punjab including Toba Tek Singh (TTS) (30°55'N, 72°25'E), Khanewal (KHW) (30°20'N, 71°55'E), Vehari (VHR) (29°48'1N 72°10'33E) and Sargodha (SGD) (32°10'N, 72°40'E), Pakistan and ii) characterization of Kinnow fruit skin blemishes and management strategies for the improvement of cosmetic look of fruit. For each study appropriate statistical design and analysis techniques were followed. For studies under aspect one, data on climatic conditions of four districts was obtained. Six orchards in each district were selected, their agronomic practices were documented and correlation matrix with different fruit quality parameters was determined. To assess fruit quality, fruit were compared for nature and extent of blemishes in each orchard of respective district. Wind, mites and thrips were identified as major blemish causal agents in all Kinnow growing districts. Wind blemishes were found significantly higher in district Vehari (88.51%) followed by Sargodha (86.67%) as compared to other districts. Mites were found non-significantly different, while thrips blemished fruit were found only in district Khanewal. For the comparison of physico-chemical characters, healthy and uniform fruit from each orchard of respective districts were harvested, packed in corrugated boxes and shifted to Postharvest Research & Training Centre (PRTC), University of Agriculture Faisalabad, Pakistan. Fruit were assessed for various quality parameters. Fruit from orchards of District Vehari were found on top in many physico-chemical characters i.e. firmness, peel colour, fruit diameter with less peel thickness, high total soluble solids (TSS) and acidity. TSS/TA ratio and vitamin C contents were significantly higher in fruit from district Sargodha whereas, total sugars were maximum in fruit from district Toba Tek Singh. Soil nutrient analysis revealed that, nitrogen and phosphorous were significantly higher in district Toba Tek Singh, while potash was significantly higher in soils of district Vehari. Regarding leaf nutrient analysis, N, P, K, Ca, Fe contents were significantly higher in 1orchards of district Vehari. The environmental profile (meteorological data) of districts showed that Toba Tek Singh had lower while district Khanewal had higher mean minimum monthly temperatures during most part of the year. Regarding mean maximum temperatures, district Khanewal exhibited higher temperatures in most part of the year. District Sargodha received higher while district Vehari received lower annual rain fall. Average monthly relative humidity (RH) was recorded higher in district Sargodha and lower in district Vehari. Fruit firmness was positively correlated with saturation capacity of soil, while total soluble solids were found negatively correlated with RH and rain fall. Vitamin C and TSS/TA ratio was also correlated negatively with soil nitrogen. Regarding storage comparison at ambient conditions, significantly higher TSS, TSS/TA ratio and juice percentage was recorded in fruit form district Toba Tek Singh, while significantly higher weight loss was recorded in fruit from district Khanewal as compared to other districts after seven days of ambient storage (25±1 °C; 60-65% RH). As regards comparison under cold storage conditions, TSS was significantly higher in fruit from Toba Tek Singh after 30 and 60 days of storage, whereas TTS/TA ratio was higher in fruits from district Sargodha after 60 days of cold storage. Juice percentage was recorded higher in fruit from district Sargodha after 30 and 60 days of cold storage. Regarding the second aspect; fruit skin blemishes and management strategies, various studies were conducted in District Sargodha. A Tree-Fruit-Environment (TFE) profile was developed to relate the Kinnow fruit rind blemishes development with environmental conditions and various insect pests and diseases. March was considered as the critical month since new flush emergence, flower bud opening and fecundation and fruit set, all took place during this month. The development of rind blemishes started soon after fruit set, and gradually increased with time. The intensity of fruit blemishes was maximum in the month of April (36%) followed by May (31%). Wind and mites were found as the most important causes of fruit blemishes. Wind breaks around the orchard had significant impact on fruit quality. Blemished fruit were significantly reduced in orchards where wind breaks were established. Similarly, percentage of A grade fruit was also significantly higher in orchards with wind breaks compared to without wind break orchard, while non-significant difference was observed in relation to canopy position (top, middle and bottom) of the tree regarding nature and extent of blemishes. In another study on effect of wind velocity, it was found that 2wind velocity and its duration also affect the development of blemishes. Wind intensity as low as 10 km hr -1 for 30 minutes significantly increased number of blemished fruit. Certain strategies were tested to overcome the problem of skin blemishes in Kinnow mandarin. The results revealed that, improved pruning techniques (removal of 8-10% of total bio-mass of tree) significantly increased the percentage of A grade fruit and improved fruit diameter as well. In experimental study targeted to reduce the canker blemishes, twice foliar application of Bordeaux spray (one in last week of April and other in last week of May) proved to be excellent in controlling citrus canker and improving the skin quality, compared with other fungicides (Allite etc.) Horticultural mineral oil (HMO) was also tested for the first time under the agro-climatic conditions of district Sargodha, for reducing blemishes caused by biotic factors. Foliar application of 1.5% HMO (one before flower opening, one after fruit set and then four sprays after 15 days interval) coupled with improved pruning (as described previously) significantly reduced the insect pest population on tree and increased the percentage of A grade fruit at harvesting. The existing postharvest pack house practices (washing, waxing, grading) were also evaluated, and it was found that these practices were also helpful in reducing the skin blemishes and improving the cosmetic look of fruit. In confirmatory studies, all the tested treatments were applied as a technology package on a relatively larger scale and results confirmed that percentage of A (25.67%) and B grade (43.33%) fruit were significantly increased as compared to control (traditional practice) (6.33% A grade; 18.67% B grade fruit ). In conclusion, it was found that the geographical locations and cultural practices certainly have an impact on Kinnow fruit quality. However, apart from Sargodha district (main Kinnow growing area); two other districts including Vehari and Toba Tek Singh have significant potential to provide good quality exportable Kinnow fruit. Regarding fruit blemishes management, establishment of orchard wind breaks, improved pruning along with application of HMO (1.5%) and Bordeaux mixture can be packaged together to increase percentage of A grade fruit of good cosmetic look.