INTRODUCTION Potato (Solanum tuberosum L.) belongs to the family Solanaceae. It is native of Peru-Bolivia in the Andes, South America (Luthra et al., 2006). Potato is one of the world’s most important non-cereal and high yielding horticultural food crops. It is considered to be the fourth major food crop after rice, wheat and maize (Zhang et al., 2016). Production is oriented principally towards internal consumption, approximately 81% of the national production is commercialized fresh for household consumption and potato processing industries use the rest to make crisps and French fries. In the case of tuber potatoes, quality can be defined as the sum of favourable characteristics of the tuber, which is a subjective and dynamic concept that depends on consumer’s lifestyles and food habits (Richards et al., 1997) and the industrial process used. A complex set of external and internal quality traits are required for fresh and processed potatoes. External quality traits include tuber shape, eye depth, skin and flesh color (Jansky, 2009). These characters are especially important for fresh market potatoes, but they may also impact processing quality. Nutritional/compositional quality parameters includes dry matter content, reducing sugar, enzymatic discoloration and vitamin C content (Storey, 2007). Tuber dormancy (resting period) of potato tubers is the physiological state after harvest, during which tubers do not sprout (Wiltshire and Cobb 1996) even when stored under conditions favorable for sprouting (Van den Berg et al., 1996). Premature sprouting and rotting are major causes of losses during post-harvest storage of potatoes, since it reduces the number of marketable tubers. MATERIALS AND METHODS An experiment was carried out to study the effect of mulching on post-harvest quality in different genotypes of potato at Centre of Excellence for Protected Cultivation, Horticultural Research Station, Dr. Y.S.R. Horticultural University, Venkataramannagudem, West Godavari District, Andhra Pradesh during rabiseason (November 2021-February 2022). The experiment was laid out in split plot design with two replications using two locally available mulching materials (paddy straw and coconut coir) along with control (earthing up) as main plot treatments and eleven heat tolerant breeding lines of potato (HT/21-1, HT/21-2, HT/21-3, HT/21-5, HT/21-7, HT/21-11, HT/21-15, HT/21-16, HT/21-17, HT/21-18 and HT/21-20) along with control (Kufri Surya) as sub-plot treatments with plot size of 3m × 1m. The tubers were planted at a spacing of 60 × 20 cm. To supplement the nutritional requirement of the crop, recommended dose of fertilizers for plateau region i.e.,125:100:125 kg NPK ha-1 was applied. Foliar spray of water-soluble compound fertilizer such as 19-19-19 kg N-P2O5-K2O was given one month after sowing. Second spray was given at 45 days after sowing with the above fertilizer and third spray was given with water soluble fertilizer 13-0-45 kg N-P2O5-K2O for better tuber growth. Weeding was done manually at regular intervals. First irrigation was given immediately after planting of tubers to ensure better emergence. Subsequent irrigations were given depending upon moisture status of soil retained as per requirement of plants. Observations on external tuber quality traits (tuber shape, eye depth, skin colour and flesh colour) were recorded as per the minimal descriptors of potato (Huaman et al., 1977). Nutritional/compositional quality traits like dry matter content (%) was estimated as per the procedure given by Luthra et al., 2013. Dry matter content was calculated using the following formula: Dry matter content (%) = Reducing, non-reducing and total sugars were estimated by Lane and Eynon (1923) method as described by Ranganna (1986). Vitamin C content was determined by following the procedures given by Ranganna (1986). Observations on sprouting and rotting of tubers were recorded. RESULTS AND DISCUSSION The analysis of variance revealed that main effects of potato genotypes were significant for dry matter, vitamin C content, reducing, non-reducing and total sugars (%), sprouting and rotting (%). Main effects of mulching materials were significant for dry matter content, sprouting and rotting (%). Interaction effects between genotypes and mulching materials were significant for dry matter content. A. Post-harvest quality of potato genotypes Tuber shape, eye depth, skin and flesh color are crucial aspects for consumers, as they are immediately obvious while making the purchase (Werij, 2011). These characters are especially important for fresh market potatoes, but they may also impact processing quality. Internal quality includes dry matter content, reducing sugar, enzymatic discoloration and nutritional quality such as vitamin C content (Storey, 2007). These characters are especially important for processing quality. 1. External tuber quality traits. External quality traits like tuber shape, eye depth, skin and flesh colour of different genotypes were presented in Table 1. Tuber shape. The shape of the tuber is one of the most eye-catching traits of the potato. To minimize waste during processing, varieties with long tubers are preferred for french fries and varieties with round tubers are preferred for chips. Five genotypes viz., HT/21-2, HT/21-7, HT/21-18, HT/21-20 and Kufri Surya produced oval shaped tubers, while HT/21-3, HT/21-5 and HT/21-11 produced oblong shaped tubers which are good for making french fries. HT/21-1, HT/21-15, HT/21-16 and HT/21-17 produced round shaped tuber which are suitable for making chips. Eye depth. Eye depth is an important quality trait because deep eyes affect the appearance of tubers and add to the cost of peeling in processing industries. So, shallow eyed potato tubers are preferred for processing. Seven potato genotypes viz., HT/21-2, HT/21-5, HT/21-7, HT/21-16, HT/21-17, HT/21-18 and Kufri Surya had shallow eyed tubers while remaining genotypes had medium eyed tubers. Tuber skin colour. Skin colour is one of the most easily noticeable traits of potato tuber. Potato genotypes under study showed lot of variability in skin colour as it ranged from white-cream (HT/21-7 and HT/21-15) to brown (HT/21-1, HT/21-2, HT/21-3, HT/21-11, HT/21-16, HT/21-17, HT/21-20 and Kufri Surya). Most of the genotypes viz., HT/21-1, HT/21-2, HT/21-3, HT/21-11, HT/21-16, HT/21-17, HT/21-20 and Kufri Surya had brown skin colour tubers. HT/21-5 and HT/21-18 had yellow skin colour. HT/21-7 and HT/21-15 had white cream colour skin. Tuber flesh colour. Tuber flesh colour in potato varied from yellow (HT/21-1, HT/21-3, HT/21-5 and Kufri Surya) to cream colour (HT/21-2, HT/21-16 and HT/21-17). The variation in tuber flesh colour is mainly due to two naturally occurring pigments, i.e., anthocyanins and carotenoids. The higher content of lutein, violaxanthin and total carotenoids are present in yellow-fleshed potatoes. HT/21-1, HT/21-3, HT/21-5 and Kufri Surya produced yellow-fleshed tubers. HT/21-2, HT/21-16 and HT/21-17 produced cream colour fleshed tubers. HT/21-11, HT/21-18 and HT/21-20 produced yellow cream colour fleshed potatoes. 2. Nutritional/compositional quality traits. Dry matter content (%). For the processing industry dry matter content is a critical component, it is a measure of the internal quality of tubers. Main effects of genotypes, mulching materials (Table 2, 3) and their interaction effects (Table 4) were significant for dry matter content in potato. Dry matter content in potato genotypes varied significantly from 15.78% (HT/21-18) to 20.91% (HT/21-2). Dry matter content was highest in genotype HT/21-2 (20.91%), followed by HT/21-17 (20.17%) and HT/21-5 (19.38%).Dry matter content was highest in genotypes under paddy straw mulching (19.45%), followed by coconut coir mulching (18.47%) when compared to control without mulching (16.80%). Genotypes and mulching materials had significant interaction effect on dry matter content. Dry matter content was highest in genotype HT/21-2 under paddy straw mulching (22.58%) and lowest in HT/21-18 under no mulching (15.23%). Dry matter content in potato is affected by environmental factors during growth of the crop, such as solar radiation, soil temperatures, soil moisture, fertilizers and haulm killing (Haverkort, 2007). Potato tubers with high dry matter content >20% are preferred to achieve good colour chips and less oil absorption during frying (Kirkman, 2007). Therefore, among the 12 potato genotypes under study, HT/21-2 (20.91%) and HT/21-17 (20.17%) having high dry matter content were found to be promising for chip making. The variation in the dry matter content among the genotypes might be due to difference in their inherent characteristics. Similar results were reported by Sadawarti et al. (2018). The increase in dry matter content under mulching materials might be due to congenial root zone temperature which leads to better crop growth and increased biomass accumulation. Similar findings were reported by Dhakal et al. (2011); Banerjee et al. (2016). Vitamin C (mg/100 g). Simple effect of genotypes was significant (Table 2) but the main effects of mulching materials and their interaction effects were non-significant for vitamin C content (Table 3, 4). Vitamin C content in potato genotypes varied significantly from 15.39 mg/100 g (HT/21-1) to 22.91 mg/100 g (HT/21-20). Vitamin C content was highest in genotype HT/21-20 (22.97 mg/100 g), followed by HT/21-3 (22.79 mg/100 g) and HT/21-5 (22.18 mg/100 g). Potato is considered as a good source of antioxidants such as vitamin C. Diets rich in antioxidants have been associated with a lower incidence of atherosclerotic heart disease, certain cancers, macular degeneration and severity of cataracts (Cook and Samman 1996). The most important factor which influences the vitamin C content of potato is variety (Hrabovska et al., 2021). The variability of the vitamin C content among genotypes might be due to the difference in their genetic constitution. Similar findings were reported by Rizvi et al. (2020). Reducing, non-reducing and total sugars (%). Significant variation in reducing sugars, non-reducing sugars and total sugars was observed among the genotypes (Table 2) while among mulching materials and their interaction effect, it was found to be non-significant (Table 3, 4). Reducing sugars in potato genotypes varied significantly from 0.62% (HT/21-1) to 0.13% (HT/21-11). Reducing sugars was lowest in genotype HT/21-11 (0.13%) followed by HT/21-17 (0.14%) and HT/21-5 (0.15%). Hence, for manufacturing good quality potato chips, optimum reducing sugars should be less than 0.15 % or 150 mg/100 g of tuber fresh weight (Sowokinos and Preston, 1988). Therefore, HT/21-11, HT/21-5 and HT/21-17 genotypes of potato under study having reducing sugars (%) which is within limits of desirable variety are suitable for processing into chips. Non-reducing sugars in potato genotypes varied significantly from 0.08 % (HT/21-11) to 0.29 % (HT/21-18). Non-reducing sugars was lowest in HT/21-11 (0.08%), followed by HT/21-5 and HT/21-18 (0.10%) and Kufri Surya (0.12%). The sugar content of the harvested crop is important for the fresh market and the sucrose levels above 1% were reported to give an unacceptably sweet taste to the boiled potatoes (Storey, 2007). None of the potato genotypes under evaluation were found to have non-reducing sugars above 1%. Total sugars in potato genotypes varied significantly from 0.21% (HT/21-11) to 0.88% (HT/21-1). Total sugars content was lowest in genotype HT/21-11 (0.21%) followed by HT/21-17 (0.24%) and HT/21-5 (0.25%). Majority of the potato genotypes except HT/21-11, HT/21-17, HT/21-5 had significantly highest total sugars when compared to control Kufri Surya (0.30%). Sugar levels in a potato tuber are conditioned by several factors, which include genotype, the environmental conditions and cultural practices during growth, and several post-harvest factors including storage (Kumar et al., 2004). Variability in the sugars (%) might be due to the difference in their genetic makeup. Similar findings were reported by Lavanya et al. (2021). 3. Sprouting and Rotting (%). Sprouting and rotting of tubers during storage after 60 days of harvest under normal storage conditions were significantly influenced by both genotypes and mulching materials but non-significantly influenced by the combination of genotypes and mulching materials (Table 4). Sprouting varied significantly among potato genotypes from 1.35% (HT/21-7) to 4.60% (HT/21-3). Sprouting was lowest in genotype HT/21-7 (1.35%), followed by HT/21-15 (1.67%) and HT/21-20 (1.84%). Sprouting was lowest in potato genotypes under paddy straw mulching (2.44%) followed by coconut coir mulching (2.68%) when compared to control without mulching (2.98%). Rotting in potato genotypes varied significantly from 2.13% (HT/21-7) to 9.33% (HT/21-17). Rotting was lowest in genotype HT/21-7 (2.13%), followed by HT/21-20 (2.22%) and HT/21-5 (2.35%). Mulching materials had significantly influenced rotting of potato genotypes. Rotting was lowest under paddy straw mulching (4.41%) followed by coconut coir mulching (4.64%) when compared to control with earthing up (4.93%). There was no significant interaction between genotypes and mulching materials on sprouting and rottingof tubers. The variations in sprouting and rotting percentage among potato genotypes might be due to the difference in their genetic makeup. Due to the presence of lower maximum temperatures under mulching materials might have increased the dormancy period and reduced sprouting and rotting in potato tubers during storage. Similar results were reported by Pulok et al. (2014). On the whole, the genotypes HT/21-7 and HT/21-20 with significantly lower sprouting by 45.12 and 35.11%, respectively and rotting by 25.78 and 22.65%, respectively after 60 days of harvest during storage under normal storage conditions compared to control Kufri Surya were found to be highly suitable for long-term storage.