Screening of Potato Germplasm Resistant Against Low Temperature Sweetening

Cold-induced sweetening (CIS), which occurs when potatoes stored at low temperature for long-term, causes changes in flavor and unwanted dark colors in fried and roasted potatoes. The culprit for CIS is an enzyme called invertase. Five potato cultivars A (FD3-10), B (FD3-9), C (TPS-9801), D (393574-61) and E (Laal-e-Faisal) were investigated for invertase activity at cold storage. The correlation between invertase enzyme, sugar content and certain acids is revealed in this study. Invertase activity at 4C was up to 6.3 nmol/min/mg of protein in the cultivars A and B; 2.5 times less in cultivar C; fructose 6.4 instead of glucose in cultivar D and 3.5 times less in the cultivar E compared with same at 4C. Malic acid concentration was found to be positively correlated with invertase activity at 4C and a significant increase at low temperature storage was revealed as compared with harvesting time. However, citric acid and oxalic acid concentrations were decreased in storage. The transcript level of invertase was found significantly high in potato tubers stored at 4C in cultivar A, B and D., less in cultivar C and negligible in cultivar E. In conclusion, LAAL-E-Faisal and TPS-9801 may be used for future variety improvement programs through breeding and molecular approaches. Practical Applications: Potatoes are consumed in natural as well as in processed form of foods. French fries and crisps are important subdivisions of the processing industry and denote more than 70% of the potato processing industries. Potatoes are mandatory for use throughout year, however, generating fresh potatoes all the way through the year is unrealistic and long term storage is needed. Presently cold-induced sweetening (CIS) is considered as one of the serious issue in potato production and processing with potatoes tolerant of CIS becoming a priority in many potato research programme. Potatoes resistant to CIS can deliver numerous economic benefits, such as reduction in use of sprout inhibitors, decreased dry matter loss, easy handling of high relative humidity, decreased pathogen problems during storage and reduction of chilling injury during harvest, storage and transit. Vacoular acid invertase gene is the main culprit in causing CIS. Genetic manipulation can be the best solution to generate CIS resistant potato. Most importantly, level of the carcinogenic element acrylamide can be greatly reduced by using CIS resistant varieties as it is also the byproduct of CIS. The CIS resistant potato generated through transformation can also provide valuable source for screening as well.