IDENTIFICATION OF POTATO VARIETIES BY MEA NS OF ISOELECTRIC-FOCUSING

The variety of potato determines both its growing properties and its s uitability as a food br raw material for the use in the food processin g industry. A declaration of the variety is required and true purity o f variety is therefore an important factor in determining the quality. Tuber proteins and esterase isoenzymes can be potentially used as var iety biochemical markers. The aim of our study was to use the isoelect ric focusing (IEF) for rapid identification of varieties. Two glass pl ates (10.5 to 24 cm) with 0.25 mm spacers were used to cast polyacryla mide gel (T = 7.5 %, C = 3 %) with 2.5 % (p/v) ampholines by the flap technique of LKB No. 2217 with Gel casting kit and Gel Bound PAGE Film For the collection of 1987, the preparations Servalyt AG pH 3 - 10 (0 .9 ml), Servalyt pH 5 - 8 (0.1 ml) and Servalyt pH 3 - 6 (0.1 ml) in 1 4.8 ml gel volume were used for protein separation. For esterase isoen zymes we used gel with 1.1 ml of Servalyt pH 3 - 6. We evaluated 32 cu ltivars. For the collection of 1988 we worked with Servalyt T pH 4 - 9 (1 ml) and Servalyt pH 3 - 6 (0.1 ml) for protein separation, the sep aration was done in inert N-2 atmosphere. We evaluated 40 cultivars. I soelectric focusing was performed in Ultraphor horizontal tank (LKB) t hermostated at 2 to 3 degrees C by a circulator cooling bath Anode Flu id 3 and Cathode Fluid 10 (Serva) were used. After a 100 V x h prerun at the constant power 1 W, 1 or 2.5 mu l samples were loaded at the an odic side of the gel using an applicator strip Serva (7 x 1 mm) or sam ples were soaked up on small pieces W No. 1 paper layered in 1 cm apar t the anode. After 25 min of run (Macrodrive 5 - LKB constant power so urce) at 1 W, 500 V and 26 mA, constant power increased to 2 W and the run ended after 40 min, when the voltage received 1500 V and the curr ent was 10 mA. IEF gels were fixed and stained with Serva Blue R or W, esterase isoenzymes were detected after Stegemann et al. (1985). Stai ned gels were scanned by Camag TLC Scanner II densitometer. The densit ometer curves were processed by Camag Trans Evaluation software on HP 310 microcomputer. Results are presented by peripheral printer or plot ter. With IEF techniques we received clear differences in protein frac tions and esterase isozymes. Densitometric scanning of the IEF gels pe rmitted a more accurate and specific quantitation of protein fractions or esterase isozymes among various potato cultivars. IEF is quick and relatively simple and reliable method and consistently good results c an be achieved by using the methodologies presented here.