EFFECTS OF TEMPERATURE SUM ON VITAMIN-C CONCENTRATION AND YIELD OF SEA BUCKTHORN (HIPPOPHAE-RHAMNOIDES) FRUIT - OPTIMAL TIME OF FRUIT HARVEST

To investigate the effects of temperature sum on vitamin C concentration (V(c)), yield and maturity of sea buckthorn fruit (Hippophae rhamnoides L.) and to predict the optimal harvest time, berries were collected from eight genotypes at an interval of about one week from August 16 to December 2. Maturity was visually observed, berry weight measured and Vc determined. Berries matured at 1165-1316 degree-days (d.d.). V(c) reached maximum at about 1229 d.d., while fruit size and yield reached maximum at 1380 d.d.. Mathematical models of polynomial equations were highly significant for predicting the effects of temperature sum on V(c), maturity and fruit yield. Optimal harvest time for maximizing V(c), yield or economic income could be determined according to differential equations. Great variations in V(c), fruit maturity and fruit size suggested good opportunities for selection and breeding. Low rank correlations in vitamin C concentration during fruit maturity, however, call for special attention in selection and breeding.