Influence of genotype and climatic environment on fruit yield and chemical composition of black currant (Ribes nigrum L.)

Sammendrag

Black currant (Ribes nigrum L.) is a widely cultivated soft fruit species, which is renowned for its high berry concentrations of proven, or presumed, health-promoting compounds. Over the last years, there has been a growing interest in the effects of genotype and environmental conditions on the quality of fruits and berries including the black currant. In the present study, we have examined the impact of environmental conditions on yield and chemical composition of seven black currant cultivars from different national breeding programs. Two experimental approaches were used: 1) Correlation analyses of the relationship between berry chemical content and weather conditions in the field at Ås, Norway (59°40’N), over a period of eight years (Paper I), and 2) Studies on the effects of post-flowering temperature and photoperiod on berry chemical content in controlled (phytotron) environments. In addition, plants of all cultivars were also grown outdoors under ambient conditions as a control (Paper II, III, IV). Black currant berry yield and weight were negatively correlated with summer temperature and positively correlated with precipitation. Elevated ripening temperature increased dry matter as well as soluble solid contents and pH of the berries. In addition, black currants had higher content of ascorbic acid, total monomeric anthocyanins and total phenolic compounds in years with cool summers with ample precipitation. In general, years with relatively low temperature and ample precipitation enhanced yield and increased the nutritional quality of the berries. Cultivation of single-stemmed potted plants of four black currant cultivars in a phytotron at constant temperatures of 12, 18 or 24 °C and different photoperiods (short day, short day with night interruption, and natural summer daylight conditions) generally supported the results from the field experiment. Thus, accumulation of both forms of ascorbic acid [L-ascorbic acid (AA) and dehydroascorbic acid (DHAA)] decreased with increasing ripening temperature over the 12-24 °C range, while the ratio between AA and DHAA increased. Likewise, the concentration of hexose sugars and, to lesser extent sucrose, decreased with increasing temperature, whereas the concentration of citric acid, which is the predominant organic acid in black currant berries, increased. This resulted in an increased sugar/acid-ratio in berries ripened under low temperature conditions. The concentration of total monomeric anthocyanins in the berries was highest at 18 °C, with both higher and lower temperatures resulting in lower accumulation. Total phenolic concentration in berries ripened under controlled climate conditions remained relatively stable across the different temperature and light regimes, whereas the antioxidant capacity was reduced at high temperature. The predominating anthocyanins in the studied black currant cultivars were delphinidin-3-rutionside and cyanidin-3-rutinoside, which accounted for 75-83 % of the total under the various environmental conditions. Analysis of individual anthocyanins, flavonols and hydroxycinnamic acids revealed different, and sometimes, opposite patterns of accumulation for compounds in the same subclass across the temperature regimes. Increased temperature over the 12-24 °C range caused a significant increase in the concentrations of delphinidin-3-glucoside, delphinidin-3-(6”-coumaroyl)-glucoside and cyanidin-3-(6”-coumaroyl)-glucoside, while the opposite trend was observed for cyanidin-3-glucoside, cyanidin-3-rutinoside, and peonidin-3-rutinoside. The highest accumulation of delphinidin-3-rutinoside was observed at 18 °C. Daylength had only minor impacts on accumulation of health related phytochemicals. In general, there were no significant differences between berries ripened under different photoperiodic treatments with identical daily light energy. On the other hand, increased daily light integral under natural daylength conditions in the phytotron stimulated the accumulation of total monomeric anthocyanins, and he same response was observed under increased radiation in the field. The concentrations of all anthocyanins and some flavonols were higher in berries ripened outdoors than in the phytotron, apparently due to screening of UV-B radiation by the glass cover. In general, plant genetic background was the main source of variation in fruit quality and had supreme influence on accumulation of bioactive compounds in black currant berries. Under both field and phytotron conditions, significant cultivar differences in berry chemical composition were observed. The present investigation also revealed that black currant cultivars may vary significantly in their inherent stability in accumulation of the various chemical compounds across varying environmental conditions. In conclusion, the present results demonstrate that plant genotype and climatic conditions during the ripening period had strong influence on chemical composition of black currant berries. The presented results may contribute to a deeper understanding of the complex relations between climate environmental conditions and berry nutritional quality of black currants.

Les publikasjonen her:

NVA : hdl.handle.net/11250/2448230