園芸作物の硝酸塩蓄積に関する研究(第13報)

Abstract

The study was carried out to investigate the variance of nitrate-nitrogen content in tomato fruit among the varieties and the physiological difference between low and high nitrate varieties.The variance of NO3-N content in ripe tomato fruit during the harvest season among sixteen varieties was investigated and these varieties were classified into three groups according to the content. The first group includes extremely early ripening varieties such as Fireball and Amature, and more than 5ppm of NO3-N was contained in the ripe fruit throughout the harvest season. The second group includes early or middle ripening varieties as Chico and Heinz 1370, and NO3-N contents were from 5 to 10ppm only at the early or middle period of the harvest season, then decreased to less than 3ppm at late period. Classified as the third group are Nozomi No.1, VF 36, and other middle or late ripening varieties, and NO3-N contents were less than 5ppm throughout the harvest season.Fluctuation of NO3-N content in the fruit was investigated in the course of ripening of some varieties. NO3-N content in the fruit of Fireball was high at the breaker stage and the level was maintained in the ripening course. While NO3-N contents in the fruits of Chico and Nozomi No.1 were lower at the breaker stage than Fireball and decreased further in the ripening course. When Taiho variety was grown on different culture conditions, the fruit grown on standard culture contained a high level of NO3-N at the breaker stage and a decline followed during the subsequent ripening period. The fruit grown under shading showed remarkable accumulation of NO3-N at the breaker stage followed by a slight decline, and the fruit on low level of NO3-N in culture solution showed a low level at the breaker stage followed by a further decline.The ripe fruit of Chico, low nitrate accumulating variety, as compared with Fireball, high nitrate accumulating variety, contained higher levels of total nitrogen, free amino acids, reducing sugar and calcium, and lower levels of organic acids and potassium.Nitrate reductase activity in the fruit of Heinz 1370, low nitrate accumulating variety, was higher level than Amature, high nitrate accumulating variety, in the ripening course.Remarkable amount of NO3-N was found in the fruit of Fireball grown on high level of NO3-N of culture solution or under shading with cheese cloth, but the content in the fruit of Chico grown on those conditions was further lower than Fireball.