온주밀감의 과실 품질에 미치는 토양 건조 처리와 생장조절제 살포의 영향

Abstract

In order to improve the fruit quality of early-ripening satsuma mandarin by increasing the sugar contents in fruit juice and inhibiting the occurrence of peel puffiness, several experiments on the effects of the season of drought stress and foliar spray of plant growth regulators were conducted. The results obtained are summarized as follows; 1. Effect of season of drought stress on sugar accumulation in juice. Sixteen uniform potted 7-year-old 'Okitsu Wase' satsuma mandarin (Citrus unshiu Mark cv. Okitsuwase) trees grafted on trifoliate orange stock in a glass house were randomly assigned to four groups; conventional soil water supply at level of ψmax of -0.3∼-0.4MPa during the whole period from July 21 (fruit dia about 30mm) through Nov. 20 (WW), mild drought stress at level of ψmax of -0.6∼-0.7MPa during the whole period (DD), drought stress during 50 days from July 21 through Sept. 10 (DW), and drought stress during 50 days from Oct. 1 through Nov. 20 (WD). Fruit growth was monitored periodically, and the concentration of free sugars and the activities of sucrose synthase (SS) and sucrose phosphate synthase (SPS) in fruit juice during maturation were determined. 1.1. Drought stress inhibited the fruit growth, but the growth became most vigorous in response to supply of water after drought, resulting in the largest fruit in DW. 1.2. The concentration of fructose and glucose in fruit juice was increased by drought stress, and the difference between fruits with and without stress did not changed during the prolonged drought, but the difference disappeared in response to supply of water after drought. The concentration of sucrose was also increased by drought, but the difference between fruits with and without stress steadily increased during the prolonged drought and maintained even under the condition without drought. 1.3. The activity of SS and SPS was increased by drought, and the pattern of change was similar to that of fructose or glucose rather than that of sucrose. 1.4. It was suggested that the increase in the activity of SS by drought represents the increase in sink strength, the increase in the concentration of hexoses accounts for the degree of active osmoregulation, and the accumulation of sucrose is the accumulated results of the increased sink strength. 2. Effect of foliar spray of plant growth regulators on the occurrence of peel puffiness. The mixture (GP, 10 mg×L^(-1), respectively) of gibberellic acid (GA₃) and n-propyl-dihydrojasmonate (PDJ), was twice sprayed, respectively, on three different times including on Sep. 25 and Oct. 15, on Oct. 10 and Oct. 30, and on Oct. 30 and Nov. 20, on 25-year-old 'Miyagwa Wase' satsuma mandarin (Citrus unshiu cv. Miyagwa Wase) on trifoliate orange stock growing in open field. GA₃ alone and GP at 10 mg×L^(-1), respectively, were twice sprayed on Sep. 25 and Oct. 15 on 'Okitsu Wase' satsuma mandarin growing in unheated plastic film house. Fruit characters were periodically observed with emphasis on peel puffiness until the following March. Contents of free sugars, inorganic elements and pectic substances, and the activities of polygalacturonase (PG) and pectin methylesterase (PME) in fruit peel were also analysed. 2.1. GP sprayed just before the color break of peel (on Sept. 25 and Oct. 15) didn't affect fruit diameter and weight at harvest, but reduced peel thickness, delayed peel coloring, increased juice Brix, juice acidity and fruit specific gravity, and inhibited the occurrence of peel puffiness. The above effects sharply decreased in the later spray. 2.2. Both GA₃ and GP sprayed just before the color break of peel significantly inhibited the occurrence of peel puffiness, reduced the contents of free sugars in peel and increased those of Ca and B. 2.3. The activity of PME in control fruit peel rapidly increased in November when peel puffiness sharply developed, and the increase in PME activity was inhibited by GA₃ and GP. 2.4. The activity of PG didn't show any trend in seasonal change, but was reduced by GA₃ and GP, mainly after November. 2.5. The content of water soluble pectin in control fruit peel sharply increased from November, and reached to the maximum level in January. But the increase was inhibited by GA₃ and GP, resulting in the steady state from December. 2.6. EDTA-soluble pectin in control fruit peel reduced after the maximum level in December, but the reduction was inhibited by GA₃ and GP. 2.7. No significant difference between GA₃ and GP was recognized for the above effects observed .