Effect of different water treatments at seedling stage on flower bud differentiation and prematurity of strawberry

Abstract: 【Objective】Flower bud differentiation is essential for fruit production, and many factors affect this process. Flower bud differentiation can be promoted through water management, but the relevant physiological mechanism is unclear. This study aimed to find the effect of water treatments at seedling stage on flower bud differentiation and prematurity of strawberry and to explore the physiological mechanism of flower bud differentiation for early- bearing cultivation.【Methods】We used the seedlings of Fragaria ananassa Duch.‘Benihoppe'as the experimental materials, and the water treatments were 10%, 20%and 30% moisture content of substrate, marked as S1,S2 and S3, respectively. Flower bud differentiation ratio, content of organic carbon(C), total nitrogen(N), endogenous hormone(GA, IAA, ABA and CTK) concentrations and hormone ratios(ABA/GA, CTK/GA, ABA/IAA and CTK/IAA) in the three treatments during the flower bud differentiation were analyzed; phenological phases(budding date, full flowering date,and beginning harvesting date) were recorded; and fruit quality(soluble solids, average firmness) and production(single fruit weight, yields of early crop, middle crop and late crop) were also investigated.【Results】Flower bud differentiation in S1 treatment was the earliest; the ratio of flower bud differentiation inS2 increased fastest during the period from 19 to 29 August, and the peak period of flower bud differentia-tion occurred from 14 to 19 August. C in S1, S2 and S3 had an increasing trend before 14 August, but ithad dropped in S1 by 19 August, and then showed an increasing trend. C in S3 showed an increasingtrend through the whole process, and was lower than those in S1 and S2 before 14 August. N in S1 dis-played a decreasing trend before 14 August, when it reached a maximal value of 1.409% and decreasethereafter. N in S3 was lower than those in S1 and S2(except on 14 August) before 24 August, and rapidlyrose to 1.582% on 24 August, which was significantly higher than those in S1 and S2. The C/N ratio in allthe treatments showed an increasing trend before 14 August. In S1 and S3, C/N ration had a drop on 14 August, while in S2 drop occurred on 19 August. C/N ratio in S1 and S2 displayed a rapid increase on 24 August, reaching 43.36 and 41.59, respectively, and at the same time, the ratio of flower bud differentia-tion was the maximal. Endogenous hormone levels varied during the process of flower bud differentiation.The content of GA in the three treatments was in the order of S3>S2>S1, except on 15 July. GA content inall the treatments was relatively low on 4 August and 14 August, and it was lowest in S1(125.4 μg·kg-1).IAA content in all the treatments decreased initially and then increased, reaching a peak on 4 August.ABA content in all treatment increased before 24 August and decreased thereafter, and it was lower in S2 than in S1 and S3 at the same date, while in S3 it was higher than in the other treatments during the peri-od from 4 to 24 August with a maximal value of 394.2 μg·kg-1on 19 August. In all treatment, CTK dis-played an increasing trend throughout the process. CTK content was highest in S3 and lowest in S2. Thehighest CTK in S3 was 200 μg·kg-1which occurred on 24 August. The relatively high ABA and CTK lev-els but relatively low GA and IAA levels might be required for flower bud differentiation process. Hor-mone ratios were also closely related to flower bud differentiation in strawberry. The ratios of ABA/GAand CTK/GA had a consistent trend, and their changes in all the treatments increased before 14 Augustand then decreased. The ratio of ABA/GA was much higher than CTK/GA. Both ratios reached their high-est values on 14 August. These ratios in S1 were the highest, with a maximal value of 2.56 and 1.2, respec-tively. Similar pattern was also found in the ratios of ABA/IAA and CTK/IAA. These findings suggest thatABA may play a dominant role in flower bud differentiation in strawberry. The budding date in S1 was theearliest, which was 13 d and 25 d earlier than S2 and S3, respectively, and therefore the full flowering dateand the beginning harvesting date in S1 were also the earliest. The period from full flowering date to begin-ning harvesting date in S2 was 24 d, 9 d and 8 d shorter than in S1 and S3, respectively. Soluble solids con-tent(SSC) and firmness in all the treatments increased at first and then decreased. The SSC in S2 was thehighest, while firmness was the highest in S1 except in May. The SSC in S1, S2 and S3 was highest in Janu-ary, which was 11.8%, 11.9% and 11.2%, respectively. The average single fruit weight and total produc-tion in S2 was the highest and the treatment exhibited significant prematurity(47.1% of the total produc-tion).【Conclusion】S2(20% moisture content of substrate) with the fastest increase in flower bud differen-tiation ratio was the best water treatment for strawberry at seedling stage. The treatment enables early bear-ing with an early crop of 47.1% of the total production and thus a highest economic return. Relatively highC/N ratio is favorable for differentiation process and ABA may play a dominant role in the flower bud differ-entiation in strawberry. Proper ABA/IAA ratio(0.57-0.73)might be needed for flower bud differentiation.