Effects of Gibberellin and Ultrasonic on Seed Germination Characteristics of Different Strawberry Cultivars

Xu YAN Yong WEN Qingxin HAN Xinmei YANG Lan LI

Abstract Four kinds of strawberry （Benihoppe， Akihime， Tuscany and Qianmei） seeds were taken as the materials， to study the effects of gibberellin in different concentrations and ultrasonic treatment on seed germination. The results showed that thousand kernel weights of seeds from different strawberry varieties had significant difference， and the sequence was Benihoppe=Akihime>Qianmei>Tuscany. Gibberellin treatment could improve germination rate of strawberry seed， and the optimal gibberellin concentrations for Benihoppe， Tuscany， Qianmei and Akihime were 5， 5， 5 and 10 mol/L. Gibberellin treatment could improve germination potential of Tuscany and Qianmei， and germination potential rose with gibberellin concentration increased within certain range， while ultrasonic treatment obviously inhibited germination of strawberry seed.

Key words Strawberry seed; Gibberellin; Germination percentage

Fragaria ananassa Duch. is perennial herb of Fragaria， Rosaceae， and its fruit is bright red， beautiful， soft， juicy， pleasant and fragrant， so it has the reputation of "fruit queen"[1]. Strawberry has a 30year cultivation history in Chengdu. Since variety is single， strawberry varieties degrade severely， which seriously affects the development of strawberry industry， and the research on new strawberry varieties and materials urgently needs to be strengthened. At present， main means of studying new strawberry varieties and materials at home and abroad is crossbreeding. Via artificial breeding， the obtained strawberry hybrid seeds and seeds of seedlings are sowed and raised， and fine varieties of individual progeny plant are selected. Strawberry seed is not easy to germinate. Due to small grain， thick seed coat， bad absorption and permeability character， germination rate of seed is lower. There may also be more inhibitors causing dormancy， and seedling formation rate of seed reproduction is low[2]. Therefore， it has great significance for strawberry breeding to improve germination rate of seed and regularity of seedling emergence and shorten germination time.

Prior scholars promoted strawberry seed germination by temperature， illumination， in vitro culture， acid treatment and hormone treatment[2-7]， and much progress has been made in improving germination rate and germination potential. In this test， the effects of ultrasonic and different GA3 concentrations on seed germination of different strawberry varieties were studied based on prior work， which could provide the basis for further exploring physiological characteristics of strawberry seed germination， and improving seed germination rate and germination potential.

Materials and methods

Materials

The test strawberry varieties contained Benihoppe， Akihime， Tuscany and Qianmei. The seeds were taken from strawberry， and then were cleaned for use.

Methods

Determination of thousand kernel weight of strawberry seed

Full seeds were selected for counting under dissecting mirror， and it was weighed by analytical balance， which was repeated for five times.

Aseptic treatment of petri dishes

Petri dishes were wrapped by newspapers， and then were put in 121 → of hightemperature steam sterilizer to sterilize for 30 min. After taken out， they were put in electrothermal constanttemperature blast dryer to dry for use.

Seed treatment

Moderate amount of seeds of each strawberry variety were taken in clean conical flask， and it was washed by running water for 30 min. In the cleaning process， it was continuously shaken until the seeds didnюt form clumps. The seeds were put in different clean test tube， and different reagents were added. Specific treatment reagents and time were shown as Table 1.

Seed cultivation

The processed seeds were cleaned by distilled water for use. A layer of degreased cotton was laid in a sterilized and dried petri dish， and then a layer of filter paper was covered on it. Ultra pure water was added to make degreased cotton and filter paper absorb moisture. 50 seeds in each treatment were put in corresponding petri dish， which was marked and recorded. All petri dishes were put in 25 → of incubator to conduct germination test， and each treatment was repeated for three times. Germination status of seed was recorded per 5 d， and its germination potential was measured on the 15th day. Germination rate and germination potential of seed were calculated according to below formula.

Data analysis

Statistical analysis of data was conducted by DPS8.0 and EXCEL2007.

Results and analyses

Analysis of thousand kernel weight

Seen from Table 2， thousand kernel weights of Benihoppe， Akihime， Tuscany and Qianmei were respectively 0.65， 0.65， 0.48 and 0.57 g， and there was extremely significant difference among varieties， in which thousand kernel weight of Tuscany strawberry was 26.15% lower than that of Benihoppe strawberry.

Effects of different treatments on germination rate of strawberry

Effects of different treatments on germination rate of Benihoppe strawberry

Seen from Table 3， Benihoppe strawberry seeds started to germinate after 5 days of treatment. During 5-15 days， seeds germinated slowly， and germination rate could reach more than 10%. Germination rate in GA3 treatment was higher than that in control， in which germination rate in 15 mg/L of GA3 reached 16.67% and was the highest， which was 6.67% higher than control， but the difference among treatments was insignificant. During 15-35 days， seeds germinated rapidly， and germination rate in each treatment respectively reached 37.33%， 25.00%， 31.33%， 21.00% and 37.33%. There was insignificant difference between GA3 treatment and control， and significant difference between ultrasonic treatment and control. When GA3 concentration was 5 mg/L， germination rate reached 46.67% and was the maximum， but the difference with control was insignificant. Germination rate in ultrasonic treatment reached the maximum after 15 days， and then changed little. On the 45th day， germination rate in ultrasonic treatment was significantly lower than that in control and GA3 treatment， and it was 20.67% lower than control. Test results showed that gibberellin treatment could promote the germination of Benihoppe strawberry seeds， but the influence on germination rate was insignificant， and ultrasonic treatment significantly inhibited strawberry seed germination in latter period.

Effects of different treatments on germination rate of Akihime strawberry

Seen from Table 4， Akihime strawberry has started to germinate on the 5th day. When GA3 concentration was 10 mg/L， germination rate was 6% higher than that in ultrasonic treatment， and there was insignificant difference with other treatments. On the 10th day， germination rate rose with GA3 concentration increased， and germination rates were respectively 13.33%， 19.33%， and 25.00%. There was extremely significant difference between GA3 treatment and control. In prior 20 days， germination rate increased rapidly in GA3 treatment but increased slowly in control and ultrasonic treatment， and germination rate between control and 10 mg/L of GA3 differed by 13.33%. In latter 20 days， the increase of germination rate in control and ultrasonic treatment was quicker. Finally， germination rate had significant difference between 10 mg/L of GA3 treatment and control， and germination rate in other GA3 treatments was higher than that in control， but there was not significant difference. Germination rate by ultrasonic treatment was always very low， which had significant difference with control and other treatments. It showed that gibberellin could improve germination rate of Akihime strawberry and promote germination time of strawberry seed， while ultrasonic treatment significantly inhibited germination of strawberry seeds.

Effects of different treatments on germination rate of Tuscany strawberry

Seen from Table 5， germination rate of Tuscany strawberry was extremely high， and the final germination rate can reach more than 75%， and germination was basically completed in 20 days. The effects of GA3 in different concentrations on seed germination rate were insignificant. In prior 15 days， ultrasonic treatment significantly inhibited germination rate of Tuscany strawberry. But with germination time prolonged， germination rate did not have significant difference between ultrasonic and other treatments. It showed that ultrasonic would postpone germination time of Tuscany strawberry， and gibberellin did not affect strawberry seed germination.

Effects of different treatments on germination rate of Qianmei strawberry

Seen from Table 6， Qianmei strawberry basically did not germinate in the first 5 days. During 5-15 days， germination rate of seed was low. On the 15th day， germination rate was 16.67% in 15 mg/L of GA3， which was 6.67% higher than that in control， and there was insignificant difference among treatments. During 20-35 days， germination rate increased rapidly except in ultrasonic treatment， in which germination rate was improved by 14% in control during 25-30 days， while it was improved by 11% in 5 mg/L of GA3 during 30-35 days. Started from the 20th day， the increase of germination rate was not obvious in ultrasonic treatment. The influence of gibberellin on seed germination was not obvious， and the difference with control in different periods was insignificant. In latter period， germination rate in control was higher than that in 10 and 15 mg/L of GA3. It showed that Qianmei strawberry seed had long dormancy period， and gibberellin had little impact on seed germination， while ultrasonic treatment inhibited seed germination.

Effects of different treatments on germination potential of strawberry

Seen from Table 7， germination potential of Benihoppe and Akihime strawberry seeds did not have significant difference among treatments， and germination potential of Benihoppe strawberry seed in control was higher than that in other treatments. Germination potential of Akihime strawberry seed in gibberellin and ultrasonic treatments was higher than that in control， and germination potential rose with gibberellin concentration increased. Germination potential of Tuscany strawberry rose with GA3 concentration increased， and there was significant difference between 15 mg/L of GA3 and control， 5 and 10 mg/L of GA3， and it was 9.33%， 12.00% and 8.00% higher than them. Germination potential in ultrasonic treatment was the lowest， which had significant difference with other treatments， and it was 9.33% lower than control. The highest germination potential of Qianmei strawberry was in 10 mg/L of GA3， which had significant difference with control and was 18.67% higher than control， and there was insignificant difference among GA3 treatments. Germination potential by ultrasonic treatment was lower than other treatments， with significant difference with other treatments. It showed that ultrasonic treatment had insignificant impact on germination potential of Benihoppe and Akihime strawberry， and significant impact on germination potential of Tuscany and Qianmei strawberry. Within certain range， GA3 could improve germination potential of strawberry seed with concentration increased.

Conclusions and Discussions

There were many factors affecting germination of strawberry seed. Prior research results showed that the effect of strawberry seed culture in vitro was the most obvious[7]. The research results showed that thousand kerner weights of different strawberry varieties had significant difference， and germination rate and germination potential of seeds from different strawberry varieties were also different. GA3 had little impact on germination rate of Benihoppe， Tuscany and Qianmei strawberry， but could promote the seed germination of Tuscany and Qianmei strawberry. Additionally， GA3 could not only improve germination rate of Akihime strawberry but also advance germination time of Akihime strawberry seed. Within certain concentration range， GA3 could improve germination potential of strawberry seed. In the test， ultrasonic treatment significantly inhibited germination of strawberry seed， which was not consistent with prior research results[8-9]. This may be due to the long ultrasonic treatment time， which destroyed the internal structure of strawberry seeds and resulted in the low germination rate of strawberry seeds， and it needed further exploration.

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