Fund Project: Effects of Plant Growth Regulators on the Seedlessness and Quality of 'Ruidu Carnelian' Grapes

Fund Project: Effects of Plant Growth Regulators on the Seedlessness and Quality of 'Ruidu Carnelian' Grapes

Fund Project: National Key R&D Program (2019YFD1001405); Ministry of Finance and Ministry of Agriculture and Rural Affairs: National Modern Agricultural Industry Technology System Funding (CARS-29-yc-4)

In the edible grape consumption market, seedless grapes are becoming more and more popular with the public. At present, there are very few seedless grape varieties with the characteristics of large grains, aroma, bright color and excellent quality. The safe and effective denuclearization of well-seeded and excellent flavor varieties has become one of the effective and fast ways to meet and enrich the consumer market. 'Ruidu Carnelian' is an excellent fresh food species selected by Beijing Forestry Fruit Tree Research, bright red, bright color, hard and crisp flesh, with a strong rose fragrance. Grain mass of 5.52 g, soluble solids 18.2%, deeply loved by growers and consumers. At present, it is widely cultivated in many areas of China, and the safe and effective cultivation of this variety will undoubtedly greatly improve its commerciality and increase the planting efficiency of fruit farmers.

In recent years, plant growth regulators such as gibberellin (GA3) and piroctrolol (CPPU) are the most commonly used agents for grape denuclearization treatment. Zhang Wenying et al. found that the grape genome contains 3 DELLA protein gene family members, which can regulate the development of grape seedless fruits by responding to GA3 signals; Shiozaki et al. believe that exogenous GA3 treatment can effectively induce the increase of grape free-form polyamines and lead to seedlessness [5]; the main role of CPPU is to promote cell division and tissue differentiation, which has a significant effect in promoting fruit expansion and development. Hou et al. have found that dipping the 'Sunshine Rose' grape with 25 mg/LGA 3 +10 mg/L CPPU two weeks after flowering can effectively prevent the fruit from browning and improve the quality of the fruit. However, the sensitivity of different varieties to these regulators is different, and the treatment time and concentration requirements are different. Hao Fengge et al. Tests on the 'Jintian Rose' grape showed that the denuclearization effect of the fruits was significantly improved by each combination of hormones, with the highest rate of seedlessness in the first time with GA3 50 mg/L+CPPU 2 mg/L at the first time at the peak flowering stage and GA3 50 mg/L+CPPU 5 mg/L at the second time after full flowering. Liu Jinbiao et al. treated the 'Jufeng' grapes, showing that the first time in the first 2 to 3 days after the flowering with GA3 8 mg / L + streptomycin 200 mg / L + CPPU 2 mg / L + CPPU 2 mg / L impregnation of the flower spike, the second time after 12 days with GA 3 25 mg / L + CPPU 2 mg / L immersion of fruit spikes, can obtain good commerciality, seedless rate of 90% of the high-quality seedless fruit. In the auxin treatment of the 'Ruidu Carnelian' grape, only the effect of the treatment of the investigation agent on its fruit quality was found by Lü Ke et al., and no reports of denuclearization were reported. In this paper, by discussing the effects of different concentrations of GA3 and CPPU treatment on the denuclearization and fruit quality of Ruidu Carnelian, in order to screen out the appropriate treatment scheme and provide an effective technical reference for the seedless cultivation of Ruidu Carnelian grapes.

1 Materials and methods

1.1 Test materials

10-year-old 'Ruidu Carnelian' grape as the test material, "V" shaped frame, north-south direction, plant row spacing of 2.0 m×3.0 m, tree disc covered with black mulch, equipped with drip irrigation, natural grass between rows, orchard soil fertilizer water and disease and pest control routine management. Test agents: Gibberellinic acid (GA 3 20%, American Hualun Biological Sciences Company); Pyroprim (CPPU 0.1%, trade name chloropyramide, Chongqing Nuoyi Pesticide Co., Ltd.); Bao Mei Ling (American Hualun Biological Sciences Company).

1.2 Test methods

The trial was conducted in 2020 in the Pinggu Grape Base of the Institute of Forestry and Fruit Sciences of the Beijing Academy of Agriculture and Forestry Sciences. Randomly selected the resulting branches with moderate growth and consistent number of leaves on the robust tree, left 1 panicle per branch as the test object, and the flower spike was trimmed 1 week before flowering, and the secondary panicle and the following large branches were removed, leaving only the spike tip 5 to 6 cm. The test consisted of 36 treatments (without controls), and the formula is shown in Table 1. At the end of the flowering period (May 27), the first treatment was carried out with different concentrations of medicinal solution dipping in flower spikes for 5 s, and the second soaking of panicles was carried out 12 days after flowering (June 7), with water as the control (CK), completely randomized group arrangement, single plant cells, and repeated 3 times per treatment.

1.3 Indicator determination

When the fruit is ripe, 3 representative panicles are selected for each treatment to determine the panicle quality, and 10 fruits are randomly picked in the upper middle and lower parts of the panicle to determine the grain quality, longitudinal and horizontal diameter, soluble solids and titrable acid content. Each fruit was cut with a paper cutter to check the number of seeds of the fruit, and the rate of seedless fruit (only the normal ripe fruit grains) was counted; 9 fruit stems were randomly taken in the upper and lower parts of the fruit panicle to determine its coarseness; the thickness of the panicle stem was measured at the second spikelet of each panicle; and 9 fruit brushes were randomly taken in the upper and lower parts of the fruit panicle to measure the length of the fruit brush. Each index was determined using an electronic balance, an electronic digital caliper and an electronic digital display glucose measuring instrument.

Seedless rate (%) = number of seedless fruits / total number of fruits×100

Fruit shape index = fruit diameter / fruit diameter

1.4 Data Processing and Analysis

The measurement results were analyzed by Excel, SPSS 21.0 and other software, and the differences were compared at the P≤0.05 level using Duncan's new compound polarity method (SSR).

2 Results and analysis

As can be seen from Table 2, the seedless rate obtained by each combination treatment is significantly higher than that of CK (clean water). This shows that the combination of GA3 and CPPU can get seedless fruits, but the seedless rate is different; the treatment 16 has the best effect, with a seedless rate of 97.33%; followed by the treatment of 32, with a seedless rate of 94.33%; the third is the treatment of 17, the seedless rate is 92.33%, and the difference between the three is not significant. From the perspective of the average number of seeds in the fruit, each treatment can significantly reduce the seed content of the fruit, especially the number of two-seed fruit and three-seed fruit is much lower than CK, and the treatment of 16 and 32 is the best, and the treatment is 17 times.

From the perspective of panicle quality (Table 3), except for the significant differences between treatment 14 (146.66 g) and treatment 11 (428 g) and CK (288.5 g), the rest of the treatments were not significantly different from CK, treatment 16 (286.33 g) and treatment 32 (256.33 g) were not significantly different from CK, and treatment 17 (196.33 g) was significantly different.

From the perspective of grain quality, the quality of the grains treated 14 (3.61 g), the treatment 17 (3.11 g), and the process 19 (2.06 g) grains were significantly reduced; the particle quality of treatment 5 and treatment 11 reached 6 g, indicating that the two treatments had the effect of increasing the fruit grains, but the seedless rate was 71.6% and 70%, and the effect was not as good as that of treatment 16. Treatment of 32 (3.98 g) also differed significantly from CK.

The thickness of the ear stem and the thickness of the fruit stem affect the appearance and commodity value of the fruit, and the length of the fruit brush is one of the important indicators to measure the grain drop and storage resistance of the fruit, so these indicators are also important factors that determine the success of the denuclearization test. From the results, most of the treatments thickened the panicle stem and fruit stem, shortened the length of the fruit brush, and reduced the commodity value and storage and transport resistance; however, the above three indicators of treatment 16 were not significantly different from CK; the length of the brush of treatment 32 (2.96 mm) was significantly different from that of CK (6.67 mm), indicating that the treatment was more likely to fall grains and the shelf resistance was greatly reduced. Combining the above indicators, under the premise of ensuring a high seedless rate, the storage resistance of the fruit and the coarseness and appearance of the fruit spike have not changed significantly.

Judging from the fruit diameter and fruit shape index, all treatments were not significantly different from CK. It can be seen from the soluble solids that there were significant reductions in treatment 22, treatment 23, treatment 28, and treatment 35, and there was no significant difference in the soluble sugars treated in most treatments; the difference between treatment 16 (19.42%), treatment 17 (20.02%), 32 treatment (18.63%) and CK (19.65%) was not significant. As can be seen from Table 4, most treatments reduce acidity, so the saccharimetric ratio increases and the taste is sweeter. The treatment of 16 sugar-acid ratio (42.4) and CK (37.3) is not significantly different, so this treatment does not change the flavor of the fruit.

3 Discussion and conclusions

In the 2019 experiment, the initial flowering and the end of bloom were designed as the initial treatment period, and the results found that there was not much difference in the effect between the two. Considering that the promotion and use is convenient for fruit farmers to operate, it is better to use the end of the flower. Many studies have shown that the coordination of various hormones is an important mechanism for inducing the formation of seedless fruits in grapes. And each growth and development event is often the result of a synergistic effect between hormones rather than a single action of a hormone. The results of the 2019 test show that the treatment with GA3 alone often does not lead to good seedless results, so the 2020 design is designed with a combination of different concentrations of GA3 + CPPU. It was also found that GA3 and CPPU synergistic treatment can improve fruit set rate, increase color, and ripen early; at the same time, the acidity of the fruit is reduced, the sugar-acid ratio is improved, and the taste of the fruit is sweeter, which is consistent with many reports. At the same time, it was found that almost all the treated fruit shape index was lower than that of the control, that is, the fruit had a tendency to become rounded after treatment, which was consistent with the reports of Liao Miaoling and others. The main reason for this change is the expansion mechanism of CPPU, which can prolong the cell division time on the one hand, and promote the volume of pulp cells on the other hand.

In this test, with the increase of treatment concentration, the thickening of fruit stalks and panicle stems was more pronounced, and the length of fruit brushes was shorter, indicating that excessive concentrations of GA3 and CPPU aggravated the wood thrombosis and hardening of fruit stems. Therefore, the concentration of growth regulators should be appropriate.

From the comprehensive point of view, the treatment of 16 is the best, which is manifested as uniform fruit grain, grain quality, panicle quality and soluble sugar are no different from CK, but the acidity is lower than the control, the sugar-acid ratio is increased, and the taste is sweeter, so the fruit quality is improved compared with CK. Moreover, there was no significant difference between the thickening of the fruit stem and the length of the fruit brush, and the seedless rate reached 97.33%.

By comparing the fruit seedlessness rate, fruit grain size, quality, storage resistance and commerciality, the flower spikes were dipped with GA 3 50 mg/L+CPPU 2 mg/L at the end of the flowering period, and the fruit ears were dipped with GA 350 mg/L+CPPU 5 mg/L when the fruit began to expand after 12 days. The rate of no nuclear can reach 97.33%. Achieving the purpose of seedless without reducing the quality of the fruit can be used as a reference application in the seedless production of 'Ruidu carnelian' grapes in North China, where the climate is similar.