Effect of plant growth regulators and citric acid on the rooting of soft- wood cuttings of persimmon rootstocks

Abstract:【Objective】Persimmon (Diospyros kaki Thunb.) is one of the important fruit tree species in our country. In recent years, pollination-constant non-astringent (PCNA) persimmons has gradually be- come the key development type in persimmon industry. Field practice in the past few years has shown that L938 (Diospyros lotus L.) and Taifu (Diospyros kaki Thunb.) are ideal rootstocks for PCNA persim- mon in consideration of their wide compatibility and strong cold resistance in northern China. However, the scale application is difficult to achieve because of the scarcity of materials. Cutting propagation would be an effective way to solve this problem. Therefore, the object of this study was to explore the effects of plant growth regulators and citric acid treatments on the rooting of softwood cuttings of per- simmon rootstocks and find a suitable rooting method.【Methods】The experiment was carried out in the scientific research base of Hebei Agricultural University from 2019 to 2020. Plant materials L938 and Taifu were planted in the research base. There were 5 sections in this study: 1) Taifu cuttings were treated with 1000, 2000, 3000, 4000, 5000 mg·L-1 IBA+NAA mixed reagent (1∶1), and 0.1%, 0.2%, 0.3%, 0.4%, 0.5% citric acid solution or water (CK), then inserted into nutrient cups filled with cutting medium; 2) Based on the first section, Taifu cuttings were treated with 3000 mg·L-1 IBA+NAA mixed reagent or 0.4% citric acid solution respectively; 3) Different rootstock cuttings Taifu and L938 were  treated with 3000 mg·L-1 IBA+NAA mixed reagent or 0.4% citric acid solution, respectively; 4) L938 cuttings were divided into 2 parts (the upper side and the middle part) before being cut into segments. Thenthesegmentsweretreatedwith3000mg·L-1 IBA+NAAmixedreagentor0.4%citricacidsolution respectively; 5) Taifu and L938 cuttings were firstly treated with 3000 mg·L-1 IBA+NAA mixed reagent or 0.4% citric acid solution, and then the cuttage test was carried out in May and July, respectively. Wa- ter treatment was used as the control in all experiments. The root length, rooting rate and rooting num- ber of the cuttings were measured after 50 days.【Results】Rooting rate of Taifu cuttings under 3000 mg·L-1 IBA+NAA treatment (85.3%) was significantly higher than those under 1000, 4000, 5000 mg·L-1IBA+NAA treatments and that of the control. There was no prominent change in the root number with different IBA+NAA treatments, while they were all significantly higher than that of the water treatment. Root length in 4000 and 5000 mg·L-1 IBA+NAA treatments were significantly less than in other treat- ments. Rooting rate of Taifu cuttings under 0.4% citric acid solution treatment (89.0%) was markedly higher than those under 0.1%, 0.2%, 0.3%, 0.5% citric acid solution treatments and that of the control. Rooting number under 0.3%, 0.4%, 0.5% citric acid solution treatments were significantly larger than that under other treatments. Root length under the 0.5% citric acid solution treatment was the highest among the six treatments. The different persimmon rootstock types (Taifu and L938) had no significant difference in the rooting rate of cuttings under both 3000 mg·L-1 IBA+NAA and 0.4% citric acid solu- tion treatments, indicating that both of these two rootstock types could produce high rooting rate as long as the treatment condition was suitable,although the rooting number of L938 were slightly higher than those of Taifu under both treatments. The upper side and middle part of L938 cuttings were used as ma- terials to test the effect of different vegetational parts on the rooting of the softwood cutting. The results showed that the difference of rooting rates between the upper and middle part of L938 cuttings was in- distinctive under both 0.4% citric acid solution and 3000 mg · L- 1 IBA + NAA treatments, although the root number of middle part was slightly more than that of the upper side. For L938 cuttings, the rooting rates in May were significantly higher than those in July under both 0.4% citric acid solution (80.0% in May and 44.7% in July) and 3000 mg · L-1 IBA+NAA (77.3% in May and 14.3% in July) treatments; the averagerootingnumber(9.69)ofcuttingsunder3000mg·L-1 IBA+NAAtreatmentinJulywasdistinct- ly higher than that of the other treatments; the average root length (5.77 cm) of cuttings under 0.4% cit- ric acid solution treatment in July was significantly longer than that under the other treatment. For Taifu cuttings, the rooting rates in May also significantly higher than those in July under both 0.4% citric acid solution (89.0% in May and 35.7% in July) and 3000 mg · L-1 IBA+NAA (85.0% in May and 9.7% in Ju- ly) treatments, which was similar with L938 cuttings; the average rooting number (5.19) of cuttings un- der 3000 mg·L-1 IBA+NAA treatment in May was clearly higher than that of the other treatments; the average root length (7.7 cm) of cuttings under 0.4% citric acid solution treatment in July was signifi- cantly longer than that under the other treatment【. Conclusion】The propagation of persimmon root- stocks by softwood cuttings could be effectively performed in May. Both 0.4% citric acid solution and 3000 mg·L-1 IBA+NAA treatments on softwood cuttings could promote rooting , meanwhile citric acid solution treatment could enhance the occurrence of lateral roots.