A method for improving postharvest resistance to black rot and maintaining quality of sweet potato tubers

Abstract

This invention discloses a method for improving the resistance to postharvest black spot disease in sweet potato tubers and maintaining their quality, belonging to the field of postharvest preservation technology for agricultural products. The method includes: selecting undamaged sweet potato tubers for callus treatment at room temperature for 48 hours, disinfecting with 1% sodium hypochlorite, rinsing with sterile water and air-drying, then soaking them in a 9.0 mmol / L benzothiadiazole (BTH) solution (containing 0.05% Tween 80) at room temperature for 60 minutes, removing them and air-drying them to complete the treatment. This invention induces the activation of the sweet potato tuber's own defense system through BTH, increasing the activity of key enzymes in phenylpropane metabolism, chitinase and other disease-resistant enzymes, promoting the accumulation of total phenols and lignin, maintaining cell membrane integrity, inhibiting starch degradation and abnormal increase in soluble sugars. Under storage conditions of 28±1℃ and 80-85%RH, it can significantly inhibit the expansion of black spot disease lesions and extend the storage period to more than 25 days. This method has no pesticide residues, is unlikely to cause pathogen resistance, is environmentally friendly, simple to operate, and cost-controllable, and is suitable for large-scale postharvest preservation of sweet potato tubers.

Description

Technical Field

[0001] This invention relates to the field of postharvest preservation technology for agricultural products, specifically a method for improving the resistance of sweet potato tubers to postharvest black spot disease and maintaining their quality, and particularly to the application of benzothiadiazole in the green control of postharvest black spot disease in sweet potato tubers. Background Technology

[0002] Sweet potato (Ipomoea batatas (L.) Lam) is a high-yield and adaptable food crop, rich in minerals, antioxidants, and carbohydrates. The skin of sweet potato tubers is relatively thin, making them susceptible to physical damage and pathogen infection during harvesting, transportation, and storage. Among these diseases, black spot disease caused by Ceratocystis fimbriata is a major disease affecting sweet potatoes, which not only leads to a 5%-50% loss in yield but also produces toxic substances such as sapote ketones that can harm human health.

[0003] Currently, the prevention and control of sweet potato black rot mainly includes biological control, physical control, and chemical control. Biological control is environmentally friendly but has low effectiveness and economic benefits; physical control has limited effectiveness; chemical control has better effectiveness but is prone to pesticide residues and environmental pollution, and long-term use can induce drug resistance in pathogens, which does not meet the requirements of food safety and green agriculture. Therefore, developing environmentally friendly, residue-free, and drug-resistant post-harvest control technologies for sweet potato black rot has become an urgent problem to be solved.

[0004] Benzothiadiazole (BTH) is a novel plant immune inducer. As a functional analog of salicylic acid, it has the characteristics of good environmental compatibility, low biotoxicity, and low susceptibility to inducing resistance in pathogens. It has been proven to effectively maintain the postharvest quality of fruits and vegetables such as navel oranges and plums, and induce disease resistance in fruits and vegetables such as mangoes, grapes, and strawberries. However, there are currently no reports on the application of BTH treatment in the control and quality maintenance of postharvest black spot disease in sweet potato tubers. Summary of the Invention

[0005] This invention provides a method for improving the resistance of sweet potato tubers to postharvest black spot disease and maintaining their quality, which can effectively solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for improving the resistance to postharvest black spot disease of sweet potato tubers and maintaining their quality, comprising three core steps: sweet potato tuber pretreatment, BTH solution preparation, and soaking treatment, as detailed below: Sweet potato tuber pretreatment: Select sweet potato tubers that are free from mechanical damage, pests and diseases, and are of uniform size. Call them for 48 hours at room temperature to reduce post-harvest damage. After washing off surface impurities with clean water, soak them in a 1% (v / v) sodium hypochlorite solution for 5 minutes to disinfect the surface and remove surface bacteria. Then rinse them 3-5 times with sterile water to remove residual sodium hypochlorite and air dry them at room temperature to avoid residual moisture that could lead to the growth of pathogens.

[0007] BTH solution preparation: A BTH solution with a concentration of 9.0 mmol / L was precisely prepared. To improve the wettability of the solution on the surface of sweet potato tubers, the nonionic surfactant Tween 80 was added to bring the final concentration of Tween 80 to 0.05% (v / v). The solution was then thoroughly mixed before use. This concentration was the optimal treatment concentration verified in the preliminary experiment, which can ensure the induction effect while avoiding physiological damage to sweet potato tubers caused by high concentrations.

[0008] Soaking treatment: The pretreated and dried sweet potato tubers are completely immersed in the above BTH solution and soaked at room temperature for 60 minutes to ensure that BTH fully contacts the surface of the sweet potato tubers and induces the defense response; after soaking, they are taken out and air-dried at room temperature to complete the post-harvest treatment. The treated sweet potato tubers can be directly stored or transported.

[0009] Preferably, the sweet potato tubers are of the "Xinxiang" sweet potato variety, and the method of the present invention has significant disease resistance and preservation effects on this main cultivated variety.

[0010] Preferably, the treated sweet potato tubers can be stored under conventional storage conditions of 28±1℃ and 80-85% relative humidity for more than 25 days, and the treatment can significantly inhibit the spread of black spot disease and maintain quality during storage.

[0011] Another objective of this invention is to protect the application of a 9.0 mmol / L BTH solution in the preparation of a postharvest black spot disease control and quality maintenance agent for sweet potato tubers, wherein 0.05% (v / v) of Tween 80 is added to the BTH solution for soaking and treating postharvest sweet potato tubers.

[0012] The mechanism of action of this invention is as follows: BTH, as a plant immune inducer, does not directly inhibit the in vitro growth of *Bacillus longifolius*, but achieves disease resistance and preservation by inducing sweet potato tubers to activate multiple defense-related metabolic pathways. It can increase the activity of key enzymes in phenylpropane metabolism (phenylalanine ammonia-lyase PAL, cinnamic acid hydroxylase C4H, 4-coumaric acid coenzyme A ligase 4CL, and peroxidase POD), promote the accumulation of total phenols and lignin, enhance the cell wall structure of sweet potato tubers, and resist pathogen infection. It can enhance the activity of disease resistance-related enzymes (chitinase CHT, β-1,3-glucanase GLU) and degrade the cell wall of pathogens through synergistic action, thereby slowing down the infection process of pathogens. Increase hydrogen peroxide in sweet potato tubers Content and superoxide anion The production rate is increased, and the expression of defense genes is activated through the action of reactive oxygen species signaling molecules, thereby enhancing disease resistance; It slows down the rise in relative conductivity and the accumulation of malondialdehyde (MDA), maintains cell membrane integrity, reduces pathogen invasion channels, and reduces cell physiological damage. It inhibits starch degradation and abnormal rise in soluble sugars during storage, avoids providing nutrients for pathogen growth, and maintains the nutritional quality of sweet potato tubers.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is the first to apply BTH to the control of postharvest black spot disease in sweet potato tubers. The optimal treatment process of soaking in 9.0 mmol / L for 60 min was determined. Under normal storage conditions, it can significantly inhibit the expansion of black spot lesions. Within 25 days of storage, the diameter of lesions is significantly lower than that of the untreated group, and the resistance to black spot disease is significantly improved.

[0014] The method of this invention can effectively maintain the post-harvest quality of sweet potato tubers while improving disease resistance, inhibiting starch degradation and abnormal accumulation of soluble sugars, maintaining cell membrane integrity, solving the problem of rapid decline in post-harvest quality of sweet potatoes, and extending the storage period.

[0015] This invention utilizes BTH to induce the sweet potato tuber's own defense system. It has no direct antibacterial properties, is not likely to induce resistance in sweet potato bud fungus, and has good environmental compatibility and low biotoxicity. After treatment, there are no pesticide residues, which meets the requirements of food safety and green agriculture development and overcomes the drawbacks of traditional chemical control.

[0016] The method of this invention is simple to operate, requires no complex equipment, has controllable BTH reagent costs, and the pretreatment and soaking steps are easy to implement on a large scale. It is suitable for post-harvest batch processing in sweet potato planting bases and fruit and vegetable preservation enterprises, and has good prospects for industrial application.

[0017] This invention provides a new technical solution and theoretical basis for the green control of sweet potato black spot disease, and also provides a reference for the application of BTH in postharvest preservation of tuber crops. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] In the attached diagram: Figure 1 The image shows the phenotypic pattern of black spot disease on sweet potato tubers during storage. The top image represents the control group (CK), and the bottom image represents the treatment group of this invention (BTH). At storage times of 5, 10, 15, 20, and 25 days, the lesion area in the treatment group was significantly smaller than that in the control group. Figure 2 The graph shows the trend of sweet potato tuber lesion diameter during storage. The horizontal axis represents storage time (d) and the vertical axis represents lesion diameter (mm). During storage of 5-25 days, the lesion diameter in the treatment group was significantly lower than that in the control group (p<0.05). Figure 3 The graph shows the effect of BTH on the in vitro colony growth of *Saccharomyces cerevisiae*. The horizontal axis represents the culture time (d), and the vertical axis represents the colony diameter (mm). There was no significant difference in colony diameter between the treatment group and the control group (p>0.05). Figure 4 The graph shows the trend of changes in starch content (A), soluble sugar content (B), relative conductivity (C), and malondialdehyde content (D) of sweet potato tubers during storage. The starch content of the treatment group was significantly higher than that of the control group, while the soluble sugar, relative conductivity, and malondialdehyde content were significantly lower than those of the control group. Figure 5 The graph shows the trend of superoxide anion production rate (A) and hydrogen peroxide content (B) in sweet potato tubers during storage. Both indicators in the treatment group were significantly higher than those in the control group. Figure 6 The graph shows the changing trends of the activities of key enzymes (PAL, C4H, 4CL, POD) in sweet potato tuber phenylpropane metabolism and the contents of total phenols and lignin during storage. The enzyme activities and metabolite contents in the treatment group were significantly higher than those in the control group. Figure 7 The graph shows the trend of CHT(A) and GLU(B) activities in sweet potato tubers during storage. The enzyme activities in the treatment group were significantly higher than those in the control group. Figure 8 The graph shows the trend of salicylic acid (A) and jasmonic acid (B) content in sweet potato tubers during storage. The hormone content in the treatment group was significantly higher than that in the control group during the critical storage period. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. Example 1:

[0021] This invention provides a technical solution for post-harvest BTH treatment and storage of sweet potato tubers: Experimental materials: “Xinxiang” sweet potato tubers harvested at 6:00 a.m. from a sweet potato base in Lin’an District, Hangzhou City were selected. The tubers were free from mechanical damage, pests and diseases, and were of similar thickness and length. They were transported back to the laboratory within 1 hour.

[0022] Main reagents and instruments: BTH, Tween 80, and sodium hypochlorite were all analytical grade; Sigma 3K15 high-speed refrigerated centrifuge, UV-2802 ultraviolet-visible spectrophotometer, DWSE-350 low-temperature constant temperature and humidity chamber, etc.

[0023] Solution: Pretreatment: Sweet potato tubers were calloused at room temperature for 48 hours, washed with clean water, soaked in 1% (v / v) sodium hypochlorite solution for 5 minutes, rinsed 3 times with sterile water, and air-dried at room temperature. Grouping: Sweet potato tubers were randomly divided into two groups of 60 tubers each, namely the treatment group and the control group. The treatment group was soaked in 9.0 mmol / L LBTH solution (containing 0.05% Tween 80) at room temperature for 60 min, then removed and air-dried. The control group was soaked in sterile deionized water containing 0.05% Tween 80 at room temperature for 60 min, then removed and air-dried. Pathogen inoculation and storage: Use a sterile punch to make 3mm × 1cm wounds at the equatorial flat area of ​​the sweet potato tubers in both groups, and inoculate each wound. Two groups of sweet potato tubers were stored in a constant temperature and humidity chamber at 28±1℃ and 80-85%RH for 25 days after the spore suspension of 20 μL of *Eriocaulon buergerianum* was absorbed. Example 2:

[0024] This invention provides a technical solution for processing effect detection: Samples were taken at 0d, 5d, 10d, 15d, 20d, and 25d of storage to detect lesion diameter, in vitro growth of pathogens, quality indicators, and disease resistance-related physiological and biochemical indicators. Each indicator was repeated three times. Statistical analysis was performed using Excel 2019 and plotted using Origin 2022. P < 0.05 was considered statistically significant.

[0025] Inhibition effect on black spot disease lesion expansion: After storage for 5-25 days, the diameter of lesions on sweet potato tubers in the treatment group was significantly lower than that in the control group, and BTH treatment had a significant inhibitory effect on lesion expansion; In vitro antibacterial experiments showed that 9.0 mmol / L BTH had no significant effect on the colony growth of *Saccharomyces cerevisiae*, indicating that the method of this invention achieves disease resistance by inducing the sweet potato's own resistance, rather than directly inhibiting bacteria.

[0026] Quality maintenance effect: After 20-25 days of storage, the starch content of the treatment group was significantly higher than that of the control group by 6.6%-12.7%; after 10-15 days and 25 days of storage, the soluble sugar content of the treatment group was significantly lower than that of the control group by 6.8%-33.6% and 13.1% respectively, inhibiting starch degradation and abnormal increase of soluble sugar; after 5-25 days of storage, the relative conductivity of the treatment group was significantly lower than that of the control group by 13.3%-33.7%, and the malondialdehyde content was significantly lower than that of the control group by 12.7%-31.9%, effectively maintaining cell membrane integrity and reducing cell physiological damage.

[0027] Changes in disease resistance-related indicators: Reactive oxygen species (ROS) index: After 5-25 days of storage, the superoxide anion production rate in the treatment group was significantly higher than that in the control group by 5.8%-31.2%; after 5-10 days of storage, the hydrogen peroxide content in the treatment group was significantly higher than that in the control group by 13.7%-25.4%. The signaling molecules of ROS effectively activated the sweet potato defense response. Phenylacetane metabolism indicators: The PAL activity, C4H activity, 4CL activity, and POD activity of the 10-20d storage group were significantly higher than those of the control group; the total phenol content and lignin content of the 15-25d storage group were significantly higher than those of the control group, which significantly promoted the accumulation of disease-resistant substances. Disease resistance-related enzyme indicators: CHT activity in the 5d and 15-25d storage groups and GLU activity in the 15-25d storage groups were significantly higher than those in the control group, effectively degrading the cell wall of pathogens and slowing down infection; Plant hormone indicators: The salicylic acid content in the 10-15 day storage group and the jasmonic acid content in the 5-10 day storage group were significantly higher than those in the control group, indicating that the disease resistance of sweet potato is regulated through hormone signaling pathways. Example 3:

[0028] This invention provides a technical solution, comparing the effects of treatment with different concentrations of BTH: Four BTH concentration gradients of 5.0 mmol / L, 7.0 mmol / L, 9.0 mmol / L, and 11.0 mmol / L were set up, and sweet potato tubers were treated according to the method in Example 1. After inoculation with pathogens, the tubers were stored for 25 days, and the diameter of lesions and starch content were measured. The results showed that the 9.0 mmol / L BTH treatment group had the smallest lesion diameter and the highest starch content. The treatment effects of 5.0 and 7.0 mmol / L concentrations were weak, and the 11.0 mmol / L concentration did not significantly improve the effect, but instead increased the reagent cost, proving that 9.0 mmol / L was the optimal treatment concentration.

[0029] Wherein: CK - control group (soaked in sterile water), BTH - treatment group of the present invention (soaked in 9.0 mmol / L BTH solution).

[0030] The lesion data are as follows:

[0031] Mushroom cake diameter:

[0032] Starch content:

[0033] Soluble sugar content:

[0034] Relative conductivity:

[0035] MDA:

[0036] Superoxide anion generation rate:

[0037] Hydrogen peroxide content:

[0038] PAL activity:

[0039] C4H activity:

[0040] 4CL activity:

[0041] POD activity:

[0042] Total phenol content:

[0043] Lignin content:

[0044] CHT activity:

[0045] GLU activity:

[0046] Salicylic acid content

[0047] Jasmonic acid content:

[0048] The method for improving the resistance to postharvest black spot disease and maintaining the quality of sweet potato tubers described in this invention has simple operation steps, requires no special large-scale equipment, and the BTH reagent used is readily available and cost-effective. The pretreatment and soaking treatments can be quickly implemented on-site after sweet potato harvest, making it suitable for large-scale batch processing in sweet potato planting bases and fruit and vegetable preservation enterprises. The treated sweet potato tubers can significantly improve resistance to black spot disease, extend the storage period, and maintain quality under conventional storage and transportation conditions, solving the industry pain points of easy rotting and rapid quality decline of sweet potatoes after harvest. It has significant industrial practicality and industrial application prospects.

[0049] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the resistance of sweet potato tubers to postharvest black spot disease and maintaining their quality, characterized in that: Includes the following steps: (1) Pretreatment of sweet potato tubers: Select sweet potato tubers without mechanical damage or pests and diseases, heal at room temperature for 48 hours, wash with clean water, soak in 1% (v / v) sodium hypochlorite solution for 5 minutes for surface disinfection, rinse with sterile water 3-5 times, and air dry at room temperature. (2) Preparation of BTH solution: Prepare a benzothiadiazole BTH solution with a concentration of 9.0 mmol / L, add Tween80 to make the final concentration 0.05% (v / v), and mix well; (3) Soaking treatment: Place the sweet potato tubers that have been pretreated in step (1) into the BTH solution in step (2) and soak them at room temperature for 60 minutes. After taking them out, let them air dry at room temperature to complete the post-harvest treatment.

2. The method for improving postharvest black spot disease resistance and maintaining quality of sweet potato tubers according to claim 1, characterized in that: The sweet potato tubers treated in step (3) are stored at 28±1℃ and 80-85% relative humidity for a period of more than 25 days.

3. The method for improving postharvest black spot disease resistance and maintaining quality of sweet potato tubers according to claim 1, characterized in that: In step (2), 0.05% (v / v) of Tween 80 is added to the BTH solution for soaking treatment of post-harvest sweet potato tubers.

4. The method for improving postharvest black spot disease resistance and maintaining quality of sweet potato tubers according to claim 3, characterized in that: The method increases the activity of phenylalanine ammonia-lyase, cinnamic acid hydroxylase, peroxidase, 4-coumaric acid coenzyme A ligase, chitinase, and β-1,3-glucanase in sweet potato tubers, and promotes the accumulation of total phenols and lignin.

5. The method for improving postharvest black spot disease resistance and maintaining quality of sweet potato tubers according to claim 3, characterized in that: The method increases the hydrogen peroxide content and superoxide anion production rate in sweet potato tubers, while delaying the increase in relative conductivity and malondialdehyde accumulation.

6. The method for improving postharvest black spot disease resistance and maintaining quality of sweet potato tubers according to claim 3, characterized in that: The method inhibits starch degradation and abnormal increase in soluble sugars during the storage of sweet potato tubers.

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