Experimental Study on the Selection of Different Drugs Protecting from Rhizoctonia solani

Shichu LI Zhaolei TANG Qing DU Kang MO

Abstract In order to achieve ideal prevention and treatment effect of maize sheath blight， 24% Jinggangmycin A+0.5% adjuvant， 24% Jinggangmycin A， Bacillus subtilis and Jinggangmycin+B. subtilis were selected. Each agent was prepared into a 500 times dilution， and the control effect was tested by two times of spray application. The results showed that the disease index of maize sheath blight could be reduced by all the treatments， which were significantly different from that of the control group， but the differences between the treatments were not significant. Jinggangmycin+B. subtilis and B. subtilis had the best control effects. Therefore， their use for preventing maize sheath blight could reduce chemical residues of maize， and avoid environmental pollution.

Key words Rhizoctonia solani; Drug; Selection

Received： August 3， 2021  Accepted： October 9， 2021

Supported by National Key R&D Program （2018YFD0100105; 2018YFD0200705）; Guangxi Innovation-driven Development Science and Technology Project （Gui AA1720405-1; Gui AA1720405-2）; Special Project of Basic Scientific Research Business of Guangxi Academy of Agricultural Sciences （2015YT29）.

Shichu LI （1964-）， male， P. R. China， associate researcher， devoted to research about identification of resistance to diseases and pests of maize germplasm resources and prevention and control of diseases and pests.

*Corresponding author. E-mail： shichuli@aliyun.com.

Maize sheath blight （Rhizoctonia solani） is mainly the most severely affected disease in maize production areas around the world. Since the 1970s， countries around the world have paid more and more attention to the damage caused by maize sheath blight. Its harm has gradually been exposed to people’s sight， so more and more countries have begun to follow up and report on it. In China， maize is the main crop of food for our lives. Since the 1970s， due to the changes in farming and cultivation systems and the increase or replacement of varieties， maize sheath blight has become the main disease in China’s maize producing areas， and its occurrence， damage， and spread have become more and more serious. Especially in Southwest China， due to the high temperature and humidity during the maize growing period， and different sources of main maize varieties currently， the disease resistance is quite different， and sheath blight has become a major disease affecting maize yield[1-6]， which causes heavy losses to maize production. Maize sheath blight is a soil-borne disease， the pathogen of which is R. solani[7-8]. Sclerotia of the pathogen can survive in the soil for many years， and therefore， the control methods for maize sheath blight are relatively lacking. The usual control method is still combination of traditional agricultural and chemical prevention and control measures. In this method， the shortcomings of traditional agricultural control are poor and slow effect， while chemical control avoids the shortcomings of traditional agricultural placement and achieves rapid control and good effects， but there are problems such as pesticide residues， environmental pollution， resistance to pesticides， and influencing food safety. According to China’s requirements for green and pollution-free production of agricultural products， the prevention and control of microbial （biological） preparations has received more and more attention in recent years， and this method of preventing and controlling hazards has gradually become a new trend[9]. The purpose of this experimental study was to find more effective drugs for the prevention and control of maize sheath blight， so as to serve for the efficient prevention and control of maize sheath blight， and to serve maize food security.

Materials and Methods

Experimental time and location

Time： January 2018 to July 2018; Location： The maize disease and pest test isolation and observation nursery in Wuxu Mingyang Experimental Base， Maize Research Institute， Guangxi Zhuang Autonomous Region Academy of Agricultural Sciences， at 108 degrees East Longitude， 22.6 degrees North Latitude， with an altitude of 109 m.

Test materials

Test drug

24% Jinggangmycin A water-soluble powder， manufactured by Hubei Wuhan Kenuo Biotechnology Co.， Ltd.; Bacillus subtilis wettable powder （effective viable count≥200×108/g）， manufactured by Shandong Jinan Youlin Agricultural Technology Co.， Ltd.; Jinggangmycin+B. subtilis wettable powder （active ingredient： 20% Jinggangmycin A， B. subtilis 200×108 cfu/g）， produced by Zhejiang Tonglu Huifeng Biotechnology Co.， Ltd.; agricultural organosilicon adjuvant （99% active ingredient）， produced by Anhui Aiyota Silicone Oil Co.， Ltd..

Test variety

Test maize variety： Yudan 8， a maize variety bred by Chongqing Academy of Agricultural Sciences， purchased at Guangxi Agricultural Science and Technology Market.

Experimental methods

Experimental design

Agent test design： A total of five treatments were set： treatment 1∶24% Jinggangmycin A+0.5% adjuvant （agricultural organosilicone adjuvant）; treatment 2∶24% Jinggangmycin A; treatment 3： Bacillus subtilis; treatment 4： Jinggangmycin+B. subtilis; and treatment 5： clear water blank control. Field trial design： The field trial adopted randomized block arrangement， with 3 repetitions， each with 5 plots， a total of 15 plots. Six rows of maize （row length 5 m， row spacing 0.7 m） were planted in each plot. Maize seeds were artificially sown， and single seedlings were retained with a planting distance of 25 cm. Each row was fixed with 21 maize plants， and conventional planting and management was adopted in the fields. No other disease and pest control was conducted during the whole growth period of maize.

Drug application period and methods

Spray application was carried out with a knapsack electric sprayer （Shunfeng 3WBD-16L type）. According to the experimental design， each test agent was formulated into a 500 times dilution， and 5 ml of Tween was added to each bucket of drug solution， followed by stirring well. The agents were applied when the dew was dried in the morning. The first application period was at the stage of 8 leaves， and the second application period was at the 12-leaf stage of maize. Each preparation was applied at the base of maize stalks with an amount that water dropped from the base of maize stalks.

Investigation period and methods

Investigation period： A field disease investigation was conducted 25 d after the second application， and was completed within the same day. Investigation method： In each plot， the middle 4 rows of maize were investigated， and the investigation recorded the incidence level of each maize plant. Investigation and recording were performed according to disease classification standards. The grading standards of sheath blight were as follows： grade 0： whole maize leaf sheaths have no disease spots; grade 1： the fourth leaf sheaths below maize ears have disease spots; grade 3： the third leaf sheaths below maize ears have disease spots; grade 5： the second leaf sheaths below maize ears have diseased spots; grade 7： the first leaf sheaths below maize ears have diseased spots; and grade 9： maize ears and leaf sheaths above maize ears have diseased spots[10].

Statistical methods

The disease index and control effect of each test plot and the average disease index and average control effect of each treatment were calculated， respectively. Finally， the SSR method was adopted for statistical analysis. The calculation methods of disease index， average disease index， control effect and average control effect were as follows[6，10]：

Disease index=[Σ（Number of diseased plants × Corresponding disease grade）/（Total number of investigated maize plants ×The highest disease grade）]×100

Average disease index=[ΣDisease index of each repetition]/3

Control effect （%）=[（Disease index of the control-Disease index of treatment/Disease index of the control]×100%

Average control effect （%）=[ΣControl effect of each repetition]/3

Results and Analysis

Effects of medicament treatments on disease index

Judging from the test results， all the four medicament treatments tested could reduce the disease index of maize sheath blight. Compared with the disease index of the control area， the average disease indexes of various treatments had great differences and the effects were obvious. The difference was that in the treatment areas， the first type： 24% Jinggangmycin A+0.5% adjuvant， the second type 24% Jinggangmycin A， the third type： B. subtilis， and the fourth type： Jinggangmycin+B. subtilis showed no significant differences in the average disease index， and the effects were not obvious （Table 1）.

Control effects of tested drugs

Through the analysis of the test results， it was concluded that the first control method： 24% Jinggangmycin A+0.5% adjuvant could achieve a control effect of 71.26%， the average control effect of the fourth treatment （Jinggangmycin+B. subtilis） reached 63.52%， and those of treatments B. subtilis and 24% Jinggangmycin A were 58.26% and 56.64%， respectively. The results of statistical analysis of differences： the control effects of （24% Jinggangmycin A+0.5% adjuvant） and （Jinggangmycin+B. subtilis） were not very different， that is， the two were similar; the average control effects of the first one （24% Jinggangmycin A+0.5% adjuvant） and the second （24% Jinggangmycin A） were quite different， that is， the two had very significant effects; and the average control effect values of the second （24% Jinggangmycin A+0.5% adjuvant） and the fourth （B. subtilis） were different， so the two also had a significant difference in the control effect. Comparing the average control effect values of these five treatment areas， the average control effect values of （Jinggangmycin+B. subtilis）， （B. subtilis） and （24% Jinggangmycin A） were not very different， so the differences between any two of the three were not obvious （Table 2）.

Shichu LI et al. Experimental Study on the Selection of Different Drugs Protecting from Rhizoctonia solani

Discussion

According to reports， most of the strains used for biological control of maize sheath blight are rhizosphere or endophytic microorganisms. For example， maize rhizosphere bacterium 515-126 have a certain control effect on sheath blight[11]; B. subtilis BS-8D can delay the infection of pathogens[12]; B. subtilis BS-8D aseptic medium can inhibit the sclerotia germination and mycelial growth of R. solani[13-14]; the endophytic bacterium DZSY21 of Eucommia ulmoides can reduce the disease index of sheath blight and induce resistance to sheath blight[15]; soil microorganism Trichoderma has a significant control effect on sheath blight[16]; and straw returning to the field can affect the growth of sheath blight hyphae and the number of sclerotia[17]. However， these research reports have basically stayed in the laboratory stage and have not been applied to actual maize production.

No maize phytotoxicity was found in this study， indicating that the 4 tested agents were safe. At present， China’s maize sheath blight control in field maize production the mainly relies on antibiotics——Jinggangmycin， other control agents are quite lacking， and biological control agents are even rarer. Their application in field disease control in maize production is progressing slowly， and there are few successful cases of large-scale application in field disease control in maize production.

From the results of this study， although the average control effect of （24% Jinggangmycin A+0.5% adjuvant） treatment was the best， but the average control effect of （24% Jinggangmycin A） treatment was not ideal， indicating that （24% Jinggangmycin A） can only play its role under the action of agricultural organosilicone adjuvant. If it is used under the conditions of maize field production， the addition of agricultural organosilicone adjuvant， on the one hand， will increase the difficulty of drug application and make it difficult for farmers to grasp. On the other hand， it increases the input of agricultural materials， and it is not easy to buy agricultural organosilicone adjuvant in the general agricultural material market. Therefore， （24% Jinggangmycin A+0.5% adjuvant） should not be widely used. The average control effects of microbial agents （Jinggangmycin+B. subtilis， B. subtilis） on maize sheath blight were over 58%， so the control effect was remarkable. Moreover， they are easy to use， easy to buy， and thus can be promoted and applied vigorously to reduce the usage of antibiotic Jinggangmycin. If they can be applied to maize field production on a large scale， good economic benefits can be produced as well as significant ecological and environmental social benefits while ensuring food security and serving the development of green agriculture. However， this study was conducted under the condition of using drug solutions at a single concentration （500 times）， and the test results were limited. As for the concentration of the liquid medicine needed to achieve the best control effect， the dosage， the application method and the best period of application need to be studied in the next step.

Conclusions

① The two microbial preparations， Jinggangmycin+B. subtilis and B. subtilis， can be safely used on maize in 500 times dilution; and ② Jinggangmycin+B. subtilis and B. subtilis are effective in preventing and controlling maize sheath blight， and can be popularized and applied to field maize production.

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