
Our study investigated the available chlorine content, contact time and difference among strains of each pathogen for sodium hypochlorite (NaOCl) to control chemically against soil-borne fungal pathogens, such as Phytophthora rot by
Recent changes in climate and cultivation environment have led to the problem of apple tree dieback caused by soil-borne diseases, which causes economic losses (Lee et al., 2016). The major soil-borne diseases reported in Korea are Phytophthora root rot by
At present, azoxystrobin for Phytophthora root rot, tolclofos-methyl and thiophanate-methyl for violet root rot, fluazinam and benomyl, isoprothiolane for white root rot are registered as control agents (Korea Crop Protection Association). However, these control agents have been used in most farms suffering from the tree dieback, but they have not had clear control effects, and the annually repetitive supplementary planting is the only alternative to control the diseases resulted in increasing of economic losses.
A variety of chemical disinfestants can be used in disease control. Among them, NaOCl can be used in seeds (Chun et al., 1997; Sauer and Burroughs, 1986), soil (Bisessar and Mcllveen, 1992), and water systems (Santos-Rufo and Rodriguez-Jurado, 2016) because it meets the registration criteria in terms of human health and environment with wide disinfection effects and a short half-life (WHO, 2011). NaOCl was first registered in the United States in 1957 as a crop protection agent, however, NaOCl is not yet registered as a control agent in Korea, it is restricted to apply in fields. Nevertheless, because the effect of the registered control agents is insignificant, it is necessary to develop a definite control agent and method for soil-borne diseases which cause dieback in apple trees.
In this study, the inhibition available chlorine content, minimum contact time, and inhibition effect among isolates for NaOCl on colony growth of the 3 soil-born fungal pathogens, compared with registered control agents was investigated
Six isolates of
The chemical used was sodium hypochlorite (NaOCl, 8.0% available chlorine content, Junsei, Japan) for growth inhibition of each pathogen. The fungicides used are as follow; azoxystrobin (WP, a.i. 10%) for
In order to determine the available chlorine content of NaOCl, cultured agar plug of each phytopathogen colony with Cork borer 2 (Ø 6.2 mm, Usbeck, Radevormwald, Germany) was placed on sterilized paper discs (Ø 8 × 1.5 mm, Advantec, Japan) on PDA medium and then a cultured agar plug on a paper disc were placed. Six available chlorine content of the chemical were chosen for the
To investigate the inhibitory contact time in NaOCl for each pathogen, 5 agar plugs of each pathogen were soaked in the determined available chlorine content in NaOCl for 5, 10, 20, 40, 80, 160, 320, 640, and 1,280 s, respectively. They were taken out, put on sterilized absorbent paper, cultured on PDA, and then incubated at 23 ± 1°C for 5 to 15 days.
Inhibition rate for each available chlorine content of Na-OCl was as follows; (control value – value of each available chlorine content of NaOCl) / control value × 100.
Finally, isolates of the pathogens were tested for showing the inhibition difference within the available chlorine content of NaOCl determined above as well as the currently registered fungicides.
As the medium preparation, 100 ml of the PDA medium was sterilized and cooled by 50–60°C, and then the standard or 2-fold amount of each crop protection agent were added. Especially, isoprothiolane was dispensed by 30 ml of PDA medium after adding standard amount 25.5 g or 2-fold amount 51 g in 100 × 40 mm plant culture dish (SPL Lifesciences Co., Ltd., Gyeonggi, Korea). All treatments were performed 3 times in 3 replications.
The colony growth diameter of each treatment was measured and the inhibition rate compared to non-treatment was calculated. The diameter of the colony growth was measured by the average of long axis and short axis and experiments were tested by 3 times with 5 repetitions per treatment.
Means could be compared to the respective control using the Duncan’s test (
The results on contact time that inhibits colony formation of each pathogen isolate by the available chlorine content determined above are shown in Table 2. Compared with the control treatment, the
Shin et al. (2014) reported that the conidia of
On the basis of above determined available chlorine content in NaOCl, Table 3 to
http://www.apsnet.org/meetings/Documents/2015_meeting_abstracts/aps2015abP667.htm), therefore, we suggest that 12.5–31.25 ml/l of NaOCl treatment would be effective to control the Phytophthora root rot without the concern for resistant isolate.
From the results of colony inhibition rate for
From the results of colony inhibition rate for
Recently, FRAC Code list 1 (2017) reported that all of the tested fungicides were concerned by occurrence of resistant isolates. In fact, there were reported that a resistance isolate for benomyl in
In conclusion, our study showed that pathogens caused soil-borne diseases, Phytophthora root rot, violet root rot, and white root rot, were effectively inhibited by 12.5–31.25 ml/l, 31.25–62.5 ml/l, and 62.5–125 ml/l of NaOCl, respectively.
This work was carried out with the support of Chungcheongbuk-do Agricultural Research and Extension Services (Project No. LP0035762017), funded by Governor of Chungcheongbuk-do as well as ‘Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ0100142016)’ Rural Development Administration, Republic of Korea.