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    Fungicide resistance of Phytophthora palmivora causing durian diseases in eastern and southern Thailand and the in vitro alternative control by cajeput leaf extracts
    (2023-03-01)
    Somnuek, S.
    ;
    Kongtragoul, P.
    ;
    Jaenaksorn, T.
    The results showed that 24 and 25 of 40 collected isolates of Phytophthora palmivora were resistant to metalaxyl and mancozeb, respectively with the 50% effective concentration (EC<inf>50</inf>) higher than 100 mg/L. Meanwhile, all isolates were resistant to fosetyl-al with EC<inf>50</inf> higher than 1000 mg/L. Moreover, mapping between the survey areas and all Phytophthora isolates with the resistant levels to the 3 tested fungicides was depicted. Interestingly, 20 of 40 isolates showed multiple fungicide resistance to all tested fungicides with different modes of action, thereby selecting for the in vitro evaluation of the cajeput extract effect. Lower than expected, only 9 out of 20 multiple fungicide resistance isolates were shown to be significantly sensitive to the 10000, 20000 and 40000 ppm of cajeput extract based on paper disc assay.
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    Sensitivity tests of dimethomorph, ethaboxam and etridiazole on Phytophthora palmivora causing stem rot and leaf blight of durian in eastern Thailand
    (2023-01-01)
    Tongsri, Veeranee
    ;
    Nianwichai, Patcharin
    ;
    Sichai, Kamonwan
    ;
    Songkumarn, Pattavipha
    ;
    Suttiviriya, Pavinee
    Importance of the work: Phytophthora palmivora is a major pathogen on durians and has been found to be resistant to metalaxyl. Objectives: To investigate the sensitivity of P. palmivora to alternative fungicides and evaluate its fungicide efficacy for controlling durian diseases. Materials & Methods: The isolates of P. palmivora were evaluated for their fungicide sensitivity to dimethomorph, ethaboxam and etridiazole on the culture medium against mycelial growth, sporangium production and germination. The representative isolates were determined for fungicide sensitivity on durian leaf tissue. The fungicides with low values for the concentration that inhibited the mycelial growth of the isolate by 50% (EC<inf>50</inf>) were used for durian disease control. Results: The mycelial growth of all P. palmivora isolates was sensitive to dimethomorph, ethaboxam and etridiazole, with mean (± SD) EC<inf>50</inf> values of 0.233 ± 0.116 parts per million (ppm), 0.007 ± 0.002 ppm and 2.945 ± 1.464 ppm, respectively. Sporangium production and germination were also sensitive to all fungicides. The mean EC<inf>50</inf> values on durian leaf tissue were 0.696 ppm for dimethomorph, 0.089 ppm for ethaboxam and 0.766 ppm for etridiazole. Dimethomorph (100 ppm) and ethaboxam (50 ppm) completely reduced disease development on detached leaves; however, etridiazole (50 ppm) showed maximum control of the disease by 55.6%. Only ethaboxam (208 ppm) extremely suppressed the disease in a seedling experiment (92.3%), while dimethomorph (500 ppm) produced much less disease control (27%). Etridiazole (240 ppm) could not control the disease in seedling conditions. Main finding: Ethaboxam had the potential to control durian disease caused by P. palmivora in the eastern growing areas of Thailand. Repeat fungicide application should be discussed regarding dimethomorph and etridiazole.
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    Cross-Resistance to Benzimidazole Group and Mancozeb Fungicides in Colletotrichum spp. Causing Anthracnose Disease
    (2022-10-01)
    Kongtragoul, Pornprapa
    ;
    Somnuek, Suriyasit
    ;
    Udompongsuk, Mongkutkarn
    ;
    Prasom, Panisa
    ;
    Jaenaksorn, Tanimnun
    Anthracnose is considered to be one of the most serious diseases for major crops cultivated in Thailand. Although chemical fungicides and newer chemicals have been recommended and used for disease management, it is still difficult to control. Thus, the monitoring of fungicide resistance development is required and very important for the success of disease control strategies. In this study, a total of 34 isolates of Colletotrichum spp. were successfully collected from anthracnose diseased plants in central Thailand. Of these isolates, 16 were collected from mango, and 2 from crinum lily or orchid and were morphologically identified as C. gloeosporioides, while the other 16 isolates from chili were morphologically identified as C. capsica. Then, all isolates were evaluated in vitro against 3 fungicides to determine their sensitivity. The results showed that 25 isolates were cross-resistant to both benomyl and carbendazim, as the 50% effective concentration (EC<inf>50</inf>) of each fungicide was >100 mg L<sup>-1</sup>. All isolates were resistant to mancozeb. Nine out of 16 isolates from mango anthracnose were confirmed as C. gloeosporioides by the sequence of internal transcribed spacer (ITS) and 5. 8S regions of rDNA. Eight cross-resistant isolates were not controlled by the treatment with 100 mg L<sup>-1</sup> of benomyl or carbendazim on ‘Nam Dok Mai’ mango fruits, but sensitive isolate was better controlled at 79.33% and 85.11%, respectively. Our results indicated that cross-resistant strains are present in the populations of anthracnose fungi in central Thailand.
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    Resistance to quinone-outside inhibitor (Qoi) fungicides in colletotrichum species isolated from anthracnose disease occurring in Thailand
    (2020-01-01)
    Kongtragoul, Pornprapa
    ;
    Imamoto, Kazuumi
    ;
    Ishii, Hideo
    Colletotrichum species are plant pathogens causing anthracnose diseases in many crops that result in significant reduction of quality and quantity of the crop products. Management of these diseases has become increasingly difficult recently due to the development of fungicide resistance in pathogens. Thus, monitoring for fungicide sensitivity in the pathogen is important to manage these diseases. The isolates of Colletotrichum species were isolated from anthracnose disease on various crops collected during 2016-2017 in central and southern Thailand. They were tested for their mycelium growth sensitivity to azoxystrobin, a quinone-outside inhibitor (QoI) fungicide and their internal transcribed spacer (ITS) and 5.8S regions of rDNA were analyzed. The results showed that eleven out of twenty four isolates of Colletotrichum species were resistant to azoxystrobin. They were able to grow on PDA amended with 100 mg/l azoxystrobin in the presence of salicylhydroxamic acid (SHAM) at 100 mg/l. Moreover, two isolates of azoxystrobin-resistant Colletotrichum spp. produced much larger lesions than azoxystrobin-sensitive isolates on mango fruits after treatment with 100 mg/l azoxystrobin. This is the first report on the occurrence of azoxystrobin resistance in Colletotrichum species present in Thailand and will contribute to the management of these important diseases in the future.