Diseases, particularly bacterial wilt caused by Ralstonia solanacearum is a major constraint to vegetable production. Protected cultivation has been proven effective in reducing disease incidence but additional control measures need to be integrated in highly infested soils to mitigate the losses due to diseases. This paper reports the effect of resistance elicitors, particularly chitosan, acetylsalicylic acid and SiO2 in mitigating bacterial wilt disease problem and other naturally occurring diseases in two field trials. Two hundred ppm chitosan, acetylsalicylic acid and their combination had reduced bacterial wilt incidence and increased the yield of tomato under protected cultivation, but not in the open field. SiO2 was not able to reduce bacterial wilt incidence in tomato but had reduced the nematode count, especially Rotylenchulus sp. in the roots, particularly when drenched. Protected cultivation still proved effective in reducing bacterial wilt incidence in both experiments. It’s potential to protect crops against bacterial wilt is further enhanced by the application of chitosan and acetylsalicylic acid, most especially the combination of these treatments. The potential of chitosan and acetylsalicylic acid in protecting plants in the open field against bacterial wilt may be enhanced by the addition of a sticker.
Wood vinegar is claimed to be pesticidal by several researchers but its bioefficacy data on specific pests are lacking. This study evaluated 17 wood vinegars against S. rolfsii causing sclerotium wilt in tomato in vitro and in vivo. Eleven out of 17 wood vinegars showed direct inhibition to S. rolfsii at 2% concentration. These include wood vinegars from bamboo, banaba, cacao, caimito, ipil-ipil, lumboy, madre de cacao, malunggay, mango, panyawan and rice hull. These wood vinegars varied in their effectiveness in inhibiting the colony growth of S. rolfsii in vitro, with wood vinegar from ipil-pil showing the highest inhibition to the fungal growth followed by wood vinegar from lumboy. Wood vinegar from ipil-ipil however was the most phyto-toxic to tomato. The wood vinegar from lumboy, is promising since it was one of the most effective in reducing the disease severity in inoculated seedlings and was one of the least phyto-toxic. The wood vinegars from malunggay and panyawan, although not very effective in vitro were the most effective in reducing the disease severity in inoculated tomato plants and retained their effectiveness longer. Lower concentrations of the wood vinegars as a whole (0.2%) was the most effective in reducing sclerotium wilt severity over time, even though this concentration showed no direct inhibition to the fungus in vitro. This finding implies that wood vinegar may possess another mode of action in controlling the disease aside from the direct antifungal activity, which could be induction of resistance in plants to specific diseases.
The identification of different vegetable diseases in a particular area is key to managing them. An inventory of diseases affecting important vegetables was conducted in selected areas in the Visayas, and Mindanao. The vegetable diseases were documented in Leyte, Samar, Biliran, Bohol and Claveria Misamis Oriental. Disease surveys were conducted and samples were brought to the laboratory for diagnosis. Pathogenicity tests were conducted for uncommon diseases and PCR and nest PCR assays were done for suspected Phytoplasma diseases. The most common and major disease that affect vegetables in Eastern Visayas is bacterial wilt caused by Ralstonia solanacearum which attacked tomato, pepper, eggplant, bittergourd and was also detected in a wilt infected lettuce. Downy mildew is another which affected bittergourd and pechay. Cercospora diseases were found to commonly affect pepper, eggplant, tomato and bittergourd. Phytophthora diseases were common in tomato, eggplant, pepper and pechay. Fusarium wilt had affected tomato and pepper in Claveria Misamis Oriental, but not common in Eastern Visayas. Emerging diseases were recorded such as Phytoplasma and Corynespora cassiicola which affected tomato and bittergourd, bacterial canker, bacterial speck, target spot, Septoria leaf spot and pith necroses were also found affecting tomato. Information gained from the inventory informed the production of extension materials aimed at farmers and farm extension officers.
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