Abstract:In this study, responses of rice under drought stress correlating with changes in chemical compositions were examined. Among 20 studied rice cultivars, Q8 was the most tolerant, whereas Q2 was the most susceptible to drought. Total phenols, total flavonoids, and antioxidant activities, and their accumulation in water deficit conditions were proportional to drought resistance levels of rice. In detail, total phenols and total flavonoids in Q8 (65.3 mg gallic acid equivalent (GAE) and 37.8 mg rutin equivalent (RE) were significantly higher than Q2 (33.9 mg GAE/g and 27.4 mg RE/g, respectively) in both control and drought stress groups. Similarly, the antioxidant activities including DPPH radical scavenging, β-carotene bleaching, and lipid peroxidation inhibition in Q8 were also higher than in Q2, and markedly increased in drought stress. In general, contents of individual phenolic acids in Q8 were higher than Q2, and they were significantly increased in drought stress to much greater extents than in Q2. However, p-hydroxybenzoic acid was found uniquely in Q8 cultivars. In addition, only vanillic acid was found in water deficit stress in both drought resistant and susceptible rice, suggesting that this phenolic acid, together with p-hydroxybenzoic acid, may play a key role in drought-tolerance mechanisms of rice. The use of vanillic acid and p-hyroxybenzoic acid, and their derivatives, may be useful to protect rice production against water shortage stress.

Phalaenopsis spp. is the most commercially and economically important orchid, but their plant parts are often left unused, which has caused environmental problems. To date, reports on phytochemical analyses were most available on endangered and medicinal orchids. The present study was conducted to determine the total phenolics, total flavonoids, and antioxidant activity of ethanol extracts prepared from leaves and roots of six commercial hybrid Phalaenopsis spp. Leaf extracts of “Chian Xen Queen” contained the highest total phenolics with a value of 11.52 ± 0.43 mg gallic acid equivalent per g dry weight and the highest total flavonoids (4.98 ± 0.27 mg rutin equivalent per g dry weight). The antioxidant activity of root extracts evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay and β-carotene bleaching method was higher than those of the leaf extracts. Eleven phenolic compounds were identified, namely, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, syringic acid, vanillin, ferulic acid, sinapic acid, p-coumaric acid, benzoic acid, and ellagic acid. Ferulic, p-coumaric and sinapic acids were concentrated largely in the roots. The results suggested that the root extracts from hybrid Phalaenopsis spp. could be a potential source of natural antioxidants. This study also helps to reduce the amount of this orchid waste in industrial production, as its roots can be exploited for pharmaceutical purposes.

Abstract:In this study, the effects of bamboo leaf were examined on mycelial growth of Pyricularia grisea, a fungus of rice blast disease that causes a great loss in rice production. The hexane extract exhibited maximal reduction on growth of P. grisea (IC 50 = 0.62 mg/mL), followed by aqueous and ethyl acetate extracts, while the methanol extract was least effective (IC 50 = 9.71 mg/mL). At 0.5-1.0 mg/mL doses, all extracting solvents showed inhibition on the growth of P. grisea, but at a 0.1 mg/mL concentration, the antifungal activity was solely observed on hexane and ethyl acetate extracts. By GC-MS (gas chromatography-mass spectrometry), 25 constituents were identified, principally belonging to long-chain fatty acids, sterols, phenols, phenolic acids, volatile oils, and derivatives of terpenes. It was suggested that compounds originated from hexane and ethyl acetate extracts such as fatty acids, oils, and phenols, and their derivatives were responsible for the antifungal activity of bamboo leaf. Non-polar constituents were accountable for the antifungal activity, although water-soluble compounds may play a role. Bamboo leaf appears to be a potent natural source to manage the infestation of P. grisea in rice cultivation.

Rice blast fungus (Pyricularia grisea) is one of the most problematic pathogen to significantly reduce rice production worldwide. In this study, after being inoculated withP. grisea, changes in phenolic components and antioxidant capacity and correlation with the resistant level against rice blast fungus were investigated. Among screened rice cultivars, AV-3 was the strongest resistant, whereas BII-3 was the most susceptible. It was found that although total contents of phenolics and flavonoids, and antioxidant capacities varied among studied varieties, no significant coefficient with the resistance againstP. griseawas observed. After rice was affected by rice blast fungus, total phenolics and flavonoids were markedly reduced, but in contrast, the DPPH scavenging activities of only the susceptible rice cultivars was reduced. Among the 11 phenolic acids detected, catechol was found only in the tolerant cultivar AV-3, whereas the amount of cinnamic acid was increased after infection. Quantity of vanillin was also promoted, except in the susceptible cultivar BII-3 that was significantly reduced. Findings of this study showed that the resistant level againstP. griseawas proportionally correlated to the antioxidant capacity. Catechol, cinnamic acid, and vanillin may play a role but it needs further elaboration. Observations of this study suggested that the infection of blast disease by reducing amount of phenolics and flavonoids that may weaken the resistance of rice against this detrimental fungus.

Rice blast fungus (Pyricularia grisea) is one of the most problematic pathogen to significantly reduce rice production worldwide. In this study, after being inoculated with P. grisea, changes in phenolic components and antioxidant capacity and correlation with the resistant level against rice blast fungus were investigated. Among screened rice cultivars, AV-3 was the strongest resistant, whereas BII-3 was the most susceptible. It was found that although total contents of phenolics and flavonoids, and antioxidant capacities varied among studied varieties, no significant coefficient with the resistance against P. grisea was observed. After rice was affected by rice blast fungus, total phenolics and flavonoids were markedly reduced, but in contrast, the DPPH scavenging activities of only the susceptible rice cultivars was reduced. Among the 11 phenolic acids detected, catechol was found only in the tolerant cultivar AV-3, whereas the amount of cinnamic acid was increased after infection. Quantity of vanillin was also promoted, except in the susceptible cultivar BII-3 that was significantly reduced. Findings of this study showed that the resistant level against P. grisea was proportionally correlated to the antioxidant capacity. Catechol, cinnamic acid, and vanillin may play a role but it needs further elaboration. Observations of this study suggested that the infection of blast disease by reducing amount of phenolics and flavonoids that may weaken the resistance of rice against this detrimental fungus.