Kotnala Balaraju

In vitro antioxidant activity of Ageratum houstonianum Mill. (Asteraceae)

Abstract Objective To determine the antioxidant property of Ageratum houstonianum leaves. Method The present study was conducted in three different solvent extracts of leaves of Ageratum houstonianum Mill. (Asteraceae) to evaluate the antioxidant properties such as 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals which were carried out at various concentrations under in vitro condition. Results It was found that ethyl acetate extract could scavenge both the oxidants at 500μg/mL with high percentage inhibition (88.26 ±0.35) of DPPH, and in the case of hydroxyl radicals the maximum percentage inhibition was 75.81 ±0.39, which were found to be greater in ethyl acetate extract than in positive controls such as Butylated hydroxytoluene (BHT) and ascorbic acid. The next higher inhibitory extract was found to be methanol. Conclusion This shows that the plant Ageratum houstonianum may be a potent source of natural antioxidant.

Elicitation of induced systemic resistance of chili pepper by iturin A analogs derived from Bacillus vallismortis EXTN-1

Abstract: Cyclic lipopeptides (CLPs) derived from plant growth-promoting rhizobacteria (PGPR) are well known as potential antifungal compounds. However, the physiological function of CLPs from Bacillus vallismortis strain EXTN-1 (EXTN-1) is still poorly understood. In this study, we proposed the potential role of iturin A analogs in modulation of induced systemic resistance (ISR) of chili pepper in response to Phytophthora capsici. Seven individual iturin A analogs were identified from EXTN-1, and iturin A analogs pre-treated plants resulted in a significant reduction of disease. However, no iturins directly inhibited growth of P. capsici in vitro antibiosis assay, indicating the existence of other possibilities for suppression of disease. The expression analysis of defense-related marker genes PR1, PR4, PR10, chitinase, peroxidase, and ß-1,3-glucanase revealed that transcript levels of these genes were dramatically up-regulated in iturin A analog treated plants after inoculation of P. capsici, suggesting that iturin-triggered plant systemic defense responses were involved in attenuating the disease symptoms. Collectively, our results clearly suggest that iturin A analogs from EXTN-1 are required for alleviation of P. capsici-mediated disease incidence.

Paromomycin derived from Streptomyces sp. AG-P 1441 induces resistance against two major pathogens of chili pepper.

This is the first report that paromomycin, an antibiotic derived from Streptomyces sp. AG-P 1441 (AG-P 1441), controlled Phytophthora blight and soft rot diseases caused by Phytophthora capsici and Pectobacterium carotovorum, respectively, in chili pepper (Capsicum annum L.). Chili pepper plants treated with paromomycin by foliar spray or soil drenching 7 days prior to inoculation with P. capsici zoospores showed significant (p < 0.05) reduction in disease severity (%) when compared with untreated control plants. The disease severity of Phytophthora blight was recorded as 8% and 50% for foliar spray and soil drench, respectively, at 1.0 ppm of paromomycin, compared with untreated control, where disease severity was 83% and 100% by foliar spray and soil drench, respectively. A greater reduction of soft rot lesion areas per leaf disk was observed in treated plants using paromomycin (1.0 μg/ml) by infiltration or soil drench in comparison with untreated control plants. Paromomycin treatment did not negatively affect the growth of chili pepper. Furthermore, the treatment slightly promoted growth; this growth was supported by increased chlorophyll content in paromomycin-treated chili pepper plants. Additionally, paromomycin likely induced resistance as confirmed by the expression of pathogenesis-related (PR) genes: PR-1, β-1,3-glucanase, chitinase, PR-4, peroxidase, and PR-10, which enhanced plant defense against P. capsici in chili pepper. This finding indicates that AG-P 1441 plays a role in pathogen resistance upon the activation of defense genes, by secretion of the plant resistance elicitor, paromomycin.

Induced suppression of soft rot disease in tobacco by combined application of Bacillus subtilis strain B4 and chemical elicitor BTH

Abstract In this study, the utility of the combined application of Benzo-(1,2,3)-thidiazole-7-carbothioic acid S-methyl ester (BTH), a systemic acquired resistance (SAR) inducer, and the plant growth-promoting rhizobacteria (PGPR), Bacillus subtilis strain B4 (B4), was investigated for the suppression of soft rot disease caused by Pectobacterium carotovorum SCC1 (SCC1) in tobacco seedlings. Soft rot disease was completely suppressed in tobacco with combined application of B4 strain and 0.1 mM BTH when compared to individual application upon pathogen challenge. In addition, the population of bacterial cells of B4 strain was found to be greater when cultured in growth media in the presence of BTH, compared to the growth of B4 strain in the absence of BTH. Spectrophotometer analysis revealed that there was an increased broad range of compounds in the culture filtrate of B4 strain when grown with BTH, compared to the culture filtrate of B4 strain alone. The combined application of B4 strain and 0.1 mM BTH induced the increased expression of PR1a::GUS on tobacco and elicited systemic resistance against SCC1 when compared to individual application. However, there was low expression of PR1a::GUS in the water-treated control. Hence, the integrated use of BTH and B4 strain might be one of the strategies for biological control of soft rot disease through induced systemic resistance (ISR) in tobacco plants.