Screening of osmotic stress-tolerant bacteria for plant growth promotion in wheat (Triticum aestivum L.) and brinjal (Solanum melongena L.) under drought conditions.

Drought stress adversely affects plant growth and productivity. Therefore, the application of plant growth-promoting bacteria is a viable option for combating drought resistance in crops. In this study, 144 bacteria were isolated from the Kutch desert soil in Gujarat. Based on osmotic stress tolerance and PGP properties, two strains, Bacillus tequilensis (KS5B) and Pseudomonas stutzeri (KS5C) were tested for their effect on wheat (Triticum aestivum L.) and brinjal (Solanum melongena L.) under drought stress conditions. Inoculation with osmotic stress-tolerant bacteria showed 15·15-29·27% enhancement in root length of wheat and 15·27-32·59% in brinjal plants. Similarly, the enhancement of shoot length ranged from 14·72 to 37·70% for wheat and 59·39-95·94% for brinjal plants. Furthermore, the inoculated plants showed significant improvement in chlorophyll content and antioxidant properties such as proline, peroxidase and polyphenol oxidase activity compared to the control. Therefore, the bacterial strains identified in this study can be used to mitigate drought stress and enhance plant biomass.

Characterization of cadmium-resistant bacteria for its potential in promoting plant growth and cadmium accumulation in Sesbania bispinosa root.

The cadmium (Cd) resistant bacteria were isolated from soils of Damanganga river, Vapi, and identified 11 potential Cd resistant bacteria based on 16S rDNA sequences. The Cd resistant bacteria belonged to four different genera: Providencia spp., Morganella sp., Stenotrophomonas sp., and Bacillus spp. The assessment of plant growth-promoting (PGP) parameters revealed that the Cd tolerant bacteria showed one or more PGP properties. Further, a pot experiment was conducted to elucidate the effects of Cd resistant bacteria on the plant growth and the uptake of Cd by Sesbania bispinosa. The bacterized seedlings recorded 36.0-74.8% and 21.2-32.9% higher root and shoot lengths, respectively, in Cd amended soil compared with control. The Cd mobilization in the root of S. bispinosa by microbial inoculants ranged from 0.02 ± 0.01 to 1.11 ± 0.06 ppm. The enhanced concentrations of Cd accumulation in S. bispinosa roots correspond to the effect of the bacterial strains on metal mobilization in soil. The present observations showed that the Cd resistant strains protect the plants against the inhibitory effects of Cd, probably due to the production of PGP properties. The present results provided a new insight into the phytoremediation of Cd contaminated soil.

Plant growth-promoting potential of bacteria isolated from active volcano sites of Barren Island, India.

UNLABELLED: To elucidate the biodiversity of plant growth-promoting (PGP) bacteria in active volcano sites of Barren Island, India, a total of 102 bacteria were isolated and screened for their multifunctional PGP properties. The results revealed that 21 isolates (20.6%) survived heat shock at 72°C and 11 (10.8%) isolates were able to grow exposed to 25% NaCl (w/v). In assaying for PGP properties, 59 (57.8%) isolates shown indole acetic acid (IAA) like substances production, 57 isolates (55.9%) produced siderophore and 34 (33.3%) solubilized inorganic phosphate qualitatively. Whereas in the production of extracellular enzymes, 42 isolates (41.2%) produced protease and amylase, 26 (25.5%) isolates produced lipase and 24 (23.5%) isolates produced cellulase. In antagonistic activity, 30 isolates (29.4%) were found antagonistic against Macrophomina sp., 20 isolates (19.6%) against Rhizoctonia solani and 15 isolates (14.7%) against Sclerotium rolfsii. The results based on 16 rRNA gene sequencing revealed that the PGP bacteria belonged to 22 different species comprising 13 genera. Based on multifunctional properties, nine isolates were further selected to determine the PGP in brinjal and chilli seeds. Of the bacteria tested, the isolate BAN87 showed increased root and shoot length of both the crops followed in plant growth promotion by BAN86 and BAN43. The outcome of this research proves plausible practical applicability of these PGPB for crop production in soils of saline and arid environments. SIGNIFICANCE AND IMPACT OF THE STUDY: The present research shows diverse plant growth-promoting (PGP) bacteria could be isolated from the active volcano site and suggests that volcano sites represent an ecological niche, which harbours a diverse and hitherto largely uncharacterized microbial population with yet unknown and untapped potential biotechnological applications, for example, plant growth promoters, as evidenced from this study. The outcome of this research may have a practical effect on crop production methodologies in saline and arid environment soils.

Isolation and Characterization of Trichoderma spp. for Antagonistic Activity Against Root Rot and Foliar Pathogens.

Trichoderma, soil-borne filamentous fungi, are capable of parasitising several plant pathogenic fungi. Twelve isolates of Trichoderma spp. isolated from different locations of South Andaman were characterized for their cultural, morphological and antagonistic activity against soil borne and foliar borne pathogens. The sequencing of these isolates showed seven different species. The isolates revealed differential reaction patterns against the test pathogens viz., Sclerotium rolfsii, Colletotrichum gloeosporioides and C. capsici. However, the isolates, TND1, TWN1, TWC1, TGD1 and TSD1 were most effective in percentage inhibition of mycelial growth of test pathogens. Significant chitinase and ß-1,3-glucanase activities of all Trichoderma isolates has been recorded in growth medium. T. viride was found with highest chitinase whereas T. harzianum was recorded with highest ß-1,3-glucanase activities.

First Report of Anthracnose Disease of Black Pepper (Piper nigrum) Caused by an Unknown Species of Colletotrichum.

Black pepper is cultivated in Andaman and Nicobar Islands, India as a spice crop. During a survey performed in June of 2007 in South Andaman, two kinds of leaf anthracnose symptoms were observed. The classic symptom, angular to irregular or circular brownish lesions with a chlorotic halo and pinhead size acervuli on the leaves, was consistent with the disease previously reported on pepper caused by Colletotrichum gloeosporioides (2). This symptom also caused splitting and the production of hollow berries. The new symptom was novel, with leaves initially exhibiting pale green or yellowish green lesions. As the disease progressed, lesion margins became brown to black with slightly raised areas containing numerous acervuli. Unlike the classic symptom, the new symptom was characterized as leaf lesions that rarely caused defoliation; berries showed no lesions. The foliar disease incidence was up to 15%, but direct economic loss of berries was not noticed. This new symptom was similar to symptoms caused by C. dracaenophilum, a species identified as a pathogen on lucky bamboo (Dracaena sanderiana) (1). A fungus was isolated in pure culture from the pale green lesions and cultured on potato dextrose agar (PDA). At room temperature (28 ± 2°C), fungal growth on PDA was slow and mycelium appeared whitish at the margin with pale pink centers. A pinkish color was observed on the reverse side of the plate, reflecting profuse sporulation. The conidia were hyaline, broadly clavate to cylindrical, and measured 12.5 to 15 × 5 to 7.5 µm (average 14 × 7.5 µm). The internal transcribed spacer (ITS) region of the fungal DNA was amplified, sequenced, and submitted to NCBI GenBank (Accession No. EU744584). The specimen was deposited in the MTCC of IMTECH, Chandigarh, India (Accession No. MTCC9344). Pathogenicity was tested in five replications on 15- to 20-day-old pepper plants and repeated twice. A 1-ml conidial suspension (108 spores/ml) of the fungus was brushed on two intact leaves of each pepper plant and incubated for 2 weeks in a glasshouse at 28°C and 70% relative humidity with natural daylight conditions. Plants brushed with sterile water served as control. Similar pale green symptoms were observed only on treated leaves and the same organism was reisolated from lesions. BLAST searches of the GenBank using the ITS sequence revealed that this fungus was a member of the genus Colletotrichum, but a species level identification could not be made with these data. The fungus was most similar in sequence to unnamed endophytic strains of Colletotrichum (96% sequence identity) and phytopathogenic isolates of C. dracaenophilum (93% sequence similarity). Although the symptomatology and sequence data were most closely matched with those documented for C. dracaenophilum (1), the morphological and cultural characteristics of the black pepper anthracnose fungus differed from C. dracaenophilum and other known species of Colletotrichum (3). Together these morphological and molecular data suggest that this form of anthracnose disease on black pepper may be caused by a novel, undescribed species of Colletotrichum. Further investigations will be required to characterize this organism to the species level. References: (1) S. G. Bobev et al. Plant Dis. 92:173, 2008. (2) P. Santha Kumari and A. Sanker. J. Mycol. Plant Pathol. 33:329, 2003. (3) B. C. Sutton. In: Colletotrichum. Biology, Pathology and Control. CAB International, Wallingford, 1992.