Isolation,partial identification and application of diazotrophic rhizobacteria from traditional Indian rice cultivars

A diversity of N₂-fixing (diazotrophic) bacteria was isolated from two traditional rice cultivars, Sataria and Kartiki, from the rice growing area of Mithila region of North Bihar, India, where low levels of nitrogen fertilizers are applied. Nitrogen-free semisolid media NFb, JMV and LGI with different carbon sources and pH-values were used for enrichment and isolation of root-associated diazotrophs. The colonization density of roots by diazotrophs, as estimated from positive pellicle formation at highest dilution in nitrogen-free enrichment media, was 10⁶–10⁸ diazotrophic bacteria per g fresh root weight. Roots of the cultivar Kartiki were found to be more densely colonized endophytically by diazotrophs as detected after chloramine T (1%) surface disinfection. To ascertain the phylogenetic affiliation of the isolates, phylogenetic oligonucleotide probes and the Fluorescent in situ Hybridization (FISH) technique were applied. Using group-specific rRNA directed oligonucleotide probes, the majority of the isolates could be identified as alpha-, beta-, or gamma-proteobacteria. Using 16S and 23S rRNA-directed genus- or species-specific probes, Herbaspirillum seropedicae, Azospirillum amazonense, Burkholderia cepacia/vietnamiensis, Rhizobia and Pseudomonas spp. were found to be the most prominent root associated culturable diazotrophs. Diazotrophic Gluconacetobacter spp. were also demonstrated as colonizers of rice roots. Burkholderia cenocepacia, Pseudomonas sp. and three diazotrophic PGPR reference strains were used for the inoculation of axenically grown rice seedlings to determine the plant growth promoting potential. Significant increases in the shoot length (up to 60%), shoot dry weight (up to 33%) and the grain yield (up to 26%) per plant were observed in non-axenic pot and field trials. Using semisolid enrichment media after surface sterilization of field grown inoculated rice roots and oligonucleotide probing of the diazotrophic enrichment cultures, a sustainable colonization with the inoculated bacteria could be demonstrated.     

Epidemiological studies on powdery mildew of mungbean and urdbean

Abstract

Powdery mildew of mungbean (Vigna radiata L. Wilczek) and urdbean ( V. mungo L. Hepper) caused by Erysiphe polyponi DC during the winter/spring season is a severe constraint in the production of bean crops in the Chhattisgarh region of Madhya Pradesh. Keeping this in view, studies were made to understand the development of powdery mildew in relation to crops, varieties, weather conditions and their effect on yield. The first appearance of powdery mildew in 33 mungbean and 18 urdbean varieties was 1 week earlier during winter 1992–93 than winter 1991–92. Its development was most rapid each year when the average maximum temperature varied from 27.2 to 30.3°C, relative humidity from 67 to 90% during the morning and 12 to 38% at noon, and wind velocity from 2.3 to 4.1 km/h. A positive correlation occurred between mildew severity and temperatures and wind velocity in most of the varieties. However, the correlation with relative humidity was negative and significant except in a few varieties. The pooled infection rates (r)/unit/day on resistant mungbean and urdbean varieties was less than 0.1 with disease scores of 1–5 while in apparently slow mildewing varieties, rvalues were also less than 0.1 but showed a score of 7–9. The effect of disease levels on grain yield of urdbean had a negative and significant correlation. However, it was negative but not significant in the case of mungbean. Grain yield was considerably higher when the crops were protected with one spray of Bavistin (1 kg/ha in 5001 of water) followed by Sulfex (3 kg/ha in 5001 of water) than in the untreated control. The disease scores in sprayed plots were also markedly less and ranged between 0 and 5 as against 1 and 9 in the untreated control in different varieties.     

Resistance to blast (Magnaporthe grisea) in a mini-core collection of finger millet germplasm

Blast caused by Pyricularia grisea [teleomorph: Magnaporthe grisea] is an economically important and widespread disease of finger millet in the world. Host resistance is the most economical and effective means of combating this disease as finger millet is predominantly grown by resource-poor and marginal farmers. At the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), we evaluated a finger millet mini-core collection of 80 germplasm accessions (about 1 % of the total germplasm collection representing major trait variability) for blast resistance both in the field and greenhouse. Field evaluation was done using a refined screening technique that included new improved rating scales for leaf, neck and finger infection. Sixty six of the 80 accessions showed combined resistance to leaf, neck and finger blast in two seasons (2009 and 2010) of field screening. A highly significant and positive correlation was found between neck and finger blast ratings (r?=?0.92), whereas small but significant correlations were found between leaf blast and neck blast (r?=?0.25) and between leaf blast and finger blast (r?=?0.30). These accessions were also screened for leaf blast resistance in the greenhouse by artificial inoculation of seedlings to confirm field observations. Fifty-eight of the 80 accessions were resistant to leaf blast in the greenhouse screen as well. These resistant accessions represented one wild (africana) and four cultivated races (vulgaris, plana, elongate and compacta) of finger millet that originated from 13 countries in Asia and Africa and exhibited considerable diversity for agronomic traits, such as maturity period, plant height and panicle type. These blast resistant accessions from the mini-core collection would be useful in finger millet disease resistance breeding programs.     

Insecticidal potential of an endophytic fungus, Cladosporium uredinicola, against Spodoptera litura

The tobacco cutworm, Spodoptera litura (Lepidoptera: Noctuidae) (Fabricius), is a polyphagous pest which has developed physiological resistance against a number of known insecticides. In order to reduce the load of synthetic insecticides, ecofriendly alternative strategies are needed. The present studies were conducted to evaluate the insecticidal potential of the endophytic fungus Cladosporium uredinicola isolated from Tinospora cordifolia (Thunb.) on S. litura. Development of S. litura was significantly prolonged when larvae were fed on diet amended with ethyl acetate extract of C. uredinicola at concentrations of 1.25–2.00 μl?g^?1. The negative effects of fungal toxin on development of S. litura further resulted in a significant reduction in adult emergence, longevity and reproductive potential at higher concentrations. A significantly higher number of adults showed morphological deformities when larvae were fed on diet amended with 2.00 μl?g^?1 concentration. The inhibitory effects on growth and development of S. litura indicate toxicity of ethyl acetate extract of C. uredinicola, which is further evidenced by reduced food utilization by larvae. The antifeedant and toxic effects of ethyl acetate extract of C. uredinicola observed in the present studies can be attributed to a bioactive compound produced by the fungus, so this study provides evidence that C. uredinicola isolated from T. cordifolia possesses anti-insect properties and may play an important role in protecting plants against insect pests.     

Induction of novel variants through physical and chemical mutagenesis in Barbeton daisy (Gerbera jamesonii Hook.)

Summary

Gerbera (Gerbera jamesonii) is an attractive ornamental flower of high economic importance. The present investigation was aimed at generating novel flower colour variants in the gerbera cultivar ‘Harley’ through physical and chemical mutagenesis. In vitro-raised shoot cultures of gerbera, established from petiole explants, were exposed to different doses of γ-rays (1.5, 2.0, 2.5, 5.0, 10.0, 15.0, 20.0, or 30.0 Gy) using a Cobalt-60 source emitting 2.51 kGy h^–1. To induce mutations through chemical mutagenesis, different concentrations of ethylmethane sulphonate [EMS; 0.1, 0.2, 0.5, 0.8, or 1.0% (v/v)] were administered for 10 min or for 20 min. The LD50 values calculated for shoot survival and the induction of mutations were approx. 6.5 Gy for γ-rays and 0.65% (v/v) EMS for 10 min, or ≤ 0.1% (v/v) EMS for 20 min. Investigations revealed a negative correlation between mutagen dose and plant survival, both in vitro and after acclimatisation. Morphological variants showing changes in leaf shape, leaf size, scape length, flower diameter, and flower colour were obtained. Significantly, early flowering was induced in all mutated plants compared to non-mutated plants.The high frequencies of colour variants obtained using Bγ-rays, or the application of EMS to in vitro-raised shoot cultures could be an effective way to improve gerbera cultivars.     

Effect of 46 years' application of fertilizers,FYM and lime on physical,chemical and biological properties of soil under maize–wheat system in an acid Alfisol of northwest Himalayas

Imbalanced fertilizer use with intensive cropping has threatened the sustainability of agroecosystems, especially on acid soils. An understanding of the long-term effects of fertilizers and amendments on soil health is essential for sustaining high crop yields. The effects of application of fertilizers, and amendments for 46 years on soil properties and maize yield in an acid Alfisol were investigated in this study. Ten fertilizer treatments comprising different amounts of NPK fertilizers, farmyard manure (FYM) and lime, and one control, were replicated three times in a randomized block design. At 0–15 cm soil depth, bulk density was least (1.20 t/m³), porosity (49.8%) and water holding capacity (61.7%) were greatest in 100% NPK + FYM, corresponding to the largest organic carbon content (13.93 g/kg). Microbial biomass C and dehydrogenase activity in 100% NPK + FYM were 42% and 13.7% greater than 100% NPK, respectively. Available nutrients were significantly more with 100% NPK + FYM and 100% NPK + lime than control and other fertilizer treatments. At 15–30 cm depth, the effect of various treatments was comparable to the surface layer. Grain yield declined by 55% and 53% in 100% NPK(-S) and 100% NP, respectively, compared with 100% NPK, whereas 100% N as urea alone eventually led to crop failure. Soil porosity recorded the greatest positive correlation (r = .933**), whereas bulk density recorded a negative significant correlation (r = −.942**) with grain yield. The results suggest that integrated use of FYM/lime with chemical fertilizers is a sustainable practice in terms of crop yield and soil health, whereas continuous application of urea alone is detrimental to the soil health.     

Bulk pollen extraction procedures and the potency of the extracted pollen

Summary Three methods of bulk extraction of potato pollen were compared for their efficiency and for the potency of extracted pollen in affecting berry set, seeds/berry and 100 seed weight. Extracting pollen from pre-dried anthers using a sieve of nylon netting with 1 mm perforations was the most economical with respect to time, labour and cost of equipment and that would be applicable for commercial production of hybrid TPS.     

Some plants like it warmer: Increased growth of three selected invasive plant species in soils with a history of experimental warming

Soil warming can affect plant performance by increasing soil nutrient availability through accelerating microbial activity. Here, we test the effect of experimental soil warming on the growth of the three invasive plant species Trifolium pratense (legume), Phleum pratense (grass), and Plantago lanceolata (herb) in the temperate-boreal forest ecotone of Minnesota (USA). Plants were grown from seed mixtures in microcosms of soils with three different warming histories over four years: ambient, ambient +1.7 °C, and ambient +3.4 °C. Shoot biomass of P. pratense and P. lanceolata and plant community root biomass increased significantly in soils with +3.4 °C warming history, whereas T. pratense responded positively but not significantly. Soil microbial biomass and N concentration could not explain warming effects, although the latter correlated significantly with the shoot biomass of P. lanceolata. Our results indicate that soil with a warming history may benefit some invasive plants in the temperate-boreal ecotone with potential impacts on plant community composition. Future studies should investigate the impact of warming-induced differences in soil organisms and nutrients on plant invasion.     

Antibacterial Activity of 2-(2′,4′-Dibromophenoxy)-4,6-dibromophenol from Dysidea granulosa

2-(2′,4′-Dibromophenoxy)-4,6-dibromophenol isolated from the marine sponge Dysidea granulosa (Bergquist) collected off the coast of Lakshadweep islands, Indian Ocean, exhibited potent and broad spectrum in-vitro antibacterial activity, especially against methicillin resistant Staphylococcus aureus (MRSA), methicillin sensitive Staphylococcus aureus (MSSA), vancomycin resistant Enterococci (VRE), vancomycin sensitive Enterococci (VSE) and Bacillus spp. Minimal inhibitory concentration (MIC) was evaluated against 57 clinical and standard strains of Gram positive and Gram negative bacteria. The observed MIC range was 0.117–2.5 μg/mL against all the Gram positive bacteria and 0.5–2 μg/mL against Gram negative bacteria. The in-vitro antibacterial activity observed was better than that of the standard antibiotic linezolid, a marketed anti-MRSA drug. The results establish 2-(2′,4′-dibromophenoxy)-4,6-dibromophenol, as a potential lead molecule for anti-MRSA and anti-VRE drug development.     

Molecular characterization and variability analysis of <Emphasis Type="Italic">Apple scar skin viroid</Emphasis> in India

Apple scar skin viroid (ASSVd) infection is a major limitation to apple fruit quality and causes huge economic losses. In surveys of apple orchards in the northern Indian state of Himachal Pradesh, fruits with dappling symptoms were noticed. ASSVd was detected from these fruits and molecularly characterized. Ten clones from three isolates were sequenced, of which seven were new sequence variants of ASSVd. The clones had significant sequence variability (94–100%) with each other. Variability was more common in the pathogenic domain of the viroid genome. Four of the clones were 330 nucleotides (nt) long, and the other six had an additional nucleotide. Phylogenetic analysis showed close affinity of the present isolates with some Chinese and Korean isolates. The study reports seven new variants of ASSVd and also provides the first molecular evidence of viroid infection (ASSVd) in apple in India.