Resistance and resilience of soil biological indicators: A case study with multi-walled carbon nanotube

Soil ecosystem is experiencing stresses due to climate change, and soil inhabitants try to demonstrate their inherent resistance and resilience against those stresses. Application of nanomaterials as agricultural inputs could bring shifts in resistance and resilience patterns of soil microbes and associated enzymes, especially under short-term heat stress. With this background, the impacts of multi-walled carbon nanotube (MWCNT) on the resistance and resilience of soil biological indicators were evaluated. An incubation experiment was conducted with varied MWCNT concentrations (0, 50, 100, 250, and 500 mg kg^-1 soil) for 90 d after 24-h heat stress at 48 ±2 ℃ to assess the impacts of MWCNT on soil enzyme activities and microbial populations vis-à-vis their resistance and resilience indices under short-term exposure to heat stress. Enzyme activities were reduced after exposure to heat stress. Resistance indices of enzyme activities were enhanced by MWCNT application on day 1 after heat stress, whereas there was no recovery of enzyme activities after 90-d incubation. Like soil enzyme activities, resistance index values of soil microbial populations followed the similar trend and were improved by MWCNT application. Multi-walled carbon nanotube has the potential to improve resistance indices of soil enzyme activities and microbial populations under heat stress, although they could not recover to their original state during periodical incubation after heat stress. This study helps to understand the relative changes of biological indicators under MWCNT and their ability to withstand heat stress.     

Maternal salinity environment affects salt tolerance during germination in Anabasis setifera: A facultative desert halophyte

The effects of maternal salinity and light incubation on the salinity tolerance of the facultative halophyte Anabasis setifera during their germination stages were assessed. Seeds were collected from non-saline habitats in Egypt and saline habitats in the United Arab Emirates(UAE). The seeds of the two populations were germinated in 0, 100, 200, 400, 600 and 800 m M Na Cl, and incubated at 25°C/15°C in both 12-h light and 12-h darkness regimes and continuous darkness. Significantly more seeds germinated in the Egyptian population than in the UAE population. Salinity tolerance was significantly greater with the Egyptian population than with the UAE population, especially under the conditions of higher salinities. The difference in salinity tolerance between the seeds of two populations was attributed to their seed mass. In addition, germination was significantly faster for the Egyptian population than for the UAE population. Most of the saline treated seeds were able to recover their germination when transferred to distilled water, but this depended on their maternal salinity and light incubation. Recovery from higher salinities was significantly better for the seeds under darkness than for those under light in the UAE population, but the reverse was true for the seeds in the Egyptian population. The higher salinity tolerance for the A. setifera seeds from the non-saline Egyptian population and the lower salinity tolerance for the seeds from the saline UAE population cannot explain their natural distribution. Further studies about other possible roles, such as levels of different promoting and inhibiting phytohormones, are needed to understand the importance of salinity as an environmentally induced maternal effect.     

Tea (Camellia sinensis) clones with shorter periods of winter dormancy exhibit lower accumulation of reactive oxygen species

Tea (Camellia sinensis (L.) O. Kuntze) is a perennial crop grown throughout the world. During winter, tea undergoes a dormancy period when growth of apical buds almost ceases, severely reducing the commercial yield of tea. Low temperatures prevail during the period of winter dormancy, which alone or in combination with high solar irradiance have the potential to induce oxidative stress in plants. We studied six tea clones under field conditions to test whether a relationship exists between oxidative stress and winter dormancy. Data on the behavior of the enzymatic antioxidative system was collected for all clones during different phases of winter dormancy. There was a strong positive correlation among clones between accumulation of reactive oxygen species (ROS) and the length of the dormancy period. Clones having shorter dormancy periods exhibited higher induction of antioxidative enzymes. Results suggest that efficient scavenging of ROS is a desirable feature in tea because it leads to lower accumulations of ROS during winter months and is associated with reduced winter dormancy.     

Biology and management of the fast‐emerging threat of broomrape in rapeseed–mustard

Broomrapes (Phelipanche and Orobanche spp.) are obligate root parasites of the family Orobanchaceae. The natural variation in Orobanchaceae exists in plants involving Triphysaria versicolor (facultative hemiparasite), Striga hermonthica (obligate hemiparasite) and Phelipanche aegyptiaca, formerly Orobanche aegyptiaca (holoparasite). The family Orobanchaceae has 90 genera. The four major parasitic species of broomrape are Phelipanche ramosa in the Brassicas, especially in rapeseed, Phelipanche cernua in tobacco and sunflower, P. aegyptiaca in solanacious crops and in Brassica juncea and Phelipanche crenata in leguminous crops. They are prevalent, infesting nearly 1.2% of the world's arable land. In India, P. ramosa and P. aegyptiaca cause severe infestations of Brassica and have threatened its cultivation in major growing areas. In addition, a single broomrape plant can release >100 000 seeds that remain viable for decades in the soil. This provides the parasite with a great genetic adaptability to environmental changes, including host resistance, agronomical practices and herbicide treatments. Different control measures, such as manual weeding, herbicide applications, solarization, crop rotation and integrated broomrape management practices, have been proposed in order to reduce the broomrape menace and improve yields in farmers' fields. Breeding for broomrape resistance also could be an economic, feasible and environmental friendly control method. The present article reviews the current status of research on broomrape in India and abroad, as well as suggests strategies for its effective management.     

Synergistic effect of inoculating plant growth-promoting Pseudomonas spp. and Rhizobium leguminosarum-FB1 on growth and nutrient uptake of rajmash (Phaseolus vulgaris L.)

Plant growth-promoting bacteria (PGPB) Pseudomonas lurida-NPRp15 and Pseudomonas putida-PGRs4 possessing multiple plant growth-promoting traits were isolated from rhizoplane of pea and rhizosphere of garlic, respectively. The effects of individuals and combinations of Pseudomonas spp. with effective root nodulating symbiotic nitrogen fixing Rhizobium leguminosarum-FB1 on plant growth, nutrient uptake and yield of the rajmash plant were studied under greenhouse conditions. Bacterial inoculation resulted in significantly higher values for plant dry biomass, N, P, K, Zn and Fe contents as compared to the uninoculated control. Furthermore, dual inoculation of P. lurida-NPRp15 with R. leguminosarum-FB1 significantly increased root and shoot dry weight, nodulation, nutrient uptake, pod yield, and nutrient content of pods of rajmash VL63 compared to controls, single and triple inoculation. The results of the study indicate the potential of harnessing the benefit of plant growth-promoting and nitrogen-fixing microorganisms to improve the growth and yield of rajmash.     

Genetic analysis and pyramiding of two gall midge resistance genes (Gm-2 and Gm-6t) in rice ( Oryza sativa L.)

Asian rice gall midge (Orseolia oryzae) is a major pest across much of south and southeast Asia. This pest is genetically diverse and many gall midge biotypes are known to exist in each country. During the last three decades, host plant resistance has proved to be the most effective mechanism of controlling the Asian rice gall midge. Seven genes conditioning resistance to gall midge larvae have been identified in rice (Oryza sativa) and are being used in cultivar improvement programs. However, some of these genes are rendered ineffective by new gall midge biotypes. Increased understanding of genetics, inheritance, allelic relationships and linkage is necessary to maximise the durability of major gene resistance by the pyramiding of these genes. The two genes, Gm-2 and Gm-6(t), are known to confer resistance against a number of biotypes in India and China, respectively. An F₃ population derived from a cross between Duokang #1 (donor of Gm-6(t)) and Phalguna (donor of Gm-2) was screened against Chinese gall midge biotype 4 at Guangdong, China, and Indian gall midge biotype 1 at Raipur, India. At each location, separately,a single gene governed resistance. The parallel segregation of 417 F₃progenies for both biotypes at two locations revealed that recombination had occurred between the two genes, establishing that the two genes are not allelic. However, the two genes Gm-2 and Gm-6(t), were found to be linked with a distance of ∼16.3 cM. A number of lines homozygous at one locus and segregating for the other locus were identified and selected. These lines were selfed to obtain lines homozygous for the favourable alleles at both loci (two locus pyramids). This is the first report on use of conventional host-pest interaction method for pyramiding two closely located Gm-resistance loci of dissimilar effects. The implications of deployment of these pyramids within and across country borders, with reference to the prevailing gall midge populations are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of dietary supplementation of Bacillus licheniformis on gut microbiota, growth and immune response in giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879)

The present study was conducted to evaluate the effect of dietary supplementation of probiotic bacterium Bacillus licheniformis on the gut microbiota, growth and immune response in Macrobrachium rosenbergii juveniles (4.0 ± 0.02 g). Five isocaloric experimental diets supplemented with different concentrations of B. licheniformis, viz. Control (without probiotic supplementation), T₁ (1.0 × 10⁶ cfu g^?1feed), T₂ (1.0 × 10⁷ cfu g^?1feed), T₃ (1.0 × 10⁸ cfu g^?1 feed) and T₄ (1.0 × 10⁹ cfu g^?1 feed) were used for the experiment. After 60 days of feeding trial, the growth performance increases significantly in all the experimental groups compared with control, and highest weight gain, specific growth rate and lowest feed conversion ratio were recorded from T₄ (P > 0.05). However, juvenile survival was not found to be significantly affected by probiotic supplementation (P > 0.05). The total bacterial count and Bacillus spp. count in the gut were significantly increased with concurrent decrease in pathogenic Aeromonas spp. and Pseudomonas spp. in all the experimental groups compared with control (P < 0.05). Compared with control, immune parameters were increased significantly in all the experimental groups (P < 0.05). Highest haemocyte count, phenol oxidase, superoxide dismutase and antibacterial activity in haemolymph were recorded from T₄ (P < 0.05). When prawns were challenged with Vibrio alginolyticus, the cumulative mortality was significantly lower in T₄ (P < 0.05). These results indicate that dietary supplementation of B. licheniformis can manipulate the gut microbiota and increase the growth and immune response of M. rosenbergii. In the present study, concentration response on the probiotic effect of B. licheniformis was observed which showed higher effects at a concentration of 1.0 × 10⁹ cfu g^?1 feed in the laboratory condition.     

Histamine receptors mediate contraction of reticular groove smooth muscle of adult goats

The present study was conducted to evaluate the effect of histamine and to characterise its receptor subtypes in reticular groove (RG) smooth muscle of adult goats. The studies were done using floor and lip regions of RG. We used tension experiments on smooth muscle of RG isolated from adult goat for functional characterisation of H₁ and H₂ receptors. Western blotting and immunohistochemistry experiments were conducted for molecular characterisation of these receptors. Histamine evoked concentration-dependent contraction of isolated RG circular and longitudinal smooth muscle preparation. Pyrilamine antagonised the action of histamine. Histamine did not induce any relaxant effect on RG preparations. Additionally, cimetidine did not produce any significant effect on histamine-induced response. Non-selective histaminic receptor antagonist cyproheptadine attenuated the contraction response to histamine in the smooth muscle. Molecular characterisation and localisation of H₁ and H₂ receptor proteins confirmed the presence of these receptors in RG. It is most likely that histamine-induced contractile effect in RG smooth muscle of goats is mediated by H₁ histaminic receptors.     

Simulation of salt and water movement and estimation of water productivity of rice crop irrigated with saline water

The HYDRUS-ID model was experimentally tested for water balance and salt build up in soil under rice crop irrigated with different salinity water (ECiw) of 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ in micro-lysimeters filled with sandy loam soil. Differences of means between measured (M) and HYDRUS-1D predicted (P) values of bottom flux (Q _o) and leachate EC as tested by paired t test were not found significant at P = 0.05 and a close agreement between RMSE values showed the applicability of the HYDRUS-1D to simulate percolation and salt concentration in the micro-lysimeters under rice crop. Potential ET values of rice as obtained from CROPWAT matched well with model predicted and measured one at all ECiw treatments. The model predicted root water uptake varied from 66.1 to 652.7 mm and the maximum daily salt concentration in the root zone was 0.46, 2.3, 4.5, 6.7, 8.4 and 10.2 me cm⁻³ in 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ ECiw treatments, respectively. The grain production per unit evapotranspiration ( \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} ) value of 2.56 in ECiw of 0.4 dS m⁻¹ treatment declined to 1.31 with ECiw of 2 dS m⁻¹. The \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} reduced to one-fifth when percolation was included in the productivity determination. Similarly, the water productivity in respect of total dry matter production (TDM) was also reduced in different treatments. Therefore, the model predicted values of water balance can be effectively utilized to calculate the water productivity of rice crop.