Bhumesh Kumar

The effect of Plant growth promoting rhizobacteria on the growth, physiology, and Cd uptake of Arundo donax L.

ABSTRACT In this study, plant growth-promoting potential isolates from rhizosphere of 10 weed species grown in heavy metal-contaminated areas were identified and their effect on growth, antioxidant enzymes, and cadmium (Cd) uptake in Arundo donax L. was explored. Plant growth-promoting traits of isolates were also analyzed. These isolates were found to produce siderophores and enzymes such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and aid in solubilization of mineral nutrients and modulate plant growth and development. Based on the presence of multiple plant growth-promoting traits, isolates were selected for molecular characterization and inoculation studies. Altogether, 58 isolates were obtained and 20% of them were able to tolerate Cd up to 400 ppm. The sequence analysis of the 16S rRNA genes indicates that the isolates belong to the phylum Firmicutes. Bacillus sp. along with mycorrhizae inoculation significantly improves the growth, the activity of antioxidants enzymes, and the Cd uptake in A. donax than Bacillus alone. Highly significant correlations were observed between Cd uptake, enzymatic activities, and plant growth characteristics at 1% level of significance. The synergistic interaction effect between these organisms helps to alleviate Cd effects on soil. Heavy metal-tolerant isolate along with arbuscular mycorrhizae (AM) could be used to improve the phytoremedial potential of plants.

Characterization of functional trait diversity among Indian cultivated and weedy rice populations.

Weedy rice, a menace in rice growing areas globally, is biosimilar having attributes similar to cultivated and wild rice, and therefore is difficult to manage. A study was initiated to characterize the functional traits of 76 weedy rice populations and commonly grown rice cultivars from different agro-climatic zones for nine morphological, five physiological, and three phenological parameters in a field experiment under an augmented block design. Comparison between weedy and cultivated rice revealed a difference in duration (days) from panicle emergence to heading as the most variable trait and awn length as the least variable one, as evidenced from their coefficients of variation. The results of principal component analysis revealed the first three principal components to represent 47.3% of the total variation, which indicates an important role of transpiration, conductance, leaf-air temperature difference, days to panicle emergence, days to heading, flag leaf length, SPAD (soil-plant analysis development), grain weight, plant height, and panicle length to the diversity in weedy rice populations. The variations existing in weedy rice population are a major reason for its wider adaptability to varied environmental conditions and also a problem while trying to manage it.

Response of soil enzymes to elevated CO2 and temperature in weeds associated with rice-wheat cropping system

Biological properties of the soil have often been proposed as early and sensitive indicators of soil ecological stress or other environmental changes. In the present investigation, the soil samples were collected from weeds associated with rice-wheat cropping system from open-top chambers to assess the effect of elevated CO2 and temperature on soil enzymes. In Rabi season, higher activity of FDA hydrolysis rate was noticed in wild oat with 26.5 (μg fluorescein/g/h) at elevated CO2 + ambient temperature levels. Dehydrogenase activity was higher at enrichment of CO2for P. minor with 35.9 (μg TPF/g soil/24 h). Urease significantly was higher in enrichment of CO2+ elevated temperature with wild oat 34.6 (μg NH4/g soil/24 h) followed by wheat (31.5μg NH4/g soil/24 h) with elevated CO2+ ambient temperature. In Kharif season, enrichment of CO2 concentration in rhizosphere of Echinochloa crusgalli recorded with higher FDA hydrolysis rate (19.8 μg fluorescein/g/h), dehydrogenase activity (39.8 μg TPF/g soil/24 h) and urease activity (45.6 μg NH4/g soil/24 h) respectively. We found the carbon dioxide enrichment significantly increased the soil enzymes like dehydrogenase, fluorescein diacetate (FDA) hydrolysis and urease activity in weeds rhizosphere than the crops.

Weed Stress in Plants

Few plant species utilize available natural resources more efficiently as compared to other species in order to establish themselves in prevailing environmental conditions. Once established in early phase of growth, they can be sustained throughout the growing season by virtue of better stand. And this is the strategy behind the success of most of the notorious weeds in any cropping system. They, hence, continue to cause huge yield losses despite every effort made by farmers to manage them. Herbicides are largely used to manage weeds globally, but its application is also known to cause stress, though minimal, in crop plants. Another factor which contributes to the success of weeds is their hardiness and resilience to abiotic and biotic stress factors. Molecular mechanism(s) responsible for traits like competitiveness and invasiveness of weeds is poorly understood till date. However, development and availability of sophisticated molecular tools pave the way to dissect the mechanism of weed dominance. Competitiveness and tolerance to stress factors are important traits observed among different weed species that can be exploited in attempts to develop crop plants tolerant to abiotic/biotic stress(es). The need of the hour is to understand the molecular mechanisms underlying weed competitiveness over crop plants in field and to utilize the responsible gene(s) by transferring them into crop plants. However, success of such approaches depends upon integration and collaboration to bring expertise together from weed science, molecular biology, and plant physiology. An effort has been made to review the traits available among weed species that make them competitive and hardy.

Weeds as a Source of Genetic Material for Crop Improvement Under Adverse Conditions

The scientific basis of weedy and invasive traits of weed species along with their evolution is poorly understood. Development and availability of the sophisticated molecular tools provide us liberty to play with different metabolic pathways at molecular level and to transfer the desirable genetic materials into crop plants, thus breaking the reproductive barriers for interspecific and intergeneric transfer of the genetic material. Advancement of the modern biotechnological tools offers tremendous promise for elucidating these important weedy traits in detail and further exploration for the various aspects of crop improvement in “cut and paste” style. Weeds are harder plants, coexisting with crops and out-compete them in almost every aspect. Competitiveness and tolerance to abiotic and biotic factors are the important traits which can be observed among various weed species and can be transferred into crop plants. Coexistence of the weeds with crop plants provide an edge over the other wild species and model species like Arabidopsis thaliana ensuring the better chance of integration of the transferred material and survival of the transgenic with minimum yield penalty. However, success of such approaches requires collaborative efforts from all the corners of weed scientists to bring together expertise in weed science, molecular biology, and plant physiology. In this chapter an effort has been made to point out the useful traits of the weeds which can be transferred into crop plants for improvement along with the few successful case studies.

Effect of elevated CO2 on Vigna radiata and two weed species: yield, physiology and crop–weed interaction

Abstract. A field experiment was conducted in a free-air CO2 enrichment (FACE) facility to investigate the effect of elevated atmospheric CO2 on growth and physiology of green gram (Vigna radiata (L.) R.Wilczek) and associated weed species (Euphorbia geniculata Ortega and Commelina diffusa Burm.f.). Physiological and reproductive behaviour and interaction of the crop and two weed species under elevated CO2 was also studied. Plants were grown under ambient (390 ± 5 ppmv) and elevated (550 ± 50 ppmv) CO2. The results showed that growth, photosynthesis and carbonic anhydrase activity increased in all the test species. Stomatal conductance and transpiration decreased in V. radiata (5.1% and 30.5%, respectively) and C. diffusa (19% and 13.7%) but increased in E. geniculata (6.5% and 27.6%), suggesting a unique adaptive potential of E. geniculata at elevated CO2. Higher accumulation of reactive oxygen species (hydrogen peroxide and superoxide) was noticed at elevated CO2 in V. radiata than in E. geniculata and C. diffusa. Potential of E. geniculata to maintain redox homeostasis in its original state may provide an advantage over two other species in adaptation to climate change. Isoenzyme patterns of superoxide dismutase and stronger activity of antioxidant enzymes suggest species-specific differential regulation and induction of new isoforms under elevated CO2. Enrichment of atmospheric CO2 at a competitive density of weeds lowered the yield (12.12%) and quality of green gram seed, with diminished protein content (16.14% at ambient CO2 to 15.42% at elevated CO2) and enhanced carbohydrate content (3.11%). From the study, it may be concluded that a rise in atmospheric CO2 concentration affects plant performance in a species-specific manner. Among the three species, E. geniculata emerged as most responsive to elevated CO2, showing higher transpiration and stomatal conductance and a stronger antioxidant defence system in a higher CO2 atmosphere. At elevated CO2, weed–crop interaction altered in favour of weeds leading to considerable yield loss of green gram seed.

Adoption and impact assessment of weed management technologies in wheat and greengram under conservation agriculture system in central India

Rice-wheat is the major cropping system in the Indo-Gangetic plains and is also practiced on considerable area in Madhya Pradesh. Rice-wheat production system under conventional practices involves tedious and time-consuming methods of field preparation and weed management; increases cost of production, deteriorates soil fertility, and do not offer desired benefits for increasing the grain yields. In conventional agriculture, burning of crop leftover residue has become a major challenge that leads to loss of precious plant nutrients and deteriorates environmental quality. In order to mitigate these problems, technically-feasible, economically-viable and ecologically-permissible technologies need to be essentially adopted. A technology is required to facilitate timely sowing in standing stubbles, minimize weed infestation, lower cost of production, improve fertilizer/water-use efficiency and improve soil health. To reap the benefits of conservation agriculture (CA), studies were conducted at farmers ’fields in rice-wheat-greengram cropping system in black-cotton soils in Madhya Pradesh for consecutive five years. Sowing was done with Happy Seeder. Emergence of weeds from upper soil surface was effectively controlled by herbicides. Results showed that the benefits of CA can well be harnessed in black-cotton soils with rice-wheat-greengram cropping system. Retention of crop residues on soil surface provided an effective mulch cover for nutrient and moisture conservation, temperature moderation and weed control.

Effect of cadmium uptake on growth and physiology of water lettuce

Cadmium (Cd) is a major pollutant metal that is extremely toxic to organisms. Cadmium contamination occurs through the use of phosphate fertilizers and sludge, and inputs from mining and smelting industries (McGrath et al. 2001). Daily consumption of Cd-contaminated foods poses a risk to human health (Shukla et al. 2007). In Japan, Cdcontaminated rice caused Itai-itai disease near the Jinzu River basin in the middle of the 20th century. Even in recent years; rice is the major source of Cd intake of people in Japan (Watanabe et al. 2000). Cadmium is not an essential nutrient and at high concentration inhibits plant growth (Aery and Rana 2003). It has also been reported that even at relatively low concentrations, it alters plant metabolism (Van Assche and Clijsters 1990). The ability of aquatic macrophytes to uptake nutrients directly from water bodies and to assimilate them into their body is the greatest benefit of phytoremediation (Galal and Shehata 2014). Several aquatic plants effective in heavy metal uptake have been identified world over (Khankhane et al. 2014).

Assessment of genetic diversity among different biotypes of Physalis minima

Physalis minima is abundant weed species in India commonly found in non-cropped and crop areas during Kharif season. Fruits of this weed species has been reported for high nutritional and medicinal values. Despite, no study has been made, so far, for their molecular diversity analysis. In the present study, genetic diversity was assessed among a total of 17 biotypes of P. minima and 1 intermediate biotype (which exhibits floral characteristics of both P. minima and P. peruviana). Using 42 random amplified polymorphic DNA (RAPD) markers, a total of 224 bands were amplified among all studied biotypes. The band size of amplified fragments ranged from 100–2200 base pairs (bp). Out of 224 bands amplified, 52 were found to be monomorphic (23.2%) and remaining 172 were polymorphic (78.8%). Average number of bands per primer were 5.33 while average number of polymorphic bands per primer were 4.09. Cluster analysis grouped all biotypes into two groups. This is the first report on molecular diversity analysis among Physalis minima biotypes.