Alok Shukla

Comparative physiological response of wheat genotypes under terminal heat stress

Wheat (Triticum aestivum L.), a staple food crop, is of great commercial importance. Its production is restricted due to multiple environmental stresses. There are indications that the wheat production is consistently limited by terminal heat stress. Previous studies revealed a varied response of different wheat genotypes under heat stress conditions. Here, comparative physiological changes in wheat genotypes viz., DBW-140, Raj-3765, PBW-574, K-0-307 and HS-240 were evaluated under timely and late sown conditions in rabi season. We observed that heat stress dramatically affects chlorophyll content and leaf area index (LAI) in sensitive genotypes whereas proline and malondialdehyde (MDA) content were higher in tolerant genotypes under late sown conditions. Further, the heat susceptibility index (HIS) for 1,000-grain weight, grain weight and grain yield of wheat genotypes viz., HS 240 and K-0-307 was highest as compared with DBW 140, Raj 3765 and PBW 574 genotypes. This finding suggests that wheat genotypes are found to differ in their ability to respond to heat, thereby tolerance, which could be useful as genetic stock to develop wheat tolerant varieties in breeding programs.

SPATIAL DISTRIBUTION AND ACCUMULATION OF CALCIUM IN DIFFERENT TISSUES, DEVELOPING SPIKES AND SEEDS OF FINGER MILLET GENOTYPES

□ Total calcium (Ca) content in different tissues, developing spikes (S1, S2, S3 and S4 stages), and distribution sites in seeds of five finger millet genotypes, which were differed in total calcium content, were analyzed. Atomic absorption spectroscopy (AAS) revealed stage-dependent quantitative changes in calcium accumulation from low to high during different stages of developing spikes and also in different tissues and grains. Results of scanning electron microscopic (SEM) energy dispersive X-ray (EDX) analysis showed differential distributions of the calcium in seed components viz. seed coat, aleurone layer and endosperm. Highest calcium content was observed in aleurone layer followed by seed coat while lowest calcium was found in endosperm of all genotypes. Major differences were found amongst genotypes with regard to the calcium distribution in seed components. The differential regulation of transport machinery might be responsible for differential calcium ion delivery and spatial distribution in the seed. A clear understanding of differential accumulation, spatial distribution and the variation of calcium within finger millet genotypes/seeds could be exploited for breeding for their bio-fortification and development of calcium rich functional foods.

First evidence of ethylene production by Fusarium mangiferae associated with mango malformation.

Malformation is arguably the most crucial disease of mango (Mangifera indica L.) at present. It is receiving great attention not only because of its widespread and destructive nature but also because of its etiology and control is not absolutely understood. Recently, Fusarium mangiferae is found to be associated with mango malformation disease. There are indications that stress ethylene production could be involved in the disease. Here we have shown the first direct evidence of production of ethylene in pure culture of F. mangiferae obtained from mango. The study also revealed that all the isolates dissected from mango acquire morphological features of F. mangiferae showing most similarity to the features of species with accepted standard features. The isolates of F. mangiferae from mango were observed to produce ethylene in significant amounts, ranging from 9.28–13.66 n mol/g dry wt/day. The findings presented here suggest that F. mangiferae could contribute to the malformation of mango by producing ethylene and probably stimulating stress ethylene production in malformed tissue of mango. Ethylene might be produced through 2-oxoglutarate-dependent oxygenase-type ethylene-forming-enzyme (EFE) pathway in Fusarium sp, which needs to be investigated.

Fused lobed anther and hooked stigma affect pollination, fertilization and fruit set in mango: a scanning electron microscopy study.

Mango malformation is the most threaten disease that limits mango production, worldwide. For a long time, due to its complex nature, the cause and causal agents were strongly disputed. Diverse Fusaria, including Fusarium mangiferae, are known to be associated with the disease. There are indications that augmented level of endogenous ethylene in response to various abiotic and biotic stresses alters the morphology of reproductive organs. Here, scanning electron microscopy (SEM) of healthy and malformed reproductive organs of mango cv. Baramasi was performed to compare the functional morphology. The SEM study revealed that anthers of hermaphrodite healthy flowers were bilobed with large number of turgid pollen grains whereas malformed flowers showed fused lobed anthers with scanty deformed pollen grains. Furthermore, the stigma of healthy flowers exhibited a broad landing pad as compared to malformed stigma which showed hooked and pointed tip. All these impaired morphology of male and female reproductive organs lead to failure of sexual reproduction. This is the first evidence to show fused lobed anther with impaired pollen grains and hooked stigma with poor stigmatic receptivity are mainly responsible for restricting the pollen germination and pollen tube growth. Here we suggest that abnormal development of anthers and pistils is due to endogenously produced stress ethylene. Further, added load of cyanide, a byproduct of ethylene biosynthesis, may also contribute to the development of necrosis which lead to desiccation of anther and pistil during hypersensitive response of plants.

Hypoxia induced non-apoptotic cellular changes during aerenchyma formation in rice (Oryza sativa L.) roots

The stress of low oxygen concentrations in a waterlogged environment is minimized in some plants that produce aerenchyma, a tissue characterized by prominent intercellular spaces. It is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD) and facilitates gas diffusion between root and the aerial environment. The objective of this study was to characterize the cellular changes take place during aerenchyma formation in root of rice that accompany PCD. Scanning electron microscopy and transmission electron microscopy were used for cellular analysis of roots. Aerenchyma development was observed in both aerobic and flooded conditions. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. There was an initial collapse which started at a specific position in the mid cortex, indicating loss of turgor, and the cytoplasm became more electron dense. These cells were distinct in shape from those located towards the periphery. Mitochondria and endoplasmic reticulum appeared normal at this early stage though the tonoplast lost its integrity. Subsequently it underwent further degeneration while the plasmalemma retracted from the cell wall followed by death of neighboring cells followed a radial path. However, pycnosis of the nucleus, blebbing of plasma membrane and production of apoptotic bodies were not found which in turn indicated nonapoptotic PCD during aerenchyma formation in rice.

In vitro selection and field responses of somaclonal variant plants of rice cv PR113 for drought tolerance.

Drought is the major environmental stress that limits rice productivity worldwide. In vitro somaclonal variation using different selection agents has been used for crop improvement. Here, rice plants of cv PR113 were selected in vitro on 30, 50 and 70 g L-1 polyethylene glycol 6,000 (PEG). Callus growth, proliferation, calli volume (first and second culture) and plantlet regeneration (third culture) were found to be decreased upto a certain level to acquire tolerance to PEG-induced drought. From the field data, 30 g L-1 PEG lines showed higher vegetative growth (plant height, tiller number, leaf number, shoot weight and root growth) as compared with 50 g L-1 PEG selected somaclone lines under limited irrigation. The yield parameters-panicle length, panicle weight, grains per panicle, 1,000-grain weight, grain yield per plant, harvest index and grain straw ratio were also higher in 30 g L-1 PEG lines as compared with 50 g L-1 PEG lines. The results, therefore indicate that 30 g L-1 PEG selected somaclone lines were more suited than 50 g L-1 PEG selected somaclone lines under stress as compared with WT. The finding suggests that rice cv PR113 somaclones generated on PEG are found to be drought tolerant under field condition with better yield.

In vitro: Response of plant growth regulators and antimalformins on conidia germination of Fusarium mangiferae and incidence of mango malformation

Mango malformation is the most important and threatening disease of recent times, primarily because of persistent lacuna in complete understanding of its nature. Diverse Fusarium spp, including F. mangiferae, were found to be associated with the disease. Here, F. mangiferae from mango cv Dashehri was morphologically characterized. Typically, oval-shaped microconidia without septum and crescent-shaped macroconidia with 3-septate were more often observed, whereas not a single chlamydospore was detected. The length and width of micro- and macro-conidia were 7.5, 55, 3.2, and 3.5, respectively. The plant growth regulators such as NAA, GA3, BAP and ethrel were found to induce in vitro germination of conidia of F. mangiferae after 12 h. In contrast, antimalformin silver nitrate (AgNO3) inhibits conidial germination in vitro and none of conidia was germinated beyond 500 ppm, however antimalformin glutathione was highly effective in stimulating conidial germination of F. mangiferae in vitro at > 1000 ppm after 24 h. We observed that the response of F. mangiferae to germinate the conidia in vitro under influence of plant growth regulators and antimalformins is not coincided with earlier findings of reduced disease incidence by exogenous application of these compounds. The present findings do not authenticate the involvement of F. mangiferae in the disease, however hormonal imbalance, most probably ethylene, might be responsible for deformed functional morphology of panicle. Further, a signal transduction mechanism of stress-stimulated ethylene imbalance causing physio-morphological changes in reproductive organs of mango flower and thereby failure of fertilization and fruit set, which needs to be investigated.

Ocimum sanctum leaf extract induces drought stress tolerance in rice

ABSTRACT Ocimum leaves are highly enriched in antioxidant components. Thus, its leaf extract, if applied in plants, is believed to efficiently scavenge ROS, thereby preventing oxidative damage under drought stress. Thus, the present study was performed in kharif 2013 and rabi 2014 season to evaluate the effect of aqueous leaf extract of Ocimum sanctum against drought stress in 2 rice genotype under glass house conditions. Here we show that various morpho- physiological (chlorophyll fluorescence, leaf rolling score, leaf tip burn, number of senesced leaves and total dry matter) and biochemical parameters (proline, malondialdehyde and superoxide dismutase content) were amended by Ocimum treatment in both the seasons. Application of Ocimum extract increased expression of dehydrin genes, while reducing expression of aquaporin genes in drought stressed rice plant. Thus, application of Ocimum leaf extract under drought stress can be suggested as a promising strategy to mitigate drought stress in economical, accessible and ecofriendly manner.

Physiological and Molecular Signalling Involved in Disease Management Through Trichoderma: An Effective Biocontrol Paradigm

Biological control or biocontrol is the use of specific microorganisms that interfere with plant pathogens and pests, and sustain organisms useful to human. It is a nature-friendly, ecological approach to overcome the problems caused by standard chemical methods of plant protection which drastically affect the environment as well as consumer. Trichoderma, a member of ascomycota was first described by Pearson (1794) and its beneficial activities as a biocontrol agent (BCA) has been known since 1930 and since then there have been extensive efforts to use them for plant disease control. Trichoderma species play an important role in controlling fungal plant pathogens, especially the soil borne pathogens, by competing for nutrients and space, producing cell wall degrading enzymes (CWDE) or through mycoparasitism (the direct attack of one fungus on another). They are not only fungal parasites but can also produce antibiotics. These processes such as the production of antifungal metabolites and hydrolytic enzymes are mediated by G-proteins and mitogen activated protein (MAP) kinases. In addition, certain strains can release a variety of compounds that induce systemic and localized resistance response in host plant, mediated by alteration in plant gene expression. This Trichoderma mediated induced systemic resistance (ISR) is regulated by various plant hormones like jasmonic acid (JA), ethylene (ET), abscisic acid (ABA), gibberellic acid (GA) and salicylic acid (SA). Among them, JA, ET and SA are the central players in defence signalling. Thus, Trichoderma encompasses different mechanisms to achieve effective disease control against a variety of plant pathogens by means of various signalling components and pathways. Another approach for improving resistance against pathogens is to express genes of Trichoderma in plants, through genetic manipulation. Recently, there has been increasing attempt in development of transgenic plants using genes from Trichoderma spp. which are responsible for biocontrol activity. Besides protecting against biotic stress, root-colonization with Trichoderma also enhances growth and productivity of host plant by improving nutrient and water uptake. Due to the effective control of plant pathogens/diseases and improvement of plant growth, several Trichoderma bioproducts are now available commercially. However, much work still needs to be done to explore its full potential for improving plant growth and managing plant diseases.

Mango (Mangifera indica L.) malformation: a malady of stress ethylene origin

Mango malformation is a major constrain in mango production worldwide causing heavy economic losses depending on cultivar type and susceptibility. The malady has variously been ascribed to be acarological, viral, fungal and physiological in nature. Here, we discuss the ethylene origin nature of malady. There are indications that most of the symptoms of mango malformation resemble with those of caused by ethylene effects. Multiple evidence reports of putative causal agents including Fusarium mangiferae to augment the endogenous pool of ‘stress ethylene’ are well documented. Therefore, over load of ‘stress ethylene’ impairs morphology malformed tissue and cyanide derived from ethylene biosynthesis causes necrosis and death of malformed cells. This review covers various factors eliciting ‘stress ethylene’ formation, role of ethylene in development of malady and regulation of ethylene action to reduce malformation in mango.