Screening and Biochemical Characterization of Wheat Cultivars Resistance to Magnaporthe oryzae pv Triticum (MoT)

Global food security is seriously threatened due to increased frequency and occurrence of fungal diseases. One example is wheat blast caused by Magnaporthe oryzae is a fungal diseases of rice, wheat, and other grasses, that can destroy the whole food production to sustain millions of people. Wheat blast was first detected in february 2016 with a serious outbreak in Asia. Assessment of the available germplasms to stress tolerant/resistant is one of the best options for developing stress tolerant crop varieties. In this study, a total of sixteen wheat cultivars were collected and test their disease severity to blast pathogen Magnaporthe oryzae pv. Triticum (MoT). Among the varieties, BARI Gom 33 exhibited partially resistance against blast pathogen, whereas all other genotypes become susceptible to MoT. Different yield and yield contributing characters of both resistant and susceptible cultivars were also evaluated and found no significant differences among them. To understand the underlying mechanism of resistance in BARI Gom 33, antioxidant enzyme activity, concentration of reactive oxygen species and cellular damage after fungal infection were also evaluated and found that activities of ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD) were higher in BARI Gom 33 than BARI Gom 25 and BARI Gom 31. The hydrogen peroxide (H2O2) and malondealdehyde (MDA) content in BARI Gom 33 was low compare to BARI Gom 25 and BARI Gom 31, which may due to greater increase of the APX, CAT and POD in resistant genotypes. Thus, it may suggest that a more efficient antioxidative defense system in BARI Gom 33 during the infection process of M. oryzae restricts the cell damage caused by the fungus. The identified genotypes can either be used directly in the blast prone area or as a source of resistance to further development of blast resistance high yielding wheat variety

Comparative study between biological and chemical agents for control sheath blight disease of rice

Biological control measures are indispensable to sustain global food security, due to it being economically profitable and environmentally sound. A comparative study was conducted to know the effectiveness of biological control measures compared with contact fungicide. Trichoderma spp. based bio fungicides Bioquick and Biospark were applied as preventive measures and contact fungicide as a curative measure for controlling sheath blight disease in rice varieties BR 71 and IR 24. Biospark and Bioquick were applied before disease development while, contact fungicide was used after the initiation of sheath blight disease. At the early stage of disease development, the effect of Bioquick, Biospark, and fungicide in terms of reducing percent relative lesion height and percent tiller infection are comparable. At 14 DAI and 18 DAI, contact fungicide performed best among the three control measures based on the two parameters. The genotypes of the rice accessions used in the study also appeared to be a factor in disease development, as evidenced by higher horizontal and vertical disease severity in BR71 than in IR24. Between comparison of Bioquick and Biospark in terms of reducing percent relative lesion height, percent tiller infection, and percent disease control, appeared to be higher in Biospark in both varieties. From this study, we can conclude that farmers can use Biospark as a biofungicide to get maximum benefit considering rice yield and ecology. However, its efficacy is slightly lower than chemical fungicides for controlling sheath blight disease of rice

Experimental study of granular material behaviour and microstructure in a photoelastic disk assembly

Bibliography: p. 202-208In this thesis, both micro and macro mechanical studies were conducted on an ide­alized granular assembly under different kinematic and static conditions. The ex­perimental approach involved the use of an analogue granular material composed of an assembly of photoelastic disks in order to permit the visualization of force transmission networks through fringe analysis. A comprehensive 2-D biaxial testing apparatus was developed along with four high precision actuators that can load a specimen consisting of an assembly of photoelastic disks in either stress or strain control mode. Two different disk cross-sections were used: namely pentagonal and circular, while between 200 and 400 disks were used to constitute a specimen of approximately 100 mm x 100 mm in size. A series of tests was conducted along proportional strain paths so that the spec­imen responses in the complete forced compression and dilation regimes could be explored. The specimens were sheared under different static and kinematic condi­tions with a special focus on the dilation regime, given its importance in granular mechanics. Initially, tests were conducted on isotropically consolidated specimens of pentagonal disks to observe typical force-displacement responses as well as force re­sponse paths. Microstructural features such as force transmission and its evolution were studied through image analysis and photoelasticity. In particular, a micro-mechanical description of the deformational processes that occur during the 'static liquefaction' of a specimen under forced dilation was established. Furthermore, strain probing tests were conducted on a specimen at the same amount of preshearing, but with different stress histories. It was found that stress history effects tend to fade away with increasing levels of straining. The effect of intergranular friction was also investigated, and it was found that it only plays a role towards providing the stability of fabric, once the latter is formed. In order to study the constitutive nature of the granular assembly, force response envelopes were determined at different probing strain levels. Both the shape and orientation of the force response envelopes elucidated the effect of pre shearing stress history as well as probing strain level on the material behaviour. Furthermore, a series of force probing tests was conducted on the same above-mentioned specimens so that the strain response envelopes could be determined at different probing force levels. Both the force and strain response envelopes gave identical behaviours in terms of the material response as a function of fabric and its evolution. One of the important findings that emerged from the force probing tests is that a plastic flow rule was established, and hence confirmed the applicability of the theory of plasticity in the modelling of granular materials. A material stability analysis was also performed on the proportional strain path test results by using Hill's criterion for the sign of the second order work. The threshold dilation rates at which instability occurs were determined for specimens subjected to different initial confinements. In some cases, material softening was ob­served before material instability had occurred. The amount of dilation and dilation rates that the material can sustain before instability was investigated for different initial confinements. The strain probing tests were further performed with circular disks in order to study the effect of kinematic constraints imposed by disk cross section and diameter on material behaviour under forced dilation. For the same initial confinement and strain path, significant differences were observed in the specimen strength as the disk cross section and diameter were changed. The microscopic force transmission and its evolution in the specimen were presented from the photoelastic observation of pictures taken at different characteristic points of loading history in order to explain the salient failure mechanisms

Interactions between the nematodes Ditylenchus angustus and Aphelenchoides besseyi on rice: population dynamics and grain yield reductions

Experiments were conducted in pots and an irrigated rice (Oryza sativa) field to determine the impact of mixed or single nematode inoculations with Aphelenchoides besseyi and Ditylenchus angustus on nematode population dynamics and yield attributes of rice cv. BR3. The reproduction rates were greater in a single nematode species inoculated with either A. besseyi or D. angustus compared to their mixed inoculation. This was probably due to competition between the two nematode species. Greater incidences of white-tip and ufra diseases were observed with single nematode species inoculations compared to mixed species inoculations. Total yield losses ranged from 24 to 47% from mixed inoculations (different ratios) of D. angustus and A. besseyi, compared to 62% from inoculation with D. angustus and 16% from A. besseyi. Single species inoculations (with either D. angustus or A. besseyi) gave greater disease incidence and greater yield reductions than mixed inoculations with both nematodes