Mukesh K. Meghvansi

Foliar Spray with Vermiwash Modifies the Arbuscular Mycorrhizal Dependency and Nutrient Stoichiometry of Bhut Jolokia (Capsicum assamicum)

Vermiwash (VW), a liquid extract obtained from vermicomposting beds, is used as an organic fertilizer for crop plants. The current study investigated the effect of a vermiwash foliar spray on the response of bhut jolokia (Capsicum assamicum) exposed to two different arbuscular mycorrhizal fungi (AMF: Rhizophagus irregularis, RI and G. mosseae, GM) in acidic soil under naturally ventilated greenhouse conditions. The VW spray significantly influenced the growth of plants receiving the dual treatment of AMF+VW. Plant growth was more prominent in the GM+VW treatment group than that in the RI+VW treatment group. The plant-AMF interactions in relation to growth and nutrient requirements were also significantly influenced by the application of VW. Interestingly, the VW treatment appeared to contribute more N to plants when compared to that under the AMF treatment, which led to changes in the C:N:P stoichiometry in plant shoots. Furthermore, the increased potassium dependency, as observed in the case of the dual treatments, suggests the significance of such treatments for improving crop conditions under salt stress. Overall, our study shows that the VW foliar spray modifies the response of a crop to inoculations of different AMF with regard to growth and nutrient utilization, which has implications for the selection of an efficient combination of nutrient source for improving crop growth.

Organic amendments and soil suppressiveness in plant disease management

Part I Soil suppressiveness: paradigms and mechanisms.- Part II Concepts in plant disease management involving microbial soil suppressiveness.- Part III Concepts in plant disease management involving organic amendments.- Part IV Integrative approaches in plant disease management.

Elemental stoichiometry indicates predominant influence of potassium and phosphorus limitation on arbuscular mycorrhizal symbiosis in acidic soil at high altitude.

The functioning of high-altitude agro-ecosystems is constrained by the harsh environmental conditions, such as low temperatures, acidic soil, and low nutrient supply. It is therefore imperative to investigate the site-specific ecological stoichiometry with respect to AM symbiosis in order to maximize the arbuscular mycorrhizal (AM) benefits for the plants in such ecosystems. Here, we assess the elemental stoichiometry of four Capsicum genotypes grown on acidic soil at high altitude in Arunachal Pradesh, India. Further, we try to identify the predominant resource limitations influencing the symbioses of different Capsicum genotypes with the AM fungi. Foliar and soil elemental stoichiometric relations of Capsicum genotypes were evaluated with arbuscular mycorrhizal (AM) colonization and occurrence under field conditions. AM fungal diversity in rhizosphere, was estimated through PCR-DGGE profiling. Results demonstrated that the symbiotic interaction of various Capsicum genotypes with the AM fungi in acidic soil was not prominent in the study site as evident from the low range of root colonization (21-43.67%). In addition, despite the rich availability of carbon in plant leaves as well as in soil, the carbon-for-phosphorus trade between AMF and plants appeared to be limited. Our results provide strong evidences of predominant influence of the potassium-limitation, in addition to phosphorus-limitation, on AM symbiosis with Capsicum in acidic soil at high altitude. We also conclude that the potassium should be considered in addition to carbon, nitrogen, and phosphorus in further studies investigating the stoichiometric relationships with the AMF symbioses in high altitude agro-ecosystems.

Vegetative and Yield Attributes of Okra and Naga Chilli as Affected by Foliar Sprays of Vermiwash on Acidic Soil

In view of concerns raised about economic and ecological consequences of agricultural chemicals, organic amendments, such as vermiwash, have been considered appropriate strategies for crop improvement. However, research work evaluating the efficacy of foliar sprays of vermiwash in vegetable crops on acidic soils is quite limited. The present investigation, therefore, was carried out to evaluate the effect of different concentrations of vermiwash (VW) on okra (Abelmoschus esculentus L.) under field conditions on acidic soil. We also evaluated the response of Naga chilli (Capsicum assamicum) to foliar spray of 20% concentration of vermiwash. Results revealed that the application of VW significantly improved the vegetative and yield attributes of both the test crops. In okra, 20% VW exhibited the largest increase in marketable weight among all the treatments. The plants of Naga chilli receiving foliar spray of 20% VW registered a 27.47% increase in shoot height and a 11.93% increase in chlorophyll content (SPAD) as compared with control. In regards to yield attributes of the Naga chilli, foliar spray of 20% VW resulted in a 23.07 % increase (significant at P = 0.05) in number of seeds per fruit and a 43.47% increase (significant at P = 0.05) in average fruit weight in comparison with control. We suggest that foliar spray of 20% concentration of vermiwash could considerably improve the growth and yield of okra and Naga chilli on acidic soil.

Assessing the Role of Earthworms in Biocontrol of Soil-Borne Plant Fungal Diseases

Earthworms are integral part of belowground communities, which are actively involved in redesigning the structure of the soil environment. In recent decades, several researches have shown the potential of application of vermicompost in controlling soil-borne plant fungal diseases. However, complexity of earthworm interactions with various abiotic and biotic components of the soil has posed a real challenge before the scientists unearthing the underlying mechanism of disease suppression. This chapter focuses on the earthworm-mediated factors contributing to soil-borne fungal disease suppression. Very briefly, we have highlighted the limitations of prevailing biocontrol methods of soil-borne fungal pathogens. Key mechanisms involved in earthworm-mediated soil-borne fungal disease suppression, such as influence on soil microbial communities, enzymatic activity, production of antifungal compounds, soil physicochemical properties, and systemic resistance in plants, are explored. Further, we have attempted to identify core areas and give future directions where concerted research efforts are still required.

Combining Application of Vermiwash and Arbuscular Mycorrhizal Fungi for Effective Plant Disease Suppression

Extensive research on several individual approaches for the suppression of plant diseases showed immediate satisfactory results. Nevertheless, the question of their sustainable effects has always been asked, but never answered convincingly. This raises several analytical and empirical challenges that remain unresolved. In particular, mimicking the multiple drug therapy in clinical science, multiple approaches for plant disease suppression have shown their potential for the mentioned sustainability issue. In this chapter, we highlight the individual capabilities and underlying mechanisms of vermiwash/compost and arbuscular mycorrhizal (AM) fungi, and their associated pragmatic constraints in achieving effective plant disease suppression. Despite the several reports, of being an eco-friendly approach and on enhancement of the plant’s growth, their combined efforts were given less importance. We made an attempt to illustrate as to how these approaches allow plants to adopt various strategies to counter the attack of phytopathogens. Also, why there is still apprehension for acceptance of these approaches? We concluded that these approaches have limitation but no drawbacks were found. These limitations involve various large-scale trials on different climates and locations, that are needed to enhance their acceptability. Further, studies on ecological, physiological, and molecular pertaining to plant defense are warranted to better understand the underlying mechanisms for plant disease suppression. It is, therefore, imperative for the associated scientific community to use the combined approach of vermiwash/compost and AM fungi in future research to better describe their capability and more precise role in plant disease suppression.

Identification of a new species of Cercospora causing leaf spot disease in Capsicum assamicum in northeastern India.

Northeastern India is one of the most important biodiversity hotspots in the world. However, hot and humid climatic conditions of the region favor growth and development of foliar fungal phytopathogens such as cercosporoid fungi. The genus Cercospora is one of the largest genera of hyphomycetes. Species of Cercospora are known to cause leaf spot disease in several cultivated and non-cultivated plants leading to considerable losses. In this study, we describe a new species of Cercospora which was isolated from the leaves of Naga chilli (Capsicum assamicum Purkayastha & Singh) grown in northeastern India. Comparison of the detailed morphological characteristics along with the DNA sequences for four gene regions, namely actin, calmodulin, histone H3 and translation elongation factor-1α of this isolate, was made with those of some previously reported Cercospora species infecting Capsicum and other similar species of Cercospora from other hosts. The results suggested that our isolate represents an undescribed taxon and warrants the establishment of a new species, Cercospora tezpurensis sp. nov.