Amar Bahadur

By Amar Bahadur

Nematodes are the most plentiful animals on earth, commonly found in soil or water, including oceans. Some species of nematodes are parasites of plants and animals. Plant-parasitic nematodes are non-segmented microscopic, eel-like round worms, obligate parasite possess stylets that live in soil causing damage to plants by feeding on roots or plant tissues. Plant-parasitic nematodes feed on roots, either within the root, some nematodes feed leaves. These nematodes cause breakdown of resistance to fungal diseases in fruit crops. Plant-parasitic nematodes living host tissue to feed on to grow and reproduce. Nematode life cycle consists of an egg, 4 pre-adult stages (juveniles) and an adult, life cycle depending on the species and the temperature. Nematodes do not move long distances (less than 6 inches per year). They are usually transported over long distances on machinery, in nursery stock, transplants, seeds, or by animals, moves soil, water and wind. They acquire nutrients from plant tissues by needle-like feeding structure (stylet/spear). Nematodes can be classified into three groups depending on feed on the plants such as ectoparasitic nematodes are always remaining outside the plant root tissues. Migratory endoparasitic nematodes move through root tissues sedentary endoparasitic nematodes penetrate young roots at or near the growing tip. They steal nutrients, disrupt water and mineral transport, and provide excellent sites for secondary pathogens (fungus and bactria) to invade the roots and decay. Several nematode species that cause problems in fruit orchards that are major limiting factors in fruit crop production cause extensive root necrosis resulting in serious economic losses. The root-knot nematode (Meloidogyne spp.), burrowing nematode (Radopholus similis) and citrus nematode (Tylenchulus semipentrans) are the major nematode pests that infect fruit crops. Parasitic nematodes that can damage tree fruit roots. Many kinds of nematodes have been reported in and around the roots of various fruit crops, only few are cause serious damage, including Root-knot nematodes (Meloidogyne spp.), Lesion nematodes (Pratylenchus species), Ring nematodes (Mesocriconema spp) are cigar-shaped that are strictly ectoparasitic, Dagger nematodes (Xiphinema spp) are relatively large ectoparasites that feed near root tips, Sting nematodes (Belonolaimus species) are ectoparasitic, Citrus nematodes (Tylenchulus semipenetrans) are sedentary semi-endoparasites. Nematodes reduce yield without the production of any noticeable above ground symptoms. Typical above ground symptoms of nematode infections stunting, yellowing and wilting. Major nematodes associated in large number of vegetables crops in India such as root-knot nematodes (Meloidogyne spp.), cyst nematodes (Heterodera spp.), lesion nematodes (Pratylenchus sp.), reniform nematodes (Rotylenchulus sp.) lance nematodes (Hoplolaimus spp.), stem and bulb nematode (Ditylenchus spp.) etc. Root-knot nematodes are important pests of vegetables belonging to solanaceous (brinjal, tomato, chili), cucurbitaceous (biter ground, cucumber, pumpkin, bottle gourd) leguminous (cowpea, bean, pea), cruciferous cauliflower, cabbage, broccoli, brussels, sprout), okra and several other root and bulb crops (onion, garlic, lettuce, celery, carrot, radish). Four species (M. incognita, M. javanica, M. arenaria and M. hapla) are more than 95% of the root-knot nematode population worldwide distribution. Stem and Bulb nematode (Ditylenchus spp.) commonly attacks onion, garlic, potato, pea and carrot etc. The nematodes spread from one area to another mainly through infested planting materials, water drains from infested areas into irrigation system, soil that adheres to implements, tyres of motor vehicles and shoes of plantation workers. Management recommendation through bio-pesticides, cultural practices, enrichment of FYM, Neem cake and other organic amendments.

Part of the book: Nematodes

By Amar Bahadur and Pranab Dutta

Trichoderma species, a cosmopolitan fungi, present in all types of soil, manure, and decaying plant tissues that can degrade domestic waste relatively quickly without emitting bad odors. Trichoderma is recognized worldwide as potential fungal bio-control agents for the management of various foliar and soil-borne plant pathogens, highly compatible with sustainable agriculture and play major role as a component of integrated pest management. Bio-control agents are an antagonism and eco-friendly approach for managing plant diseases. Trichoderma as bioagent area effective not only against soil-borne plant pathogens, but also against nematodes without any adverse effect on beneficial microbes. Trichoderma is capable of growth promotions in crops. There are two major mass production methods of Trichoderma spp. viz., solid state fermentation and liquid state fermentation. In solid, fungus is grown on various cereal grains, agricultural wastes, and byproducts, and these products are used mainly for direct soil application to suppress the soil-borne inoculums. In a liquid state, Trichoderma is grown on media such as molasses and yeast in deep tanks and fermentation can be made into different formulations such as dusts, granules, pellets, wettable powders. As seed-treating agents or bio-priming agents, Trichoderma formulations can be successfully used against several soil-borne diseases caused by Pythium, Phytophthora, Rhizoctonia, Fusarium and Sclerotium, spp. in several crops.

Part of the book: Trichoderma

By Pranjal Kr. Kaman, Daisy Senapoty, Vithanala Shiva Sai Swaroop, Hiranya Kr. Deva Nath, Apurba Das, Pranab Dutta and Amar Bahadur

Among the many plant diseases, those brought on by soil-borne pathogens are the ones that result in significant losses. Rhizoctonia solani, one of many soil-borne pathogens, has been identified as a potential culprit for yield loss due to its broad host range. Prior to the development of extremely potent and selective fungicides, chemical treatment is not a practical option. However, the dangers associated with agrochemicals are reducing their use. Scientists are becoming more interested in biological management in this situation because it is an environmentally beneficial method. Biological control is the process through which one organism controls another. Trichoderma has become one of the most important biocontrol agents currently available due to its extensive antagonistic pathways. There are 89 species in this genus, and numerous strains have been discovered to be powerful biocontrol agents for plant diseases. The species T. viride, T. hamantum, T. koningii, and others make up the majority of the Trichoderma biocontrol agents. Direct and indirect antagonistic mechanisms are the two categories. Mycoparasitism, antibiosis, and pathogen enzyme inactivation are examples of direct methods. Indirect mechanisms include competition for nutrients and space, the activation of plant defensive systems (such as induced systemic resistance), and others. Their antagonistic characteristics are affected by a number of variables, including pH and temperature.

Part of the book: Challenges in Plant Disease Detection and Recent Advancements