Preface Ever growing population, the increased awareness for quality food, dwindling land resource, environmental pollution of mother planet, resistant to chemicals in pathogen population are some of the grave problems faced by the mankind. Need of food for billions in future is a challenge to agricultural professionals including plant pathologists. Further exploitation of hybrid vigor will be a difficult venture in many crops. In this connection, plant protection specialists have to play a vital role in protecting plants and avoiding food losses.  Most obvious diseases such as foliar diseases were studied first unlike their counterparts; soil borne plant diseases which are generally less understood. The soil is much more complex chemically, biologically and physically than the atmosphere above the ground. There exist many intricacies and complexities in rhizosphere, fungistasis, microbial interaction and bio-control processes to a greater extent in soil borne plant pathogens compared to aerial/foliar pathogens. Soil borne plant diseases will continue to be a hazard both in field and horticultural crops, which have been documented through out the history of mankind. Monoculture has become the feature of modern agriculture. Crop plants tend to be produced commercially where they are best adopted and are planted repeatedly in such sites. Crops such as banana, tomato, cotton, tobacco, cucurbits, pigeonpea, chickpea and wheat have suffered the onslaught of soil borne plant pathogens. If a soil borne pathogen is present and favored by that particular environment, the soil infestation increases rapidly. In the absence of proper management much of the best suited land for the crop is lost.

INTRODUCTION Modern agriculture relies more on monoculture, which is highly energy intensive and has a narrow genetic base. This has disturbed the normal ecosystem and sometime results in disease epidemics. The problem becomes much more serious in case of soil borne pathogens, as soil medium is a highly complex living system and is also the habitat of many micro organisms including the pathogens whose activities are influenced by interaction in it. Many serious plant diseases are associated with soil-borne plant pathogens, which cause root rot, crown rot, damping off, blights, fruit decay and wilts in field and horticultural crops. Soil borne plant pathogens, which are most tricky and challenging ones, cause sustainable economic loss. Many important fungal pathogens reside in the soil and infect roots of crops often causing significant yield losses. Soil-borne diseases result from a reduction in biodiversity of soil organisms.

INTRODUCTION Rhizoctonia solani Kuhn (teleomorph: Thanatephorus cucumeris (Frank) Donk is cosmopolitan in soils. It is a destructive plant pathogen with an almost unlimited host range. The fungus inhabits in soils and causes damping-off of seedlings, root, crown and stem rots, and occasionally foliar blight (Baker, 1970). R. solani is an important symbiont with the saprophytic seedling stage (protocorm) of many orchids (Warcup, 1985). It aggressively colonizes organic matter and is one of the fastest growing fungi. According to available information, the isolates of R. solani possess the following-characteristics (Plate 2.1).

INTRODUCTION All plant species grown on this universe are attacked by insect-pests and diseases, resulting huge yield losses in agriculturally important species. Among diseases, extensive yield losses occurred due to soil borne fungal plant pathogens. Soil borne fungal pathogens infect roots or stem bases, their dispersal and survival stages are primarily confined to the soil. Although many soil pathogens may also produce air or water dispersed spores which results in long distance dispersal. Soil borne fungal diseases are specifically those diseases where the soil borne fungi has the capacity to survive in soil for long periods in the absence of their hosts, or survive in the soil outside of seed or host residues, but infection and symptom expression are confined to the subterranean organs of the plant. Soil borne fungi may be divided into two classes: i) The  soil inhabiting fungus which is characterized by its ability to survive indefinitely as saprophyte (e.g. Rhizoctonia, Sclerotium) and ii) The soil invading or root inhabiting fungus which is characterized by an expanding parasitic phase and a declining saprophytic phase after  the hosts death.

INTRODUCTION   The form genus Sclerotium was described by Saccardo (Saccardo, 1913) to include fungi that produce sclerotia and had sterile mycelia. Several fungi were inc1uded in this genus, and all were characterized by production of small, dark brown or black spherical sclerotia that were internally differentiated into a rind, cortex and medulla. Several plant pathogenic fungi with this sclerotial type and with no known sexual or conidial state were placed in the genus Sclerotium. However, as the teleomorphic states were discovered, affinities to the Basidiomycotina (Punja, 1988) or Ascomycotina (Krause and Webster, 1972) were established for some members of the form genus.

INTRODUCTION Biological control involves the suppression of pests/organisms with other organisms.  It is an eco-friendly method for management of plant pathogens which can be done exploiting the fungi (Ampelomyces, Trichoderma, Coniothyrium, Candida etc.) or bacteria (Agrobacterium, Bacillus, Pseudomonas and Streptomyces) from rhizosphere,  as well as phylloplane and endophytes (Jayaraman and Verma, 2002). The rhizosphere microfloras are predominantly composed of gram negative pseudomonads.  The fluorescent pseudomonads constitute a large proportion of the rhizosphere microflora presumably due to their nutritional variability being able to use a large number of organic substances (Stolp and Gadkari, 1981). However earlier workers used fluorescent pseudomonads extensively they now prefer Bacillus sp. due to their spore forming ability and heat tolerance which make its formulation easier.

INTRODUCTION Throughout the history of agriculture, humans have struggled to reduce the adverse effects of plant disease on their crops. Early agriculturalists realized the benefits of cultural practices such as crop rotation and the use of organic soil amendments in promoting plant productivity. It is now well established that many of these effects are achieved by promoting the natural microbiological processes that keep plant disease in check. Cultural practices were mainstays of traditional agricultural systems and still provide the primary approaches for management of many soilborne diseases today. For example, disease suppressive soils, into which pathogen(s) can be introduced without causing the expected levels of disease severity, can result from alterations in cropping patterns or other cultural practices. Recently,

INTRODUCTION Wheat has served as a source of staple food to the mankind since times immemorial. The production of wheat in India got a fillip after green revolution. Wheat production in India has increased by over ten times in the past five decades and India has become the second largest wheat producer in the world. Today, wheat plays an increasingly important role in the management of India’s food economy (Gandhi, et al., 2001). Wheat, primarily the winter cereal of Indo-Gangetic plain, is a major contributor to the agricultural economy of India, occupying nearly 25.9 m ha area with 71.8-mt production (Anon., 2003). India is also second most populous country with one billion people. Demographers indicate that by 2012 India’s population will reach 1.2 billion. With this ever increasing population, there is also an increase in the demand for food grains. Depending on the rate and nature of economic growth and given the population growth rate about 4 or more per cent, annual rate of growth in the demand for wheat is likely to increase in the near future.

INTRODUCTION In India, temperate fruits are grown successfully at locations above 3000 feet mean sea level in hilly areas of Himachal Pradesh, Jammu and Kashmir, Uttranchal, Sikkim, parts of North Eastern states like Assam, Arunachal Pradesh, Nagaland, Meghalaya etc. Mount Abu hills of Rajsthan and Nilgiris of Tamil Nadu also provide suitable agro-climatic conditions for growing some temperate fruits. Apart from apple; pear, peach, plum, apricot, cherry, almond and walnut are major temperate fruits being grown over 3.38 lakh hectares of area and play pivotal role in the economy of hilly farmers whose land is not otherwise considered suitable for traditional agriculture. They contribute about 11.5 percent of total area under fruits in the country, yet production is only 5 percent of the total. Incidence of many fungal, bacterial and viral diseases in these fruit crops is a major impediment in their successful cultivation and soil borne pathogens are of foremost importance and are responsible for premature death of the trees in the orchards. Amongst these, white root rot, collar rot, seedling blight, crown gall, hairy root are the major constraints which can cause as high as 40 percent damage in certain situations (Sharma and Sharma, 2001). Threat from the replant problem is causing concern due to its negative effect on the establishment of replanted sites due to soil sickness.

INTRODUCTION ‘Wilting’ is a broad terminology used by Plant Protection Scientists.  Any disturbance or damage to the normal physiology of the plant leads to ‘wilting’ of plants.  Wilting in cotton is attributed to many factors and it is necessary to single out the actual cause for wilting before suggesting any remedial measure (Kannan, 1991). Wilting in cotton could be due to any one or more factors as indicated below:

INTRODUCTION The fine feeder roots of many vascular plants are invaded by specific nonpathogenic fungi forming a distinct morphological unit known as mycorrhiza (In Greek, Mykes mean mushroom or fungus, rhiza mean root). Physiologically mycorrhiza represents a case of symbiosis. The term mycorrhizae were coined by a German botanist Albert Bernard Frank in 1885 which literally mean “fungus-roots”.  Mycorrhizal fungi form a symbiotic association with agricultural and horticultural crops in addition to certain tropical tree species. Mycorrhizal fungi are broadly classified in to two groups: 1) Ectomycorrhizae   2) Endomycorrhizae.

INTRODUCTION Burgeoning human population and its elevated living standard have greatly demanded more agricultural production. But unfortunately agricultural crops suffer deadly due to many biotic and abiotic stresses. Of biotic stresses, phytonematodes, the hidden enemies of crops are real threat to successful and profitable cultivation of agricultural crops (Plate. 11.1). These, endoparasitic nematodes, Meloidogyne spp. and Heterodera spp., are mainly dreadful causing wrecking havoc to agricultural scenario. Chemical control of these, tiny parasites created residue, resistance, resurgence, hazardous and pollution problems to the growers as well as soil and atmospheric environment. To overcome these hazards, efforts are being made to go for non-chemicals means of nematodes management strategies in crops. Hence, a research work carried out on management of these endoparasitic nemas particularly Meloidogyne spp. and Heterodera spp., through non-chemical methods is reviewed in subsequent status.

INTRODUCTION In arid and semi-arid regions of India, besides weather aberrations, diseases caused by certain soil-borne pathogens are responsible for low productivity of agricultural crops. In addition to losses caused in annual crops, occurrence of these diseases in forestry takes away a major share. Because of the requirement for free water, diseases of aerial plant parts are much less common than those involving roots when plants are grown in dry regions where humidities are low and rains are infrequent and/or of short durations. Under these conditions, pathogens like Macrophomina phaseolina, Ganoderma lucidum, Cylindrocarpon lichenicola, Neocosmospora vasinfectum, Sclrotium rolfii and species of Fusarium (F. oxysporum, F. solani, F. equiseti, etc.) cause root rots and wilts in many commercially valuable and perennial plants. Certain agro-climatic factors are attributed for the development of few specific diseases caused by soil-borne plant pathogens. Low organic matter, small microbial population coupled with poor moisture retention capacity of soil favour survival and multiplication of soil-borne pathogens (Fig. 12.1).

INTRODUCTION Fungi naturally present in soil and rhizosphere of various crops serve as potential biological control agents of various plant pathogens. Species of fungi occurring in the genus Trichoderma have gained significant importance for use as agents for control of several diseases of cultivated crops. The last decade has witnessed a tremendous break-through in the research efforts on biological control of plant diseases in India especially by using species of Trichoderma and Gliocladium. Several economically important plant diseases of a variety of crops were effectively managed by using Trichoderma based biofungicides. The work on biocontrol of pigeonpea wilt by Bacillus subtilis by Dr. R S Vasudeva and his associates, published as a series of papers in Annals of Applied Biology during 1950 to 1965 can be considered as a starting point for Indian work on biological control of plant pathogens (Mukhopadhyay, 1994).

INTRODUCTION The genus Pratylenchus was established in 1936. It has a cosmopolitan distribution prevalent in temperate, sub-tropical and tropical regions. The species of Pratylenchus are popularly known as lesion nematode or meadow nematode. They are migratory endoparasites. Various pulse crops are damaged by them. P. thornei attacks chickpea,  P.zeae on mungbean (Walia and Seshadri, 1986); P. mulchandani on urdbean (Nanad Kumar et al., 1969) and Pratylenchus sp.on lentil (Mishra and Gaur, 1980) and cowpea (Aung and Prot, 1990). Besides pulses species of Pratylenchus attack a number of other crops also. The infested plants exhibit various types of symptoms and results in heavy yield losses. Investigations have been made on various aspects of host-nematode relationship, distribution, host range, yield losses, biology, life cycle, disease cycle, interaction with other microorganism and management through cultural, physical, chemical, biological methods and host resistance.

INTRODUCTION Soil-borne pathogens cause heavy losses to most agricultural crops. Repeated planting of a crop in the same piece of land results in a high inoculum build-up, which forces the farmers either to change the crop or the land. Thus, the search for new, effective, inexpensive and non-hazardous methods for the control of soil-borne diseases is a continuous one. Over the years, efforts have been made to manage the soil-borne pathogens by employing fumigants, chemical pesticides, biological control agents, different type of soil amendments and also by causing modifications in different cultural practices. But, pathogen control is often hampered by the fact that both the inoculum of the pathogens and the lethal agents applied to the soil are affected by the soil’s physical, chemical and biological environment. Keeping in view the bottlenecks with different methods of management of soil-borne pathogens; harnessing of solar energy i.e. soil solarization is an effective method to control soil-borne pathogens.

INTRODUCTION Many economically important diseases are caused by Phytophthora spp. There are as many as 60 described Phytophthora species, most of which are primary invaders of plant tissues with limited saprophytic ability. Some important diseases with respect to symptoms, etiology and management have been described in this chapter as given below.

INTRODUCTION Plants are susceptible to different types of pathogens, which are responsible for production of varied symptoms and causing losses. In the absence of the crops pathogens perpetuates in different manners and survival in the soil is one of the most important amongst these. Because of the constant presence of the pathogen in the soil, these become more destructive. These may reduce the plant growth, results in rotting of different plant parts, reduce yield or may cause the death of the plant. The destructiveness of soil borne pathogen increases because of the ability to survive in the soil as dormant structures for several years. Efficient control of soil borne diseases is thus difficult but can be achieved by employing various disease management practices in an integrated manner (Verma and Varma, 1992; Gupta, 1996, Gupta and Sharma, 1999).