eChapters

Introduction

Biological control of plant pathogens is currently accepted as a key practice in sustainable agriculture. Plant parasitic nematodes and mycorrhizal fungi are commonly found inhabiting the same soil and colonizing roots of their host plants. These two groups of microorganisms exert a characteristics, but opposite effect on plant health. The potential role of mycorrhizal fungi as biocontrol agent for the control of nematode plant diseases has recently received considerable attention. The literature on the various aspects of VAM research such as interaction of VAM- mycorrhizal fungi with nematode pathogens (Sikora, 1995, Pinochet et al. 1996), biotechnology and future of VAM commercialization (Wood and Cumming, 1992) and trends in mycorrhizal research (Sahay et al. 1998) has been reviewed. The damage due to nematodes diseases is generally decreased in mycorrhizal fungi has shown an antagonistic influence on the population of plant parasitic nematodes (Nagesh et al. 1999, Kantharaju et al.

Protected Cultivation

Protected cultivation (PC) may be defined as the “modification of the natural environment to achieve optimum plant growth” (Singh, 2005). Modifications can be made to both the aerial and root environments to increase crop yields, extend the growing season and permit plant growth during periods of the year not commonly used to grow open field crops. PC may also indicate comprehensive systems of ‘Controlled Environmental Agriculture’ in which all the aspects of natural environment are modified for maximum plant growth and economic return.

Introduction

Nematodes are cosmopolitan and ubiquitous in occurrence. These have been reported in all kinds of ecological niche. Accordingly, different kinds of nematode fauna had evolved with distinct morphological features and physiological variability. However, development and perception keep changing with the ambient environment. Agriculture has progressed with leap and bounce as human being has managed this to its maximum utility. The fast changes in agriculture definitely influenced the ecological niche and affected the flora and fauna. Consequently, specific and unspecific kind of relation evolved between host and parasite. With the thumb rule of ecological balance or homeostasis. In the dynamic Mother Nature, multispecies heterogeneous complex is sustained and nature do not perpetuate homogeneity.

Introduction

Banana is the forth ranked agricultural crop in the world and first among fruits. A large number of pests and diseases threaten banana production. The major constraints in production are diseases and pests transmitted through the conventional planting materials. Although the average yield for bananas worldwide is over 40 t per hectare, production in India averages only 20 t per hectare. The nematode parasites are among the most important pests on commercial and subsistence banana production and their control remains difficult, as the nematodes are involved in the destruction of primary roots that disrupt the anchorage system resulting in toppling or uprooting of plants. The most widespread and important are burrowing nematode, Radopholus similes, some species of root lesion nematode, Pratylenchus coffeae and P. goodeyi, species of root knot nematode, Meloidogyne incognita and M. javanica; the spiral nematode, Helicotylenchus multicinctus, H. mucronatus and semi endo-parasitic nematode Rotytlenchus reniformis.

Introduction

Seed spices have prominent place in India’s national economy because of their very high domestic consumption and growing demand for export. This group of spices, being consisting of mostly annual crops, is grown extensively in rotation with food and cash crops and also as inter crops under rain fed as well as irrigated conditions.

There are about 20 seed spice crops grown in India. Out of which nine are important in terms of production and export. The most important ones are coriander, cumin, fennel and fenugreek (major seed spices) and ajowain, aniseed, black cumin, celery and dill (minor seed spice crops). Although these crops are grown all over India but Haryana, Rajasthan, Madhya Pradesh, Uttar Pradesh, Orissa, Tamil Nadu and Andhra Pradesh are the main seed spice growing states.

Introduction

Rice (Oryza sativa L.), one of the most important cereal crops of India, occupies 23.3 per cent of total cropped area of the country. Rice contributes 43 per cent of total food grain production and 46 per cent of total cereal production. It continues to play a vital role in the nation’s food grain supply. It is also a staple food of nearly half of the world population. Rice is primarily a high caloric food having protein content (6-17%) with high biological value and a low amount of fat (2-2.5%). B-group vitamins content in rice grains are at par with wheat, however, calcium content in rice is generally low. It ranks third after wheat and maize in terms of worldwide production. Asia accounts for 90 and 92% of the world’s rice area and production, respectively. Thus, rice production, consumption and trade are concentrated in Asia. Among the rice growing countries in the world, India has the largest areas under rice crop and ranks second in production next to China.

Introduction

Maize (Zea mays Linn) is the most widely distributed crop of the world. It adapts easily to a wide range of production environments and is grown in tropical, subtropical and temperate regions of the world. It holds a unique position in world agriculture ranking third after rice and wheat in terms of area as well as production. In India too, it is the third most important cereal crop and is cultivated in 8. 17 m ha (2007-08) area. It contributes nearly 8% to the national food basket and more than Rs 100 billion to agricultural gross domestic products with an annual production of 19. 73 million tons. It is used as a source of human food (24%) animal feed (11%), poultry feed (52%), starch (11%), brewery and seed (1% each). In India it is largely grown in Northern states where it serves as an important staple food for an economically vulnerable population of submountainarean and hilly regions.

Introduction

Plant paprasitic nematodes are one of the limiting factors in the production of horticultural crops in the country. The visible symptoms of nematode attack are: Reduced individual plant growth, varying degrees of chlorosis, wilting of the foliage and sometimes death of the plants.

The roots, damaged by nematodes are not efficient in the utilization of available moisture and nutrients in soil resulting in reduced functional metabolism. Nematode infested roots are easily infected by various pathogenic fungi and bacteria and aggrevate root damage. These deleterious effects on plant growth result in reduced yield and poor quality of crops as in citrus, banana, grapevine, pineapple, papaya and vegetable crops. Decline or death of highly prised ornamentals and turf is often the result of nematode infestation.

Introduction

India has the distinction of being the largest producer of pulses in the world. Among the important pulse crops cultivated in the country are: chickpea, pigeonpea, lentil, mungbean, urdbean, fieldpea, rajmash and lathyrus. The pulse crops occupied an area of 22.85 million ha with a total production of 13.07 million tones and average productivity of 572 kg/ha. Being a high protein grain, pulses have special status in the diet, particularly for vegetarian population. Apart from being a good source of protein, they are also good source of energy, essential amino acids and vitamins in the daily diets of the people, especially of low-income group. Pulses have importance in sustainable agriculture by way of fixing atmospheric nitrogen in the soil.But with intensification of agriculture and introduction of irrigation and other facilities the area and production under pulses is declining so much so that per caput availability of pulses has declined from 69 g day-1 to about  36 g day^-1.

Preamble

In India, agriculture plays an important role as it accounts for about 18% of the GDP and supports nearly 58% of the total working population for employment. Food grain production increased significantly from a low level of 50 million Tons during 1950-51 to a record of 230.7 million Tons in 2007-08. The demand for food is growing rapidly due to increasing population and rising income levels, hence we need to produce about 320 million Tons of foodgrains by the year 2025. It implies more pressure on our exhisting land, soil and water resources which are already in short supply, degraded, fragile and this similar situation is being faced by mainly developing countries today. Plant parasitic nematodes are of great economic significance. Since most of them live in the soil hence represent one of the most difficult pest problems in terms of identification, demonstration and management.

Introduction

The cereal cyst nematode, (Heterodera avenae Woll.) a causal organism of ‘molya’ disease in wheat and barley, since after its first report (by Wollenweber, 1924, Vasudeva, 1958 and Prasad et al., 1959), it has been timely reviewed about its spread and losses caused in the various parts of wheat and barley growing areas of the world. It has been reported to occur in Australia, Canada, Israel, South Africa, Japan, in most of the European countries, North America, India, Morocco, Tunisia, Pakistan, Libya, Turkey and Australia (Prasad et al., 1959, Smiley et al., 1994, Rumpen horst et al.,1996, Krall et al., 1999, Nicol, 2002 and Rao et al., 2002). Its economic importance has been assessed by mapping the yield losses caused in cereals i.e. ranged from 15-20% in Pakistan, 40-92% in Sauthi Arabia, 23-50% in Australia (Nicol, 2002) and 40-50% in India (Mathur 1969, Mathur et al., 1980, Handa et al., 1985, Mathur, et al., 1987).

The highly specialized organs that receive physical and chemical stimuli from the environment and various body parts, and transform them into stimuli are called sense organs or sensory receptors. These organs are closely associated with nervous system. The physical stimuli such as change of heat, light intensity and quality, acoustical stimuli and chemical stimuli like hear, taste, smell, touch, lateral line etc are received by the sense organs such as ear, eye, nose and others. These are more prominent sense organs. Less obvious ones in fishes are sensory crypts and papillae, ampullae of Lorenzini and Savi.

The crustaceans have various sense organs whose action are mediated through the nervous system. Crustacean antennae are important sites for the reception of environmental information, mainly chemical, and aesthetases, the olfactory hairs on the first pair, are usually well developed. The aesthetases help not only in locating food but also in recognizing other individuals and their sexual state.  The frequent grooming of the antennae by many decapods prevents fouling of the receptor sites (Bauer, 1971).

Most of the aquatic organisms spend much of their lives and energies for reproduction. The young ones mature, develop sperms or eggs, spawn, and then recover to repeat the breeding cycle that continues till their death. In a majority of fish species males and females are separate individuals, fertilization is external and large number of eggs are produced (on an annual basis, its fecundity) which develop, hatch and mostly grow without parental care. The sperm and eggs are usually produced in such quantities that they represent a large expenditure of energy. The spawning process may be preceded by migrations or nest building, and followed by care of the young. Thus the success of any fish is ultimately determined by the ability of its members to reproduce successfully in a fluctuating environment and thereby to maintain viable populations.  As each fish species occurs under an unique set of ecological conditions, it has an unique reproductive strategy with varied anatomical, physiological, behavioral and bioenergetics adaptations. Unlike the finfishes, in shellfishes sexes are separate. The shellfishes use various signals to attract the opposite sex.

Excretion is the process of elimination of metabolic wastes that include toxic nitrogenous end products of the protein metabolism and the gas such as carbon dioxide (CO₂). These nitrogenous wastes are excreted through urine. Fecal matter is not included in the excretory products as it is simply the undigested food materials, and are not metabolic end products. The membranes of aquatic animals, that is permeable to gases, pass water and solutes between environment and body. Most aquatic animals maintain in their bodies a reasonably constant proportion of water and solutes. When it is different from the surrounding water, it requires some mechanism for regulation, which is known as osmoregulation. Most invertebrates in the sea have nearly the same salt concentration (isosmotic or isotonic) as the environment. Sharks and rays (elasmobranches) tend to have a slightly higher concentration of salts and urea (excretory end products) than seawater but the body fluids of most teleosts (bony fishes) have much lower salt concentration than seawater. Freshwater fishes, which live in a medium of lower salt concentration (hyposmotic or hypotonic), have the threat of hydration, so they have special mechanisms to get rid of excess body water. Marine fishes that live in an environment of high salt concentration (hyperosmotic or hypertonic) have the regulatory mechanisms by which excessive loss of water from the body is prevented and body osmolarity (proper osmotic concentration) is maintained by retaining less toxic nitrogenous excretory products. Marine fishes, which lose water osmotically across the gills and must get rid of salt, tend to drink large volume of seawater and produce very small quantities of urine (Fig-6.1).

The respiration of animals includes the exchange of gases either at the surface of the body or through the internal processes involving circulatory system. The gases that are exchanged are oxygen (O₂), carbon dioxide (CO₂) and the inert gas like nitrogen. When the organism respires, the O₂ that is taken up from the external environment is transported by the vascular system to individual cells within the tissues. At the same time this system picks up CO₂, an end product of cellular metabolism, and releases it to the environment. Thus respiration is a term applicable either to a whole organism or one of its cells. The mechanical process, by which respiration is achieved, is called ventilation.  This ventilation rate of aquatic organisms is controlled directly by the concentration of dissolve oxygen (DO₂) in water.

Respiration in aquatic medium is produced by a water current passing in a single direction. The area of respiratory surface is thus an important limiting factor in the movement and growth of the animal. For aquatic animals, if the water is at all deficient in O₂, the rate of breathing is naturally accelerated, and the animal appears to respire hurriedly. Other factors, which lead to an increased rate of respiration, are the stresses.

Various activities of the body in different external environmental conditions are co-ordinated by the appropriate message from the neurons due to the stimuli from the environment. These messages pass in the form of impulses through the co-ordinated links between a number of neurons or nerve cells. The constant passage of messages require a very little energy but high level of O₂ .There is interaction between the nervous and endocrine system with the areas of interchange among the two systems. Some neurons show the action of both the systems and thus termed as neurosecretory or neuro-endocrine. Fishes have a well-developed nervous system. Broadly the nervous system can be divided into central nervous system (CNS) and peripheral nervous system (PNS).The brain and spinal cord are the parts of the CNS. The motor and sensory nerves link the receptor and effector organs. All nerve tissues other than brain and spinal cord are grouped under PNS. Peripheral nervous system consists of nerves, ganglia and receptors. The nerves carry sensory information from special receptor organs like eyes, internal ear etc. to the integrating centers of the brain and spinal cord. The PNS also carries information via different nerve cells from the integrating centers of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscle system for appropriate action in response to the original external and internal stimulus. The PNS can be divided into somatic and visceral. The term visceral is sometimes used in referring to the autonomic or involuntary nervous system (ANS), controlling visceral functions. The ANS helps to co-ordinate the activities of many glands and organs, and it is closely connected to the integrating centers of the brain.

Embryologically, the circulatory system is the first organ system to develop in the living animals. The form and function of this system vary considerably among the animals and are shaped by a variety of environmental factors i.e. phenotypic plasticity. Oxygen (O₂) acquisition and carbon dioxide (CO2) elimination occur simultaneously at the gill site of fish and shrimp. The gases are transported around the body by the circulation of the blood.

3.1. Circulatory System of Fishes

In fishes, heart is simply a muscular enlargement and modification of a part of the main blood vessels, lying between the hepatic capillaries and the gills. Fishes have a closed circulatory system with a heart that pumps blood in a single loop throughout the body. From the heart, blood goes to the gill capillary bed. Then via the systemic capillaries it returns back to the heart. Usually the gills account for approximately 30% of the total resistance to blood flow, the rest being in the visceral and somatic vasculature. Tuna requires more O₂ and the gill area is large with gill resistance up to 57%.

The knowledge of food, feeding habit, anatomical adaptations and the physiology of digestion of the candidate aquaculture species is highly essential to develop cost-effective artificial feed for successful culture practices. The digestion of poikilothermic aquatic fishes and shellfishes is influenced by many factors, and is different from the digestion of terrestrial animals.

2.1.    Anatomy and Physiology of Fish Digestive System
2.1.1.  Feeding Behavior of Fishes

Based on the feeding habit, the fishes are generally classified as herbivores, omnivores, carnivores and detritivores. Within these categories, the fishes further categorized as euryphagous, having a mixed diet, stenophagous, consuming a limited combination of food types and monophagous, accepting only one type of food. A majority of fishes are euryphagous carnivores, and their feeding mode and food types are associated with the body form and digestive system. Fish generally change their feeding habits depending upon the availability of food. Fishes may be classified as predators, grazers, strainers etc. Plankton is a collective term for variety of marine and freshwater plant or organisms that drift on or near the surface of the water. Most fishes eat the material that is smaller than them. The smallest fishes eat these planktons, which act as their main food and all smaller fishes are the food of the bigger fishes. Largest shark feed on plankton by straining these tiny marine plants and animals from the water. The zoo-planktons, comprise protozoa, small crustaceans, jelly fish, and mollusks, together with the eggs and larvae of many species of marine and fresh water.

Aquaculture is the culture of aquatic organisms per unit water area per unit time for maximum profit. The economically important finfishes and shellfishes, whose body physiology is adjustable to varied environmental conditions, are considered as aquaculture candidate species. So, an overall knowledge on the physiology of such species is required to improve the culture practices.

1.1. Finfish

A fish may be defined as a vertebrate, adapted for a purely aquatic life, propelling and balancing itself by means of fins, and obtaining oxygen  (O2) from the water for survival and life processes. As the fishes have fins, they are also known as finfishes. Fish describes a life from rather than a taxonomic group. They share certain features with other vertebrates. These are gill slits, a notochord, a dorsal hollow nerve cord and tail. In number of individuals, and may be also in number of species, fishes are presently superior to other vertebrates, including mammals. There are 20,000 different species of fishes. Fishes form largest group of vertebrates, Pisces. The various types of fishes differ so much in shape, color and size that it is difficult to believe they all belong to the same group of animals. Fish in general are cold-blooded and adjusted either to freshwater, brackishwater or marine environment.

Anar butterfly, Deudorix isocrates (Fab.)

The pest has been found boring into fruits of pomegranate. Besides it may attack guava, aonla, apple, ber, citrus, litchi, loquat, sapota, etc., pomegranate is the most preferred host for this pest. It may destroy up to 50 percent fruits. The female lays eggs singly on calyx of flowers or small fruits. On hatching, the caterpillars bore inside the developing fruits and are usually found feeding on pulp and seeds just below the rind; subsequently bacteria and fungi causing fruit rot also attack the infested fruits. The conspicuous symptoms of damage are offensive smell and excreta of caterpillars coming out of the entry holes, the excreta is found stuck around the holes. The affected fruits ultimately fall down and are of no use; even if the fruits be picked before falling down, these fruits have no market value.