eChapters

Abstract

Surveys made systematically in different remote places of Tamil Nadu brought to light more than 1000 indigenous techniques adopted for pest control in various crops of agriculture, horticulture and store grains. Target animals included array of insect species and animal pests namely rodents, mites, molluscs and microbes like nematodes and viruses. Various kinds of plant species reveal their modes of action distinctly.

Abstract

Plant roots influence the biological, chemical and physical properties of rhizosphere soil. These effects are a consequence of their growth, their activity and the exudation of organic compounds from them. There is now considerable scope for the new ideas to be extended to the rhizosphere. The role of soil microorganisms in sustainable productivity has been well construed. In recent years, root inhabiting (rhizozosphere) bacteria (rhizobacteria) is gaining importance. The beneficial effects of plant growth promoting rhizobacteria (PGPR) has been variously attributed to their ability in improving the crop production, protection against phytopathogens, soil health and environmental quality. However, there is a need for isolation, identification and improvement of potent PGPR’s to utilize them ultimately as promising bio-inoculants. This review embodies some recent developments to evolve strategies for the better biotechnological exploitation of PGPR’s.

Systematic management of plant diseases dates back to 1885 with the invent of Bordeaux mixture by Milardet. Thereafter, a number of contact and systemic fungicides have been reported over the years for the management of various plant pathogens, of which many have become obsolete and many are still being used with excellence. However, the ecological hazards caused by the chemical fungicides have prompted scientists to search for other avenues of crop protection. Most of the conventional chemical and biological plant protection procedures, as well as the use of disease-resistant cultivars, tend towards the direct control of pests and diseases by their elimination. But these practices generally and particularly in case of monoculture crops like rice, raise problems. The risk of developing pesticide resistance in plant pathogens is enhanced by the long term use of the same chemical. The resistance genes of the plants can also be overcome by changes in the pathogens. Therefore the situation demands development of new strategies for plant protection which can supplement the use of resistance breeding and chemical control.

Agriculture is the main source of income of the rural masses in India and the disease accounts for more than 30% losses every year. According to a WHO estimate of 1990. There were 25 million cases of acute occupational pesticides poisoning in developing countries each year. ILO 1996 estimates suggests that out of 14% of all known occupational injuries 10% of all total injuries are caused by pesticides. Further more developing countries are a dustbin for the developed countries. More than 20, 000 tonnes of obsolete pesticides are dumped in Africa alone. The biopesticides are amenable to small scale and local production. Presently there is an increased awareness regarding environmental and food safety. The biopesticides as such can be used as an essential and fundamental component of integrated pest management. It helps to manage the disease which are difficult, otherwise to be managed and so also these control the pests resistant to conventional pesticides. Paulitz and Belanger (2001) has reviewed the potential of biological control in green house systems.

Introduction

Biological-based crop protection against plant viruses aims to develop sustainable, non-chemical, crop management technologies that utilize natural-occurrants and phytotoxins to control economically important diseases. In this area the efforts were made since the realization that viruses can not be controlled directly unlike other pathogen.

At present in the absence of any direct control of the viruses, strategies so far have been adopted to control them indirectly; like controlling the vectors of viruses (insects, nematodes, fungi etc.), using barrier crops, and use of resistant cultivars. However, success had been very limited. As the biological sciences advanced, many biological systems were utilized to control the diseases in plants caused by viruses, promising among them is using apical-meristem culture techniques to produce virus free plantlets as starting material.

Introduction

Soil supports richest number and kinds of microorganisms interacting with each other and thus by modification or alteration in soil conditions greatly influence the microbial community and their activity in soil ecosystem. Soil physico-chemical and the biological factors interact to provide rapidly changing ecological niches and microbial components fluctuate in response to change in soil conditions. There are large evidences that agricultural practices often favour antagonistic microorganisms (Cook and Baker,1983; Yarham,1979) and therefore, biological control of plant pathogens could be possible through manipulation of soil condition. Soil organic matter also has a profound influence on microorganisms in soil, particularly those, including some pathogens, saprophytic and obligate plant parasites. Soil organic matter is distributed at discrete sites within the soil and determines to a great extent which parts of pore space are occupied. 

Abstract

The rhizosphere or the zone of influence around roots harbors a multitude of microorganisms that are affected by both abiotic and biotic stresses. Among these are the dominant rhizobacteria that prefer living in close vicinity to the root or on its surface and play a crucial role in soil health and plant growth. Both free-living and symbiotic bacteria are involved in such specific ecological niches and help in plant matter degradation, nutrient mobilization and biocontrol of plant disease. While the rhizosphere as a domain of fierce microbial activity has been studied for over a century, the availability of modern tools in microbial ecology has now permitted the study of microbial communities associated with plant growth and development, in situ localization of important forms, as well as the monitoring of introduced bacteria as they spread in the soil and root environment. Plant-microbe researchers have studied the diversity of rhizobacteria in a variety of plants, cereals, legumes and others along with assessment of their functionality based on the release of enzymes (soil dehydrogenase, phosphatase, nitrogenase, etc.), metabolites (siderophores, antifungals, HCN, etc.), growth promoters (IAA,

Plant diseases caused by variety of pathogens pose a serious challenge and economic threats to various agricultural crops all around the world. It has been evidenced that despite wide use of chemical pesticides in crop production, the losses due to pests and diseases are significant. Phytonematodes are one of the major groups of organisms that live in diverse habitat and continue to challenge variety of agricultural crops all around the world. Since early times the major agricultural crops have been plagued by these noxious nematodes that feed on various plant parts viz. roots, rhizome, sucker, tubers, seedlings, stem, leaves, buds, crowns and cause damage worth more than 100 billion dollars annually. The major crops severely affected by these pests are, vegetables, fruits, sugarcane, sugar beet, cotton, oil seed, pulses, tobacco, tea, coffee, cereals, spices, medicinal and aromatic plants.

Genus : Olea 
Species : europaea L.
Family : Oleaceae
Chromosome No. : 2n=2x=46

Amongst the fruit crops, Olive is undoubtedly one of the world’s oldest cultivated crop and its cultivations dates back to 3000 B.C. and till date is recognized as a symbol of peace and prosperity. Olive is an evergreen subtropical plant, but for flowering and fruiting it does require chilling as most of the temperate fruits do. Although slow to grow, olive is a very long lived plant and with its typical dense foliage of olive green and silvery leaves also serves as an ornamental type. The centre of origin includes Palestine, Lebanon, north west Syria and Cyprus. The Greeks and Roman were well aware of the significance of olive oil during 900 to 600 B.C. and oil was considered as a luxury item in body anointment. From its native place olive established itself in the Mediterranean region especially Italy, Spain and from here to other parts of the world.

Genus   : Prunus
Species : avium cerasus, mahaleb L.
Family : Rosaceae
Chromosome No. : 2n = 16, 24, 32

Records indicate that cherries were in cultivation ever since the beginning of civilization. Cherries exhibit vast genetic variability as is evident from the different species which vary in their ploidy level. Sweet cherries (Prunus avium L) are diploid while sour cherries (P. cerasus, L.) are tetraploid, and commercially more important than the other species. Duke cherry has resulted from hybridization between sour and sweet cherry with intermediate tree and fruit characters. Successful cherry cultivation revolves around climatic factors, prime being the extent and spread of rainfall, variation in day and night temperature, occurrence of frosts, high heat day largely determine the type of cherry that will grow successfully in a particular areas. Hence cherry improvement around the world has so far been localized to few selected areas where different cherries have been successfully grown.

Genus : Prunus 
Species : domestica institia L. 
                saliciana Lindl.
Family : Rosaceae
Chromosome No. : 2n - 48

Of all the stone fruits, plums are the most varied. They belong to the genus Prunus of the subfamily Prunoideae of the family Rosaceae. All plums have a basic chromosome number of x=8. Plums and related species have been placed in the subgenus Prunophora section Euprunus and Prunocerasus. Six species have been placed in the section Euprunus. Their chromosome number range from diploid to hexploid and are native to the land extending from Europe to China. Thirteen species native to the North American continent are all diploid in nature and have been placed in the sections Prunocerasus. Separation of the plums into the two sections does not appear to have any genetical basis since the species appear to be closely related. Prunus domestica, the European plum, is believed to be the most recent crop species to have arisen within the section Prunophora. Prunus insititia.

Genus : Prunus 
Species : armeniaca L.
Family : Rosaceae
Chromosome No. : 2n = 16

Of all the temperature fruits belonging to tribe pruneae, apricots after cherries are more exacting in their climatic requirements. For this climate specific, apricots are often described as a fruit that fails where other fruits grow successfully. Apricots lavish continental climate, which is characterized by low rainfall (50 cm per year), warm summers and without much variation in winter temperatures and this winter temperature in temperate regions remain close to -33o C. Apricot trees are said to be drought resistant and can sustains low atmospheric humidity but is very sensitive to low soil moisture content.

Genus : Prunus 
Species : persica Batsch
Family : Rosaceae
Chromosome No. : 2n = 16

The peach, Prunus persica (L) Batch is unique among the temperate fruits as it is adaptated to varied climatic conditions and it is for this reason that peach and its close relative the nectarine, in a short period has spread rapidly to different parts of the world. Peach is a tree of temperate zone, but has attained higher quality (fruit colour, taste etc.) in areas where the summer temperatures are relatively warm to hot. With the discovery of low chill types ‘Honey’ and ‘Peen to’ forms from southern China, peach cultivation has been spread to warm temperate regions of the world. Normally peach requires from 500-1000 hours of cold/chill hours below 7.2oC for growth and flowering in the spring. Peach history as a garden crop in China is well documented, and forms varying in flesh colour (white, yellow or red), free stone or cling stone, flower colour, large and showy flower type seen presently were also present at very early time i.e. the beginning of the present century.

Genus : Cydonia / Pyrus
Species : oblonga Mill. vulgaris Pers. 
                cydonia L.
Family : Rosaceae 
Chromosome No. : 2n= 34

The fruit of pome class referred as Cydonia oblonga (also Pyrus cydonia) is an ancient fruit and yet its significance is not fully recognized and crop has received very less attention. There is hardly any mention of this old fruit in respect of its merit, its cultivation or in the form of some standard literature. One reason could be that amongst pome fruits where quince is placed, better fruit form, raw eating quality persisted, which markedly restricted quince improvement. Quince fruit lacks dessert class except when cooked but is commercially used for flavouring, in preparation of jellies marmalade and preserves. However in near East and Persia, quince cultivation is highly improved through the selection of better varieties which are eaten raw.

Genus : Pyrus 
Species : communis L.
Family : Rosaceae 
Chromosome No. : 2n= 34

Pear like apple is also a prehistoric crop and unlike apple its cultivation in Europe started much before that of apple at an early time. According to Homer (1000 B.C.) the ancient Greek said that pears were one of the “gifts of god’s”. Romans also enormously added to the knowledge of pear cultivation. Pliny in Rome had described 35 cultivars (23-79 AD). The variation in fruit characters described earlier match to the range of fruit characters which are found in presently grown commercial cultivars. In Europe for its buttery soft texture and distinct aroma many consider European pear as the most detectable of all temperate fruits, while the Asian pears for their firm crisp texture and juiciness are preferred more in China and Japan – their native place. Pears are readily consumed as fresh, dried, cooked or as preserves or to make perry and pear wine.

Genus : Malus  
Species : domestica (Borkh.)
Family : Rosaceae 
Chromosome No. : 2n = 34, 51, 68

Like many other fruit crops, apple too is a very old crop in cultivation. Theophratus as early as third century B.C. has indicated that the Greeks and Romans knew apple culture and among the temperate fruit crops, apple is the most ubiquitous of all fruits and is extensively grown all over the world. Huge genetic variability present has permitted the better adapted types to be selected for plantation under different agro climatic conditions.  Through continuous selection both from wild population and also from hybrid seedlings, varied types or varieties have been selected, some are suitable for cultivation in warm temperate regions and others for extreme cold conditions.  This has resulted/added to the gene pool of desired types of apples enormously. At present cultivars are available destined for specific purposes like dessert, cooking, juice, cider and for large number of other uses.

Genus   : Macadamia
Species : integrifolia Maiden and Betch
Family : Protaceae 
Chromosome No. : 2n =28

Macadamia nut is known as ‘Australian Nut’ or ‘Queensland Nut’ because of its origin in the rainforests of New South Wales and Queensland. The crop is sensitive to frost hence the site which suits orange and lemon tree cultivation is also good for macadamia. Macadamia through cultivated commercially in Australia it is in Hawaii that maximum improvement and advancement in terms of selection of superior cultivars has taken place and in short time of about 100 years macadamia culture has become a very fruitful entrepreneur. Presently there is huge gap between the macadamia nut demand and supply therefore efforts are being made to introduce macadamia into other tropical and subtropical parts of the world.

Genus : Pistachia 
Species : vera L.
Family : Anacardiaceae
Chromosome No. : 2n = 30

Among the nut crops Pistachio nut (Pistacia vera L.) occupies a significant place for its delectable and nutty flavoured kernels which in large quantity is imported to India mainly from Iran and Afghanistan. On account of its demand for very exacting climatic requirements the crop has failed to establish successfully in number of new regions where efforts were made to introduce this crop, despite the fact that it resists drought and adverse soil conditions much better than more important fruits of the family Anacardiaceae. Pistachio trees are long lived but grow very slowly in early years of its plantation compared to many of the deciduous fruit trees. Alternate bearing is also a wide spread phenomena in this crop. Pista is a fruit of temperate region and can withstand wide fluctuation in temperature. The exact place of its origin though not definite, is often regarded to be indigenous to central Asia, where large stands of wild pistachio trees are found growing in abundance.

Genus : Corylus 
Species : avellana L.
Family : Betulaceae
Chromosome No. : 2n=2x=28

European filbert Corylus avellana L, is known by several names common being Cob, cobnut, hazel, Spanish or Lambert nut, which has been due to its origin, fruit shape, husk and the general appearance. ‘Filbert’ has also come from name ‘full beard’ as the nut of commerce is fully enclosed by the long husk. It is this husk or involucres which very often has been used to distinguish between various species and cultivars. Corylus the genus has been derived from korys which indicate bonnet, hood or helmet and there are several other views of its name being derived after the name of some renowned places. The word ‘hazelnut’ is from anglosaxon haesel meaning hood. Further the term hazelnut is used in European and Filbert in Asian countries for and its other species. However in America, the term is used to refer to three native species C. archericana, C. californica and C. cornuta. Filbert is an important member of birch family, Betulaceae which has a long history of cultivation (8000 to 5500 B.C.). 

Genus : Castanea 
Species : avellana
Family : Fagaceae
Chromosome No. : 2n = 24

Before the history was started to be written chestnut nuts in Japan and China were harvested, collected and eaten and aptly has been an important food for man around the world especially in Asia, Asia Minor, Europe and North America for hundreds of years. As early as 50 B.C., chestnut was brought to southern Europe by Greeks from Asia Minor and red Indians in North America prior to its discovery. Used nuts of chestnut was a staple food especially during famine times.

Genus Castanea has 13 species and belongs to the family Fagaceae which also has important forest plants like Oak (Quercus), and beech (Fagus). Species of this genus are grown for ornamental and also for their edible nuts. Three species of chestnut are economically important as they produce edible nuts, are highly variable and selection has been practiced for hundreds of years to select high yielding, large fruited type. The species other than C. dentata (American chestnut) are called ‘Chinkapins’.