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HETEROSIS BREEDING IN VEGETABLE CROPS

Nagendra Rai, Mathura Rai
  • Country of Origin:

  • Imprint:

    NIPA

  • eISBN:

    9789389992694

  • Binding:

    EBook

  • Number Of Pages:

    546

  • Language:

    English

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Vegetable  production in our country is still dominated by the locally available genotypes or open-pollinated varieties, which are low-yielding and susceptible to various insect pest and diseases.  This is mainly due to farmers' ignorance and poor extension activities.  Hence, there is a need to grow vegetable hybrids for increasing production and productivity along with quality.  Development or hybrids from the existing ones play a pivotal role not only for increasing the productivity but also helps to combat several problems faced by farmers.  Thus to achieve these objectives, the authors have made an effort to give information for development of vegetables hybrid both theoretical and practical aspects in the form of book entitled, Heterosis Breeding in Vegetable Crops.   This publication contains 17 s in two sections.  The first section includes 10 s related to theoretical aspect of heterosis. viz. (i) Introduction to Heterosis (ii) Basis of Heterosis (iii) Commercial Exploitation of Heterosis (iv) Reproduction, Pollen and Pollen Biotechnology (v) Population Improvement of Parents/Hybrids Varieties (vi) Genetic Purity Testing of Hybrids (vii) Hybrid Varieties Testing and Release Procedures in India (viii) Biotechnology and Vegetable Improvement (xi) Intellectual Property Right related Issues in Hybrid Technology and (x) Economics, Import and Export.  Second section consists of practical aspect of hybrid seed production deals seven s, viz. (xi) Solanaceous Crops-tomato, brinjal, chilli and bell pepper, (xii) Malvaceous Crops-okra, (xiii) Cole crops-cabbage and cauliflower (xiv) Cucurbitaceous Crops-bitter gourd, bottle gourd, cucumber, muskmelon, watermelon, pumpkin, ridged and smooth gourd (xv) Root Crops-carrot. (xvi) Bulb Crops-onion and (xvii) Hints for Hybrid Cultivation.  All the s cover references, illustrations and tables.  The publication also contains characteristics of national released hybrids with colored photographs.  This would be useful to teachers, scientists, students, extension workers, vegetable industry and farmers of this country. 

0 Start Pages

Preface In India, vegetables are grown from dry temperate to humid tropics between the altitudes from sea level to snow line. The vegetables are rich source of vitamins, minerals, antioxidants, phytochemicals and provide protection against health hazards. A diet rich in vegetables ensures nutritional security and productive life. Most of vegetables are short duration, cultivated as sole, mix, relay, catch crops provides ample scope in crop diversification, provides opportunity for higher employment generation consequently higher economic return. It also provides raw material for establishment of processing industries and value addition, the the recent past tremendous progress has been made in the vegetable production and India has emerged second largest producer of vegetable in the world after China. It shares about 14% of world vegetable production. The total production of vegetable has increased from 23.4 mt in the year 1961-62 to the tune of 90 mt in the year 2003-04 with annual increase of about 3.5%. The export of vegetable is in increasing trends. The export of vegetable in the year 2000-01 was Rs.1480 crores which has increased to Rs.1950 crores in the year 2004-05 registering a growth rate of 17.9%. However, considering the demand to meet the recommended requirement of 300g vegetables per caput per day for ever growing population with annual growth rate of 1.93% and for export market India needs to produce about 150 mt of vegetables by 2011. The focus of research for increasing the national productivity of vegetable crops by the year 2011 encompasses many research areas including popularisation of hybrid varieties, integrated nutrient management, disease/pest management, diversification, value addition and post harvest management. In this direction the sincere efforts made by the authors will be of immense use in popularising the hybrid technology. The book, Heterosis Breeding in Vegetable Crops, has two sections, the first section deals with basic principles of heterosis and the second section includes techniques for development of hybrids in 16 vegetables along with improved production technology. This would be useful to teachers, scientists, students, extension workers, seed industries and farmers. Authors express their gratitude to Dr. Mangala Rai, Secretary, DARE, Govt. of India and Director General, Indian Council of Agricultural Research, New Delhi, India for encouragement and suggestions; Dr G. Kalloo (DDG, Horticulture and Crop Sciences) for technical guidance and for writing the foreword. The authors are grateful to Dr. K.M. Bujarbaruah, Director, ICAR Research Complex for NEH Region, Shillong for permission to write and publish this book. Thanks to Dr. Omvir Singh, Principal Scientist, NBPGR Regional Station, Srinagar and Dr. N. Ahmed, Professor and Head (Vegetable Crops), Sher-E-Kashmir University of Agriculture and Technology, Srinagar for providing important literature. The authors expresses sincere thanks to Late Dr. C.B.S. Rajput, Ex.-Director, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi for encouragement and motivation. The help extended by Mr. K.K. Patel, Mr. P. Sharma, Mr. B. Dey, Mr. B.S. Asati and Mr. R.M. Yadav is highly appreciated.

 
1 INTRODUCTION

Vegetables are rich source of nutrients, vitamins and minerals. Phytochemical contents in vegetables and their strong antioxidant potential in scavergering ree radicals have generated tremendous attention among the consumers. Consumption of vegetables has significant health-promoting effect and can reduce the incidence of cardiovascular diseases, cancer, Acquired Immuno Deficiency Syndrome (AIDS) and various other degenerative diseases. Human health, in recent years, has assumed an unprecedented status. The rising population levels, increase in mental stress and changes in dietary habits have resulted in various forms of degenerative diseases including cardiovascular, cancer and ageing. As a result, there has been an alarming explosion in consumers’ interest in health. In recent past, tremendous progress has been made for increasing vegetable production in the country. India has emerged as the second largest producer of vegetables next to China. During 2000-2001, India produced 93.92 million tonnes of vegetables from 6.24 million ha of land, accounting a productivity of 15.0 tonnes/ha. During 1991-1992, total vegetable production was 58.54 million tonnes from 5.59 million ha of land, with productivity of 10.5 tonnes/ha. Thus, in last one decade country has multiplied its vegetable production one-and-a-half times. Presently, India’s share is more than 13.60%. Our country will need to produce 215 million tonnes vegetables by 2015 to meet the demand of domestic and export markets. The increase in vegetable production by increasing area under vegetable cultivation is limited due to continued decrease of land holdings. Hence, it is essential to increase vegetable productivity to fulfill country’s requirements for food and nutritional security and poverty alleviation.

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2 BASIS OF HETEROSIS

Genetic Basis of Heterosis There are three theories to explain the genetic basis of heterosis: (1) dominance hypothesis, (2) over-dominance hypothesis and (3) epistasis. Dominance Hypothesis Davenport (1908) first proposed this hypothesis and he considered that heterosis is a consequence of action and interaction of favourable dominant genes brought together in a hybrid. Bruce, Keeble and Pellew explained it in 1910. This hypothesis suggests that at each locus the dominant allele have favourable effect, while recessive allele has unfavourable effect. In heterozygous state, deleterious effects of recessive alleles are masked by their dominant alleles. Thus, heterosis results from masking of harmful effects of recessive alleles by their dominant alleles. The harmful effects of recessive alleles, which becomes homozygous due to inbreeding. Therefore, according to dominance hypothesis, heterosis is not the result of heterozygosity; it is the result of prevention of expression of harmful recessive allele by their dominant alleles (Fig.1). In this hypothesis, there are two objections (i) the first objection relates to the failure in isolation of homozygous lines for all the dominant genes, and (ii) the second objection is directed at the symmetrical distribution in F2. Both the objections are discussed below:

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3 MANIFESTATION OF HETEROSIS

Basic Requirements Hybrid seeds could be produced at cheap rates only if the crop species have certain built-in morphological or physiological mechanisms, suitable for the control of parentage for successful hybrid seed production and its floral morphology, is amenable to it. Some of the basic requirements and techniques employed in large-scale commercial hybrid seed production of crop plants are as follows: Availability of a proven heterotic hybrid combinations which could distinctly and profitably surpass the yield levels of commercial variety being grown. Availability of an easy, economic and effective means of eliminating or rendering functionless of male part of bisexual seed parent, mechanically, genetically or even biochemically. Availability of a strong fertility restoration system (in case of the use of cytoplasmically governed male sterility system) or availability of a tightly linked marker gene system in genetically governed male sterility along with full and detectable expression of self-incompatibility. Absence of modifier genes or gene systems in case of the use of self-incompatibility for hybrid seed production. Complete synchronization of flowering in both seed and pollen parents. Free, unrestricted and natural transfer of pollen from pollen to seed parents. Good seed setting on seed parent. A skilled organized effort for large-scale seed production, certification, processing and well-knitted distribution of hybrid seeds.

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4 REPRODUCTION, POLLEN BIOLOGY AND POLLEN BIOTECHNOLOGY

Reproduction Since the life of an individual plant is limited in duration, it has developed certain mechanism by which it can reproduce itself inorder to continue the perpetuation of the species and also to multiply in number. Mode of reproduction determine the genetic constitution of crop plants, that is, whether the plants normally homozygous or heterozygous. A knowledge of the mode of reproduction of crop plants is also important for making artificial hybrids. The various modes of reproduction found in crop plants may be broadly grouped into the following two categories : (i) Asexual and (2) Sexual. Asexual Reproduction Heterosis breeding systems depend upon the reproduction system of plants, whether the plant is propagated asexually or sexually. Therefore, before development of hybrids, information regarding type of flower, flowering habits and floral biology is required in hybridization programme (emasculation and pollination). In a sexual reproduction, plants develop from vegetative parts of plants (vegetative propagation) or may develop from unfertilized gametes, ovular tissues, and modified cells (apomixes). Vegetative reproduction includes plant regeneration from underground stems such as tubers in potato, bulbs in onion and garlic, underground tubers such as sweet potato, corms in yams, and rhizomes in ginger and turmeric. In certain cases, aerial parts are used for propagation as stem cuttings in tapioca, sweet potato, watercress, and drumstick, root suckers in curry leaf and globe artichoke and turfts in chive. In apomixes, sexual reproduction or gamete fusion is replaced with other form of asexual reproduction. In this case, embryo develops without fertilization. Apomixis may be of different types: (1) Apogamy—where embryo develops from a gametic cell of embryo sac other than egg cell. Apogamy may be haploid or diploid. Diploid apogamy has been reported in onion. (2) Polyembryony—where more than one embryo develops from a seed, resulting in more than one seedling. In this case, embryos usually develop from nucellus integuments, or chalaza in addition to normal syngametic embryo. (3) Parthenogensis where embryo develops from an unfertilized egg. This may be at haploid or diploid level. Sometimes, embryo development take place from unfertilized egg of a diploid plant. This is called haploid parthenogenesis. It originates in plants due to environmental effects, especially due to effects of high or low temperature, use of foreign pollen, application of chemicals, and use of irradiated pollen. Haploids parthenogenesis produces haploids.

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5 POPULATION IMPROVEMENT OF PARENTS/HYBRID VARIETIES

Concept Basic concept of this type of improvement is to accumulate, infuse and improve the frequency of favourable genes in established population. This includes the removal or substitution of an undesirable gene with a counterpart favourable one with the superior performance in a given environment, incorporation of a balanced gene combination for better performance - per se or may be even bringing in a better plant type congenial for better physiological activity and biochemical versatility, resulting in better performance of a population. As per theory of Hayes (1963), most of the commercial varieties/hybrids can be improved in one way or the other for one or more of the agronomic attributes. This is primarily because some of the lines in each hybrid generally excel in comparison with other in their ability to transmit desirable characters to their hybrid progeny and thus provide scope for the improvement of the weak inbred lines of the hybrid to further better its performance. The choice of the particular population improvement technique mainly depends upon the genetic information. Since by and large, population improvement techniques envisage controlled crossing followed by selection and recrossing by further selection. This information is vital. Therefore, before deciding upon the choice of a particular methodology, such information as the type of gene action involved in the expression of attribute under improvement, nature of genetic associations, extent of heritability, various possibilities of genetic manipulations should be available. Some of the procedures, which could be successfully utilized in population improvement of parents used in released hybrid populations, are backcross method of breeding, convergent improvement, gamete selection, technique for the removal of complementary genes and step ladder method of breeding.

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6 HYBRID VARIETIES TESTING AND RELEASE PROCEDURES IN INDIA

Hybrids are released for commercial cultivation either by the Central or State Varieties Release Committee. The release of a hybrid for commercial cultivation is based on conclusive demonstration of its superiority over the best existing hybrids (included as check in evaluation trials) in yielding ability or in some other features of economic importance, e.g. abiotic and biotic stresses etc. Due to above reason, hybrids are extensively evaluated for their performance, resistance to diseases and insects, and quality in multilocational trials. The multilocational trials are conducted under All India Coordinated Vegetable Improvement Projects, which play a key role in testing, identification and release of new hybrids. Before release of hybrids, three activities and operations are involved. These are:

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7 GENETIC PURITY TESTING OF HYBRID SEEDS

Meaning and Importance Genetic purity denotes the percentage of seeds (by weight) belonging to the variety/hybrid under certification. It is one of the primary criteria of seed quality. The efforts of plant breeders become fruitful only when sufficient quantities of good quality seeds of improved varieties/hybrids reach farmers / growers. This is necessary to take all round care at every step of seed multiplication before the seed is delivered for marketing. Hence, genetic purity testing is of critical importance not only to farmers but also to plant breeders, seed producers as well as quality control enforcing agencies. Increasing emphasis on hybrid cultivars due to their better performance and quality produce, more money and expertise have been put in further research of hybrid development. In this context, protection of parental lines is assuming critical importance and for that purpose, several breeding institutes do adopt various strategies for identification, characterization and protection of their parental lines as to avoid pilferage and misuse of their proprietary lines by other organizations. Use of random amplified polymorphic DNA (RAPD) and other molecular markers for evaluating seed purity of F1 hybrids and their parental lines are closely related, thus, helps in assessing contamination of F1 seeds even with the seeds of sib (inbred seed and seed from self-pollination of parental lines). For genetic purity testing of hybrids seeds, it is imperative that parental lines of hybrid be adequately characterized on the basis of maximum number of distinguishable descriptors (morphological, biochemical or molecular markers).

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8 BIOTECHNOLOGY AND VEGETABLE IMPROVEMENT

Origin, History and Definition The term biotechnology was coined by Karl Ereky, a Hungarain engineer, in 1919. The origin of biotechnology can be traced back to prehistoric time when armers and gardeners have been making use of hybridization and grafting among plants with a view to bring about an improvement in existing attributes. Using these approaches, several hundred varieties in ornamental plants were produced. Microorganisms were already used for processes like fermentation, formation of yoghurt and cheese from milk, vinegar from molasses, production of butanol and acetone from starch by Clostridium acetobutylicum or the production of antibiotics like penicillin from Penicillium notatum. Four defferent phases of biotechnological research were witnessed during the last century. In 1920, Chain Weizmann used Clostridium acetobutylicum to convert starch into butanol and acetone (during world war I, acetone was used as an essential component of explosives). Alexander Fleming in 1929 discovered penicillin from Penicillium notatum and wounded soldiers were given treatment using this antibiotic during world was II. In 1970s with the discovery of restriction enzymes, which led to the development of recombinant DNA, technology brought a revolution in the field of biology. The latest phase in the history of biotechnology is the study of structure and function of whole genome (DNA) and whole proteome (protein). This area of research is described as genomics and proteomics, respectively. Some more important activities in the field of biotechnology are given in Table1 In fact, biotechnology is the product of interaction between science of biology and technology. It is the technological exploitation and control of biological system. Biotechnology has wide range of its uses and accordingly Office of Technology Assessment described biotechnology as: (i) old biotechnology that includes fermentation, i.e. formation of vinegar from molasses and that of cheese and yoghurt from milk, production of antibiotics from certain fungi and process of baking and brewing and (ii) new biotechnology that includes the techniques of recombinant DNA and PCR polymerase chain reaction, cell culture and fusion and bioprocessing which became possible only through the researches in molecular biology. However, no efforts have been made to distinguish between old and new biotechnology. Keeping in view the importance of biotechnology, attempts have been made to define it. Following are some of the definitions of biotechnology, however, none of the definitions of biotechnology seems to be complete. The first definition seems to be comprehensive and wide.

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9 INTELLECTUAL PROPERTY RIGHTS - RELATED ISSUES IN HYBRID TECHNOLOGY

Definition and History The dictionary meaning of property is ‘estate whether in lands, goods or money’; such property is often referred to as tangible, material or physical property. The laws of the land protect the ownership of and the associated rights to physical property. In contrast, “intellectual property is an idea, a design, an invention, a manuscript, etc. which can ultimately give rise to a useful product/ application. The development of such property, as a rule, requires intellectual inputs, ingenuity and innovativeness; it also demands considerable monetary and other resources. Therefore, inventor of an intellectual property would like to ensure at least a fair reward for copied, imitated or reproduced; this minimizes the returns to the original inventor. Intellectual property right recognizes the right of an inventor to derive economic benefits from his invention (i.e. intellectual property); this right is called intellectual property right (IPR), (Singh, 2002). The governments, however, recognize the IPR, only so long as it is not to the detriment of the society. In India, innovation and novel techniques were retained within the families / small social groups that developed them, and there was no other system of protecting their rights to the knowledge so generated. The brief history of intellectual property right in India is: In 1856, the British Government in India introduced the Act of Protection of Inventions. This act was based on the British Patent Law of 1852. In 1872, Patents and Designs Protection Act was passed. In 1883, the Protection of Inventions Act was introduced. It was consolidated as Inventions and Designs Act in 1888. On 15 August 1947, the Indian patents and designs came under the management of Controller of Patents and Designs. The Indian Patent Act (1970) was introduced in the parliament in 1965, was modified in 1967 and passed in 1970. Protection of designs is covered by the Indian Patent and Design Act (1911) with amendments in 1978 and amended rules in 1985. Trademark protection is in force since 1 June 1948 under the 1940 Act. This act was amended as Indian Trade and Merchandise Marks Act (1958), which became effective on 25 November 1959. The copyright laws in India are as per international standards.

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10 ECONOMICS, IMPORT AND EXPORT

Introduction Hybrid is the first generation cross-produced through crossing between two genetically different plants, lines or varieties. The seeds produced in this way are called hybrid vigour, which serves as a key for increasing the yield of many self, and cross-fertilized crops. With limited possibilities of horizontal expansion in area and to meet the ever-increasing demand of quality vegetables by growing populations, the exploitation of hybrid vigour is best option for increasing both productivity and quality. Vegetable hybrids under optimum crop production and protection management produce economically more yield than improved, open-pollinated varieties. The uniform size, early maturity, improved nutritional quality, adaptability to adverse environments and resistance to various biotic and abiotic stresses, are additional advantages of hybrids resulting in better monetary returns to growers. Development of hybrids in vegetables brought about a near revolution but still India has not been able to harvest full potential of hybrid technology as compared to USA, Japan, Canada, Europe and Israel. About 10-12% of the total vegetable area is under hybrids in India as against 75-90% in Japan or USA. In India, only tomato and cabbage are leading vegetable crops, occupying 30-35% area under hybrids while rest of the vegetables cover less than 15%. The hybrid seed production and their cultivation, therefore, should be popularized on warfooting to achieve the targets. Many hybrids have been developed both by public and private organizations as given in Chapters 6 of Table 6, which are competing among themselves to produce best hybrids to compete in world market and selling seeds on very high rates ranging from Rs 5,000 to 50,000/ kg of seed. Though, they are making very huge profits but their contribution in promotion of hybrid technology is exemplary and cannot be overlooked.

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11 SOLANACEOUS CROPS

Tomato Genetic Resources Tomato, a warm season crop, sensitive to frost, is usually cultivated in sub-tropical and mild cold climates. The National Bureau of Plant Genetic Resources (NBPGR), New Delhi, is the main centre for maintenance of tomato germplasms in India. The Bureau has systematically assembled more than 2,900 germplasms. Some of the promising germplasms identified for different traits on the basis of their morphological variations (Fig.1; see Plate-1) are given in Table1.

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12 MALAVACEOUS CROP

Okra Genetic Resources Okra [Abelmoschus esculentus (L) Monch.] s a crop of the tropical and subtropical owland regions of Africa, Asia, America and warmer temperate region of the Mediterranean. It is believed to be originated from tropical Asia or may have been existing in Africa and India as polyphylatic species. A. tuberculatus, one of the ancestors of okra occuring in India, has nine wild taxa, of which A. esculentus is popularly grown for pod production. The main region of cultivation and diversity of okra in India, Sri Lanka, Pakistan, Nepal and Bangladesh, are represented by various local cultivars of A. esculentus and A. moschatus (Table1).

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13 COLE CROPS

Cabbage Genetic Resources Historical evidences indicates that modern hard-headed cabbage cultivars are descended from wild non-heading Brassica originating in the Eastern Mediterranean and in Asia Minor. The ancient Greeks held these early forms of cabbage in high regard and believed that they were a gift from the God. The Clelts and, the Romans disseminated cabbage throughout Europe. In fact, the Latin name Brassica is derived from the Celtic word bresi meaning cabbage. Over a period of centuries, hard-headed cabbage types evolved in northern Europe, while loose-heading, heat resistant types developed further in South. Cabbage was first introduced USA when the French explorer Jacques Cartier planted seed in Canada on his voyage in 1541. Cabbage is grown for the thickened main bud called head. The Portuguese introduced cabbage much earlier than cauliflower. There are reports that it was also grown during the Mughal period. In India, much varieties of cabbage are not available. However, genetic resources of cabbage for high yield and resistance to biotic stress are given in Table1.

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14 CUCURBITACEOUS CROPS

Bitter Gourd Genetic Resources Bitter gourd or balsam pear (Momordica charantia L.) is one of the most popular cucurbitaceous vegetable, commonly cultivated in many countries. Probably, India is the centre of origin and secondary centre of diversity of this crop. Bitter gourd is an annual monoecious herb, belongs to the genus Momordica that comprises 60 species. Out of these, only M. charantia, M. cochinchinensis, M. dioica, M. balsamina (balsam apple), M. cymbalaria (syn. M. tuberosa) are under cultivation. Momordica charantia is grown all over the country in tropical and subtropical climates and rich genetic diversity occurs in northern plains including tarai region, the northern-western plains, the central region/plateau and the western and eastern peninsular regions. Kakrol (M. dioica) is cultivated in West Bengal, Assam, parts of Bihar, while sweet gourd (M. cochinchinensis) is popular particularly in Tripura, Assam, Andaman Nicobar, Tamil Nadu, Uttar Pradesh, Bihar and West Bengal. M. denundata (Thw) Clarke (syn. M. dioica var. denundatais) is found abundantly in Kerala, M. macrophylla in Assam and M. sabangulata Blume is commonly found in Karnataka, Maharashtra, Meghalaya and Sikkim. In India, NBPGR , New Delhi, and IIVR, Varanasi, are actively engaged in the collection of bitter gourd germplasms.The NBPGR, New Delhi, has evaluated 33 collections for 37 characteristics. Variability has been reported in vine length (105-335 cm), number of primary branches (3-7), number of fruits/plant (1-25), fruit girth (8-27 cm), fruit length (9.5-20 cm) and fruit yield/plant (0.5-2.8 kg). Accessions, UB-22, UB-66, IC-74158, C-1621 and K-3374, have been found better yielder. At IIVR, Varanasi, 121 genotypes have been evaluated for yield and yield-contributing traits. VRB-40 & IC-44415A have been identified as promising lines. Accessions showing better charecters for different traits are given below (Ghosh and Kalloo, 2000):

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15 ROOT CROP

Carrot Genetic Resources Wild carrot (Queen Anne’s Lace) grows in emperate region around the world but the extent of genetic variability in wild population has not yet been evaluated in Daucus carota or related species. Constance (1971), Heywood (1983) and Mathias (1971) have contributed much to our understanding of Umbelliferae systematics, but relatively little carrot germplasm has been collected for distribution. The cultivated carrot, Daucus carota L, intercrosses freely with almost all the wild forms. Although, no incompatibility has been observed but protandry is the main reason for cross-pollination. However, there is no barrier for selfing. Carrot variety Brasilia is resistant to nematode, Meloidogyne incognita, while species Daucus carota subsp. hispanicus has resistance to other nematode, M. hapla (Simon, 1993). The genetic material, resistant to disease and pest of carrot, which can be used for developing hybrids for abiotic stresses, are given in Table1.

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16 BULB CROP

Onion Genetic Resources In onion, much variation exists in bulb characteristics for size, shape, colour of skin and flesh, number of hearts, skin retention, firmness, pungency, TSS, yield etc. Bulbs may be white, red, brown or yellow, round, globe, flat or spindle shaped. Diversity is also found in field tolerance to Stemphyllium blight, purple blotch, basal rot and thrips. Various workers have also reported tolerance to soil salinity, reduced bolting, keeping quality and high dry matter content. In India, NBPGR, New Delhi, is a nodal agency engaged in collection, evaluation and maintenance of onion germplasms both from indigenous and exotic collections. Accessions numbering more than 1,000 onion germplasm lines are being maintained at NBPGR, New Delhi. Other centres maintaining sizeable number of germplasms are IIHR, Bangalore, Mahatma Phule Krishi Vidyapeeth, Rahuri, NHRDF also NRC on Onion and Garlic, Nasik; IARI, New Delhi, PAU, Ludhiana and IIVR, Varanasi. Indigenous collections account for more than 95% of the germplasm lines maintained in onion, which indicates the existence of large amount of variability within the country for short-day onions. However, it also indicates the necessity to enrich the existing germplasm pool by importing more exotic collections. Promising germplasms for different attributes are given in Table1.

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17 HINTS FOR CULTIVATION

Tomato Tomato, a warm season vegetable, requires a long season to produce a profitable crop. The optimum range of temperature for its cultivation should be 21–24ºC. The mean temperatures below 16ºC and above 27ºC are not desirable. The minimum, optimum and maximum soil temperatures for seed germination are 10º, 30º and 35ºC, respectively. Maximum seed germination occurs at 24ºC. Maximum fruit setting occurs at night temperature of 15-20ºC. Flowers fail to set fruit below 13ºC and beyond 38ºC. Formation of red colour due to lycopene is inhibited when temperature exceeds 32ºC. Lycopene is highest at 21-24ºC, while its production drops off rapidly above 27ºC. Tomato plants are highly susceptible to high rainfall areas if proper drainage is not available. It is grown in many types of soil from sandy to heavy clay. A well-drained fairly fertile loam soil with a fair moisture-holding capacity is ideal for growing its good crop. It prefers a soil having a pH of 6.0 - 7.0. Application of liming is beneficial if it is cultivated in acid soils. It can be grown almost round the year. The planting seasons vary from place to place. In northern India, for spring summer crop, it is sown in November and transplanted in second fortnight of January. In area, where frost does occur, it is sown in July-August and transplanted in August-September. In hilly areas, it is sown in March-April and transplanted in April-May.

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18 End Pages

GLOSSARY Abortion of pollen-grains: Shedding of pollen-grains before attaining full maturity. Adaptation: The process by which individuals (or parts of individuals), populations or species change in form of function in such a way to survive better under given environmental conditions. Additive gene effect: Gene action in which the effects on a genetic trait are enhanced by each additional gene, either an allele at the same locus or genes at different loci. Allele: An allele is an alternative form of a gene. Allogamy: When pollen-grains from flowers of one plant pollinate the flowers of another plants. Anther culture: The culturing of anthers in vitro for generating haploid plantlets. Anthesis: Full flower expansion including anther extrusion. Antibody: Substances in a tissue or fluid of the body that acts in antagonism to a foreign substance (antigen). Antigen: A substance, usually a protein, introduced into a living organism that elicits an antibody formation.

 
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