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Edible legumes are excellent sources of dietary protein and oils. Winged bean, otherwise known as Goa bean, Manila bean, princess pea, asparagus pea or four angled bean is becoming popular as a tropical legume vegetable. It is a multivitamin and multimineral packed legume. This wonder vegetable was considered as the vegetable of the twentieth century. It is also known as ‘soya’s rival’ or ‘God sent vegetable’. All parts of the plant are edible namely leaves, flowers, immature pods, immature seeds, mature seeds and tubers. It is also named as ‘a supermarket on a stalk’ because the plant combines the desirable characteristics of common bean, pea, spinach, mushroom, soya bean and potato. Its vernacular names are:  Bengali, Chara-koni-sem or lakar-sem; Tamil, Morisuavarai; Kannada, Shambe kayi; Malayalam, Chaturapayar or irachipayar and Marathi, Chavdhari ghevda.

Lesser yam, Lesser Asiaticyam (Dioscorea esculenta) is among the most ancient species of the genus and its centre of origin is stated by various authorities as India, Vietnam or Papua New Guinea and the Philippines. It is domesticated as a staple food in Southern China from 2nd and 3rd centuries. Today, it is widely distributed throughout the tropics, but is little used except in South East Asia, where it is grown to such an extent that it ranks third in production and utilization of yams after D. rotundata,D. cayenensis and D. alata. Wild types of D. esculenta also exist in Malaysia, New Guinea and Philippines.  The wild types have more leaves, large roots, longer stolons, more fibrous tuber flesh and more thorny roots and shoots.

Classification
The wild types of D. esculenta (Family: Dioscoreaceae) exist in Malaysia, New guinea and Philippines. Wild types have more vigorous foliage, larger leaves, longer stolons, more fibrous tuber flesh and more thorny roots and shoots.  On the basis of thorniness, the cultivated types are distinguished into two botanical varieties.

Dioscorea alata is commonly called greater yam or larger yam or water yam.  This is the most widely distributed species of yam. This species originated in South East Asia, probably in Burma. From there, it first spread to India, Malaysia, Indonesia and the eastern portion of South East Asia.  Later it served as food for voyagers and thereby spread to other parts of the tropics.  Immigrants from India and Malaysia introduced it to Madagascar, from where it was partially introduced into East Africa and Portuguese and Spanish voyager traders of the 16th century probably introduced it into West Africa and later to West Indies.

Coleus, commonly known as Chinese potato, is a minor tuber crop of the tropical regions of India, Indonesia, Malaysia, Sri Lanka and Africa. It is considered as a native of India , where its cultivation is mostly confined to the southern states. In Kerala, it is commonly known as koorka or cheevakizhangu. In Malaysia it is called ubi kemili, kentang kechil, kembili and kumbili java. It is also known as hausa potato, Sudan-potato, country potato, fra-fra potato, fra-fra-salanga, ratala, pomme de terre du Soudan, hausakartoffel, innala, saluga, tumuku and fabirama. 

Nutritive status
The nutritive status of this crop compares favourably with many of the major tuber crops.  Coleus tuber, with its characteristic  flavour has a special preference among consumers. Compared to other tuber crops, it fetches premium price in the market, although it is known as poor man’s potato. The tubers are used for the preparation of various delicious side dishes. Reliable data on area and production of this crop are not available. Despite the high market price and consumer preference, it is not available throughout the year.

The term arrowroot is commonly applied to many starch producing plants belonging to different species whose economic part is the rhizome, eaten fresh or made into flour. The term applies both to flour and the plant. All the plants of the arrowroot group have underground rhizomes or tubers from which arise reed like erect stems. The word ‘arrowroot’ is derived from the pointed shape of the rhizome or its known ability to cure arrow injuries. The word itself is derived from the carib word araruta meaning mealy roots. The arawak, a people native to the Caribbean islands, considered arrowroot a dietary staple. They called it aru-aru meaning meal of meals.

Tripura is situated between 22º 56’to 240 32’ N latitude and 91010’ to 92021’E longitude with tropic of cancer passing through it. The total geographical area of state is about 10,491 km2 of which 57.98 % area is under forest cover.  Agriculture is an important sector in the state, which contributes 26 % of the State GDP of which the major contribution is from horticultural crops like fruits (pineapple, litchi and oranges), vegetables (potato TPS), plantation crops (cashew nut, coconut, rubber and tea) and spices (ginger, turmeric and black pepper). More than 75 % of the population either directly or indirectly depends on agriculture. The small and marginal farmers constitute about 90 % of total farming community and the average size of land holding is 0.97 ha (1990-91) in comparison to 1.25 ha (1976-77), which is the lowest among the seven other North Eastern states.

California’s Napa Valley, situated at the northern end of the San Francisco Bay 30 miles (48 kilometers [km]) from the Pacific Ocean, is the most famous wine appellation in the United States. This small valley, 56 km long and 8 km wide at its broadest point, has produced some of North America’s finest wine grapes from the 1850s to the present. Today it contains approximately 18,616 hectares [ha] of vineyards along the valley floor, in the foothills and mountains flanking the main valley and in the smaller valleys in the eastern part of Napa County [45].

Root and Tuber crops are the most important food crops of man after cereals. Tuber crops are efficient producers of carbohydrates especially under suboptimal conditions of rainfall, fertility and low input conditions encountered in tropics. The group contributes about 6 % of the world’s dietary calories. In fact, one out of 6 kg of human food comes from roots and tubers. Tuber crops find an important place in the dietary habits of small and marginal farmers especially contributing to food security of tribal populations. Tuber crops grown in India include Cassava, Sweet potato, Dioscorea, Colocasia, Amorphophallus and minor tuber crops like Chinese potato, Arrowroot, Canna, Yam bean etc. The biotechnology can contribute to the solution of the major problems and realize greater benefits for tuber crops.

Ethylene is a primary plant hormone involved in the senescence of plant tissues including flowers and leaves. In carnation flowers, inhibition of the synthesis or action of ethylene delays the onset of senescence symptoms and lengthens the vase life of flowers. Leaves of cut chrysanthemum of some cultivars frequently become yellow, sometimes prior to the onset of flower senescence, in response to exogenous ethylene. Generation of transgenic plants with suppressed production or action of ethylene is an excellent way to lengthen the longevity of these ornamental plants. This paper reviews our studies on generation and characterization of carnations with reduced ethylene production and chrysanthemum with reduced sensitivity to ethylene.

Use of morphological markers has continued till today for characterization of several crops including horticultural crops with the Mendel’s principles of inheritance by following visible traits in the progenies of sexual crosses. Genetic markers play an essential role  in the study of variability and diversity, in the construction of linkage maps, and in the diagnosis of individuals or lines carrying certain linked genes. Within this context, the limitations of morphological markers became quickly apparent. They tend to be restricted to relatively a few traits, display a low degree of polymorphism, are often environmentally variable in their manifestation, and can depend on the expression of several unlinked genes. Furthermore, some may affect plant viability or seed set, distorting gene frequencies in the progeny. Morphological markers were largely supplemented by biochemical markers, particularly isoenzymes that could be easily scored by electrophoresis (Ganapathy and Scandalios 1973; Tanksley 1983). The limitations of isoenzmyes as markers, in particular both the limited number of polymorphic enzymes that can be conveniently stained and the environmental effects on expression pattern, were apparent already twenty years ago (Tanksley 1983).

The term DNA sequencing refers to methods for determining the order of the nucleotide bases, adenine, guanine, thymine and cytosine, in a molecule of DNA. In molecular terms ,the definitive understanding of a DNA molecule comes from determining its nucleotide sequence.The function of a gene can be deduced from its nucleotide sequence,for example by comparing the sequences of genes with known functions.

The first DNA sequences were obtained by academic researchers, using laborious methods based on 2 – dimensional chromatography in the early 1970s.  Following the development of dye-based sequencing methods with automated analysis, DNA sequencing has become easier and orders of magnitude faster.  Knowledge of DNA sequences of genes and other parts of the genome of organisms have become indispensable for basic research studying biological processes, as well as in applied field like diagnostic or forensic research.  The advent of DNA sequencing has significantly accelerated biological research and discovery.

Plant Growth Promoting Rhizobacteria (PGPR) are free-living bacteria  having beneficial effect on plants by root colonization. They stimulate plant’s growth. Intensive research work is carried out on use of various PGPR as plant growth promoters on various crops. There are reports which show that PGPR promoted growth and reproductive parameters of cereals, pulses, ornamentals, vegetable crops, plantation crops and even  tree species. The important PGPR used in vegetable crops are Azospirillum, Azotobactor, Pseudomonas fluorescens, Phosphate Solubilising Bacteria (PSB) and Bacillus subtilis.

India is a vast country with varied soil and agro-climatic conditions and therefore is able to grow a wide range of vegetables. In view of their productivity, diversification, nutrition, value addition and export, vegetables are an important component in Indian agriculture. Up to 1939, vegetable seeds were used to be imported from Australia, U.K., U.S.A., but after World War I and II, India started seed production of vegetables. In the recent past, the seed industry has made rapid strides over the past three decades and has contributed significantly to the quantum jump in agricultural production and India emerged as the second largest producer of vegetables, next to China in the world. During 2005-2006, India produced 113.5 million t of vegetables from 7.2 million ha with a productivity of 15.76 t/ha. The seed industry has increased certified and quality seed production and distribution by the organized sector to about 60 lakh quintal from 300q in 1964-65. India can be proud of having launched and managed both crop improvement and seed improvement as simultaneous and parallel programmes playing complimentary and synergistic roles.

The history of plant breeding is divided into 4 periods- knowledge of plant breeding before 1900, application of genetic principles (1900-1940), plant breeding research after 1940 and the recent developments in plant breeding. Emphasis is given on the land marks in genetic improvement of vegetable crops.

The major land marks  in genetics and breeding of crop plants are listed below.

Plant diseases are mentioned in some of the oldest books available (Homer, C – 1000 B.C. mentioned about the therapeutic properties of sulphur and in Old testament – 750 B.C.) and were feared as much as human diseases and war.

Food irradiation involves exposure of food to short wave energy to achieve specific purposes like extension in shelf life, insect disinfestations and elimination of food-borne pathogens and parasites. Compared to heat or chemical treatment, irradiation is more effective and an appropriate technology to destroy food-borne pathogens without much loss to the quality of food. It offers a number of advantages to producers, processors, retailers and consumers. Irradiation is a cold process and can be used to pasteurize and sterilize foods without affecting freshness and texture of food. Unlike chemical fumigants, irradiation does not leave any harmful toxic residues in food and is more effective. It is efficient and can be used to treat prepacked commodities. The FAO estimates that about 25% of world’s total food production is lost due to insects, bacteria and rodents after harvesting. Use of radiation can play an important role in cutting these losses and reducing dependence on chemical pesticides. The food borne diseases claim millions of lives all over the world every year. Irradiation of food can reduce these incidences by destroying harmful microorganisms.

Polyembryony is the occurrence of more than one embryo in a seed. It includes all those instances in which there is a clear indication of the actual occurrence of two or more embryos in a developing ovule (Tisserat et al. 1979). The additional embryos in polyembryony result from the differentiation and development of various maternal and zygotic tissues associated with the ovule of seed. Earlier, polyembryony is said to have an abnormal feature but now it is considered as a desirable character in citrus, mango, jamun, almond, etc. to obtain true to type planting materials. The polyembryony is one of the apomictic processes which have been described to occur in the ovules of angiospermic species (Koltunow, 1993). Polyembryony in horticultural crops occurs as facultative apomixis wherein simultaneous growth of multiple embryos of somatic origin co-exist in the same seed containing sexual embryo resulting from either selfing or cross pollination.

Vegetables are the most extensively utilized plants for  exploitation of heterosis for  development of hybrids. As the importance of heterosis breeding increased, male sterility proved an asset particularly in crops like onion and carrot which produce many but small sized flowers making hand emasculation tedious. Large scale hybrid seed production sometimes remains handicapped because of high labour cost, unavailability of trained labour at crucial times i.e. at blooming, bad weather conditions like continuous rains etc. The phenomenon of male sterility has always been of long term interest for  researchers of various disciplines of applied, strategic and basic sciences. It is of special interest for  plant breeders to produce more efficient and economic hybrid seed. Discovery of certain male sterile mutants which  eliminate more laborious operations of emasculation combined with various marker genes further facilitate identification of undesirable types even at seedling stage has widened the very basis of hybrid seed production. This technique has also reduced the total cost of hybrid seed production. Onion crop provides one of the rare examples of very early recognition of male sterility (Jones and Emsweller 1936), its inheritance and use in hybrid seed production (Jones and Clarke 1943). Since then male sterility is reported in fairly large number of crops including vegetables.

Horticultural crops are ideal and valuable assets of nature to mankind. They are popular among masses since time immemorial but their importance was realized only in the recent past due to their high nutritive value, good taste and pleasing quality. They provide essential nutrients and minerals for proper functioning of human body and aesthetic surroundings for peaceful living. India is an important centre of diversity and several horticultural crops  originated here.  The horticultural crops constitute 13.08% of total crop area and contribute about 28% to GDP. The sub-continent extends from 8° 04’ - 37° 06’ North latitude and 68° 07’- 97° 25’ East longitude and it has tropical, sub-tropical and temperate climates which favour successful growing of a large number of horticultural crops.  India has a wide variety of climate and soil on which a large number of horticultural crops like fruits, vegetables, potato and other tropical tuber crops, ornamentals, medicinal and aromatic plants, plantation crops, spices, cashew and cocoa are grown. Of late, major emphasis was laid on development of high yielding varieties and high production technologies and their adoption in areas of assured irrigation paved the way towards food security.

In the backdrop of a predominantly agrarian economy, India has made tremendous advances in modern agriculture to meet both the food and nutritional security. In recent years, horticulture has assumed great importance mainly to augment nutritional security and secondarily as a highly cost-effective, remunerative and eco-friendly enterprise having vast export potential. To meet the challenges of research and development, tracer techniques have added the much needed fillip as they can be ingeniously applied to resolve issues which are not ordinarily possible using conventional techniques.