·         Bunchy top disease is widely reported in many countries such as Pacific Islands, Australia, Fiji, Malaysia, Srilanka, Egypt and India.

·          In India was reported in 1940 from Kerala.

Primary symptoms:

·         When infected suckers are planted, short narrow leaves which are chlorotic and exhibit Mosaic symptoms are produced.

·         The leave arise in dusters giving a Rosette appearance.

·         They are Brittle with numerous dark green dots or patches and the margins rolled upwardly.

·         The plants do not grow taller than 2 to 3 feet. Moreover they fail to produce any fruit.

Secondary symptoms:

·         The Secondary symptoms may occur when the healthy plants in the field are freshly infected by the Virus, which may happen at any stage of growth.

·         During secondary infection the Premature leaves fail to unfold.

·         More over numerous Spots and Streaks appear on the blade.

·         These symptoms are common along the secondary veins and on the midrib and petiole.

·         The leaves which are formed subsequently exhibit similar symptoms but more intensively.

·         The leaves become paler and much reduced in size which finally develops the characteristic Rosette or "Bunchy top" appearance.

·         The infected leaves are generally more rigid than the normal ones but they do not wilt. The diseased plants neither die nor recover from the infection.

Causal Organism:

·         The causative organism is a Virus.

·         It is transmissible only through an Insect vector.

·         The Virus is present in all parts of the plant body, including the Rhizomes and suckers.

·          The Virus is transmitted by the banana aphid, Pentalonia nigronervosa.

·         The disease symptoms appear in about 35 to 45 days after inoculation by the insect.

·          The Aphid is required to feed on the infected plant for a minimum period of about 17 hours before it can transmit the disease.

·          The Incubation period inside the victor may be from 90 minutes to 48 hours and they retain their infective capacity for about 13 days.

·         The aphids usually attack the host around the basal portion of the pseudopodium. However they do attack the upper leaf sheath, and petioles


·         The disease can be excluded by strict Quarantine regulations.

·         Measures to check the Insect vector will give some control.

·         Always healthy Suckers must be used to avoid the disease.

·         Systematic Eradication of the diseased plants, suckers and clumps must be carried out.

·         Citrus occupies over 10,0 00 hectares in India.

·          It is a native of sub-Himalayan region and China from where it has spread to various parts of the world. C. sinensis (sweet orange) C. aurantifolia ( acid lime ) C. medica ( Citron) are some  of the very important species of citrus under cultivation.

·          Among the various diseases bacterial canker is one of the severe diseases of citrus in India.

·          If affects Acid lime more than other species of citrus.

·         According to Fawcett bacterial canker had its origin in India from where it spread to the rest of the world.

Casual Organism

·         This disease is caused by the bacterium Xanthomonas campestris .

·         The pathogen affects all plant parts above ground level, i.e., the leaves, twigs and fruits.

·         In 1915, HASSE was the first to establish the bacterial nature of the disease and to describe the organism as Pseudomonas citri.

·          In 1957, Breed et al included it under Xanthomonas citri.

·         It is a short rod shaped bacterium, motile by a single polar flagellum. Symptoms

·         The symptoms appear upon the infected plants as minute roundish spots, which enlarge slightly and turn brown and corky.

·          The size of the lesions, (2 to 10mm) varies with the plant species.

·         The canker lesions on the fruits very often coalesce to form a patch.

·         The market value of the fruit is considerably reduced by these canker spots.

·          The leaves when infected severely suffer by defoliation and the infected twigs and stem exhibit die back symptoms.

·          The plants are also stunted and the fruit yields are reduced considerably.

Dissemination of the pathogen:

·         The thorny variety of citrus gets wounded by the thorns moving in the wind.

·         Opening up wounds for the entry of the pathogen, from air, rain water and other sources.

Control measures:

·         The disease can be checked by periodic sprays with Streptomycin sulphate at 500 p.p.m..

In the case of nursery seedlings the canker can be controlled by sprinkling Neem cake suspension 10-20 times during a year

·         Meristem (Gr. Meristo - divisible) is defined as a group of young and`undifferentiated cells possessing the property of Active cell division.

·         The Meristems are also called Formative tissues as cells divide and form new cells.

·         The Meristematic cells are Small and Isodiometric. The cells are thin-walled and rich in cytoplasm with a large nucleus.

·         A Meristem formed of such cells is known as Eumeristem.

·         The cells of meristem are compactly arranged without intercellular spaces.

·         The vacuoles are absent. The plastids are in the form of Pro-plastids.

·         Meristems in plants are classified based upon the time of Origin, Function, Stage of development and division.

·         Based on the position, meristems are classified into a namely Apical meristems, Intercalary meristems and Lateral meristems.

Apical Meristem

·         Apical meristem occurs at the growing points of the place the tips of stem and root.

·         The cells of the apical meristem and give rise to the various tissues in the primary body of the plants.

·         The increase in length of these organs is due to the of the apical meristems.

Intercalary Meristem

·         Intercalary meristems are placed between Permanent meristerns are part of Apical meristem left behind as terms move on in growth.

·          The intercalary meristems found in the Internodes of the stems and leaf sheaths of monocotyledons.

·         The intercalary meristems are short are transformed into permanent tissues later.

Lateral Meristem

·         Lateral meristems lie parallel with the sides of plant organs.

·          The vascular cambium and the cork cambium or phellogen are lateral meristem.

·         These meristems increase the diameter of the plant organ.

·         The cells of these meristems divide in only one plane.

·         Bioinformatics is the branch of science which uses the applications of information technology and computer science into the field of molecular biology.

·         It was Paulien Hogeweg who invented the term Bioinformatics in 1979 to study the processes of information technology into biological systems.

·          The science of bioinformatics actually develops algorithms and biological software of computer to analyze and record the data related to biology for example the data of genes, proteins, drug ingredients and metabolic pathways.

·         As biological data is always in raw form and there is a need of certain storage house in which the data can be stored, organized and manipulated.

·          Biological software and databases provide the scientists this opportunity so that the data can be extracted from these database easily and can be used by the scientists. 

·         Bioinformatics joins mathematics, statistics, and computer science and information technology to solve complex biological problems.

·          These problems are usually t the molecular level which cannot be solved by other means. This interesting field of science has many applications and research areas where it can be applied.

·         Sequence Analysis
The application of sequence analysis determines those genes which encode regulatory sequences or peptides by using the information of sequencing.

·         For sequence analysis, there are many powerful tools and computers which perform the duty of analyzing the genome of various organisms.

·         These computers and tools also see the DNA mutations in an organism and also detect and identify those sequences which are related.

·          Shotgun sequence techniques are also used for sequence analysis of numerous fragments of DNA.

·         Special software is used to see the overlapping of fragments and their assembly. 

Prediction of Protein Structure

·         It is easy to determine the primary structure of proteins in the form of amino acids which are present on the DNA molecule but it is difficult to determine the secondary, tertiary or quaternary structures of proteins.

·          For this purpose either the method of crystallography is used or tools of bioinformatics can also be used to determine the complex protein structures.

Genome Annotation

·         In genome annotation, genomes are marked to know the regulatory sequences and protein coding.

·          It is a very important part of the human genome project as it determines the regulatory sequences.

Comparative Genomics

·         Comparative genomics is the branch of bioinformatics which determines the genomic structure and function relation between different biological species.

·         For this purpose, intergenomic maps are constructed which enable the scientists to trace the processes of evolution that occur in genomes of different species.

·         These maps contain the information about the point mutations as well as the information about the duplication of large chromosomal segments.

Health and Drug discovery

·         The tools of bioinformatics are also helpful in drug discovery, diagnosis and disease management.

·          Complete sequencing of human genes has enabled the scientists to make medicines and drugs which can target more than 500 genes.

·          Different computational tools and drug targets has made the drug delivery easy and specific because now only those cells can be targeted which are diseased or mutated.

·          It is also easy to know the molecular basis of a disease.

Modern computeres used in bioinformatics

·         Computers can be classified into different types based on memory size and processing speed.

·         The major types of computers are supercomputers, mainframe computers, super mini computers, modern portable computers.

·         Supercomputers –  The computers that have the memory as high as 256 megabytes are called called supercomputers or maxi computers.

·         They are 4000 times faster than the fourth generation computers.

·         ILLIAC-IV is a super computer that can do 64 calculations at a time.

·         It is used for scientific research, weather forecasting, oil exploration, weapons research,seismic data processing.

·         Mainframe computers – The large computers having a memory of 128 megabytes are called mainframe computers. They are named so because their peripherals are fitted on a frame – like cabinet. Eg. ACOS 100, ICL 9.

·         They are large general- purpose computer with a large memory and excellent processing capabilities.

·         They are ideal for transaction processing, financial applications, payroll, investment analysis, banking, airlines reservation etc.

·         Super mini computers – computers having 32 – bit word and 80 megabytes memory are known as super mini computers or midrange computers. Eg. VAX-II, TDC 332, Wipro’s pyramid 90X etc.

·         They are used in research and development, on line production control, data processing.

·         Minicomputers – computers having 500 Kb -5Mb of memory are called minicomputers. Eg. ICL 39, TDC 316  SN – 23 ETC.

·         These are multi- user systems for 8 users at a time.

·         They have excellent memory capabilities and processing speeds.

·         They are suitable for smaller concerns to enter into the age of computing, as they are easily affordable.

·         Microcomputers – the small modern computers having 256 kilobytes of memory are called microcomputers. They are called so because of their miniature size and of using microprocessor.

·         The microcomputers are categorised into two types- work stations and personal computers

·         The workstations are faster and lie between midrange computers and PCs.

·         Engineers, designers, architects and film-industry animators are heavy users of workstations.

·         PCs a compact, powerful and versatile machine.

·          They are used in learning programming, computer based games and funs, business uses, Accounting, music composing.

·         Modern portable computers- laptops and notebooks are designed on the basis of mobile computing technology.

·         These are small computers that are battery-operated and hence can be  used anytime and anywhere.

·         Pocket computers- hand held computers fit into the users pocket and have reduced weight. The three major pocket computers are electronic organizers, palmtop computers, pen computers

·         Personal digital assistants(PDA) – the PDA is b ased on mobile computing technology.it helps the user in organizing his schedules.

The cultural operations are unique to each and every group of horticultural plants. Based upon the method of cultivation, horticulture has been grouped into the following divisions:

·         POMOLOGY is the cultivation of fruit crops. It deals with propagation, improvement, cultivation, training, pruning and protection of fruit crops and harvesting, storage and marketing of the fruits.

·         Pomology is concerned with the cultivaton of major fruits and many under-exploited fruits.

·         Fruit culture being an economic proposition, the area under various fruits steadily increases year by year. Improved varieties and cultural practices including plant protection measures are being developed regionwise for each fruits.

·         The major fruits includes mango, banana, olive, plum, pineapple, pomegranate, dates, sweet cherry, sour cherry, apricot, strawberry apple, guava, pear, peach, cranberry.

·         OLERICULTURE refers to the cultivation of vegetable crops. It deals with the propagation, improvement, cultivation, training, aftercare and protection of vegetable crops.

·         Vegetables crops are commercial crops supporting market gardening, trunk gardening or commercial gardening.

·         Vegetables constitute an important component of a balanced diet for man. Vegetables supply important vitamins and minerals that the human body needs for a healthy and active life.

·         FLORICULTURE refers to the cultivation of plants which give economic flowers. Growing jasmines, roses, chrysanthemum, etc on commercial scale for cut flowers or for extraction of essential oils is the important aspect of floriculture.

·         GARDENING is growing ornamental plants to decorate indoor and an outdoor area is called gardening. Foliage plants, flowering annuals, biennials, perennials, climbers, succulents, cacti, palms, ferns etc are grown in gardens to have good scenery in these places.

·         Laying out of gardens in the interior of houses and other buildings is called indoor gardening. Laying out of gardens in parks, outside the buildings and open places to imitate the natural scenery is called landscape gardening.

·         ARBORICULTURE is growing of tree species alone in specific locations is called arboriculture. Places where such trees are grown are called arboreta. These arboreta are extensively used for aesthetic, educational and scientific purposes.

·         SPICES are plant products used in cookery to season of flavour food. Plant yielding spices are called spice crops. This aspect of horticulture deals with propagation, improvement and cultivation of different spice crops. Importance is also given for storage and export of spices.

·         PLANTATION CROPS are usually grown in large stretches of lands are called plantation crops. This aspect of horticulture deals with propagation, improvement and cultivation of different plantation crops and storage and marketing of their products.

·         MEDICINAL PLANTS which give active principles used in drugs are called medicinal plants. The active principles may be alkaloids or steroids, which are responsible for preventive and curative actions of drugs. Eg Belladonna, Quinine tree, Foxglove, Ephedrine.

·         AROMATIC PLANTS are those which accumulate volatile essential oils in their parts. The essential oils can be extracted from them by means of steam distillation or solvent extraction. They are used in making perfumes, soap, deodorants and toilet preparations.

·         NURSERY is a place where young plants are raised for planting or sale. The young plants may be raised from seeds or grafts or cuttings or layers. horticultural nursery industry has become one of the important branches of horticulture because of the great demand of nursery stocks in every season.

·         PROCESSING INDUSTRIES in which fruits and vegetables are collected during the cropping season and processed to preserve them for making them available while there is no cropping. Such processing industries show rapid development in recent years. They process fruit into jam, jelly, marmelods, squashes, syrups.

·         Fruits and vegetables are the rich sources of vitamin-A, vitamin- B, vitamin-C and minerals such as calcium, phosphorus and iron.

·         As they supply vitamins and minerals to protect people from their deficiency ,they are known as protective foods.

·         Every adult should consume 90g of fruits and 300g of vegetables per day to meet the requirement of vitamins and minerals in human diet.

·         Horticulture provides more food per unit area than the agriculture. For example, grain yield of cereals is 5-10 tonnes/ha but fruit trees give 20-45 tonnes/ha and vegetables give 10-20 tonnes/ha.

·         This high productivity resolves the problems of food shortage due to low yield of agricultural crops.

·         Horticultural crops contribute to the national income by the way of foreign exchange via selling horticultural products.

·         From india, horticulture products like fruits,vegetables, processed fruit and vegetables, spices, cut flowers, seeds, products of plantation crops, etc are exported to other countries.

·         Horticultural crops need more intensive cultural practices so that they require more number of labours for cultivation. Thus horticultural crops generate job opportunities to rural people.

·         Horticultural crops are more profitable than cereals. For example, fruit crops occupy only 1% of total cultivable area of India but they share 4.9% total income from all crops. Therefore, horticultural crops give more remuneration to growers.

·         Fruits have high calorific value. So they are used as high energy food to meet calories requirement of people.

·         Horticultural products are used as raw materials for several industries. For example, rubber, coir and sago industries relay on horticultural crops.

·         Ornamental plants and flower plants occupy a great position in the civilization.

·         Beautiful flowers and foliages are used in flower arrangements to decorate interior of houses and official buildings.

·         Mental problems cause unhappy mood and depression in people. They can be treated with horticultural therapy, by which their attention is diverted to beautiful flowers and garden plants.

·         Here, attractive colours and smell of the flowers help the people to relieve from the unhappy mood. Horticultural therapy is popular in the USA, France and China.