eChapters

The research work carried out throughout citrus growing countries of the world including India showed utility of different rootstocks for citrus plants, which varies greatly with scion variety and agro-climatic condition. A wide range of citrus rootstocks are available, each having desirable attributes. The success of a rootstock is determined by its tolerance to prevailing conditions of soil, climate and diseases. Citrus plants are unusual in that many species and cultivars including the commercial rootstocks reproduce true to type from seed. Commercial citrus rootstocks are usually highly polyembryonic but there can be 1-40 zygotic seedlings in the seedbed.

Citrus fruits are originated in the tropical and sub tropical regions of South East Asia, particularly in India and China. North East India is the native place of many citrus species. Citrus fruit has been cultivated in an ever-widening area since ancient times. Although oranges are the major fruit in the citrus fruits accounting for about 70 per cent of citrus output, the group also includes small citrus fruits (such as tangerines, mandarins, clementines and satsumas), lemons, limes and grapefruits. Citrus fruits are consumed as fresh fruit or utilized for preparing processed citrus products. Approximately one third of total citrus production is utilized for processing. India ranks sixth in the production of citrus fruits in the world. In India, it is primarily grown in Maharashtra, Andhra Pradesh, Punjab, Karnataka, Uttaranchal, Bihar, Orissa, Assam and Gujarat. Citrus fruits have several beneficial health and nutritive properties. They are rich in Vitamin C and folic acid, as well as a good source of fiber. In addition they contain potassium, calcium, folate, thiamine, niacin, vitamin B6, phosphorus, magnesium and copper.

Genus : Citrus
Species : Sinensis aurantium, limon, medica grandis L. paradisi Macf. reticulata Blanco
Family : Rutaceae
Chromosome No. : 2n = 18

Citrus is one of the most important and popular fruit of the world which is widely cultivated in almost all of the tropical and subtropical parts of the world. Amongst the subtropical fruits in respect of average it occupies the third position. In India too it is next to mango and banana in commercial perpective. Citrus fruits on account of extensive adaptability are successfully cultivated in tropical, subtropical and even in the marginal temperate regions where the condition are somewhat favourable with its attractive appearance (foliage) distinct flavour and above all its excellent fruit quantity, citrus is liked by one and all. Fruits are not only refreshing and delicious but are also very rich in vitamin C and is good source of A and B, with fruit sugar acids, minerals like Ca, P, Fe. They are essential and play significant role in health promoting constituents in human diet, significance of citrus fruits in diet is very well established. Limes and lemons

Citrus is one of the most important fruit crops of the world. The most important commercial citrus fruits in India is mandarin oranges followed by sweet oranges, lemons and acid limes. Citrus fruits are used for fresh fruit juices, processing into squashes, marmalades and its essential oils from peel are widely used in flavouring, perfumery and cosmetic industry. The citrus peel is one of the important sources for manufacture of pectin.

It is believed that most of the species under the genus citrus are native to tropical and subtropical regions of South-East Asia, particularly India, China and in the region between these two countries. The north-eastern region of India is considered as one of the natural homes for few species of citrus. The other major citrus producing countries of the world are Brazil, USA, India, China,Mexico, Spain, Egypt, Italy, Indonesia and Trukey.

Sweet Orange (Cirus sinensis Osbeck) or Mosambi

Sweet orange is one of the most widely favored citrus fruit of of the world. Its scientific name is Citurs sinensis Osbeck. The sweet oranges are generally round to oval in shape; tight skinned with solid central core. The skin is yellow to orange in colour, smooth and pulp is yellow to orange or reddish. The segments are tightly attached to one another. The commercially important varieties are Malta (Blood Red), Mosambi and Satgudi. Other exotic varieties like Valencia, Washington Navel of USA and Shamouti of Isreal.

Genus Citrus (Citrus spp.) belongs to family Rutaceae and subfamily Aurantioedae. Citrus fruits are cultivated over a wide range of agroclimatic conditions because of their ability to adapt to different situations. Citrus is considered to be one of the most remunerative fruit crops in India, having a lasting niche in the international trade and world finance. Most of the Citrus species are believed to be native to tropical and subtropical regions of southeast Asia, particularly, northeastern India and the region between China and India (Ghosh, 2007). Trees belonging to genus Citrus are comparatively small in size (other perennial fruit crops) and evergreen in nature that are grown in tropical, subtropical and even mild temperate climates. Citrus fruits are nonclimacteric so they do not ripen further once removed from the trees. So it is important that they are picked at the right stage of maturity.

Citrus crop includes lime, lemon, sweet orange, mandarin orange, Kamala orange, grapefruit, malta and pomelo etc. The disease which attacks one species of citrus mostly attacks other species also.

Subtropical and Tropical Fruits

Most of the area of India experience subtropical and tropical climate. Subtropical and tropical fruits contribute maximum to the overall fruit production. Major fruit crops cultivated in subtropical and tropical region are citrus, mango, litchi, guava, sapota, pomegranate, banana, ber, sapota, grapevine, papaya etc. Various pests affect the fruit production by infesting at various stages of the tree growth quantitatively as well as qualitatively. The pests of these crops are described fruit wise.

Citrus

Most of the area of our country is tropical and subtropical, where the citrus, Citrus spp. cultivation is practiced and main citrus growing areas are in Maharashtra, Andhra Pradesh, Punjab, Karnataka, Uttarakhand, Bihar, Orissa, Assam and Gujarat. As for as the ranking in the world

Citrus butterfly: Papilio demoleus, P. polytes : Papilionidae

The pest is distributed all over the world and has a host range that includes citrus and other rutaceae plants like Aegle marmelos. Adult has the head and thorax black with a creamy-yellow coloration on the underside of the abdomen. Wings are dull black, orna-mented with yellow markings and a distinct red patch on the hind wing. The underside is orange and yellow coloured and can be seen when it flirts for honey collection or just before egg laying. The Antenna is black and clubbed.

Origin and history: Citrus is the leading fruit crop in the world. In India, citrus ranks second in area sharing 12.8% of the total area under fruit crops with 9.6% share in production. Under citrus group, mandarins are the most important, occupying 50% of the total area under citrus followed by sweet orange and limes. Citrus fruits are grown mainly in Maharashtra, Andhra Pradesh, Punjab, Karnataka and North-Eastern region. 

1.    Nagpur mandarin was introduced in India in 1894 by Shriji Raja Bhosle. 

2.    Kinnow can be grown in high density planting by using the cultivar  Troyer Citrange'  as a root stock by spacing the plants at 1.8 x 1.8 m2. 

3.    Classification of citrus was given by Tanaka and Swingle. 

4.    Grape fruit is also known as Forbidden fruit, Breakfast food.

Citrus is a major fruit crop grown all over the tropical and subtropical region of the world. Maximum citrus species are native of tropical and subtropical regions of South East Asia specially India, China in the area between these two countries. It is mainly cultivated in China, Brazil, India, USA, Mexico, Spain and Egypt in the world. China is the leading producer country in the world followed by Brazil, India and USA. India is the third largest citrus producer which has 4.8 per cent of the world’s total citrus production.

The prime objective of any plant breeder is to develop high yielding varieties and make the quantity of quality seed of those varieties to farmers for commercial cultivation to realize the benefits of superior varieties. This necessitates, the production of seed of improved varieties in large scale in order to make them available to farmers without losing their genetic purity. Seed production is a continuous process. The seed of improved varieties are produced in several stages, each class producing a special class of seed. The various classes of improved seeds are recognized in order to facilitate seed production and to ensure continuous supply of quality seed. A seed production programme for the production of quality seed has different classes of seeds viz; nucleus seed, breeder seed, foundation seed, registered seed and certified seed. The Association of Official Seed Certifying Agencies (AOSCA) has defined these seed classes as follows:

1. Nucleus Seed

Basic or nucleus seed is the original seed of a released and notified variety. Nucleus seed is multiplied by single plant progeny system, using the concept of maintenance breeding, where purity of the original parental stock is maintained. It is available in very limited quantities and taken from the individual plant of a variety for purification. It is directly under the controlled of concerned crop breeder. This seed has hundred percent genetic and physical purity. Breeder seed is multiplied out of this material and about 500-1000 plants are kept for continued multiplication of nucleus seed.There is no need of any type of tag on nucleus seed but concerned breeder issue a certificate for purity.

3.1 Introduction

Genetics deals with genes and cytogenetics with chromosomes that harbour genes. On the other hand, plant breeding strives to upgrade the genotypes of crop plants. So, the plant breeding methods should be based on genetic principles. Dear students, you should have clear understanding of genetics in broad sense so that you can appreciate the applicability of breeding methods. As I have already pointed out that you have been taught the course ‘Principles of Genetics and Cytogenetics’ in the first semester, only a brief discussion is followed for your review and better understanding.

3.2 Character

When we call ‘character’ or ‘trait’ in genetics, we mean any morphological, anatomical, biochemical or behavioural feature of an organism. For instance, flower colour, blooming period, leaf size, size of guard cells in stomata, vitamin C content, disease resistance etc. A single gene or a number of genes may govern the development of a character and, often it is influenced by the environment. Characters may be qualitative or quantitative.

Fruit crops can be classified into many groups or categories based on certain criteria, which may vary according to climatic and soil requirements, growth habits and of late with consumer rating. Horticultural and botanical classifications are two important types of classification followed in fruit plants. Classification often helps to identify the names and to group the plants. It also gives an account about relatedness among them which further suggest the breeding possibility and grafting compatibility. Different types of classifications followed are discussed here:

CLASSIFICATION BASED ON CLIMATIC REQUIREMENT

Fruit plants are classified based on their climatic adaptability and it is also known as ecological classification. In horticultural point of view, this classification has got much significance. Fruit growers can select crops suited to a particular region by following the demarcations given here. Fruit plants are categorized into the following groups in this classification.

Temperate fruits

Fruit crops need exact climatic requirements for their growth and development, flowering and fruiting. These plants are grown only in places where winter is distinctly cold, they are deciduous and become dormant during this season. Plants should be exposed to specific chilling temperature for certain period for flower induction. These plants are suitable to higher elevations and they can withstand frost. eg. Apple, plum, peach, pear, almond, walnut.

Classification of fruits: Classification is the system of grouping or placing of an individual according to nomenclature. It is very useful to the pomologist, it helps to:

•    To identify and naming the crop.

•    To study the close relationship.

•    To know their hybrids and crossing behavior.

•    To know their compatibility & inter grafting ability.

•    To know their adoptability to soil & climate.

Pomology: Pomology is a branch of horticulture which deals the cultivation utilization and management of the fruit crops. eg. Mango, Banana, Citrus, Papaya, Guava etc. The term pomology is a combination of two words “Poma” in Greek means Fruits later subsequently transfer in to “Pome” in Latin word means Fruits and Logos means Study.

1. Fruit : Types and their Classification

Fruit:The botanical definition of fruit is a seed-bearing part of a flowering plant or tree that can be eaten as food

or

Fruits are matured ovaries plus any associated flower parts and contain the seeds of the plant. The ovary may be subdivided into two or more carpels (then termed compound ovary) each bearing one to many ovules. Individual carpels develop into sections of a whole fruit, as with citrus where each familiar segment of the fruit represents one matured carpel. If the ovary is not subdivided, then it is termed simple. The ovules will mature into seeds if fertilized. Fruit has three parts.

I. Classification of fruit crops

1. Based on botanical relationship

2.1 INTRODUCTION

Owing to a varied agro-ecological and eco- edaphic condition prevalent in one or other part of the country, quite a large number of crops are grown in different parts of India. India is rich in bio-diversity with four hotspots out of twenty-five in the world. About 356 domesticated plant species having economic and botanical importance and 326 species with their wild relatives are found in Indian sub-continent. Besides the above, 9500 other plant species are also available. More than 50 different types of fruits, 50 different types of vegetables, 95 types of spices and condiments, medicinal and aromatic plants, plantation crops and ornamental crop plants have been recorded. To avoid confusion and identity, the horticultural plants are grouped into different categories based on similarity or dissimilarities. Grouping of the crop plants with similar characteristics is referred as classification.

Classification is system of placing an individual or a member in various groups or to categories them according to particular plan or sequence which is in conformity with the nomenclature. From time-to-time for purposes of convenience plants or fruits have been classified in various ways that makes possible to refer them to a large number of kinds under a group name without enumerating or specifying individually. The basis of these groupings varies according to the features of fruits or growth of the fruit plants that have been under classification at the time.

Knowledge of classification of horticultural plants is very useful to the horticulturists because it serves: (1) to identity and name them, (2) to afford at least some idea of the closeness of their relationship i.e. line of descent to other kinds, (3) to suggest with what other kind they possibly may or may not be interbred or crossed, (4) to suggest the kinds with which they possibly may or may not be inter-grafted, and (5) often to suggest certain soil and the cultural requirements, climatic adaptations etc. However, the classification of fruit trees or fruits and vegetables on the basis of consumer’s rating also gained attention in recent years. The consumers’ rating is mainly based on the size, shape, nutritive value and marketability of them. Each of these classifications is quite different from the other classification or groupings.

Basically, the fruit trees, as suggested by many authors, have been classified on the basis of their botany comprising of taxonomic ancestry, morphologic features, physiological functions, adaptability etc. or on the basis of agricultural and horticultural requirements. But the consumers’ rating has not been properly covered in the earlier classification. Generally based on botanical relationship the plants are classified as under.

Grouping plants in different categories on the basis of similarities and dissimilarities is referred to as classification, which helps for study of these crops in various perspectives. India is endowed with a rich diversity of horticultural plant wealth due to varied agro-climatic conditions. Number of fruits, vegetables, ornamental crops, spices, condiments, plantation crops, etc. is under commercial cultivation in different parts of the country under different sets of growing conditions.

The systematic study of all these crops becomes a difficult and more repetitive part. To avoid it; classification of horticultural crops on different aspects has been made to deal with all these plants separately. Classification of horticultural crops has been made in different groups on similarity or dissimilarity of attributes. Plants having similarity in either of the traits are placed under one group. The overall objective of the classification is to categorize the horticultural plants and make the recollections very easy and convenient.

2.1 Clean Cultivation

This type of cultivation is extensively followed in India. It involves regular ploughing of the land followed by removal of weeds. Tilling the orchard soil regularly provides a weed free environment in the orchard. Traditional tillage with the spade or hoe involves shallow cultivation and partial burying of weeds. Use of animals for ploughing reduces the labour cost but some superficial tree roots get damaged in ploughing. Tractor drawn tool can be used during initial years when the orchard trees are not fully grown. Branches hanging low, spreading in the inter-row spaces hinders the movements of the tractor even in widely spaced rows at maturity in most of the orchards. Under such situations small power tillers can be used. Tillage controls weeds partly through burying weeds and partly through exposing underground parts of weeds to desiccation. The land around the trunk must be cleaned separately with the help of spade as it is difficult to operate a power implement in the vicinity of the trunk. This is very instrumental in saving soil moisture. It has immense effects on the soil properties. Cleaning removes the protecting layer of vegetation and exposes the soil surface to weathering, and thus reduces the frequency of additions of organic matter to soil. Cultivation physically disturbs soil, mixing upper and lower layers. In this management system, the interspace between the trees is kept clean by tillage by removal of weeds. Clean cultivation by tillage influences the soil aggregate size and stability, porosity and pore size distribution, and the development of sub-surface layers of high bulk density (hard pans). The first change that occurs with tillage is the disruption of established soil pore continuity (Chan and Mead 1989). Organic carbon and nitrogen decline to a new equilibrium value depending on tillage intensity, cropping system and climate.