eChapters

Botanical Name: Camellia sinensis L.

Family: Theaceae

Chromosome No: 30

Place of Origin: China

Common Name: Tea

9.1 Introduction

Tea (Camellia sinensis L.) of family Camelliaceae or Theaceae is the oldest and second most widely consumed beverage in the world following water. Tea is an evergreen plant that mainly grows in tropical and subtropical climates. India is world’s 2nd largest tea producer after China with production of 1.25 million tonnes in 2020. In India it is grown in an area of 6 lakh hectares, contributing one fourth of world total tea production annually. Interestingly, India is also the world’s largest consumer of the beverage and using nearly 30 percent of the world’s tea output. India stands third in terms of tea export after Kenya (including neighbouring African countries) and China. The total tea export was US$ 501.16 million in April 2020 to November 2020 and for November 2020 it was US$ 71.61 million.

Botanical Name: Coffea arabica, Coffea canephora

Family: Rubiaceae

Chromosome No: 44, 22

Place of Origin: Africa

Common Name: Coffee

8.1 Introduction

Coffee is widespread throughout the tropics with more than 70 species. All cultivated species originate from Africa. Economically important today is Coffea arabica (Arabica, 64 % of world production) and Coffea canephora, (Robusta, 35 %). It is cultivated worldwide on approximately 10.3 million hectares and represents the sole economic income for more than 25 million families. The crop is produced and exported by more than 60 nations and ranks as one of the top cash crops in developing countries with 3.19 lakh MT production per annum in India in 2018-19 from more than 459 thousand hectares crop area. The coffee plant is a fast-growing tropical bush tree, with two types of shoots: upright growing orthotropic main shoots (stem), and horizontally growing plagiotropic shoots (branches). Traditionally, coffee trees are cultivated only for the berries, which are processed using dry or wet techniques directly in the growing areas to the final raw product, green coffee; this serves as the basis for various coffee products. Both the coffee species tolerate shade and share quite similar growth requirements with various forest crops and trees, thus predisposing them to be grown in agro-forestry ecosystems.

Botanical Name: Anacardium occidentale L.

Family: Anacardiaceae

Chromosome No: 42

Place of Origin: Brazil

Common Name: Cashew, cashew tree, caju

7.1 Introduction

Cashewnut (Anacardium occidentale L.) is an important tropical tree crop which leads the edible nuts in international trade with 29% market share only after hazelnuts (35%) and followed by walnuts (21%) and almonds (16%). It is one of the major exports earning crops which accounts nearly Rs. 2515 crores contributing about 1.5% of the total Indian exports. It was only during the past two decades it gained the status of horticulture crop. India is the world’s largest producer of cashewnut. The cashew cultivation area in India during 2018-19 was 10.89 lakh hectares with an annual production of 743 thousand metric tons of fruits. Maharashtra is a much-advanced state for horticulture which occupies large area (1.9 lakh hectares) under this crop (Directorate of Cashew & Cocoa Development, Cochin, Kerala). Cashew exports amounted to over 566 million U.S. dollars from India in fiscal year 2020. This included cashew kernels and cashew nut shell liquid. India’s main export markets for this commodity included South Korea, China, Spain, United States and Belgium (Department of Agriculture, Cooperation & Farmers Welfare).

Botanical Name: Theobroma cacao L.

Family: Sterculiaceae

Chromosome No: 20

Place of Origin: Tropical South America

Common Name: Cacao, cacao bean, cocoa, cocoa bean

6.1 Introduction

Cocoa (Theobroma cacao L.) is a perennial plant and is used as beverage crop. The generic name Theobroma means the “Food of the God”. The word cacao refers to the tree, while the word cocoa refers to the drink made from its seeds. The roasted product of the dried beans is called as Cacao nibs that are used for the manufacture of various products. When cacao nibs are ground, the resulting product is called chocolate liquor or mass, which contains around 55% fat. The fat that is pressed from chocolate liquor is termed as cacao butter. It is mainly used for the manufacture of chocolates, in pharmaceutical preparations and soap making. After pressing out the fat the resultant product with reduced fat content is called cacao powder. For preparation of chocolates cacao powder is mixed with cacao butter and sugar with a definite ratio. Milk chocolates are prepared by adding milk to the above mixture. The cocoa powder contains 22- 25% fat, 20.4% protein and 35% carbohydrate with caloric value of 452 cal. Rind or shell of pod is used as a cattle feed.

Botanical Name: Borassus flabellifer L.

Family: Arecaceae

Chromosome No: 36

Place of Origin: Tropical region of Africa, Asia and New Guinea

5.1 Introduction

Palmyrah is a monocotyledon and perennial crop. The word “Borassus” was derived from a Greek word and it means the leathery covering of the fruit and “flabellifer”, means fan-bearer. The distinguishing characters of palm in this genus are their palmate, fanlike leaves and dioecious character, i.e., male and female flowers are borne on separate trees (sex ratio 1:1), allotetraploid (X= 8 or 9, n = 18), the male tree has a heteromorphic XY pair of chromosomes while the female has an XX pair (Sankaralingam et al., 1999). Next to coconut, palmyrah is the most abundant palm found in the world. Palmyrah thrives in arid conditions and is grown extensively in Tamil Nadu. Palakkad district of Kerala is popularly known as land of palmyra trees. Palmyra trees are known as the icon of this district and have a vast cultural, heritage and literary association.

Botanical Name: Elaeis guineensis Jacq.

Family: Arecaceae / Palmae

Chromosome No: 32

Place of Origin: Guinea Coast of West Africa

Common Name: Oil Palm

4.1 Introduction

The cultivated oil palm Elaeis guineensis Jacq. is a native of West Africa and exists in wild, semi- wild and cultivated forms. It was introduced as an ornamental crop in 1860 and planted at National Botanical Garden, Kolkata. Research on oil palm in India started during 1960 with the establishment of a research station at Thodupuzha by the Department of Agriculture, Kerala with Dura and Tenera germplasm imported from Malaysia and Nigeria. National Research Centre (NRC) for oil palm is situated at Elur, Andhra Pradesh. Oil palm crop is one of the highest oil yielding crops among all perennial crops. It gives 4 to 6 tonnes of edible oil/ha from 3 to 25 years of its life span compared to less than one tonne of oil per ha from other cultivated oil yielding crops. This oil palm is considered as golden palm due to its high yielding capacity. Among the 10 major oilseeds, oil palm is accounted for 5.5% of global land use for cultivation, but produced 32.0% of global oils and fats output.

Botanical Name: Cocos nucifera L. Family: Arecaceae / Palmae Chromosome No: 32 Place of Origin: Malaysia Common Name: Coconut 2.1 Introduction Coconut (Cocos nucifera L.), is widely known as ‘Kalpavriksha’ (i.e., tree of heaven) as each and every part of the palm is useful in one way or the other and is an important perennial oil yielding crop of humid tropics. It provides food security and livelihood opportunities to 20 million people around the globe and 10 million people in India (Chowdappa et al., 2017). Even though India is the largest coconut growing country in the world, its contribution to the export market is not significant. Coconut as an edible oil and food crop, is now slowly transforming into raw material for various pharmaceutical, nutraceutical and cosmetic products. Coconut is rich in fibre, vitamins and minerals. Because of its health benefits beyond its nutritional content, it has been considered as “functional food”. Hence, there exists a huge scope for coconut-based agribusiness in India, which will increase the present 8% level of value addition to 25%. The coconut-based value-added products are desiccated coconut powder, coconut milk, coconut cream, coconut milk powder, coconut flour, coconut water concentrate, coconut jelly (Nata-de-coco), coconut vinegar, virgin coconut oil, coconut chips, coconut pickle, coconut ice cream, neera and neera based value added products such as syrup, squash, honey, jaggery, candy and sugar (Chowdappa et al., 2017).

Botanical Name: Phoenix dactylifera L.

Family: Arecaceae

Chromosome No: 2n = 36

Place of Origin: Countries around Persian Gulf

10.1 Introduction

Date palm is a nutritive fruit rich in sugar and iron and predominantly seen in desert oasis. It is the main fruit crop in arid and semiarid regions, particularly in the arid regions of western Asia and North Africa. The palm tree is well adapted to desert environments that are characterized by extreme temperatures and water shortage. Beyond the arid climates, date palm can also be grown in many other countries for food or as an ornamental plant including the continents of Americas, Southern Europe, Asia, Africa and Australia. The majority of date palm growing areas are located in developing or underdeveloped countries where dates are considered the primary food crop, thus playing a major role in the nutritional status of these communities. By-products from date palm are used in building structures, animal feed, and also in several items such as baskets and ropes. The date palm tree has been in cultivation since 2400 BC. It is one of the oldest cultivated fruit trees on earth. India is the leading importer of dates. According to FAO statistics, in 2011 India was the largest world importer of dates (256,295 mt) and its neighbour Pakistan, in 2012, was the world’s sixth largest producer (600,000 mt). The major date palm growing areas in India are Kutch (Gujarat), Rajasthan and certain parts of the Punjab, as well as Tamil Nadu state to some extent. In Kutch, there are more than 2 million date palms, the majority of them grown from seeds and offshoots, providing a huge biodiversity for experimentation and improvement of products. Efforts by the Indian government in the last decade have resulted in an increase of date palm cultivation from 8,973 to 16,000 ha and establishment of a prominent effort in Rajasthan (Shah, 2014).

Botanical Name: Areca catechu L. Family: Arecaceae / Palmae Chromosome No: 32 Place of Origin: Philippines, Malay, Indonesia, Cochin, China and Malaya Peninsula Common Name: Betel nut 3.1 Introduction Arecanut (Areca catechu L.), commonly known as Supari or Betel palm or Arecanut palm, is cultivated primarily for its kernel obtained from the fruit which is chewed in its tender, ripe or processed form. It is an important cash crop of India. The economic produce is the fruit called ‘betel nut’ and used mainly for masticatory purposes. Its cultivation is restricted in South Western and North Eastern regions of the country. The chromosome number of Areca catechu L. was first determined as 2n=32 (Venkatasubban, 1945) and it belongs to family Arecaceae. It is one of the important commercial crops grown in parts of Karnataka, Kerala, Assam, Meghalaya, West Bengal, and Andaman and Nicobar Islands. The cultivation of arecanut has also been extended to other states like Tamil Nadu, Andhra Pradesh and Maharashtra. India is the largest producer and consumer of arecanut in the world holding 62% of the area and 60% of the production. The other major arecanut growing countries are Indonesia, Bangladesh, China, Myanmar and Thailand. Arecanut being a profitable plantation crop, it is important to understand the package of practices and seasonal operations to be followed in the nursery, in young gardens and in old plantations to get maximum returns. To get additional income in the adverse periods, concept of cropping system is very important. The exact origin of areca nut is not known till date but, arecanut is a palm which grows in much of the tropical Pacific, Asia, and parts of East Africa (Kumar, 2013).

Threats

There are sixteen threat factors have been identified from Indian mangroves (Kathiresan 2010). However, habitat conversion for agriculture and aquaculture activities, environmental pollution by upstream anthropogenic activities, Climate change processes (e.g. sea level rise; increasing frequency of cylones, etc.) are the major threat factors for mangroves. Mangroves are able to cope up with short-term oscillations and long-term fluctuations of climatic conditions, but the consequences of global climate change, such as increased extreme events, will have unprecedented effects on biota and threaten the resilience and recovery potential of the ecosystems (Harris et al. 2018; Sippo et al. 2018). Despite conservation measures, the mangroves still experience an annual loss of 0.2-0.7% during 2000-2012 and they remain the most threatened ecosystem of the world (Hamilton and Casey 2016).

Mangrove forests are ecologically significant and economically important (Kathiresan 2018). They provide ecosystem services worth at least US$ 1.6 billion each year and support coastal livelihoods worldwide (Costanza et al. 1997). They serve as the nursery, feeding and breeding grounds for crabs, prawns, molluscs, finfish, birds, reptiles and mammals. A large amount of global fish catches (up to 80%) is dependent on mangroves, thereby ensuring the food security of coastal people (Ellison 2008). The mangroves provide firewood, timber, cattle feed, honey, medicines and tourism development. They protect groundwater aquifers from seepage of seawater, thereby ensuring water security for coastal population. Mangrove forests remove coastal pollution particularly toxic heavy metals. They offer coastal protection against the fiery effects of natural calamities such as tsunami, storm surges, cyclone and floods (Kathiresan and Bingham 2001; Kathiresan and Qasim 2005; Kathiresan and Rajendran 2005). The potential of mangroves in carbon capture and sequestration is remarkable in mitigating the impacts of global warming and climate change (Kathiresan et al. 2013, 2014).

West Bengal

In West Bengal, mangroves are present in Sundarbans, the large deltaic complex of three major rivers, the Ganges, Brahmaputra and Meghna, and 62% of total area is shared by Bangladesh and 38% by India. The Sundarban Biosphere Reserve (SBR), at the confluence of the Bay of Bengal covering an area of 9,630 km², lies between 21°40′N and 22°40′N latitudes and 88°03′E and 89°07′E longitudes, spreading in districts of South and North 24-Parganas in West Bengal, India. The major portion of SBR is designated as Reserve Forest, covering nearly 4260 km² and the area under mangrove vegetation is 2112 km² (FSI 2019). Compared to 2017 assessment there has been a decrease of 2 km² area of mangroves. The mangroves and their associates in the SBR exhibit great generic and species diversity and it is abode to rare and highly endangered flora and fauna, as well as, the only mangrove-tiger (Royal Bengal Tiger - Panthera Tigris tigris) kingdom in the world. Recognizing importance and uniqueness, the United Nations Educational, Scientific and Cultural Organization (UNESCO) declared the Indian part of Sundarbans as a ‘World Heritage Site’ in 1987, and also designated the ‘Sundarban Biosphere Reserve’ under the UNESCO Man and the Biosphere (MAB) program in 2001. Recently, Sundarbans has been declared as a Ramasar Site, considering ecological significance. Totally 33 true mangrove species belonging to 21 genera and 13 families have been identified in Indian Sundarbans. Among the mangrove species listed, Rhizophora apiculata, Bruguiera parviflora, Ceriops decandra, Kandelia candel, Aglaia cucullata, Excoecaria indica, Xylocarpus moluccensis, Xylocarpus granatum, Heritiera fomes, Scyphiphora hydrophyllacea, Brownlowia tersa, Nypa fruticans, Acanthus volubilis, Dolichandrone spathacea and Phoenix paludosa are under serious threat in Sundarbans (Kathiresan 2008; Gopal and Chauhan 2006). Particularly Heritiera fomes (locally called Sundari, from which Sundarbans derives its name), Nypa fruticans and Phoenix paludosa are declining rapidly due to the reduction of freshwater input (Gopal and Chauhan 2006).

Distribution of Mangroves in India

Mangrove forests in India are found along the coastline of 9 States and 4 Union Territories (Fig. 5). The mangrove habitats are broadly classified into three namely, Deltaic (Eastern Coast Mangroves), Estuarine & Backwater (Western Coast Mangroves) and Insular mangroves (A & N Islands) (Mandal and Naskar 2008). India has a total mangrove cover of 4975 km²; of which, 57% is present along the east coast (Bay of Bengal); 31% along the west coast (Arabian Sea) and the remaining 12% in the Andaman and Nicobar Islands (FSI 2019).

Origin and diversification of Mangroves

Mangroves are quite old, possibly arising just after the first angiosperms (Duke 1992). Based on the fossil evidence and recent molecular studies, it is believed that mangroves originated along the shorelines of ancient Tethys Sea and there was a dispersal along the Tethys seaway westward into the Atlantic and further into the east Pacific (long before the closure of the Panama Isthmus) and eastward into South east Asia and Australia during the Late Cretaceous or early Eocene around 80 million years ago (Duke 2006). Nypa seems to be earliest fossil evidence. However, prior to closure of Tethys sea, around 40-55 million years ago, the mangrove genera - Nypa, Acrostichum, Rhizophora, Avicennia, Pelliciera, Sonneratia, Bruguiera, Ceriops, Heritiera, and Aegiceras - were present around shoreline (Duke 2017). The closure of Tethys Seaway by the mid-Tertiary (34-50 Million years ago) by northward movement of African landmass, created a physical barrier that completely terminated the Atlantic East Pacific (AEP) and Indo-West Pacific (IWP) exchange route, and resulted in subsequent diversifications within the AEP and IWP regions influenced by region-specific events (Ellison et al. 1999; Duke 2006). The plate tectonics and other vicariant events like Pleistocene sea level rise are attributed to the current distribution pattern and disjunct distributions of species within genera. Duke (2017) hypothesised two separate westward dispersal routes in AEP: (i) a southern path along the coasts of West Africa, South America and, (ii) a northern path along the North American east coast, whereas he hypothesised two isolated pathways in IWP towards eastward dispersal: (i) a northern path along the coast to the Middle East, Southeast Asia and, (ii) a southern path along the coasts of East Africa, India, and Australia. Further he noted that collision of India and Australia with Middle East and Southeast Asia respectively, resulted complication in dispersal route. Based on the available records it is presumed that diversification of mangrove plants has largely been driven by three key processes of speciation viz., Allopatric speciation, Peripatric speciation and Parapatric speciation (Duke 2017).

Mangroves Definition

A mangrove is tree, shrub, palm or ground fern, generally exceeding one and a half meter in height that normally grows above mean sea level in the intertidal zone of marine coastal environment and estuarine regions of the tropical and subtropical coastlines (Duke 1992). The mangrove is also defined as assemblages of salt tolerant trees and shrubs. Mangroves are taxonomically heterogenous and more related to environment than terrestrial or aquatic plants.

The term ‘mangroves’ is used to define both a group of plants and a community. To avoid confusion, Macnae (1968) proposed the term ‘mangal’ for the mangrove forest community, and the term ‘mangroves’ for the plants. Other terms for the mangrove forest community are coastal woodland, oceanic rainforest, intertidal forest, tidal forest, blue carbon forest, mangrove forest, and mangrove swamp.

Generally, mangrove species are grouped into two types: Exclusive and Non-Exclusive. The exclusive species are limited to the mangrove habitat, and they are also referred to as strict mangroves, obligate mangroves or true mangroves. The non-exclusive species are mainly distributed in a terrestrial or aquatic habitat, but they also occur in the mangrove habitats and they are referred to as semi-mangroves, back mangroves or mangrove associates. Tansley and Fristch (1905) are the first to introduce the criteria to classify mangrove species into true mangroves and mangrove associates. Tomlinson (1986) used rigid criteria to distinguish true mangroves from mangrove associates. In his criteria, true mangroves possess all or most of the following features:

29.1 Introduction

An environmental factor that interferes with the complete expression of genotypic potential of a crop is called stress. The stresses may be biotic (pathogens, insect-pests, etc.) or abiotic. The main abiotic stresses are drought, mineral deficiency/toxicity and heat or cold. The losses due to abiotic stresses can be minimized by:

Crop management: The degree of stress can be reduced by suitable agronomic/soil management practices, e.g., irrigation to relieve drought stress, soil amendments to reduce salinity.

Development of resistant cultivars: This offers the cheapest, easiest to apply and most eco-friendly approach to reduce losses due to any stress.

Indirect breeding: Evaluation of materials under stress often helps in identification of a resistant line that may become an important commercial cultivar.

???????Direct breeding: It is deliberate breeding of materials for stress resistance. When a genetically variable material is grown under the stress environment, selection can be based on survival, yield and other traits contributing to stress resistance.

28.1 Introduction

The stress that is caused by biological agents or factors such as diseases, insect-pests and parasitic weeds is called biotic stress. The term disease can be broken into two words: “dis” (means negative, reverse or opposite) and “ease” (means comfort, or freedom from pain or discomfort). Hence, plant disease can be defined as any harmful alteration from the normal functioning of physiological processes. Diseases may be bacterial, fungal or viral. A wide range of insects infests various crop plants. The extent of damage caused to crop plants by various organisms is usually in the order fungi > bacteria > viruses > nematodes = insects. But the relative importance of these organisms varies to a great deal in different crops. Breeding of cultivars resistant to diseases and/or insect-pests is the cheapest, safest and most dependable means of limiting the losses due to them. Resistant cultivars form an important component of integrated management of diseases and insect-pests.

28.2 Breeding for Resistance to Biotic Stresses-Diseases

Agrios (1970) has defined disease as: “Disease is a series of invisible and visible responses of plant cells and tissues to a pathogenic microorganism or an environmental factor that result in adverse changes in form, function or integrity of plant and may lead to partial impairment or death of the plant or its parts.” The organism causing disease is called pathogen, while the plant affected by the disease is called host.

The principles underlying breeding for resistance to diseases are much the same as for other characters, except for one important difference, i.e., the diseases caused by pathogens are the product of interaction between two genetic systems, that of the host and that of the parasite. Both systems are capable of variation and evolution and affect the interaction between host and pathogen. Here the breeder is required to deal with the heritable traits of both the host plant and the pathogens invading it.

27.1 Introduction

Crop improvement depends on genetic variation present in nature or created by hybridization followed by segregation and recombination. Again, gene transfers are possible only from the lines and species that are sexually compatible with the concerned species. Interspecific gene transfers pose many problems, including the loss of F₁ hybrids during embryo development due to abortion of the endosperm in the developing hybrid seeds. Embryo rescue technique was developed to rescue such interspecific hybrid embryos, and it has been widely used for this purpose. It is to be mentioned that embryo rescue can be used only in such cases where sexual hybridization is successful in producing zygotes that begin to develop into embryos.

Besides, the technique of somatic hybridization by protoplast fusion was developed to enable gene transfer from the species that do not produce zygotes on hybridization. This method has been extensively used and some useful lines have been derived. But this method is limited to utilization of genes present in plant species. Again, the results of somatic hybridization are unpredictable since many somatic hybrids fail to regenerate complete plants and the transfer of specific genes or groups of genes depends entirely on chance.

The recombinant DNA technology (also called genetic engineering) has permitted the transfer of genes from any organism into any organism. Besides, chemically synthesized genes can be transferred and integrated into genomes of various organisms to enable the expression of these genes. A gene transferred into an organism by genetic engineering is called a transgene. 

26.1 Introduction

We have already discussed the basics of tissue culture techniques in Chapter 2. Plant tissue culture techniques in combination with recombinant-DNA technology are essential requirements for development of transgenic plants (will be discussed in next chapter). However, tissue culture techniques like anther, pollen, ovule and meristem culture can themselves be used for improvement of different traits or as an aid to conventional breeding methods. In recent years, isolated microspore culture has been preferred as a breeding tool and an experiment system for various genetic manipulations. Besides, using protoplast fusion and hybrid embryo rescue, distant hybridization has been successfully achieved in many crops. Protoplast fusion technique can be used for the transfer of cytoplasmic male sterility from one species to another in very short duration. Somaclonal variation generated during tissue culture can also be utilized for recovery of variants showing disease resistance or other desirable characters.

25.1 Introduction

The method of selection in which a gene/QTL (Quantitative Trait Locus) is selected on the basis of the genotype of the molecular marker (also called DNA marker) linked to this gene/QTL is known as marker-assisted selection (also called marker-aided selection). The idea of marker-assisted selection (MAS) was first advocated by Tanksley (1983). MAS can be used in combination with the conventional breeding methods or novel breeding schemes could be devised to take full advantage of the marker data. MAS has been widely used for introgression of the desired genes and QTLs using backcross programmes.

25.2 Marker-Assisted Backcrossing (MABC)

The backcross programme based on molecular marker is usually called marker-assisted backcrossing (MABC). MABC has three activities: (a) foreground selection, (b) background selection and (c) recombinant selection.

25.2.1 Foreground Selection

The use of molecular marker to select the gene/QTL being introgressed is known as foreground selection. The objective of foreground selection is to select the target gene, i.e., the gene being introgressed, without phenotypic evaluation for the trait governed by the target gene. Foreground selection for a gene/QTL will be highly desirable in a variety of situation, some of which are listed below: