eChapters

Introduction

Agriculture is highly dependent on environment, and it’s very difficult to get favourable climate and other conditions for optimum crop growth and development as per crop need. Open field conditions are having a high direct affect of the prevailing weather conditions on crop growth, and also on population dynamics of viruses, fungus, bacteria, insects, etc. With time crops has adopted themselves to specific seasons, but the fast changing climatic conditions happening across the globe has changed the climatic characteristics of a season. This has resulted in untimely rains, high temperature fluctuations and changes in other abiotic and biotic factors in geographically varied locations where it was not supposed to be earlier based on various geographical factors deciding the climatic conditions of that area. Therefore, there is need to develop suitable technologies to sustain these challenges. How to address these issues, can we manipulate the climatic conditions or can we provide protection to the crops against climatic fluctuations and various other related stresses.

Introduction

Citrus spp. grown in almost all the states of India. Citrus fruit, consisting of mandarin oranges (Citrus reticulata Blanco), sweet orange (Citrus sinensis Osbeck) and lime (Citrus aurantifolia Swingle) are grown commercially in tropical, sub-tropical, arid, irrigated and mountainous regions in varying soil and weather condition. The citrus tree on the whole do well in dry climate, with a rainfall between 75 and 125 cm but certain species such as pummel and certain mandarin oranges thrive in heavy rainfall areas of Konkan, Assam and Coorg. It is grown almost all kinds of soil, varying from heavy black soil to shallow open soils. A hard substratum or a sticky impervious layer is very injurious. Soils having a high water table should be avoided. Although the citrus industry in India has faced many challenges, there has been a consistent increase in area and production owing to the awareness for sustained production (Table 1).

Introduction

Vegetable crops are an important component of Indian Agriculture. They are known for their short cycle and high productivity per unit area providing a valuable source of income leading to improve livelihood. The prosperity and advancement of a nation largely depend on achieving nutritional security to its people. The vegetables play a vital role as major supplement to food and nutritional security of our people. They are important source of nutrients like b- carotene, vitamin B, C, E as well as folic acid, iron, magnesium, etc. and they also supply fair amounts of carbohydrate, protein, fiber, antioxidants and energy.

Introduction

India (8^o-30^o N and 68-97.5^ºE) exhibits a wide range in topography and climate, which has a bearing on its vegetation and floristic composition. This subcontinent is one of the World’s 12 leading Biodiversity Centres, encompassing 16 different agro-climatic zones, 10 vegetation zones, 25 biotic provinces and about 426 habitats of specific species. It has been estimated that about 45,000 plant species (nearly 20% of the global species) occurs in the Indian Sub-continent. About 3,500 species of both higher and lower plant groups are of medicinal values. More than 80 per cent of medicinal and aromatic plants (MAPs) are collected from 17 million hectares of Indian forest land. However, many of these, due to over-exploitation have become rare (Rheum emodi, Aconitum deinorrhizum), threatened (Rauvolfia serpentina, Berberis artistata) or endangered ones (Sassurea lappa, Dioscorea deltoidea). Problems arising out of rapid genetic loss of medicinal plants forced the need for international co-operation and co-ordination to undertake programmes for conservation of medicinal plants to ensure that adequate quantities are available for future generations.

Introduction

Beauty, purity, love and passion are some of the emotions symbolized by the flowers. The feelings of love, affection and joy are conveyed effectively with these non-speaking beauties of nature, for example a lotus conveys purity, rose love, pansy thoughts and narcissus egotism. Flowers have a definite role to play at almost all occasions of human affairs like birth, marriage, worship, adornments and death. Besides flowers, other ornamental plants also play an important role in environmental planning of urban and rural areas and from wasteland development to overcoming pollution. An important aspect of floriculture is that it is a good avenue to generate gainful employment for youth and women of peri-urban and rural areas.

Introduction

Vegetables are the vital sources of minerals, vitamins and dietary fibres and play an important role in supplying nutrition to human health. Vegetables require comparatively lesser quantities of agro-inputs to grow. Vegetables are rich source of vitamins, minerals and plant fibres which provide food and nutritional security. These also generate high income and employment, particularly for small farmers. Vegetables being a rich and cheap source of vitamins and minerals, occupy an important place in the food basket of Indian consumers, a majority of whom are vegetarian. This persistent vegetarianism coupled with rising per capita income is fuelling a rapid growth in consumption of vegetables. Presently, India is producing more then 70 types of vegetables which are capable of meet out the economic and nutritional requirement of the country (Table 1). There has been a revolution in the production of vegetables in the country in the last four decades.

Introduction

Horticulture is the science of cultivation, management, postharvest handling, value addition and marketing of fruits, vegetables, ornamental, aromatic and medicinal plants, spices and plantation crops. Looking to its important role in nutritional security, poverty alleviation and employment generation, it has rightly been emerged in form of horticulture industry and as one of the most significant sectors in the world. The production of fruits, vegetables and flowers has acquired much importance in recent times due to their increasing demand. Changing lifestyles of people across the globe, attempts to overcome the stressful lifestyle, inclination towards healthy and balanced eating habits have made people include fruits and vegetables in their daily diet. In the case of flowers, the demand for fresh flowers has steadily increased not only for decoration but also for many other purposes like essential oils, cosmetics, aroma therapy, dry flowers, pot-pourries, natural dyes, medicines, etc. Rising incomes and growing consumer interest in a variety of fresh fruits and vegetables year-round is stimulating international trade in horticulture.

Okra/Ladies finger/Bhindi
1. Leaf blight/Spot
Pathogen
Cercospora abelmoschi Ell. & Ev.
Symptoms
The fungus grows as shooty to dark olivaceous, ectoparasite covering entire leaf lamina. Pathogen initiates as small isolated fungal growth on lower side of leaf but very soon it spreads on both sides. Pathogen reduces severely the photosynthesis area. Infected leaves fall down very quickly after dropping and rolling. It causes severe loss in seed production crop as well as in the late sown crops.

1. Damping off
Pathogen
Pythium spp
Phytophthora spp
Fusarium spp
Sclerotium spp
Symptoms
It is a term used to describe the damage caused by various fungi to the seed and emerging seedling in the reduced plant stand and sometimes it is so serious that  resowing becomes inevitable. Major symptoms are the failure of the seedlings decay or sudden death of the emerged seedlings roots and lower stems of emerged seedlings become soft and watery and may be reddish brown in colour.

Cauliflower, Cabbage and Knol khol
1. Leaf spot
Pathogen
Alternaria brassicae (Berk.) Sacc.
Symptoms
Alternaria leaf spot usually appear in early stage in cauliflower while at later stage symptoms in cabbage appear as circular light brown spot in leaves. Concentric rings are clearly visible on the spots. In older plants on leaves, petioles and stem, brown to black circular to slightly elongated spots appear.

Tomato
1. Damping off
Pathogen
Pythium aphanidermatum
Fusarium spp.
Sclerotium spp.
Symptoms
Damping off is the most important disease of tomato. Several seed and soil borne fungi can kill before the tender redical and plumule establish in the nursery bed. The pre emergence damping off and seed rotting is the usual cause of poor seedling stand. This type of damping off causes hidden loss but the post emergence damping off is more serious problem. Seedlings get infected near the soil line (collar region) after emergence and give wire stem symptoms. The tissue become soft, water soaked and weak causing the seedlings fall over and later on they die. The entire action is so fast that leaves remain green but they are unable to stand further.

Vegetables
Peas
1. Rust
Pathogen
Uromyces fabae (Pers.) de Bary
Symptoms 
The fungus produces characteristics rust pustules on the host. Pustules are mostly found on the leaf blade, though often they may be found on the petiole and stem of pea plants. The sori are small, roundish, open, and powdery as well as brown coloured. In severe infections, the leaf may wither, resulting in considerable damage to the crop. As the plants near maturity, the fungus produces the telial stage on the host.

1. Damping-off
Pathogen
Pythium aphanidermatum (Edson.) Fitz.
P. debaryanum                  
Rhizoctonia solani Kuhn.
Fusarium spp.
Sclerotium spp.
Symptoms
Damping-off of onion seedlings occurs in two stages:
    (i)    Pre emergence
(ii)    Post emergence
In pre emergence stage, plumules are killed before they reach the soil surface. They may be infected, killed even before the hypocotyls have broken the seed coat.

Tremendous genetic diversity occur within different crops of this family with respect to their adaptability. Some cucurbits are grown in tropical, subtropical or arid deserts whereas other prefer to grow in temperate conditions. Harvested fruits and vegetables can be potentially exposed to numerous abiotic stresses during production, handling, storage and distribution (Hodges, 2003). However, when the abiotic stress is moderate or severe, quality losses almost always are incurred at market (Toivonen, 2003). Annually about 42% of the crop productivity is lost owing to various abiotic stress factors (Oerke et al., 1994). One of the key factors for abiotic stress in crop plants is the ill effect of global warming which may cause reduced precipitation, less snow pack, and earlier snow melt, leading to drought conditions. In addition about 20% of the world’s irrigated lands are affected by salinity (Zhu, 2001), a situation worsened by climate changes.

2.1 Insect Pests

Insects are often a major obstacle to the successful production of cucurbits (York, 1992). They can severely reduce yield, injure or kill plants, spread diseases and adversely affect fruit quality. A number of insect pests, mites and nematodes have been found to infest cucurbitaceous vegetables but fortunately, in India, fruit flies and a few species of beetles are of economic importance; aphids and blister beetles though of regular occurrence, seldom cause severe damage.
 
Other insect pests reported to infest the cucurbitaceous vegetables are pumpkin caterpillar, Diaphania indica (Sounders), snake gourd semilooper, Plusia peponis Fab., white fly, Bemisia tabaci Genn., stink bugs, Apspongopus spp. and flea beetle, Phyllotreta spp. etc. These biotic pressures on the crops are increasing day by day due to round-the-year intensive cultivation of photo and thermo insensitive cultivars as well as indiscriminate use of toxic agro-chemicals in the present era of chemicalized agriculture.

1.1 Introduction

‘Cucurbits’ is a term coined by Liberty Hyde Bailey for cultivated species of the family Cucurbitacae. During this current century the term has been used not only for cultivated forms, but also for any species of the family Cucurbitacae. Cucurbits are frost sensitive, predominantly tendril-bearing vines which are found in subtropical regions around the globe. A few numbers of species those are native to or cultivated in temperate climate are prolific seed producing annuals or perennials that live for one season until killed by frost (Robinson and Decker-Walters 2004). Other vernaculars applied to the family Cucurbitacae and several of its members are ‘gourd’, ‘melon’, ‘cucumber’, ‘squash’ and ‘pumpkin’.

Current status of researches on VA mycorrhiza and their benefits to the plants carried out by the mycorrhizasts of the country has been described in detail in chapters II to X.

Prior to the establishment of any specific forum, the pace of research on VA mycorrhiza in the country was not of desired level. However, the activities related to research on VA mycorrhiza gained unexpected momemtum when Mycorrhiza network came into exixtence in the year 1989. The network provided not only assistance and guidance of various types to the scientists working on VA mycorrhiza in the country but also offered them periodical platforms to exchange their informations and thoughts on status of researches on VA mycorrhiza and to propose future strategies of research. During the National conferences held in different parts of the country the panel of experts made certain observations regarding future prospects and strategies for research on VA mycorrhiza. They have been mentioned in the present chapter.

The understanding of VAM symbiont and VAM symbiosis is of prime importance in manipulating VAM associations for the welfare of plants. Many contributions have been made worldover in the areas of taxonomy, morphology, anatomy, histology, cytology and genetics of VAM fungi and/or their associations with the plants. However, the share of Indian mycorrhizasts in such contributions is negligible. The following description gives an account of work done by the mycorrhizasts of the country in these areas.

Since a method to cultivate VAM fungi in pure culture is not available as yet, clean and high quality VAM inoculum production is not possible. However, VAM technology is gradually getting a place in agriculture as well as reclamation and afforestation programmes. The inoculum currently being used includes infested fields soils, sievings from such soils, soil and roots of greenhouse plants, or pot culture inoculum derived from surface disinfected spores of a single VAM fungus on a host plant grown in a sterilized growth medium. Attempts are being made to manipulate VAM fungi, rooting media, hosts and fertilizers in order to secure superior quality of inoculum by these methods on a large scale. In addition, other techniques like tissue culture, hydroponic system etc. are also being attempted to cultivate VAM fungi in pure culture. The Indian mycorrhizasts have also attempted to devise and develop improved methods for production and storage of commercial VAM inoculum. The following description gives an account of Indian work related to production and storage of consistently high quality disease free VAM inoculum.

During the last thirty years, there has been a growing appreciation of the impor tance of VAM fungi in improving the plant growth and yield. They have been extensively studied also in India. Considering the potential importance of these organisms in the recovery of disturbed sites and their possible use in land reclamation, researches regarding their relationship to ecosystem recovery have now been initiated also in India.

Large areas of land in the country called wastelands are degraded and lying unutilized due to various constraints. Part of it called culturable, has the potential for the development of vegetation cover. On the other hand, part of it called unculturable, has no potential for the development of vegetation cover. In addition to these natural wastelands, there are large tracts of wastelands created due to human activities such as mining, deforestation etc. Such wastelands are also culturable and a vegetation cover can be developed on them after removing the constraints with some efforts.