Diseases of Ornamental, Aromatic and Medicinal Plants

Flower cultivation at the commercial level has attained immense significance in the area of crop diversification and contributes a lot to the cultivator's economy. With the worldwide boom in the floriculture trade, the production of highquality and disease-free flowers has become an important challenge in commercial floriculture. Various biotic and abiotic factors affect flower production in open fields and controlled environments. Among the cut flowers, anthurium, carnation, china aster, chrysanthemum, gerbera, marigold, orchid, rose, etc. are covered in this chapter with regard to their plant diseases. Anthracnose, black spot, botrytis blight, crown rot, leaf spot, powdery mildew, mosaic, root-rot, rust, twig blight, stem necrosis, stump rot, white rust, wilt etc. are important diseases of the above cut flowers that shall be discussed in detail and suitable management strategies shall also be presented in the chapter.

Ornamental crops have deceptively benefited humankind since very early times and the importance of ornamental crops is being recognized by every individual from birth to death. It may be cultivated for cut flowers, dry flowers, live or dried plants, bulbs, and tuber, gardening/landscaping and also used in perfume, medicines, flavouring and colouring agents. Plant diseases are a major bottleneck in flower production and the losses caused by plant pathogens in important potted flowers have been estimated to be as high as 100%. Phyto-pathogens directly reduce the production and marketability of potted flowers. In this chapter, diseases of important potted flowers viz., azalea (Rhododendron obtusum), begonias (Begonia spp.), coleus (Plectranthus scutellarioides), gardenia (Gardenia jasminoides) and poinsettia (Euphorbia pulcherrima) are discussed with detailed emphasis given to disease aetiology, diagnostic symptoms, disease cycle and their management

Flowering geophytes are important ornamental or florist crops that mainly have tuberous roots, tuberous stems, true tuber and rhizomes or corms. The global trade of florists' crops including flowering geophytes is projected to be more than $100 billion annually. Plant pathogens have a direct impact on the production and marketability of flowering geophytes. In this chapter, important flowering geophytes viz., caladium, cyclamen, daffodils, gladiolus, lily, tuberose and tulip and their major diseases are described with special emphasis on disease aetiology, symptoms/signs, biology, disease cycle and management. 

Turf grasses are extensively planted for ornamental landscaping or decorative purposes and for upgrading outdoor grounds in tropical and warm temperate regions. Most of the important turf is known by various common names such as Bermuda, couch, kweek and Doob. They are also valuable for soil stabilizing and livestock herbage. Turfgrass experiences a variety of disease problems, many of which result in a significant damage to turf appearance. In many instances, diseases are considered for low-quality turf, although other factors may also be responsible for this. Turfs are affected by several algal, fungal, and bacterial pathogens. This chapter provides a detailed account of the symptomatology, aetiology, biology, and management of a few important prevalent turf diseases viz., algae problem, anthracnose, Rhizoctonia patches, leaf and sheath spot, blight, Pythium damping off, rust and powdery mildew.

Nematode infestation in ornamental crops affects the quantity and quality of flower yield, reducing flower size, total flower number, and the productive life of the plant. The most devastating nematode genera affecting ornamental crops are root-knot nematode, Meloidogyne species; foliar nematode, Aphelenchoides species; stem and bulb nematode, Ditylenchus species and root-lesion nematode Pratylenchus species. Nematode management in ornamental plants is difficult for many reasons, but practising nematode-free planting material, using cultural methods like a nursery or field cleanliness and application of nematicides can reduce the nematode populations. Hot water treatment of planting material is effective in eliminating nematode infection in vegetatively propagative materials. The use of resistant cultivars and biocontrol agents may also limit nematode damage in the plants. In this chapter, the problem of nematodes in important ornamental plants viz., Chrysanthemum, tuberose, crossandra, orchid, anthurium, gladiolus, gerbera, jasmine, lilies, narcissus, tulip and hyacinth are described, and information on general approaches of nematode management are discussed. 

Aromatic plants provide the chief raw materials for cosmetics, perfumery and food industries. In recent years, with the rising need for therapeutic herbal medicines, attention towards aromatic plants has increased. Because of inherent and remedial pharmacological characteristics, aromatic plants are also exploited as natural medicines, and are mainly used for the extraction of essential oils, which have tremendous application in various industries. Aromatic plants become infested with many diseases that cause degradation of the quality and quantity of the required economic product. Considerable success has been achieved in managing the disease through cultural practices and biological and chemical control. The present chapter focuses on major diseases caused by fungi, viruses and bacteria threatening the bioactive potential, biomass, yield and various plant products of important aromatic plants, viz., basil (Ocimum spp.), citronella (Cymbopogon spp.), eucalyptus (Eucalyptus spp.), Geranium (Geranium spp.), mint (Mentha spp.), rose (Rosa spp.), orchid (Orchis spp.), tuberose (Polianthes tuberosa), etc. To enhance metabolite productive potential and raw material quality, necessary strategies of management for diseases have been defined, which are presented in the chapter.

Tuberous medicinal plants (TMP) are an important group of plants in which roots are modified into tubers and used for medicinal purposes. Many TMPs viz., Ashwagandha (Withania somnifera), safed musli (Chlorophytum borolivianum), Patarchur (Coleus forskohlii), asparagus (Asparagus adscendens), turmeric (Curcuma longa), Holostemma adakodien, Typhonium trilobatu, etc. are currently used in the preparation of stimulants, tonics, carminatives and expectorants. Plant diseases especially those caused by fungi, bacteria and viruses pose a serious threat to the profitable cultivation of tuberous medicinal plants. Important diseases of tuberous medicinal plants include root rot, wilt, tuber rot, rhizome-rot etc, which are mainly caused by soil-borne pathogens such as Fusarium, Verticillium, Sclerotium, Rhizoctonia and Pythium species. Growers generally use fungicides/pesticides to control these diseases. However, chemical residues in the plant tissue resulting from pesticide application make TMP medicine unsafe for human health. Biological control using antagonistic fungi and bacteria is a good substitute for chemical pesticides. In this chapter, we present an elaborate description of the important diseases of TMPs along with their sustainable management options.

Medicinal plants constitute an important group of horticultural crops and many non-tuberous medicinal plants viz., aloe vera (Aloe vera), basil (Ocimum sanctum), mentha (Mentha arvensis), noni (Morinda citrifolia), isabgol (Plantago ovata), mulethi or liquorice (Glycyrrhiza glabra), rosa grass (Cymbopogan nardus), etc. are currently used to prepare stimulants, tonics, carminatives, and expectorants. Various biotic and abiotic stresses affect the production of these medicinal crops. Among the biotic stresses, diseases caused by fungi, bacteria, viruses, and nematodes are major constraints. Diseases of aloe vera (such as anthracnose, dry rot, rust, soft rot), noni (dry rot, leaf blight, soft rot, root-knot), basil (anthracnose, leaf spot. powdery mildew, wilt), mentha (leaf spot, root-rot, rust, wilt), isabgol (Downey mildew, wilt), rosa grass (leaf blight. Red leaf spot), liquorice (leaf spot, root-rot) pose a serious risk to the successful cultivation of these medicinal plants. The economically significant diseases of non-tuberous medicinal plants are discussed and the relevant information is described in this chapter.

Medicinal plants are regularly attacked by the plant parasitic nematodes, which can seriously harm these crops. However, only a few medicinal plants have been reported with regard to the extent of crop damage caused by the nematode. Root-knot nematodes (Meloidogyne spp.), root lesion nematodes (Pratylenchus spp.), and stunt nematodes (Tylenchorhynchus spp.) are major nematode pests that affect medicinal plants and significantly reduce their yield. The economically significant medicinal plants that are infected by nematodes include Ashwagandha (Withania somnifera), Basil (Ocimum spp.), Brahmi (Bacopa monnieri), Coleus (Coleus forskohlii), Henbanes (Hyoscyamus sp.), Noni (Morinda citrifolia), Menthol mint (Mentha spp.), Safed Musli (Chlorophytum borivillianum), etc. In the present chapter, nematode infestation in the above medicinal plants has been described in detail, and appropriate management options are suggested to avoid yield losses.