Phytoplasma is recognized as the serious constraints for the many economically ornamental plants all around the world. It may reduce the quality and yield of ornamental plants and is recognized internationally because of its unspecifi c symptoms, severe losses, and diverse epidemiology. The epidemics of these diseases have compelled the withdrawal of many ornamental plant species such as gladiolus, lily, chrysanthemum, and rose from cultivation. So far, more than 42 ornamental plant species were reported as infected by phytoplasma. The general symptom includes fl ower malformation, growth abnormalities, yellowing or decline of leaves, elongation and etiolation of internodes, witches' broom, stunting, little leaf, and virescence. The knowledge on the diversity and identifi cation of phytoplasma has been explored with the molecular tools and techniques showing that phytoplasma infecting the ornamental plant Candidatus Phytoplasma asteris belongs to a major 16Srl group. The other known groups of phytoplasmas are 16Srll, 16Srlll, 16SrV, 16SrVl, 16SrVll, 16SrlX, 16SrX, 16SrXll, 16SrXlll, and 16SrXV. For the detection of phytoplasma in the infected plant parts or tissues, the 16S rRNA gene fragments were amplifi ed using phytoplasma universal primer pairs P1/P7 in a polymerase chain reaction (PCR) followed by primer pairs R16F2n/R16R2 in the nested PCR. Nevertheless, for the fi ner detection of phytoplasma-related Candidatus Phytoplasma asteris, DNA samples were used to extend the RP and Tuf gene fragments by PCR using aster yellows group-specifi c primer pairs RP(l)F1A/RP(l)R1A and fTufAy/rTufAy, respectively. However, the restriction fragment length polymorphism (RFLP) analysis of RP gene fragments digested with Alul, Msel, and Tsp5091 restriction enzymes indicates the presence of aster yellows group. The aim of the present chapter is to provide an overview of the phytoplasma-associated diseases in ornamental plants, their mode of transmission, and the molecular techniques employed to detect the phytoplasma in the infected plant parts or tissues.

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In recent years, the development of the floriculture sector has received rising attention, particularly for the benefit of small-scale agricultural enterprises producing domestic seedlings of perennial ornamental plants and for export to neighbouring countries. Plant diseases, including those associated with phytoplasma infections and plant viruses, are affected by this industry, as are other sectors of the agricultural economy.In a number of commercial cut flowers and ornamental plants, phytoplasma and plant virus infection causes diseases, causing major economic losses globally.Therefore, phytoplasma and plant virus diseases are the key constraints in the production of lucrative ornamental plants and lower their quantum and quality, gaining international importance due to unspecific symptoms, different losses and complex epidemiology around the world. These disease epidemics forced the removal of several varieties of floricultural plants such as gladiolus, lily, chrysanthemum and rose from cultivation. In various ornamental plants in botanical gardens and various floriculture farms, symptoms of general yellowing as well as plant stunting, shoot proliferation, phyllody, virescence, lower cost of flowers and reddening of leaves were observed. The prevalent mode of distribution of plant viruses is vector transmission, vegetative propagation or seed, although in some cases, viruses are transmitted by mechanical contact. Begomoviruses in economically important ornamental plants, especially in the tropical and subtropical regions, are among the most dangerous epidemic-causing pathogens, but phytoplasmas of ornamental plants have been widely distributed geographically. Information on phytoplasma and begomovirus infecting ornamental plants has been addressed in this study

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