Comprehensive review on sesame phyllody, genetic diversity, symptom expression, vectors and management strategies

Insect pests and diseases are the major biotic stresses to crop plants. Some are highly dreadful and cause yield loss even up to 100 %. Sesame crop face a serious problem worldwide due to the insect vector-transmitted phytoplasma disease called phyllody. The transmission was facilitated by various leafhoppers (Cicadellidae: Hemiptera). The predominant phytoplasma group infecting the sesame crop is 16SrI and 16SrII in most of the sesame-growing countries. The phytoplasma subgroup 16SrII-D is the most common one in India, Oman, the Republic of Korea, Thailand and Turkey. The leafhopper species, Orosius albicintus vectoring the transmission is replaced with the species Hishimonas phycitis, which is the dominant one in the sesame ecosystem in terms of population and transmission (88.33 %) of the disease. In most of the sesame-growing countries, the symptoms expressed in phytoplasma infected sesame plants are yellowing, virescence, shoot apex fasciation, floral sterility, change in flower color and cracking of capsules. Diversity in the symptoms expression is due to the changes in host plant anatomy, biochemical and physiological changes and variations in the enzymes and phytohormones levels. The effector protein SAP54 is mainly responsible for inducing the phyllody symptoms in phytoplasma infected plants. Since phytoplasma is an obligate pathogen, direct management methods may not be feasible. Targeting the vector population with an integrated pest management strategy would reduce the disease incidence and improve the yield parameters of the sesame crop. In this review, the progress made so far in understanding the phytoplasma infection in sesame, different groups and subgroups of phytoplasma, the diverse symptoms observed in different geographical locations and the management practices followed are discussed comprehensively.