ANIL KUMAR, Dr. P.SAYIPRATHAP, B. R.2021-12-092021-12-092021-12-09https://krishikosh.egranth.ac.in/handle/1/5810178895INVESTIGATIONS ON PREVALENCE, TRANSMISSION AND MANAGEMENT OF STERILITY MOSAIC DISEASE OF PIGEONPEA (Cajanus cajan (L.) Millsp.)Sterility mosaic disease (SMD) is caused by Pigeonpea sterility mosaic virus (PPSMV). Strain variability coupled with recent characterization of another Emaravirus (PPSMV-II) made a complex etiology of this difficult to manage the viral disease. In this context, the present study was carried out at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, Hyderabad, Telangana from 2017 to 2019 to determine the prevalence of SMD, variability in PPSMV isolates in southern India, host range, the occurrence of different strains and to find out broad-based resistance source in pigeonpea genotypes. A comprehensive and systematic survey was conducted in southern India during the 2017 rainy season indicated a huge variation in disease incidence ranging from 0-47.50 per cent. In Andhra Pradesh, less SMD incidence (0.06 %) was recorded Guntur district While, in Anantapur and Chittoor districts, the disease incidence was 5.90 per cent and 11.80 per cent respectively. In Karnataka, SMD was found to be a major production constraint throughout the state. Among the ten districts surveyed, higher disease incidences of 14.71 and 19.78 per cent was recorded in Gulbarga and Kolar district respectively. In Tamil Nadu, less SMD incidence (4.08 %) was observed in the Pudukottai district, whereas, highest disease incidence was recorded in the Krishnagiri district (16.25 %). In Telangana, there was less incidence of SMD in all surveyed locations that ranged from 0 to 8.0 per cent. In the Nalgonda district, SMD incidence was 0.60 per cent, whereas, in Medak district, it was 1.50 per cent. Analysis of the RNA-3 partial nucleotide sequence identity among the seven isolates of PPSMV-I and PPSMV-II in southern India indicated significant sequence variability. Among the 11 Nicotiana species and five herbaceous plants tested for PPSMV infection by sap inoculation, the virus successfully transmitted on to Nicotiana benthamiana but not on to the pigeonpea. Of the 24 accessions of 12 wild Cajanus species, xii 16 cultivated crop species and 46 weed species tested by mite inoculation, Cajanus platycarpus, C. scarabaeoides, and C. lancedatus, Phaseolus vulgaris cvs. Top crop, Kintoki, and Bountiful (F: Fabaceae), and weed species, Crozophora rottleri(F: Euphorbiaceae) were infected with both the virus (PPSMV-I and PPSMVII). Though few mites were observed on a weed species Macroptilum atropurpureum (F: Fabaceae), the virus was not infected. The pigeonpea sterility mosaic disease (SMD) samples were collected from three hotspot locations (Patancheru, Bengaluru, and Coimbatore) in southern India when tested for infection of PPSMV-I and PPSMV-II by RT-PCR, all the samples from Patancheru location were found mixed infection of both the viruses. Whereas, few samples from Bengaluru and Coimbatore were found infected with only PPSMVII. There is a significant sequence variability in partial nucleotide sequences of the RNA-1 and RNA-2 segments of PPSMV-I and PPSMV-II isolates in southern India. Interestingly nucleotide sequences of RNA-1 and RNA-2 segments of PPSMV-II isolates showed close relationship with Fig mosaic virus (FMV) than PPSMV-I. This suggested that these two emaraviruses infecting pigeonpea have followed two independent evolutionary paths. Sap transmission inoculation of PPSMV on to Nicotiana species, mite transmission inoculation on to wild Cajanus species, cultivated crop and weed species, as well as random inoculation and single mite transmission on to susceptible pigeonpea genotype, ICP 8863 were not successful in separating out PPSMV-I and PPSMV-II from Patancheru inoculum. Hence in the present study, it could not be possible to ascertain the role and severity of individual virus strain in causing SMD in pigeonpea. A comprehensive analysis of data from the two field trials conducted at Bengaluru and Patancheru locations for the management of SMD during the 2018 crop season confirmed that three sprays of proporgite @ 0.15 per cent recorded least SMD incidence (2.00 %) with 80.33 per cent yield increase over control. Spraying of salicylic acid (SA) @ 0.10 mM and gibberellic acid (GA) @ 250 ppm offered reasonably good levels of SMD control as well. Twenty pigeonpea genotypes were screened for broad-based resistance to SMD at Bengaluru, Coimbatore, and Patancheru locations during the 2017-18 and 2018-19 rainy season. The susceptible test genotypes exhibited the typical SMD symptom between 13-16 days of postinoculation (dpi). Among the genotypes, ICPL-16078, ICPL- 16086 and ICPL-16087 were showed resistance reaction (40 % incidence) at the Bengaluru location. Based on the level of disease reaction in evaluated pigeonpea genotypes for two consecutive years, Bengaluru isolates could be considered as severe strain in causing SMD in pigeonpea.EnglishThesis