Epidemiological Factors Influencing the Development of Pigeonpea Sterility Mosaic Virus Disease in Pigeonpea

Background: In a region of Karnataka, India with a varied type climate PPSMV infection on pigeonpea occurs in a severe form and considered as green plague and one of the most devastating diseases as it appear in severe form resulting in reduction of 100% yield loss transmitted by vector eriophyid mite Aceriacajani Channabasavanna. However, not much systematic and strategic research work being carried out on epidemiology. In spite of various control measures, Sterility Mosaic Disease has continued to be major constraint in pigeonpea production. A lot of variation exists among the genetic background of different varieties in different regions. These variations render it difficult to evolve a common management strategy to control SMD epidemics. Therefore, it is necessary to know the severity of disease and factors associated with disease development which helps in devising suitable management practices.
Methods: To study the influence of sowing dates on SMD and vector population under field conditions. A total of twelve sets of sowings were made at different time interval starting from first week of January 2012 to December, 2012. The SMD disease incidence and mite population were recorded in each treatment at fifteen days interval. Under artificial environment, pigeonpea seedlings of variety ICP8863 were raised. Inoculation of virus was done at different stage of plant growth viz., 15, 30, 45, 60, 75, 90 days after sowing. The observation on terminal disease incidence was recorded at 90 DAS to study the impact of host age on SMD. The eight pigeonpea varieties were sown near the SMD infected plot so as to facilitate the movement of vector population under natural conditions to study the reaction of pigeonpea varieties to SMD. Naturally grown weeds present in and around the sterility mosaic screening nursery were collected at weekly interval to see the presence of mites. In a glass house experiment, twenty-three cultivated species of economic importance and three Nicotiana species were sown three replications to see the alternate host for the virus.
Results: The fluctuation in disease incidence and mite population was recorded throughout the year and early stage of crop growth recorded less disease incidence with lower mite population and gradual increase was recorded at later stage of crop growth period. The maximum disease incidence and mite population was recorded in crop sown during month of June and July where mean temperature was 24 to 26oC, RH 67 to 71% and rainfall of 2.13mm. The disease incidence recorded at different months of sowing had a significant positive correlation with mite population. Pigeonpea plants inoculated up to age of 30 days showed complete sterility with 100% disease incidence. The Resistant genotypes recorded less per cent disease incidence and symptom development at 60DAS. Whereas susceptible variety recorded maximum diseases incidence at early stage of crop growth and showed complete sterility. PPSMV and its vector survived on the ratooned pigeonpea plants and its wild relatives Atylosiascaraboeides during off season.