Seed transmission of Pseudoperonospora cubensis and identification of host resistance against downy mildew of cucumber
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Date
2023
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Punjab Agricultural University
Abstract
Downy mildew caused by Pseudoperonospora cubensis is a major disease of cucumber causing severe losses to farmers by affecting foliage. Surveys were conducted in different districts of Punjab for recording disease incidence and severity. It was deduced that the disease was most prominent in district Sangrur followed by Ludhiana, Hoshiarpur, Moga and Bathinda. During survey, the fruits collected from naturally infected vines revealed the presence of sporangia and oospores of P. cubensis in seeds when observed under microscope. To investigate seed transmission, seed grow out test was performed and P. cubensis was observed to be highest in the seedlings of Sangrur (33.33%) followed by Ludhiana (20.00%) Hoshiarpur (13.33%), Moga (6.67%) and no transmission was observed in fruits collected from Bathinda. Seed infectivity assays were conducted by artificial inoculation of healthy seeds and fruits using both sporangial and oospore inoculum. Microscopic studies revealed the presence of P. cubensis in seed coat as well as in embryo and seed to seedling transmission of P. cubensis was determined through seed grow out test. Transmission of P. cubensis from healthy seeds subjected to sporangial and oospore suspension was 40% and 26.66%, respectively. Transmission of P. cubensis from seeds of artificially inoculated fruits with sporangial suspension and oospores suspension was 46.66% and 20%, respectively. Molecular confirmation was done to detect the seed borne nature of the pathogen through DNA extraction from seed coat and embryo of naturally infected seeds and artificially inoculated seeds and fruits. PCR assays using ITS-4 and ITS-5 primers amplified 800bp band of P. cubensis. The pathogen has mainly reported to be soil borne but the present study showed that P. cubensis is also transmitted through seed. Forty cucumber genotypes were screened by artificial inoculation of plants in pots and under natural conditions in polyhouse as well as in laboratory conditions using detached leaf assay and leaf disc assay to identify sources against downy mildew. Cultivars PCG-10 and Punjab Kheera-1 were found to be moderately resistant.
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Kritika (2023). Seed transmission of Pseudoperonospora cubensis and identification of host resistance against downy mildew of cucumber (Unpublished M.Sc. thesis). Punjab Agricultural University, Ludhiana, Punjab, India.