Sharma,PankajNavkiran Kaur2024-01-232024-01-232023Navkiran Kaur (2023). Understanding sunflower - Macrophomina phaseolina interaction under water stress conditions (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810206507A total of 35 isolates of Macrophomina phaseolina causing charcoal rot were collected from eleven kharif and rabi crops from different districts of Punjab and adjoining states. Macrophomina phaseolina isolated from sunflower field, Ludhiana was characterized on cultural and morphological and molecular basis. The isolates infecting sunflower showed highest sequence homology of ITS genomic region with M. phaseolina isolate from Indore, Madhya Pradesh NCBI accession no. MT127404. This isolate was further used to standardize the inoculation techniques under field and polyhouse conditions. Tooth pick inoculation technique was found most effective for large scale screening while sorghum grain inoculation method was proficient under polyhouse conditions. A set of 71 sunflower genotypes were evaluated using tooth pick inoculation technique against charcoal rot under irrigated and restricted irrigation conditions. Four genotypes viz; 75B, EC6078261, OPH137, and OPH 172 were found moderately resistant under irrigated conditions whereas only two genotypes 75B and EC6078261 showed moderately resistant reaction in restricted irrigated conditions. The present study was first attempt to investigate the water stress-Macrophomina phaseolina interaction on different components of physiological, plant growth and yield parameters along with disease incidence. A significant reduction in total chlorophyll content (54.78 %), relative water content (47.06 %), membrane stability (51.75 %), sugar (69.00 %), protein (13.90 %) and proline (56.66 %) content was observed with inoculum density of 4 g/kg soil at soil moisture levels of 40 % and 60 %. The inoculum density of 4 g/kg of dry soil resulted in maximum mortality during seedling stage and growth period. Thus, varied inoculum density and water stress conditions made the sunflower plants more prone to dismissive physiological alterations. It led to biomass reduction viz; root length (41.27 %), root width (76.74 %), root weight (85.37 %), shoot length (56.71 %) and shoot weight (79.06 %). Thus it resulted in per plant seed yield reduction (95.45 %) at 52.62 to 100 % disease severity at higher inoculum density (4g, 6g, and 8g/kg dry soil). The expression levels of the defense related genes LOX, ACCO1, PAL, SOD, and APX were also modified under varying degree of water stress and inoculum density. The strong correlation between low soil moisture and disease severity implies that the proper irrigation of the field can be suggested as cultural management practices for the farmers.EnglishThesis