Dr. Virendra Kumar SinghArvind Kumar2024-09-262024-09-262023-08-09Arvind Kumar (2024).“Incidence and variability of Sclerotium rolfsii causing collar rot of chickpea (Cicer arietinum L.)” Thesis, Ph.D. BANDA UNIVERSITY OF AGRICULTURE & TECHNOLOGY BANDA-210001, UTTAR PRADESH (INDIA)https://krishikosh.egranth.ac.in/handle/1/5810215045Chickpea (Cicer arietinum L.) is an important and oldest pulse crop. Collar rot caused by Sclerotium rolfsii is an important disease of Chickpea. An intensive roving survey was conducted in 2021-2022 for the assessing prevalence and incidence of collar rot in seven growing districts (Banda, Hamirpur, Mahoba, Chitrakoot, Jhansi, Jalaun, and Lalitpur) of Bundelkhand region of Uttar Pradesh. A total of 63 locations were surveyed and observed that the disease was prevalent at all the locations. The collar rot incidence ranged from 4.0 to 17.0%. The highest disease incidence (17.0%) was recorded from Lodhipur village of Muskara block in Hamirpur district and the lowest collar rot incidence (4.0%) was recorded from Chakrauli village of Karwi block in Chitrakoot district. In order to diversity study of collar rot pathogen a total of twenty nine isolates of Sclerotium rolfsii were isolated from diseased plant samples collected from surveyed locations. It was observed in diversity study of pathogen that all the isolates of the Sclerotium rolfsii highly diverse in mycelial and sclerotial morphological traits on PDA medium. Among the mycelial traits significant variations were recorded in colony diameter, colony colour, type and appearance of colony growth on PDA medium after 72 hrs of incubation at 27 °C. ‘Most of the isolates were medium growth rate which recorded 50 to 80 mm colony diameter and fast growing isolates which recorded 80.33 to 90.00 mm colony diameter after 72 hrs of incubation’. Based on the colony appearance seven isolates were showed fluffy, sixteen isolates showed dense and remaining six isolates were showed the sparse mycelial growth on PDA medium. Variation among the isolates on the basis of colony colour was also recorded, that the isolates were produced white, extra white and dull white colour colonies on PDA medium.The variability in sclerotial traits of isolates was recorded significantly. The numbers of sclerotia were highly varied among the isolates and ranged from 106.33 to 1005.33 per plate (90 mm). The isolates also showed variation in test weight (weight of 100 sclerotia) of sclerotia, ranged from 68.66 mg to 538.33 mg per hundred sclerotia. The size of sclerotia also varied in different isolates and ranged from 0.93 mm to 1.59 mm in diameter. The colour of sclerotia was mostly brown, light brown and dark brown at maturity. Shape of sclerotia was also varied among the isolates and most of the isolates were produced spherical to oval shape sclerotia. The sclerotia in most of the isolates were distributed in scattered to peripheral manner over the PDA plates. In order to determination of mycelial compatibility groups (MCG) among the isolates were paired to each other on PDA plates and the isolates also paired themselves to ensure self-compatibility. There were 435 combinations of twenty nine isolates, out of which only 211 combinations showed compatible reactions while remaining 224 combinations showed incompatible reaction. Based on compatible and incompatible reaction three MCGs were distinguished among twenty nine isolates. In case of pathogenic variability, isolates from different locations showed difference in their virulence on different variety. Among the all isolates the isolates SRC22, SRC25, SRC27 and SRC28 considered as most virulent as it causes highest diseases incidence in all selected variety of chickpea. The physiological requirement of pathogen for maximum mycelial growth of different isolates of S. rolfsii was observed on Czapek’s dextrose agar and Potato dextrose agar medium and maximum sclerotia production on Potato dextrose agar medium while, on 25 ℃ temperature and pH level 7.0 observed maximum mycelial growth and sclerotia production. Genetic similarities were analyzed through the data obtained on the basis of 10 RAPD primers from the 29 isolates of the Sclerotium rolfsii and presented varying degree of genetic relatedness. Jaccard’s similarity coefficient ranged from 0.05 to 1.01. The highest similarity 1.0 was observed between genotypes SRC-11 and SRC-29. The lowest similarities were revealed between the isolates SRC-5 and SRC-25, SRC-13 and SRC7, SRC-18 and SRC8, SRC-25 and SRC-18 registered the minimum similarity value (0.0) indicating the maximum genetic distance between them. Among the different type of soil the maximum collar rot disease incidence was recorded in black soil (66.02%), followed by light brown soil with (61.13%) incidence.EnglishThesis