Survey, Pathogenicity and Molecular Characterization of Root Pathogens Associated with Root Rot of Cedrus deodara (Roxb.) G. Don in District Solan, Himachal Pradesh, India

Abstract

Root rot disease is one of the most serious diseases that significantly reduces the plant's productivity, commonly known as collar rot, foot rot, or damping off. The main symptom of this condition is damping off. The newly emerging seedlings collapse and die in areas with severe infection, and the majority of seedlings may die before or after emergence. Due to Root rot disease in C. Deodara which is our state tree, the damage caused by it to the seedlings there was urgent need to identify and study the disease so as to develop proper management strategies. In Himachal Pradesh, a field survey was carried out to know the disease incidence of root rot pathogen  in the Cedrus growing regions in district Solan. The survey included the Kanaghat, Solan, and Chail mountains. The Kandaghat range covered Kiari, Karol, and Bisha nurseries, the Solan range Shilli, Nauni nurseries, and the Chail range Chiunth, Chail, and Gaura nurseries were all covered. During the survey of root rot pathogen of Cedrus deodara, 10.90 to 62.15%incidence was recorded in district Solan nurseries. Maximum incidence of the root rot was recorded in Kandaghat range (37.35%) followed by Solan range (33.85%) and Chail range (30.93%), respectively. Amongst nurseries found that,Bisha nursery had maximum incidence (62.15%) followed by Nauni (48.46%) and Chiunth nurseries (44.65), respectively. Cultural and morphological characteristics of root rot pathogen were studied and identified as Rhizoctonia solani. ITS1/ITS4 markers were employed for the molecular identification of the pathogen that caused the root rot in Cedrus deodara, which was confirmed to be binucleate Rhizoctonia AG-E. For the root rot pathogen, isolation frequency was also observed in three solan ranges. Isolation frequency of Chail range comprising of two ranges showed the maximum of 37.71%followed by Kandaghat (34.42%) and Solan (19.37%), respectively. Numerous pathogens were isolated, however, three pathogen,  binucleate Rhizoctonia AG-E, Fusarium oxysporum, and Phoma exigua were found to occur most frequently. Binucleate Rhizoctonia AG-E was the most often isolated of the three primary pathogens, occurring at a maximum frequency of 50.23%, followed by P. exigua (18.98%) and F. oxysporum (7.49%). Three different methods were used to test the pathogenicity of binucleate Rhizoctonia AG -E for their ability to produce root rot symptoms. The soil infestation inoculation method recorded the highest disease incidence (83.48%) followed by the root dip (34.53%) and stem application (23.76%), respectively.