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Title: Morphological and molecular variability among Indian isolates of Rhizoctonia solani causing banded leaf and sheath blight in maize

Author
item SINGH, VIMLA - Icar-Indian Institute Of Maize Research
item AMARADASA, BIMAL - University Of Florida
item KARJAGI, CHIKAPPA - Icar-Indian Institute Of Maize Research
item Lakshman, Dilip
item HOODA, KARAMBIR - Icar-Indian Institute Of Maize Research
item KUMAR, AUNDY - Indian Agricultural Research Institute

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2018
Publication Date: 3/8/2018
Citation: Singh, V., Amaradasa, B.S., Karjagi, C.G., Lakshman, D.K., Hooda, K.S., Kumar, A. 2018. Morphological and molecular variability among Indian isolates of Rhizoctonia solani causing banded leaf and sheath blight in maize. European Journal of Plant Pathology. 152:45-60. https://doi.org/10.1007/s10658-018-1447-2.
DOI: https://doi.org/10.1007/s10658-018-1447-2

Interpretive Summary: The banded leaf and sheath blight (BLSB) disease caused by the soilborne fungus Rhizoctonia solani is a constraint to maize production and improvement programs in the tropics. Traditional biological approaches to pathogen identification are often inaccurate, inconvenient, and time consuming. Precise identification, characterization and determination of morphological and molecular diversity of Rhizoctonia isolates are essential for disease management practices with pesticides and biocontrol agents, and breeding for disease resistance. For this purpose, Rhizoctonia isolates were collected from diseased leaves from seven diverse maize cropping zones of India and were examined for species identification, cultural, morphological and molecular variability, and pathogenic behavior. Among the 62 Rhizoctonia isolates identified, 61 isolates were determined to be of AG1-IA type; one isolate was identified as Waitea circinata. No relationship could be established between geographical origin of the isolates with the pathogenicity, morphological, or molecular groups. This study provided evidence that the genetic flexibility of the pathogen allows for its adaptation to variable ecological niches and long-distance introduction of new genotypes into the region. The information generated from this study will be helpful to scientists working on the epidemiology and management of this pathogen.

Technical Abstract: Rhizoctonia solani, a devastating soil borne fungus inciting banded leaf and sheath blight (BLSB) disease is a constraint in maize production and improvement program. Rhizoctonia isolates collected from seven diverse maize cropping zones of India were examined for species identification, cultural and morphological variability, pathogenic behaviour and molecular variability. Sequence comparison of the ITS-5.8S rDNA region of 62 isolates did not reveal much diversity within and among the isolates. The 61 isolates clustered with the anastomosis group (AG) AG1-IA reference strain in the phylogram distinctly separated from the AG1-IB and AG2-2IIIB reference strains. However, one isolate separated as Waitea circinata with the reference strain. The establishment of AG for these isolates, the primary objective of sequencing and phylogeny, was achieved. In the AG1-1A cluster, 22 isolates fell into distinct clades. BLSB isolates from geographically different gene pools shared identical sequences supporting long-distance clonal dispersal of mycelia and sclerotia. No relationship could be established between geographical origin of the isolates and the genetic profiles, because the Rhizoctonia isolates within a clade represented most of the sampling sites. This study confirms that the genetic flexibility of the pathogen allows for its adaptation to variable ecological niches and long-distance introduction of new genotypes into the region. This study also emphasizes that epidemiological studies may complement the molecular studies. It is inferred that recombination events between isolates in nature following clonal expansion may be one reason for similarities between the isolates from diverse agro-ecological regimes.