CRIS Project Title:  
Biologically based management strategies for control of soil-borne pathogens of ornamental crops as an alternative to methyl bromide pre-plant soil fumigation

INTRODUCTION:  
Conducts research on important soil-borne fungal pathogens of ornamental plants, including Rhizoctonia solani. Current research interests include: characterization and utilization of hypovirulent isolates of R. solani for biological control and/or growth promotion of ornamental plants in the greenhouse; characterization of fungal double-stranded RNAs (dsRNAs), fungal genes and biochemical processes affecting virulence; transformation and transfection of R. solani with fungal dsRNAs; and, exploration and development of biorationals and composts as disease suppressive alternatives to methyl bromide.

PROGRESS:  
Cloned and characterized the expression of arom gene of Rhizoctonia solani under virulent and quinate-induced hypovirulent conditions. Evaluated a botanical formulation as an effective antibacterial agent to control soilborne bacterial plant pathogen. Screening and characterizing Streptomyces isolates for biocontrol of Rhizoctonia solani and other plant pathogens.

PLANS:   
To investigate, develop characterize and use hypovirulent isolates for the control of soil-borne pathogens causing damping-off and stem rot diseases in ornamental crops, with emphasis on R. solani. Explore and develop organic amendments and biorationals for the management of soil-borne pathogens inducing damping-off and stem rot diseases in ornamentals with emphasis on R. solani. Investigate the effectiveness of microbial antagonists in combination with reduced risk pesticides in the management of R. solani and other soil-borne fungal pathogens.

RECENT PUBLICATIONS (most recent first):

2006. Lakshman, DK, Liu, C, Mishra,PK, and Tavantzis, SM. Characterization of the arom gene in Rhizoctonia solani, and transcription patterns under stable and induced hypovirulence conditions. Curr Genet 49:166-177.

2003. Liu C, Lakshman DK, and Tavantzis SM. Expression of a hypovirulence-causing double-stranded RNA (dsRNA) is associated with up-regulation of quinic acid pathway and down-regulation of shikimic acid pathway in Rhizoctonia solani. Curr Genet 42:284-291.

2003. Liu C, Lakshman DK, and Tavantzis SM. Quinic acid induces hypovirulence and expression of a hypovirulence-associated double-stranded RNA in Rhizoctonia solani. Curr Genet 43:103-111.

2000. Strauss, EE, Lakshman DK, and Tavantzis, S. Molecular characterization of the genome of a partivirus from the basidiomycete Rhizoctonia solani. J. Gen. Virology 81:549-555.       

1998. Lakshman, DK, Jian, J, and Tavantzis, SM. A double-stranded RNA element from a hypovirulent strain of Rhizoctonia solani occurs in DNA form and is genetically related to the pentafunctional AROM protein of the shikimate pathway. Proc. Natl. Acad. of Sci. USA 95: 6425-6429.

1998. Jian, J, Lakshman, DK, and Tavantzis, SM. A virulence-associated, 6.4-kb, double-stranded RNA from Rhizoctonia solani is phylogenetically related to plant bromoviruses and electron transport enzymes. Molecular Plant-Microbe Interactions 11:601-609.

1997. Jian, J, Lakshman, DK, and Tavantzis, SM. Association of distinct double-stranded RNAs with enhanced or diminished virulence in Rhizoctonia solani infecting potato. Molecular Plant-Microbe Interactions 10:1002-1009.

1995. Castello, JD, Lakshman, DK, Tavantzis, SM, Rogers, SO, Bachand, GD, Jagels, R, and Carlisle, J. Detection of infectious tomato mosaic virus in fog and clouds. Phytopathology 85:1409-1411.

1994. Lakshman, DK, and Tavantzis, SM. Spontaneous appearance of genetically distinct double-stranded RNA elements in Rhizoctonia solani. Phytopathology 84:633-639.

1994. Singh, RP, Boucher, A, Lakshman, DK, and Tavantzis, SM. Multimeric non-radioactive cRNA probes improve detection of potato spindle tuber viroid (PSTVd). J. Virological Methods 49:221-234.

1992. Lakshman, DK, Tavantzis, SM, Boucher, A, and Singh, RP. A rapid and versatile method for cloning viroids and other circular plant pathogenic RNA's. Analytical Biochemistry 203:269-273.

1992. Lakshman, DK, and Tavantzis, SM. RNA progeny of an infectious two-base deletion cDNA mutant of the potato spindle tuber viroid acquire two nucleotides in planta. Virology 187: 565-572.

1993. Lakshman, DK, and Tavantzis, SM. Primary and secondary structure of a 360-nucleotide isolate of potato spindle tuber viroid. Archives of Virology 128:319-332.

1992. Singh, RP, Lakshman, DK, Boucher, A, and Tavantzis, SM. A viroid from Nematanthus wettsteinii plants closely related to the columnea latent viroid. Journal of General Virology 73: 2769-2774.

1987. Rao, ALN, Lakshman, DK, Ohki, ST, and Hiruki, C. Serological relationships among six isolates of red clover necrotic mosaic virus: Identification of a new serotype. Phytopathology, 77:995-999.

1986. Lakshman, DK, Hiruki, C, Wu, XN, Leung, WC. Use of 32P RNA probes for the dot-hybridization detection of potato spindle tuber viroid.  Journal of Virological Methods 14: 309-319.

1985. Lakshman, DK, Gonsalves, D, and Fulton, RW. Role of Vigna species in the appearance of pathogenic variants of cucumber mosaic virus. Phytopathology 75:752-757.

1985. Lakshman, DK, and Gonsalves, D. Genetic analyses of the large lesion mutants of two cucumber mosaic virus strains. Phytopathology, 75:758-762.

Book chapters:
1995. Tavantzis, SM and Lakshman, DK. Virus-like double stranded RNA elements and hypovirulence in phytopathogenic fungi. In "Pathogenesis and Host-Parasite Specificity in Plant Diseases: Histopathological, Biochemical, Genetic and Molecular Basis” Chapter 18, K. Kohmoto, R. P. Singh, and U. S. Singh Eds. CRC Press.

1996. Rubio, V, Tavantzis, SM, and Lakshman, DK. Extra-chromosomal elements and degree of pathogenicity in Rhizoctonia solani. In “Rhizoctonia Species: taxonomy, molecular biology, ecology, pathology and disease control” Chapter II.3, B. Sneh, S. Jabaji-Hare, S. Neate, and G. Dijst eds. Kluwer Academic Publishers.

2002. Tavantzis, SM, Lakshman, DK, and Liu, C. Double-stranded RNA elements modulating virulence in Rhizoctonia solani. In “dsRNA genetic elements – Concepts and applications in agriculture. Forestry, and medicine” Ed. S. Tavantzis. CRC Press.

Invited research report:
Lakshman, DK (2006). Double-stranded RNA-mediated hypovirulence of Rhizoctonia solani. Association for Advancement in Plant Protection Newsletter (India). 1(1): 3.

Published abstracts (selected):
2005. Lakshman, DK, Liu, C, Mishra, PK, Stellos Tavantzis, SM. Characterization and substrate induced transcriptional regulation of the pentafunctional arom gene of Rhizoctonia solani. Phytopathology 95: pS56 (abstract # 544).

2003. Cubeta, MA, Ceresini, PC, Shew, HD, Cody, BR, Boerema, ME, Lakshman, DK, and Tavantzis, SM. Occurrence of the M2 dsRNA in populations of Rhizoctonia solani AG-3 from potato and soil. Proc. Intern. Cong. Plant Pathol. Pp. 110.

1990. Lakshman, DK and Tavantzis, SM. Evaluation of transgenic plants engineered with antisense, mutated cDNA of potato spindle tuber viroid. American Potato J. 67:559.

1989. Tavantzis, SM, Lakshman, DK, Burian, LC, and Bandy, BP. A transgenic plant approach to studying viroid pathogenesis. Phytopathology 79:1195.

1985. Ohki, ST, Lakshman, DK, and Hiruki, C. Electron-microscopy and low molecular weight dsRNA analysis of spot mosaic-infected wheat. Phytopathology 75:1357.

1982. Palukaitis, P, Ankeny, MD, Lakshman, DK, and Zaitlin. Effect of a-amanitin and actinomycin-D on the replication of potato spindle tuber viroid in suspension culture. Annual meeting for the American Society of Virology, Cornell University, Ithaca, NY.

cDNA sequences deposited to GenBank (Acc. Number):
Arom               Aromatic amino acid synthesis (arom) gene of R. solani (AF482690)
M1                   Virus-like dsRNA of R. solani, isolate Rhs 1AP (AF020042)
M2                   Virus-like dsRNA of R. solani, isolate Rhs 1A1  (U51331)
dsRNA1          Partitivirus of R. solani, isolate Rhs 717  (AF133290)
dsRNA2          Partitivirus of R. solani, isolate Rhs 717  (AF133291)
PSTVd-M        Mild strain K-5, potato spindle tuber viroid  (M93685)
PSTVd-M        Genomic variant, KF-5/M3  (AF483470)
PSTVd-M        Genomic variant, KF-5/M4  (AF483471)
PSTVd-S         Severe strain, host repaired mutant, St4/17  (AF483472)
PSTVd-S         Severe strain, host repaired mutant, St4/22  (AF483473)    
CLVd              Strain of Columnea latent viroid  (M93686)

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