Isolates from two multinucleate Rhizoctonia species, namely Rhizoctonia solani and Rhizoctonia circinata, and binucleate Rhizoctonia spp., were evaluated for the presence of lectins, using human erythrocytes. Isolates from R. solani had similar lectins across the anastomosis groups. Agglutination profiles, however, revealed individual preferences for human blood types but with a general preference for type A over B and O. R. solani lectins had a general affinity for N-acetyl-D-galactosamine and mucin. Also, some isolates from the binucleate Rhizoctonia AG-DII, had lectins that showed strong affinity for glycoproteins, fetuin and mucin. There was no lectin activity in members of R. circinata. The lectins in members of the genus Rhizoctonia varied in content and character across the species sampled but had similar affinity for mucin. Furthermore, 62% of the self-anastomosing and 35% of the non-self anastomosing isolates tested showed lectin activity. The presence of lectins in both self-anastomosing and non-self anastomosing isolates suggests that lectins may not be directly involved in the recognition process in hyphal anastomosis.
Artificial suppression of radish damping-off disease was induced by repeated soil inoculations with Rhizoctonia solani, binucleate Rhizoctonia (BNR) and Sclerotium rolfsii in pot systems. Soils repeatedly inoculated with R. solani and BNR showed suppressive to disease caused by R. solani and S. rolfsii, while soils repeatedly inoculated with S. rolfsii were suppressive to disease caused by S. rolfsii but not by R. solani. Species of Trichoderma were consistently isolated from soils repeatedly inoculated with R. solani, BNR and S. rolfsii. These Trichoderma spp. accumulated selectively in relation to the fungal species that was repeatedly added to the soils. The ratios of the frequencies of T. viride, T. harzianum and T. hamatum were 5:2:2 and 8:5:2 in soils repeatedly inoculated with R. solani and BNR, respectively. In S. rolfsii-inoculated soils, T. koningii was predominantly isolated. T. viride, T. harzianum and T. hamatum isolates obtained from either R. solani or BNR after repeated additions to the soils suppressed radish damping-off disease caused after challenge inoculations with R. solani or S. rolfsii. Among the Trichoderma species, T. viride consistently yielded high levels of suppression. However, isolates of T. koningii obtained from S. rolfsii-infested soils suppressed disease caused by S. rolfsii but failed to suppress disease caused by R. solani. Generally, the species of Trichoderma accumulated in a selective pattern that was closely related to the species of fungal pathogen used to induce the suppressive soil.
Isolates from 18 anastomosis groups (AGs) of binucleate Rhizoctonia were screened for lectin activity. had low to moderate lectin activities. Among these, members of AG-D and AG-I had the highest activity. Partially purified lectins from AG-D preferentially agglutinated human blood type A to type B and O. Mucin and galactose were the most potent inhibitors among the tested carbohydrates. The molecular masses of these lectins ranged from 12.7 kDa for the monomer to 62 kDa for the pentamer type. Proline, alanine, glutamic acid, aspartic acid, leucine, threonine, serine and tyrosine were the major amino acid components of these lectins. Lectins from AG-D were stable at 4-50°C and from pH 6.0 to 10.0. When assayed with isoelectric focusing, these lectins gave bands at pI 9.30. Specificity of lectins from AG-D to galactose and its derivatives suggest a possible recognition role in this fungal species.
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