An analysis of the strain relationships of maize dwarf mosaic virus

Abstract

Maize dwarf mosaic virus (MDMV) is one of the Potyviruses whose strain relationships have not been clearly defined. Many of the characteristics which have been traditionally used in the strain definitions are now known to be unreliable. By replacing these characters with characteristics of the capsid protein, new strain relationships were revealed. Serological analysis by immunoblot provided an easy and convenient method to analyze these strains. By utilizing regression analysis, the relative epitope concentration and the relative epitope compatability could be determined. The analysis provided clear distinction between strains A, B, E, and O. Strains D and F could not be distinguished from MDMV-A. The analysis of the molecular weights demonstrated the following average molecular weight for each strain: MDMV-A--35,770, MDMV-B--36,620, MDMV-D--33,970, MDMV-E--33,830, MDMV-F--34,410, and MDMV-O--37,890 da. The transblot analysis of MDMV-A and MDMV-B isolates provided an overall picture of these two strains. The MDMV-A isolates ranged in molecular weight from 31.200 to 39.500. This wide range indicated a large amount of heterogeneity in the population. Undefined strains could be responsible for this. The range of MDMV-B isolates was narrower (34.610 to 38.190). The smaller amount of heterogeneity indicated here could result from the more restricted definition that has been utilized for MDMV-B. Peptide mapping of tryptic digests indicated strains A, D, E, and F were closely related. These strains demonstrated 31, 27, 31, and 31 peptides, respectively. Similarities in the patterns produced by these strains were also noted. Strains B and O had 23 and 21 peptides, respectively. There were few similarities in the pattern of the two-dimensional analysis. A pictorial concept of the MDMV strains was generated utilizing the serological difference indexes of MDMV-A and MDMV-O. This concept agreed with the results of the other analysis. The four external vertices were formed by strains A, B, E, and O which demonstrated distinct differences. The internal vertices were formed by strains D and F. Their reactions were restricted to the plane generated by MDMV-A. This reinforces the other indications that MDMV-D and MDMV-F are isolates of MDMV-A rather than true strains.