Genetic heterogeneity of Phthorimaea operculella granulovirus: restriction analysis of wild-type isolates and clones obtained in vitro.

Genetic heterogeneity of a wild-type granulovirus (Tunisia isolate) of the potato tuber moth Phthorimaea operculella (Phthorimaea operculella granulovirus, Phop GV) has been studied. The heterogeneity was indicated by the presence of several submolar fragments in the profiles obtained by use of several restriction endonucleases. It was also demonstrated by variations in the restriction profile of the wild-type Tunisia isolate that had underwent since 1991 in our laboratory numerous passages in vivo. A comparison of the Tunisia isolate used in Egypt in the biological control programme with other PhopGV isolates indicated that it could not be related to any of the 3 genotypes previously defined. Five clones obtained from the Tunisia isolate in vitro were further grown both in vitro and in vivo. The restriction analysis of these clones demonstrated that none of them was identical to the parental wild type virus and to any other PhopGV geographic isolates. Genotypic differences between the clones were also shown. A 19 kbp BamHI fragment absent in the original Tunisia isolate but present in its passages since 1995 at a submolar concentration, was always present at a molar concentration in its clones. The presence of this fragment reflects probably a selection of one or more variants present in the original isolate and its possible adaptation to the growth in our laboratory conditions.