AGRIS-FAO dbase: Studies on plant viruses-soil colloids interaction. 1. Stability and infectivity of CMV associations with kaolinite and montmorillonite.

Stability and infectivity of cucumber mosaic virus, strain D (CMV-D), associations with kaolinite and montmorillonite were determined, as affected by: i) nature of clay minerals; ii) nature of clay saturating cations; iii) exposure to dissociating salt solutions (2 M LiCl). Infectivity experiments carried out with sediments following centrifugation of the virus-clay mixtures (sd fractions), showed that, in absence of LiCl, the higher values were obtained with kaolinite, in the order Li(+) K(+) over NH((4))(+) = Mg(++) over Na(+) over Ca(++) clay saturating cations, ranging between 91 and 30 % of the untreated control, whereas comparable montmorillonite fractions gave infectivity values with all cations about 10 - 15 % of the control. In presence of 2 M LiCl, montmorillonite preserved infectivity of the same fraction (Lsd fraction), which in the case of Li(+)- or Ca(++) -saturated samples, was higher when compared with the corresponding sd values, thus revealing for these cations an amplifying effect on infection. This did not occur with kaolinite which, however, gave an Lsd fraction more infectious than the other clay. The results confirmed that clay minerals preserve infectivity of virus preparations exposed to critical conditions, thus providing an explanation for the persistence in soil infectivity of viruses which are normally not soil-borne. Under appropriate soil conditions these viruses may form complexes with clay minerals thus retaining an infectivity which may be enhanced by addition of cations as those contained in fertilizersconditions these viruses may form complexes with clay minerals thus retaining an infectivity which may be enhanced by addition of cations as those contained in fertilizers