Further studies on the non-transmission of plum pox potyvirus through seeds
Seed transmission of plum pox potyvirus (PPV - EPPO A2 quarantine pest) has been re-examined (Myrta et al., 1998), using seeds from apricot and plum cultivars infected with well-characterised PPV isolates. The question of seed transmission of PPV is raised as conflicting results have been obtained. The authors recalled that seed transmission was reported in apricot in Hungary, by Szirmai (1961), in Romania in peach and plums (Savulescu ; Macovei, 1965; Coman ; Cociu, 1976) and in Hungary by Németh ; Kölber (1982). However, these findings were not confirmed in many other studies. Jordovic (1963) in Yugoslavia and Schimanski et al. (1988) in Germany could not detect PPV in seedlings grown from infected seeds of plum and apricot. In Italy, Eyard et al. (1991, see also EPPO RS 96/174) and Triolo et al. (1993) found no PPV transmission through seeds of 4 apricot cultivars, and Dulic-Markovic and Rankovic (1997) found similar results in Yugoslavia with apricot and peach.
In the present studies, PPV-infected apricots (cv. Tirynthos from south-eastern Italy and Greece; cv. Bebeco from Greece, cv. Cafona from central Italy) and plums (cv. Pistilka from Albania) were used. Seeds were collected from mature symptomatic fruits, and PPV isolates infecting mother trees were identified by DASI-ELISA. Serological tests were done immediately after seed collection (on approximately half of each seed lot, on seed coats, cotyledons and embryos), during germination and on one year-old seedlings. Characterization of isolates showed that both PPV-M and PPV-D were present in the tested trees (PPV-M in Cafona, Bebeco and Tirynthos (GR); PPV-D in cv. Tirynthos (IT); mixture in plum cv. Pistilka). ELISA tests showed that mature seeds of all cultivars had a high rate of infection (e.g. 70% for plum cv. Pistilka, 89% for apricot cv. Tyrinthos (GR), 94% Bebeco, 95% Tyrinthos (IT), and 97% Cafona). PPV was almost always found in the seed coat, it was only detected in two seeds out of 936 in cotyledons and was never found in embryos. During seed germination, the number of positive seed coats was greatly reduced and none of the plumules and radicules of seeds with infected cotyledons was positive. No PPV symptoms were observed in the leaves of the seedlings, and all ELISA tests were negative in one-year old seedlings. Again, these studies demonstrate that PPV is highly unlikely to be transmitted by seeds.
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