Involvement of phytoplasmas in a decline of Ulmus chenmoui in Central Italy

To verify the role of phytoplasma infections in a decline of Ulmus chenmoui in Central Italy, two plots of seedlings established in two locations were studied. Roots and twigs with leaves were sampled in June and in September 1996 from 11 U. chenmoui plants located at San Rossore (Pisa), and in July 1996 and September 1997 from nine U. chenmoui plants at Presiola (Ravenna). The plants at San Rossore showed a generalized decline consisting of small, pale green leaves and death of small twigs, whereas those at Presiola had an healthy appearance in 1996 and started to decline in 1997. Molecular analyses resulted in the identification of elm yellows-related phytoplasmas in three out of the twenty plants examined (two from San Rossore and 1 from Presiola). The same phytoplasma was identified in both locations in yellows-diseased elm hybrids employed as positive controls. Phytoplasmas belonging to other groups were also detected in one U. chenmoui plant and in weeds and insects tested from the Presiola plot. Restriction fragment length polymorphism analyses on 16Sr DNA, spacer region and ribosomal protein fragment coding for the 3' end of rpl22 and the entire rps3 genes, did not show a genetic variability in elm yellows phytoplasmas detected in U. chenmoui. No differences among these isolates, phytoplasmas infecting other elm species in these plots and the reference elm yellows isolates were found.