Studies on pear decline disease in Uruguay
Pear decline (PD) caused by 'Candidatus Phytoplasma pyri' (subgroup 16SrX-C of apple proliferation or AP group of phytoplasmas) is an important pear disease (Pyrus communis L.). Pear production in Uruguay is based on 'Williams' plants initially grafted on quince that are planted deep and thus transformed into scion-rooted trees. Less vigorous rootstocks like Pyrus spp. and quinces that could be more susceptible to decline are beginning to be used for precocity. Surveys were conducted on plants grafted on different rootstocks to know if PD was present in the pear growing area of Uruguay (southern part near Montevideo city) by searching for premature reddening, upward rolling of leaves and decline. Phytoplasmas were observed in 35 of 70 samples using the DAPI (4',6-diamidino-2-fenilindol) staining test. Ten positive and 10 negative samples were analyzed by polymerase chain reaction (PCR) assay using AP-group specific primers f01/r01. A 930 bp amplicon was obtained only from all DAPI positive samples. The f01/r01 amplicon was sequenced and showed 100% identity with the 16S rRNA gene sequence of PD phytoplasma in the NCBI database. A relationship was observed between phytoplasma detection, reddening, psylla infestation and premature leaf fall in this survey in 1995. Presence of PD-symptoms and phytoplasma detection by PCR were also evaluated in an experiment where 20 pear scion/rootstock combinations were compared during 2005-2011. Plants of self-rooted 'Williams' or grafted onto OH×F 40 and OH×F 69 stocks showed less early reddening and leaf fall than plants grafted onto quince rootstocks. Phytoplasma detection in this trial varied among seasons and was not associated with the presence of symptoms. Phytoplasmas were detected in pear psylla insects during the whole 2009-2011 seasons in four pear orchards. An association between the effectiveness of psylla control, phytoplasma detection and early reddening and leaf fall was found in an experiment with traditional 'Williams' self-rooted plants in 2011. These results indicate the presence of PD phytoplasma in Uruguayan pear orchards and in psylla insects during the whole season.
Maeso, D., Federici, M.T., Martínez, A., Silvera, M. and Goncalvez, L. (2021). Studies on pear decline disease in Uruguay. Acta Hortic. 1303, 343-350
European pear, Candidatus Phytoplasma pyri, Cacopsylla bidens, scion-rootstock affinity