Citrus gummosis incidence and role of ants (Lasius grandis) and snails (Helix aspersa) as vectors of the disease in Tunisia

Abstract

© 2018 Blackwell Verlag GmbH Surveys were conducted between November 2011 and December 2013 to determine the distribution and the incidence of citrus gummosis in Tunisia. Forty-two citrus orchards in three different citrus areas were surveyed. Symptoms of gummosis were observed in 59.52% of the orchards. The highest incidence was observed in the Cap Bon area. The involvement of some invertebrates in the epidemiology of citrus gummosis was also confirmed. Species of ants (Lasius grandis), snails (Helix aspersa and Rumina decollata) and worms (Armadillidium vulgare) collected from 2012 until 2014 were tested for the presence of Oomycetes. Phytophthora nicotianae and Phytopythium vexans were isolated from the bodies of Lasius grandis and also from bodies and faeces of Helix aspersa. However, no Oomycetes were isolated from the bodies of Rumina decollata and Armadillidium vulgare. In vitro assays, Helix aspersa was fed with P. nicotianae- and Ph. vexans-infected citrus bark showed the existence of those pathogens in 79.1% of the faeces of snails. In vivo assays, snails and ants were able to transmit the pathogens vertically from the base of potted 2-year-old trees citrus variety Clementine Mandarin cv. Hernandina, to other parts of the tree.