Occurrence of Globisporangium and Phytopythium species associated with apple and peach seedlings decline in Tunisian nurseries

Abstract

Considerable losses of apple and peach tree seedlings were observed on 2012 in Tunisian nurseries and orchards. In the current study, surveys were conducted on apple and peach seedlings in ten and six nurseries respectively. Sampling was undertaken from symptomatic roots of seedlings showing various levels of decline. Isolation studies revealed the presence of Globisporangium ultimum (10.46% of apple seedlings and 18.96% of peach seedling), Phytopythium mercuriale (7.79% of apple and 22.29% of peach seedlings), and Phytopythium helicoides (5.8% of apple seedlings). On apple, a detached twig assay on the ‘Golden Delicious’ variety showed that P. mecuriale caused smaller necrotic lesions than G. ultimum and P. helicoides. A stem inoculation assay on the same variety supported the high virulence of G. ultimum which caused the death of seedlings. On the apple rootstock ‘MM106ʼ a soil inoculation assay supported the stem inoculation assay in that G. ultimum was the most virulent causing root rot and root weight reductions, followed by P. helicoides and P. mercuriale having the lowest virulence. On peach, a detached twigs essay on the ‘Carnival’ variety showed that G. ultimum and P. mercuriale caused necrotic lesions. A stem inoculation assay on both ‘Carnival’ and ‘Royal Glory’ varieties supported the virulence of these two oomycetes species which caused stem necrosis. On the peach rootstock ‘Garnem’ a soil inoculation assay showed that only G. ultimum was virulent causing root rot. These results suggest that these pathogens could function as potential decline inoculum sources that might limit post-plant tree growth in orchards.