Four Phytophthora Species Causing Foot and Root Rot of Apricot in Italy

In the summer of 2006, 1-year-old apricot (Prunus armeniaca L.) trees with leaf chlorosis, wilting, and defoliation associated with root and crown rot were observed in a nursery in Sicily (Italy). Of 3,000 plants, ~2% was affected. Four Phytophthora spp. (45, 25, 20, and 10% of the isolations of the first, second, third, and fourth species, respectively) were isolated from decayed roots and trunk bark on BNPRAH (3). Axenic cultures were obtained by single-hypha transfers. Isolates of the first species formed petaloid colonies on potato dextrose agar (PDA) and had an optimum growth temperature of 25°C. On V8 agar (VA), they produced persistent, papillate (often bipapillate), ovoid to limoniform sporangia (length/breadth ratio 1.4:1). They did not produce gametangia when paired with A1 and A2 isolates of Phytophthora nicotianae. The second species formed arachnoid colonies, had an optimum growth of 30°C, and produced uni- and bipapillate, ellipsoid, ovoid or pyriform sporangia (length/breadth ratio 1.3:1). All isolates were A2. The third species formed rosaceous colonies on PDA, had an optimum temperature of 28 to 30°C, and produced papillate (sometime bipapillate), ellipsoid or limoniform (length/breadth ratio 2:1), caducous sporangia with a tapered base and a long pedicel (as much as 150 μm). All isolates were A1 type. The fourth species formed petaloid-like colonies on PDA and had an optimum growth of 26 to 28°C. On VA, it produced papillate (sometimes bipapillate), ovoid (length/breadth ratio 1.3:1), and decidous sporangia with a short pedicel ( References: (1) S. O. Cacciola et al. Plant Dis. 90:680, 2006. (2) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) H. Masago et al. Phytopathology 67:425, 1977.