Ocurrencia de hongos y etiología de la secadera de la fresa con diferentes sistemas de manejo agronómico

In México, strawberry dry wilt (Fragaria x ananassa) has been associated with a fungus complex in which only the implication of Fusarium oxysporum (Fox) is evident. Therefore, in the present study the association of fungi and pseudofungi with the disease was determined in different systems of agronomical management, and pathogenicity was verified. Two samplings were made in the 2002/03 season and three in 2003/04 in 16 localities of the Valley of Zamora, Michoacán, México, where 2640 sections of roots and 365 of necrotic crowns were sown, along with 400 sections of asymptomatic tissue in potato-dextrose-agar (PDA) culture medium and a selective medium with antibiotics and PCNB (PARPH) fungicide. Fox, F. solani (Fso), Cylindrocarpon sp. (Cyl), Pythium aphanidermtum (Pyt), Phytophthora sp. (Phy), Rhizodonia fragaride (Rhi), Verticillium albo-atrum (Ver) and Colletotrichum sp. (Col) were associated with the dry wilt. Fox was the most frequent species (p=0.05) and the only one that showed an increase from flowering to fructification of 47 to 62% in root and 77 to 83% in crown. In plantations with plastic mulch and drip irrigation (A + G), Fox decreased by 18% with respect to unmulched soil with gravity irrigation, whereas Cyl increased by 15% in A + G (p=0.05). The clay and clay loam soil contrasted in the detection of Fox (46.8 and 12.4%) and Rhi (9.1 and 43.7%). Symptoms of wilting with necrosis in root and crown and general death were reproduced with individual inoculations of Fox (100%), Pyt (100%), Phy (100%), Rhi (60%) and combinations of Fox with Rhi (100%), Pyt (100%) and Cyl (100%). This is the first report that implies Phytophthora sp., P. aphanidermatum and R. fragariae as causal pathogens of dry wilt in México. The morphological identification of Fox and Rhi was confirmed by sequencing of the intergenic region of the rDNA.