First Report of Phytophthora cryptogea Root and Crown Rot on Peach Trees in Chile

Plant Disease
G GuzmánW F Wilcox

Abstract

Phytophthora cryptogea Pethybridge and Lafferty was consistently isolated from the Nemaguard rootstock (Prunus persica × P. davidiana) of peach trees in Chile. Symptoms included reddish necrotic tissues at the base of the trunk often extending to the main roots, root rot, gummosis, foliar chlorosis, lack of vigor, and dieback, with severely infected trees dying. Isolations with corn meal agar (Difco, Detroit, MI) amended with antibiotics and fungicides (ACMA) (2) and pure cultures were obtained by hyphal tip transfers to ACMA. Ten isolates from different locations were identified by morphology and growth at cardinal temperatures (1). These isolates produced hyphal swellings and sporangia by using carrot juice broth (2) for 48 h followed by the addition of 1% (w/v) nonsterilized soil extract. Sporangia were nonpapillate, internally proliferating, noncaducous, ovoid to obpyriform, and with mean dimensions of 36 × 24 μm. All isolates were typed as A1 using a P. cinnamomi A2 culture as the test isolate and produced oospores on clarified V8 juice agar amended with thiamine, tryptophan, and β-sitosterol (2) after 15 to 30 days at 20°C in the dark. Mycelia grew between 5 and 30°C, with optimal growth at 20°C and no growth at 35°C. The...Continue Reading

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