First report of Asian rust of soybean caused by Phakopsora pachyrhizi in Cuba

Centre of Genetic Engineering and Biotechnology, State Council of Cuba, CubaSoybean(Glycine max)isofincreasingimportanceinCubanagriculture.Two species of rust attacking soybean, Phakopsora pachyrhizi andP.meibomiae,havebeenidentifiedelsewhere(Onoetal.,1992).AseverePhakopsorasp.rustoutbreakinsoybeanoccurredinSeptember2006andsince then, minor outbreaks in legumes and beans (Phaseolus vulgaris)havealsooccurred.InApril2009,asevererustoutbreakinsoybeandevel-opedatphenologicalstageR3oftheplants,leadingtothecompletedefo-liation of two 50 ha fields of soybean cv. Conquista in Jovellanos,Matanzas province. First symptoms in the field consisted of yellowing ofthe lower leaves of plants leading to defoliation and early maturation.Symptomsontheuppersideofleavesconsistedofyellowspotsthatturnedbrown then necrotic, surrounded by wide yellow areas. Uredinia devel-oped on the undersides of the leaves. Anamorphic sori (Malupa-type)were amphigenous, circular, minute, pulverulent, whitish becoming palecinnamon-brown,scatteredoringroupsondiscolouredspots,subepider-mal becoming erumpent, cone-like, 1–2 mm diameter, surrounded byparaphyses, with a central opening. Paraphyses were cylindrical toclavate,25–45 lm(morefrequently37AE5 lm) · 6–14 lm,slightlythick-enedattheapex,7AE5–17AE5(12AE5) lm,colourlesstopaleyellowish-brown.Uredinospores were sessile, obovoid to broadly ellipsoidal, 25–35(28) · 17–22AE5 (18AE7) lm; wall 1–1AE5 lm thick, minutely and denselyechinulate, colourless to pale yellowish brown, sometimes pale cinna-mon-brownwithage.A positive reaction was obtained when sap from rust-affected leaveswas tested with immunological test sticks containing a specific antibodyto P. pachyrhizi, (QuickStix). Real-time PCR was conducted on sapfrom affected leaves using SYBR green as label and the specific primersdeveloped by Frederick et al. (2002) for the diagnosis of each species.The results of the PCR confirmed the presence of both P. pachyrhizi andP. meibomiae causing mixed infections within the same plant, althoughhigher concentrations of DNA of P. pachyrhizi were noted, presumablydue to the faster growing and more aggressive nature of this species.According to Bromfield (1984), P. meibomiae was previously reportedin Cuba in 1926, but there were no further records of its presence insoybeans and other legumes since this time. This is the first reportof Phakopsora pachyrhizi attacking soybeans in Cuba and theconfirmation by advanced diagnostic procedures of the presence ofP. meibomiae.References