Pathogens within the Diaporthe complex cause seed decay, stem blight and stem canker on soybean, representing a serious threat for this crop species. We herein utilize worldwide sequence data retrieved from Genbank in order to assess the species boundaries between the soybean stem canker causal agents, and define whether or not they should be regarded as members of the same biological species. These studies were complemented with compatibility tests, in order to validate our findings from a biological standpoint. Species delimitation assays supported the occurrence of a speciation event between D. caulivora and D. phaseolourm var. meridionalis. A speciation hypothesis between D. aspalathi and D. phaseolourm var. meridionalis was also supported, based on three reciprocally monophyletic substitutions at locus EF1-α. Compatibility tests further validated species delimitation assays indicating that D. caulivora has developed barriers to gene exchange with D. phaseolorum var. meridionalis. Clarification of the specific boundaries of the SSC pathogens and related entities will be an important asset to future research in soybean pathology, epidemiology and breeding.

Dieffenbachia picta ("comigo-ninguém-pode") é uma espécie difundida em todo o mundo devido ao seu valor ornamental. Na Argentina, é cultivada nas províncias de clima mais quente e nos arredores da cidade de Buenos Aires. Na primavera de 2007 um grande número de plantas apresentou sintomas de murcha e presença de lesões encharcadas (anasarca) nas folhas inferiores, principalmente em plantas de 4 a 6 meses de idade. Em seguida, constatou-se murcha da planta devido ao apodrecimento do caule e raiz. Um organismo peronosporomycete foi isolado de tecidos afetados. O patógeno foi identificado como Phytophthora nicotianae com base em características culturais, morfologia das estruturas vegetativas e reprodutivas, e testes moleculares baseados na sequência da região ITS do DNA ribossômico. Os testes de patogenicidade foram conduzidos e os postulados de Koch atendidos. Em estudos complementares, as variedades de D. picta Alex, Compact, Marianne e Camilla foram suscetíveis, enquanto a variedade Tropic snow (D. amoena) foi resistente. Este é o primeiro relato de P. nicotianae causando podridão radicular de Dieffenbachia picta na Argentina e nas Américas.

Dieffenbachia picta is a worldwide appreciated crop due to its ornamental value. In Argentina it is cultivated in warm provinces and in the outskirts of Buenos Aires city, where in spring 2007 a great amount of plants were lost in commercial greenhouses. Symptoms such as wilting and soaked lesions in the basal leaves began in four- to six-month-old plants causing plants to wilt due to basal stem and root rot processes. A Peronosporomycete was consistently isolated from diseased tissues. The pathogen was identified as Phytophthora nicotianae based on cultural characteristics, morphology of vegetative and reproductive structures, and on the analysis of the sequence of the nuclear ribosomal internal transcribed spacer (ITS) region. Pathogenicity tests were carried out and Koch's postulates were fulfilled. In complementary studies, the dieffenbachia varieties Alex, Compact, Camilla and Marianne were susceptible to the infection caused by P. nicotianae, whereas Tropic snow (D. amonea) was resistant. This is the first report of P. nicotianae causing stem and root rot of D. picta in Argentina and in the Americas.