Leonardo Araujo

Cytological aspects of incompatible and compatible interactions between rice, wheat and the blast pathogen Pyricularia oryzae

Blast, caused by the fungus Pyricularia oryzae, is an important disease affecting rice and wheat yield worldwide. This study investigated the cytological aspects of incompatible (non-host resistance) and compatible (host resistance) rice- (R_Po) and wheat- (W_Po) Pyricularia oryzae isolate interactions. Inoculations of rice and wheat with the R_Po and W_Po isolates of P. oryzae, respectively, were expected to be compatible interactions (host resistance), whereas inoculations of rice and wheat with the W_Po and R_Po isolates of P. oryzae, respectively, were considered to be incompatible interactions (non-host resistance). For the compatible interactions (rice-R_Po and wheat-W_Po), fungal hyphae penetrated and colonized the epidermal cells and also invaded many neighboring cells. By contrast, in the case of the incompatible interactions (rice-W_Po and wheat-R_Po), fungal hyphae were not able to penetrate nor colonize the epidermal cells, but when penetration did occur, the hyphae were restricted to the first-invaded epidermal cell. The frequency of appressorial sites exhibiting infection hyphae within the epidermal cell underlying an appressorium was greater in the case of the compatible interactions. By contrast, unsuccessful penetrations with cytoplasmic granulation occurred with high frequency in the incompatible wheat-R_Po and rice-W_Po interactions and the number of necrotic epidermal cells underlying the appressorium was low for the rice-W_Po interaction as well as for the wheat- R_Po interaction, where no symptoms of necrosis were exhibited. However, the opposite was observed for the compatible interactions. The present study presents cytological features associated with incompatible and compatible rice- and wheat-P. oryzae interactions that may be useful to studies involving variability, coevolution, diagnosis, and regulation of quarantine or even in a rice or wheat breeding program whose aim is to transfer genes involved in non-host resistance to host resistance due to similarities in downstream mechanisms.

Water relation, leaf gas exchange and chlorophyll a fluorescence imaging of soybean leaves infected with Colletotrichum truncatum

Considering the potential of anthracnose to decrease soybean yield and the need to gain more information regarding its effect on soybean physiology, the present study performed an in-depth analysis of the photosynthetic performance of soybean leaflets challenged with Colletotrichum truncatum by combining chlorophyll a fluorescence images with gas-exchange measurements and photosynthetic pigment pools. There were no significant differences between non-inoculated and inoculated plants in leaf water potential, apparent hydraulic conductance, net CO2 assimilation rate, stomatal conductance to water vapor and transpiration rate. For internal CO2 concentration, significant difference between non-inoculated and inoculated plants occurred only at 36 h after inoculation. Reductions in the values of the chlorophyll a fluorescence parameters [initial fluorescence (F0), maximal fluorescence (Fm), maximal photosystem II quantum yield (Fv/Fm), quantum yield of regulated energy dissipation (Y(NPQ))] and increases in effective PS II quantum yield (Y(II)), quantum yield of non-regulated energy dissipation Y(NO) and photochemical quenching coefficient (qP) were noticed on the necrotic vein tissue in contrast to the surrounding leaf tissue. It appears that the impact of the infection by C. truncatum on the photosynthetic performance of the leaflets was minimal considering the preference of the fungus to colonize the veins.

Análise microscópica da resistência do arroz à queima das bainhas mediada pelo silício

A queima das bainhas, causada pelo fungo Rhizoctonia solani Kuhn, e uma das mais importantes e destrutivas doencas que afetam a producao de arroz no mundo. Embora o silicio (Si) seja capaz de reduzir a intensidade da queima das bainhas, os mecanismos de resistencia mediados por esse elemento permanecem desconhecidos. Assim, este trabalho teve como objetivo investigar a nivel microscopico o efeito do Si na resistencia do arroz a infeccao por R. solani. Plantas de arroz das cultivares BR-Irga-409 e Labelle foram cultivadas em solucao nutritiva contendo 0 ou 2 mM de Si e inoculadas no estadio de maximo perfilhamento utilizando-se pedacos de palito de dente colonizados por R. solani. Ambos cultivares supridas com Si apresentaram intensa e homogenea deposicao de Si nos tecidos das bainhas colonizados por R. solani. A maior concentracao de Si nas bainhas de plantas de arroz de ambas cultivares contribuiu para reduzir os sintomas da queima das bainhas. Com o auxilio da microscopia de luz e da microscopia eletronica de varredura, observou-se menor crescimento micelial do fungo sobre as bainhas foliares das plantas de ambas cultivares que foram supridas com Si. Seccoes das bainhas de plantas de ambos cultivares supridas com Si exibiram intensa autofluorescencia nos tecidos proximos a regioes necrosadas devido a colonizacao por R. solani. Em conclusao, o suprimento de Si as plantas de arroz desempenhou um papel importante na reducao dos sintomas da queima das bainhas.

Development of mango wilt in mango cultivars submitted to salt stress

Mango wilt, caused by Ceratocystis fimbriata, is one of the most important diseases affecting mango yield worldwide. Salt stress can affect host defense responses against pathogens infection. The aim of this study was to evaluate the development of mango wilt in 2 mango cultivars submitted to salt stress. Mango plants from cultivars Tommy Atkins and Ubá, considered to be moderately resistant and resistant to mango wilt, respectively, were grown in plastic pots which contained 20 kg of washed sand and daily irrigated with 3 L of a modified Hoagland solution during 40 days before being submitted to salinization. For this process of salinization, the plants received nutrient solution containing 0, 30, 60, and 90 mmol·L–1 of sodium chloride (NaCl) during 50 days. At the 50th day, the plants were inoculated with C. fimbriata, and disease BASIC AREAS Note Development of mango wilt in mango cultivars submitted to salt stress Juliana Cristina Vieccelli1, Leonardo Araujo2, Ueder Pedro Lopes3, Dalmo Lopes de Siqueira1, Fabrício de Ávila Rodrigues4* 1. Universidade Federal de Viçosa Departamento de Fitotecnia Viçosa (MG), Brazil. 2. Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina Fitopatologia São Joaquim (SC), Brazil. 3. Universidade Federal Rural de Pernambuco Departamento de Fitopatologia Unidade Acadêmica de Garanhuns Garanhuns (PE), Brazil. 4. Universidade Federal de Viçosa Departamento de Fitopatologia Viçosa (MG), Brazil. *Corresponding author: fabricio@ufv.br Received: May 30, 2016 – Accepted: Oct. 3, 2016 development was evaluated at 42 days after inoculation. During this period, the plants were also submitted to salinization. After disease evaluation, the stems of plants from each treatment were collected to determine the concentrations of chlorine (Cl) and sodium (Na). Plants from the 2 cultivars showed reduced mango wilt symptoms as the NaCl doses increased from 0 to 90 mmol·L–1. Plants submitted to the highest NaCl doses showed greater Cl and Na concentrations on the stem. In conclusion, the resistance of plants against C. fimbriata infection can be potentiated when submitted to salt stress regardless of their basal level of resistance to mango wilt.

Infection process of Phakopsora gossypii in cotton leaves

Tropical rust caused by the biotrophic fungus Phakopsora gossypii is an emerging disease in cotton that has caused significant yield losses of crop/cotton cultivated in Brazil. Considering the current importance of tropical rust and the need to obtain additional basic information about its causal agent to better control this disease, the present study aimed to determine the infection process of P. gossypii in cotton leaves using scanning electron microscopy (SEM). Thirty-day-old plants were inoculated with a suspension of P. gossypii uredospores, and leaf fragments were collected 42 h after inoculation (hai) as well as 20, 25 and 35 days after inoculation (dai) for SEM observations. By 42 hai, the uredospores of P. gossypii had germinated and produced a germ tube and an appressorium that may directly penetrate the leaf cuticle. At 20 dai, closed uredia containing uredospores were observed on the abaxial leaf surface. At 25 dai, the uredia started to open and became fully open by 35 dai and contained many uredospores. By 25 dai, fungal hyphae were growing abundantly in the mesophyll next to the uredia that formed in the leaf fragments with total or partial removal of the epidermis. The results of the present study provide novel information regarding the infection process of P. gossypii in cotton leaves, which might be useful for the development of new and more effective strategies for tropical rust control.

Differential leaf gas exchange performance of mango cultivars infected by different isolates of Ceratocystis fimbriata

Caused by the vascular fungus Ceratocystis fimbriata, mango wilt is considered to be one of the most serious threats in mango-producing regions worldwide. However, changes in leaf gas exchange level and the mechanisms underlying host responses to this fungal infection remain poorly described. This study aimed to evaluate potential changes in the leaf gas exchange of different mango cultivars (Uba, Espada, Haden and Tommy Atkins) in response to two Brazilian isolates of C. fimbriata (CEBS15 and MSAK16) to non-invasively assess cultivar variability in relation to the basal level of resistance to mango wilt. Both isolates, regardless of the cultivar, caused reductions in stomatal conductance and, thus, a reduction in CO2 assimilation via diffusive limitations. Taking into account the full length of the internal lesion and the radial colonization of the stem tissues, both isolates showed equivalent aggressiveness when inoculated into the Haden and Tommy Atkins cultivars. Conversely, when compared to the CEBS15 isolate of C. fimbriata, the MSAK16 isolate was more aggressive in cv. Espada and less aggressive in cv. Uba.