No abstract

Three field experiments were carried out to assess the level of resistance of several cultivars to early blight (EB) and to examine the association between host resistance and either foliage maturity or tuber skin types. A total of 26 cultivars were used in Exps. 1 and 2, and 24 in Exp. 3. Plants were inoculated with isolates of Alternaria grandis at 31 days after planting. EB severity was quantified in each plot every seven days. The approach to determine the resistance levels of potato cultivars was based on multivariate analysis techniques. The tested cultivars responded as either resistant, moderately resistant, moderately susceptible or susceptible to EB. Most of the cultivars were classified as susceptible or moderately susceptible to EB. Resistant cultivars were mid-season, mid-late or late maturity. None of the susceptible cultivars were later maturity (mid-late or late maturity). In most cases, susceptible cultivars were earlier maturity (early or mid-early maturity). Most resistant cultivars had rough, mid-rough or smooth skin. None of the susceptible cultivars had rough skin. In most cases, susceptible or moderately susceptible cultivars had smooth skin. Obtaining potato cultivars that are resistant to this destructive disease will help reduce production costs and the need for costly fungicides.

Asian grapevine rust (Phakopsora euvitis) is a serious disease, which causes severe leaf necrosis and early plant defoliation. These symptoms are unusual for a strict biotrophic pathogen. This work was performed to quantify the effects of P. euvitis on photosynthesis, carbohydrates, and biomass accumulation of grapevine. The reduction in photosynthetic efficiency of the green leaf tissue surrounding the lesions was quantified using the virtual lesion concept (β parameter). Gas exchange and responses of CO2 assimilation to increasing intercellular CO2 concentration were analyzed. Histopathological analyses and quantification of starch were also performed on diseased leaves. Biomass and carbohydrate accumulation were quantified in different organs of diseased and healthy plants. Rust reduced the photosynthetic rate, and β was estimated at 5.78, indicating a large virtual lesion. Mesophyll conductance, maximum rubisco carboxylation rate, and regeneration of ribulose-1,5-bisphosphate dependent on electron transport rate were reduced, causing diffusive and biochemical limitations to photosynthesis. Hypertrophy, chloroplast degeneration of mesophyll cells, and starch accumulation in cells close to lesions were observed. Root carbohydrate concentration was reduced, even at low rust severity. Asian grapevine rust dramatically reduced photosynthesis and altered the dynamics of production and accumulation of carbohydrates, unlike strict biotrophic pathogens. The reduction in carbohydrate reserves in roots would support polyetic damage on grapevine, caused by a polycyclic disease.

Downy mildew caused by Plasmopara viticola is one of the most destructive diseases of Vitis vinifera worldwide. Grapevine breeding programs have introgressed P. viticolaresistant traits into cultivated V. vinifera genotypes and launched interspecific hybrids with resistance against downy mildew. In general, pathogen infection affects primary metabolism, reduces plant growth and development and modifies the secondary metabolism toward defense responses, which are costly in terms of carbon production and utilization. The objective of this work was to evaluate the photosynthesis impairment by inducible defenses at the leaf level in V. vinifera cultivars resistant to P. viticola. Photosynthetic limitations imposed by P. viticola in susceptible and resistant grapevine cultivars were evaluated. Histochemical localization of hydrogen peroxide and superoxide and the activity of ascorbate peroxidase were assessed. Measurements of leaf gas exchange, chlorophyll fluorescence and the response of leaf CO 2 assimilation to increasing air CO 2 concentrations were taken, and photosynthetic limitations determined in cultivars Solaris (resistant) and Riesling (susceptible). The net photosynthetic rates were reduced (−25%) in inoculated Solaris plants even before the appearance of cell death-like hypersensitive reactions ("HR"). One day after "HR" visualization, the net photosynthetic rate of Solaris was reduced by 57% compared with healthy plants. A similar pattern was noticed in resistant Cabernet Blanc and Phoenix plants. While the susceptible cultivars did not show any variation in leaf gas exchange before the appearance of visual symptoms, drastic reductions in net photosynthetic rate and stomatal conductance were found in diseased plants 12 days after inoculation. Decreases in the maximum Rubisco carboxylation rate and photochemical impairment were noticed in Riesling after inoculation with P. viticola, which were not found in Solaris. Damage to the photochemical reactions of photosynthesis was likely associated with the oxidative burst found in resistant cultivars within the first 24 h after inoculation. Both chlorophyll degradation and stomatal closure were also noticed in the incompatible interaction. Taken together, our data clearly revealed that the defense response against P. viticola causes a photosynthetic cost to grapevines, which is not reversible even 12 days after the pathogen infection.

Um dos grandes problemas na comercialização de goiabas é a incidência de doenças pós-colheita que coincide com o amadurecimento dos frutos. Avaliou-se o efeito de produtos alternativos [fosfito de potássio, cloreto de cálcio, fécula de mandioca, 1-metilciclopropeno (1-MCP), etanol seguido de dicloro s. triazinatriona sódica dihidratada (etanol+cloro)] e de tratamento hidrotérmico, isoladamente e em associação, no controle da antracnose e nas características físico-químicas de goiabas 'Pedro Sato'. Os tratamentos foram realizados em goiabas naturalmente infectadas, em três estádios de maturação, armazenadas a 22 ou 25ºC por oito dias. A incidência da antracnose foi avaliada pelos sintomas visuais e observação dos sinais do patógeno em microscópio óptico e os parâmetros físico-químicos avaliados foram cor da casca, firmeza da polpa, perda de massa fresca, sólidos solúveis, acidez titulável e ácido RESUMOascórbico. As associações de tratamentos etanol+cloro/fécula, hidrotérmico/ fécula e etanol+cloro/1-MCP reduziram a antracnose nos três estádios de maturação, em pelo menos algum período do armazenamento, promovendo um maior período de conservação dos frutos, com um atraso de dois a quatro dias no aparecimento da doença. A manutenção da qualidade das goiabas com as associações de tratamentos foram evidenciadas pelo atraso na mudança de coloração da casca e menor redução na firmeza da polpa, com destaque para etanol+cloro/1-MCP. Observou-se correlação positiva entre a incidência da antracnose e o estádio de maturação, expresso pela cor da casca do fruto. A maior eficiência das associações de tratamentos no controle da antracnose relacionou-se diretamente ao atraso no amadurecimento dos frutos, evidenciado pelos parâmetros cor da casca e firmeza da polpa. ABSTRACTOne of the major problems in guava commercialization is the incidence of postharvest diseases, which coincides with fruit ripening. The effect of alternative products [potassium phosphite, calcium chloride, cassava starch, 1-methylcyclopropene (1-MCP), ethanol followed by sodium dichloro s. triazinetrione dehydrate (ethanol+chlorine)] and hydrothermal treatment, singly and in association, was evaluated on anthracnose control and on the physicochemical characteristics of 'Pedro Sato' guava. Treatments were applied to naturally infected guavas, in three maturity stages, which were stored at 22 or 25ºC for eight days. The incidence of anthracnose was evaluated by visual observation of symptoms and signs of the pathogens under an optical microscope, and the evaluated physicochemical parameters were skin color, pulp firmness, fresh mass loss, soluble solids, titratable acidity and ascorbic acid. The association of treatments ethanol+chlorine/cassava starch, hydrothermal treatment/cassava starch and ethanol+chlorine/1-MCP reduced the incidence of anthracnose in all three maturity stages in at least one storage period, leading to longer shelf life of fruits and a delay of two to four days in the onset of the disease. The maintenance of guava quality by means of tr...