Efeito do fosfito na reação de pimentão e pimenteira a Phytophthora capsici

Phosphite has been recommended to enhance plant resistance against Phytophthora. This work evaluated the response of hot and sweet pepper (Capsicum annuum L.) to Phytophthora capsici from juvenile up to the adult stage following treatment with phosphite. Sweet pepper hybrids considered to be resistant to P. capsici, like Reinger, Nathalie and Athenas, were evaluated. The susceptible checks were hybrid Magali R and cvs. Myr 10 and Ikeda. Hot pepper Criollo de Morelos 328, CM 334, BGH 3756, BGH 5122, CNPH 294 and Locorte were used as referential resistant lines. Phosphite did not have an effect on the hot pepper resistant lines because of their genetic homozygozity, while no protection was observed for the Athenas hybrid claimed to be resistant. Heterozygous hybrids recognized as resistant, like Reinger and Nathalie, showed higher survival following phosphite treatment, and their reaction was equivalent to the resistant cvs. CM 328 and CM 334, except for the fruiting stage. Depending of the hybrid heterozygous genotype, phosphite possibly acts through indirect phytoalexin induction through the inhibited pathogen.Fosfito tem sido recomendado para aumentar o sistema de resistência de plantas atacadas por fitopatógenos. Este trabalho avaliou a ação do fosfito nas reações de pimentão e pimenteiras (Capsicum annuum L.) a Phytophthora capsici na fase juvenil até a fase adulta, tratadas com fosfito. Os híbridos de pimentão considerados resistentes a P. capsici foram Reinger, Nathalie e Athenas, enquanto que o híbrido Magali R e as cvs. Myr 10 e Ikeda constituíram as referenciais suscetíveis. As linhagens de pimenta Criollo de Morelos 328, CM 334, BGH 3756, BGH 5122, CNPH 294 e Locorte, foram usadas como padrão referencial de resistência ao patógeno. O fosfito não afetou a reação das linhagens resistentes devido sua homozigosidade genética. Não houve ação protetora do fosfito nos hospedeiros suscetíveis, inclusive no híbrido Athenas. Os híbridos heterozigotos considerados resistentes, como Nathalie e Reinger, tiveram uma sobrevivência equivalente ao CM 328 e 334, mas sua reação de resistência não persistiu na fase de pós-transplante. Possivelmente, o fosfito age através da indução da produção de fitolexinas no hospedeiro indiretamente por meio do patógeno inibido

Defence-related components in cucumber susceptibility to target spot

Target spot is an important disease in cucumber culture. Due to differences in the susceptibility of cucumber cultivars to the disease, the objective was to evaluate the behavior of three cvs. in terms of leaf trichome density and biochemical variables in the interaction with the pathogen Corynespora cassiicola. The density of trichomes was evaluated on both sides of the leaves. The activity of peroxidase and polyphenol oxidase enzymes and the levels of free and bound phenolic compounds were evaluated one, three and five days after inoculation or not with the pathogen. The enzymatic activity was higher in the Safira cv., less susceptible to the disease, in relation to the Taiko and Soldier cvs. Inoculated plants showed higher peroxidase activity, showing that the response to infection was accompanied by the synthesis of this enzyme, and it increased with the days after inoculation. The levels of phenolic compounds varied according to the cvs. and as a function of time, with the highest levels in the Safira and Soldier cvs. Higher density of trichomes was found in the Safira cv., with no differences between Soldier and Taiko cvs. The adaxial side of the leaves had a greater number of trichomes than the abaxial side. No direct relationships were observed between biochemical and trichome variables and disease severity in cucumber cvs., since the Soldier cv., the most susceptible to the disease, did not differ in relation to 'Taiko' in enzymatic activities, free phenolic compounds and number of trichomes, including higher levels of bound phenolic compounds.A mancha alvo constitui importante doença na cultura do pepino. Em virtude de diferenças na suscetibilidade das cultivares de pepino em relação a doença, objetivou-se avaliar o comportamento de três cvs. quanto a densidade de tricomas foliares e de variáveis bioquímicas na interação com o patógeno Corynespora cassiicola. A densidade de tricomas foi avaliado em ambas os lados das folhas. A atividade das enzimas peroxidase e polifenoloxidade e os teores dos compostos fenólicos livres e ligados foram avaliados após um, três e cinco dias da inoculação ou não do patógeno.  A atividade enzimática foi superior na cv. Safira, menos suscetível a doença, em relação às cvs. Taiko e Soldier. As plantas inoculadas apresentaram maior atividade da peroxidase, evidenciando que a resposta à infecção foi acompanhada pela síntese dessa enzima, e foi crescente com os dias após a inoculação. Os teores de compostos fenólicos foram variáveis em função das cvs. e em função do tempo, com os maiores teores nas cvs. Safira e Soldier. Maior densidade de tricomas foi constatado na cultiva Safira, não havendo diferenças entre as cvs. Soldier e Taiko. O lado adaxial das folhas apresentou maior número de tricomas em relação ao abaxial. Não foram observadas relações diretas das variáveis bioquímicas e de tricomas com a severidade da doença nas cvs. de pepino, uma vez que a cv. Soldier, a mais suscetível a doença, não diferiu em relação à ‘Taiko’ nas atividades enzimáticas, compostos fenólicos livres e número de tricomas, apresentando, inclusive, maiores teores de compostos fenólicos ligados

Temporal progress and spatial patterns of quiescent diseases in guava influenced by sanitation practices

ABSTRACT: Postharvest diseases are a major problem in guava crops as the symptoms normally appear during fruit ripening. This study aimed to detect and characterize the temporal dynamics and spatial patterns of the most important guava diseases in orchards with and without removal of crop residues as a sanitation practice. The experiment was conducted in an orchard of ‘Pedro Sato’ guavas, over two consecutive seasons, and data were collected from the flowering to the fruit ripening stage. In immature guavas treated with paraquat and ethrel, Colletotrichum spp. was detected from the 5th day of incubation. Anthracnose was detected in flowers at incidences higher than 50 % and black spot in fruit larger than 5.5 cm in length. The monomolecular and the exponential models provided the best fit to anthracnose and black spot incidence progress curve data, respectively. Both diseases showed a predominantly random spatial pattern in the orchard. The removal of crop residues reduced the rate of disease progress in at least one season, and was effective in reducing the areas under the quiescent disease progress curves (AUDPC) of anthracnose. Anthracnose incidence increased from 57 to 96 % and black spot from 1 to 48 %, respectively, at fruit maturation levels 1 and 3. A negative correlation was found between disease incidence and the color of the fruit skin (°h). Fruit harvested during the later maturation stages showed higher incidence of the diseases. Due to the wide distribution and early infection of quiescent diseases, starting at flowering, preventive management should consider disease monitoring and removal of crop residues

Morphological and physiological characterization of Tranzschelia discolor, effect of moisture on pathogenesis and control of peach rust

O efeito de diferentes períodos de molhamento foliar (no intervalo entre duas e 48 horas), após a inoculação, na freqüência de infecção (pústulas/cm2) e na latência (tempo para o aparecimento de 50% das pústulas esporulantes) de Tranzschelia discolor, agente causal da ferrugem do pessegueiro, foi avaliado em mudas de pessegueiro das cultivares Ximarrita (um ensaio) e Flor da Prince (dois ensaios), inoculadas sob condições controladas (23 ± 2°C e fotoperíodo de 12 horas). O período mínimo de molhamento foliar para a infecção foi de quatro horas. A freqüência de infecção aumentou com o aumento do período de molhamento. A caracterização morfológica de isolados de T. discolor foi realizada comparando-se as dimensões de urediniósporos e teliósporos do fungo, coletados de folhas de ameixeira, nectarina e pessegueiro, por meio de análises de variância uni e multivariada. A caracterização fisiológica foi investigada através de inoculações cruzadas em mudas de pessegueiro (Ximarrita e Flor da Prince), nectarina (Rubrosol) e ameixeira (Rubi I), sob condições controladas (23 ± 2°C e fotoperíodo de 12 horas). A análise de cluster mostrou que os isolados provenientes de pessegueiro e nectarina apresentaram grande similaridade entre si, distanciando-se do isolado de ameixeira. Os isolados coletados de pessegueiro e nectarina causaram infecções recíprocas, embora a severidade da doença tenha sido sempre maior no hospedeiro fornecedor do inóculo, e não infectaram a ameixeira. O isolado coletado de ameixeira só causou infecção na própria ameixeira. Os isolados mostraram especialização fisiológica, sugerindo a existência de formae speciales dentro dessa espécie. A reação das cultivares de pessegueiro Regis, Aurora II e Ximarrita (primeiro ensaio) e Aurora II, Coral, Dourado, Flor da Prince e Rio Grande (segundo ensaio) à ferrugem, avaliada através da freqüência de infecção e do período latente, mostrou que a cultivar Regis foi a que apresentou menor freqüência de infecção. A eficiência de fungicidas no controle da ferrugem de plantas de pessegueiro e nectarina foi avaliada em áreas experimentais localizadas em Paranapema - SP. Os fungicidas tebuconazole e mancozeb e captan, aplicados alternadamente, apresentaram elevada eficiência no controle da ferrugem do pessegueiro, já o difenoconazole e o triadimenol foram ineficientes. Os melhores produtos no controle da ferrugem de plantas de nectarina também foram o tebuconazole e o mancozeb. O difenoconazole sozinho ou em mistura com o propiconazole não promoveu um controle satisfatório da doença em plantas de nectarina. Um sistema de previsão da doença baseado em variáveis climáticas foi testado e não se aplicou para o patossistema em questão, uma vez que a faixa de temperatura e de umidade favoráveis para o desenvolvimento da doença é muito ampla e as condições favoráveis (temperaturas média maior ou igual a 13 °C e máxima igual ou inferior a 30°C e mínimo de 4 horas de molhamento) sempre foram satisfeitas.The effect of different post inoculation wetness periods (two - 48 hours) on pustule frequency (pustules / cm2) and latency (period required for appearance of 50% of sporulating pustules) of Tranzschelia discolor, casual agent of peach rust, was evaluated by inoculation with Tranzchelia discolor of peach seedlings of cultivar Ximarrita (one trial) and Flor da Prince (two trials) kept under controlled conditions (23 ± 2°C and photoperiod of 12 h). The minimum leaf wetness period for infection was 4 hours. Infection frequency increased with the leaf wetness period. The morphological characterization of T. discolor was performed through univariate and multivariate analysis of variance of urediniospore and teliospores dimension. The spores were collected from plum, nectarine and peach leaves. Physiological characterization was evaluated through inoculations of peach (Ximarrita and Flor da Prince), nectarine (Rubrosol) and plum (Rubi I) seedlings kept under controlled conditions (23 ± 2°C and photoperiod of 12 h). Cluster analysis showed that isolates from peach and nectarine were very similar among themselves, differing, however, from the plum isolate. Peach and nectarine isolates caused reciprocal infections on peach and nectarine, but not on plum. Disease severity, however, was always higher in the host which provided the inoculum. The plum isolate was specific to its host. The results suggested the existence of physiological specialization of the pathogen at the species (level, formae speciales probably occurring). Reaction of peach cultivars to the pathogen was evaluated through the determination of infection frequency and latent period using the following cultivars: Regis, Aurora II and Ximarrita (1st trial) and Aurora II, Coral, Dourado, Flor da Prince and Rio Grande (2nd trial). Regis showed the smallest infection frequency. Fungicide efficiency for the rust control was evaluated in the field in Paranapanema, SP. Tebuconazole and mancozeb + captan applied alternately showed high control efficiency in peach, whereas difenoconazole and triadimenol did not. The best products for nectarine plants were tebuconazole and mancozeb. Difenoconazole alone or in combination with propiconazole did not promote a satisfactory control in nectarine plants. A forecast system of the disease based on weather variable was tested but it was not applicate for the pathosystem under study. The temperature and moisture ranges favorable for disease development is too wide and favorable conditions (medium temperatures higher than or equal to 13°C and maximum equal to or smaller than 30°C and a minimum wetness period of 4 h) were always satisfied

Quantification of monocyclic parameters and chemical control of peach rust

A ausência de um controle eficiente da ferrugem do pessegueiro é a causa do aumento da importância dessa doença em regiões subtropicais. Visando um conhecimento das interações patógeno-hospedeiro-ambiente foi avaliado o efeito da temperatura na germinação de uredósporos do fungo e nos parâmetros monocíclicos da doença. O estudo das temperaturas de 8, 18, 23, 28 e 36"graus"C indicou a faixa de 10 a 22"graus"C como sendo a ótima para a germinação. A temperatura de 18"graus"C proporcionou uma maior frequência de infecção e um maior período latente do que a temperatura de 23"graus"C a eficiência de onze defensivos agrícolas foi avaliada através de testes "in vivo" "in vitro" foram determinadas a porcentagem de germinação de uredósporos em meio ágar-água com defensivo nas concentrações de 1, 10 e 100 PPM e a ED50. In vivo a eficiência dos produtos foi avaliada em plantas adultas dos cultivares flor da prince e auroraII. Os experimentos consistiram de quatro aplicações dos produtos nas dosagens comerciais recomendadas. A intervalos quinzenais os produtos Mancozeb Captan e Tebuconazole foram os mais eficientes tanto in vitro como in vivo. O efeito protetor curativo e erradificante do inseticida Cartap foi avaliado em mudas do cultivar tropical. O tratamento protetor apresentou eficiência máxima, na forma curativa houve redução da doençaThe lack of an efficient control of the peach rust caused by Tranzschelia discolor (Fuckel) Tranzschel & Litivinov is the main cause of increase in importance of this disease in subtropical regions. The establishment of an adequate disease management system is possible only after the knowledge of the pathogen - host - environment interactions. In order to get a better understanding of these relationships the effect of temperature on the germination of uredospores of T. discolor and the monocyclic parameters of the disease was evaluated. The optimum estimated temperature range for uredospore germination was 10 to 22°C in the study where the temperatures employed were 8, 18, 23, 28 and 36°C. The monocyclic parameters (infection frequency and latent period) were quantified on growth chamber condition on peach plants of the cultivar Flor da Prince, at the temperatures of 18 and 23°C. The temperature of 18°C gave a higher infection frequency and a larger latent period then the temperature of 23°C. The efficiency of eleven chemical products on the control of the disease was evaluated though in vitro and in vivo tests. The percentage of uredospore germination in water - agar at the concentrations of 1, 10 and 100 ppm of the chemicals and the ED50 were determined. The efficiency of the products to control of peach rust, at field condition, was also evaluated in adult plants of cultivars Flor da Prince and Aurora II. The trials consisted of four applications, at the commercial dosages recommended, in a 15 days interval, the evaluation being made through the disease severity and the defoliation degree. Mancozeb, captan and tebuconazole were the most efficient, both in vitro and in vivo conditions. Bitertanol and propiconazole did not differ from control. The protective, curative and erradicant effects of the insecticide cartap was evaluated in peach plants of the Tropical cultivar, under the temperature of 21 ± 4°C. The protective treatment showed maximum efficiency, with no pustule formation on the leaves. In the curative form, cartap reduced significantly the infection frequency and increased the latent period in relation to the control. The erradicant treatment gave partial control of the disease, with a great number of active pustules being observed some days after the product application

Quantification of monocyclic parameters and chemical control of peach rust

A ausência de um controle eficiente da ferrugem do pessegueiro é a causa do aumento da importância dessa doença em regiões subtropicais. Visando um conhecimento das interações patógeno-hospedeiro-ambiente foi avaliado o efeito da temperatura na germinação de uredósporos do fungo e nos parâmetros monocíclicos da doença. O estudo das temperaturas de 8, 18, 23, 28 e 36"graus"C indicou a faixa de 10 a 22"graus"C como sendo a ótima para a germinação. A temperatura de 18"graus"C proporcionou uma maior frequência de infecção e um maior período latente do que a temperatura de 23"graus"C a eficiência de onze defensivos agrícolas foi avaliada através de testes "in vivo" "in vitro" foram determinadas a porcentagem de germinação de uredósporos em meio ágar-água com defensivo nas concentrações de 1, 10 e 100 PPM e a ED50. In vivo a eficiência dos produtos foi avaliada em plantas adultas dos cultivares flor da prince e auroraII. Os experimentos consistiram de quatro aplicações dos produtos nas dosagens comerciais recomendadas. A intervalos quinzenais os produtos Mancozeb Captan e Tebuconazole foram os mais eficientes tanto in vitro como in vivo. O efeito protetor curativo e erradificante do inseticida Cartap foi avaliado em mudas do cultivar tropical. O tratamento protetor apresentou eficiência máxima, na forma curativa houve redução da doençaThe lack of an efficient control of the peach rust caused by Tranzschelia discolor (Fuckel) Tranzschel & Litivinov is the main cause of increase in importance of this disease in subtropical regions. The establishment of an adequate disease management system is possible only after the knowledge of the pathogen - host - environment interactions. In order to get a better understanding of these relationships the effect of temperature on the germination of uredospores of T. discolor and the monocyclic parameters of the disease was evaluated. The optimum estimated temperature range for uredospore germination was 10 to 22°C in the study where the temperatures employed were 8, 18, 23, 28 and 36°C. The monocyclic parameters (infection frequency and latent period) were quantified on growth chamber condition on peach plants of the cultivar Flor da Prince, at the temperatures of 18 and 23°C. The temperature of 18°C gave a higher infection frequency and a larger latent period then the temperature of 23°C. The efficiency of eleven chemical products on the control of the disease was evaluated though in vitro and in vivo tests. The percentage of uredospore germination in water - agar at the concentrations of 1, 10 and 100 ppm of the chemicals and the ED50 were determined. The efficiency of the products to control of peach rust, at field condition, was also evaluated in adult plants of cultivars Flor da Prince and Aurora II. The trials consisted of four applications, at the commercial dosages recommended, in a 15 days interval, the evaluation being made through the disease severity and the defoliation degree. Mancozeb, captan and tebuconazole were the most efficient, both in vitro and in vivo conditions. Bitertanol and propiconazole did not differ from control. The protective, curative and erradicant effects of the insecticide cartap was evaluated in peach plants of the Tropical cultivar, under the temperature of 21 ± 4°C. The protective treatment showed maximum efficiency, with no pustule formation on the leaves. In the curative form, cartap reduced significantly the infection frequency and increased the latent period in relation to the control. The erradicant treatment gave partial control of the disease, with a great number of active pustules being observed some days after the product application