RESUMO A reação in vitro e a campo de 23 cultivares e clones de batata a dois isolados de Phytophthora infestans foram avaliadas utilizando-se dois métodos. No teste in vitro, utilizou-se o método de folíolos destacadas cuja severidade da doença foi avaliada 6 dias após a inoculação. Os experimentos de campo foram conduzidos no outono de 2013, em dois locais distintos do Município de Pelotas, Estado do Rio Grande do Sul, Brasil. Foram realizadas sete avaliações da severidade da doença; e, a partir desses valores, foi calculada a área abaixo da curva de progresso da doença (AACPD). Os tubérculos foram colhidos para determinar o rendimento (g parcela-1). O isolado do grupo de compatibilidade A2 foi o mais agressivo para a maioria dos genótipos de batata. Com base nos valores de AACPD foi possível agrupar as diferentes reações dos genótipos de batata. Os clones C2553-1-06, C2573-4-06, C2550-4-06, C2551-2-06 e CIP392,617.54 apresentaram resistência moderada a alta aos dos isolados de P. infestans. Os valores de severidade e AACPD obtidos in vitro e nos testes a campo foram correlacionados positivamente para ambos os isolados de P. infestans, porém, em algumas interações, foram observadas inconsistências. A produção de tubérculos foi negativamente correlacionada com a AACPD.

ABSTRACT The in vitro and field reactions of 23 potato cultivars and clones to two isolates of Phytophthora infestans were tested. The in vitro test used the detached potato leaflets method, and disease severity was evaluated 6 days after inoculation. Field experiments were conducted in autumn of 2013, in two locations in Pelotas City, Rio Grande do Sul State, Brazil. Seven evaluations of the disease severity were performed. From the severity values, the area under the disease progress curve (AUDPC) was calculated. Tubers were harvested to determine the yield (g plot-1). The A2 mating type isolate was the most aggressive for the majority of the potato genotypes. It was possible to group the different reactions of the potato genotypes based on the AUDPC values. Clones C2553-1-06, C2573-4-06, C2550-4-06, C2551-2-06, and CIP392,617.54 showed moderate-to-high resistance to the two isolates of P. infestans. The values of severity and AUDPC obtained in vitro and field tests were positively correlated for both P. infestans isolates, but in some interactions, inconsistencies were observed. Tuber yield was negatively correlated with AUDPC.

Abstract The purpose of this study was to estimate the combining ability between two groups of potato parents in early generations of selection. Twelve potato families, derived from two groups of parents crossed in a 4x3 partial diallel design, were evaluated, in a randomized complete block design with three replications. Additive effects of genes were predominant for the traits tuber shape uniformity, tuber pointiness, tuber curvature, general tuber appearance, tuber size uniformity, tuber number, total tuber yield, and average tuber weight. With regard to general combining ability, for all tuber appearance traits, the foreign parents ‘Pukara’ and ‘Asterix’, and the national parent ‘Eliza’ contributed with complementary favorable alleles. For tuber yield component traits, the foreign parent ‘Rioja’ and the national parent ‘Eliza’ were outstanding. The specific combining ability indicated ‘Pukara’/‘Eliza’ as the most promising cross for the development of superior genotypes for the traits general tuber appearance and tuber number.

Six plant growth promoting rhizobacteria isolates - two Streptomyces (DFs1296 and DFs1315), three Bacillus (DFs1414, DFs1420 and DFs1423) and one Pseudomonas (DFs1421) - were used to microbiolize tomato seeds for the control of bacterial spot caused by Xanthomonas gardneri. Three assays were conducted in a completely randomized design with six replications. In each assay, X. gardneri suspensions (10(8)CFUmL-1) were spray-inoculated on the leaves. In the first and second assays, three and four leaves, respectively, were assessed for disease severity. In the third assay, three leaves per plant were assessed for the number of lesions per leaf, leaf area and dry weight. Results showed that one of the Bacillus sp. isolate (DFs1420) consistently provided the greatest relative reduction (48%) of tomato bacterial spot severity.

A busca por alternativas ao uso intensivo de agrotóxicos no controle de doenças tem recebido grande atenção da pesquisa agrícola. Rizobactérias têm reconhecida capacidade de reduzir doenças em diversas culturas e promover de crescimento de plantas. O objetivo deste trabalho foi avaliar a eficácia de seis isolados de rizobactérias, pré-selecionadas, no controle de Ralstonia solanacearum e Fusarium oxysporum f. sp. lycopersici (FOL), em casa de vegetação e relacionar este comportamento a produção de compostos "in vitro". Foi avaliada a capacidade de estas rizobactérias produzirem quitinases, amilases, lipases, compostos antibióticos e de solubilizar fosfato. A microbiolização das sementes com a rizobactéria DFs1421 (Pseudomonas sp.) reduziu os valores de AACPD de murcha bacteriana em ambos os ensaios (36,6 e 91,7% no primeiro e segundo ensaios respectivamente). Este controle pode ser associado à produção de compostos responsáveis pela antibiose observada "in vitro". Isolados de Streptomyces (DFs1296 e DFs1315), bem como de Bacillus (DFs1414) e o indutor químico ASM reduziram significativamente a murcha de fusário, variando de 22,5 a 76%. O controle observado por parte das rizobactérias pode ser atribuído à atividade quitinolítica e/ou antibiótica por compostos voláteis.

Replacing the intensive use of pesticides for alternative methods in disease control has been an important aim for agricultural research. Rhizobacteria are known to be capable of reducing diseases levels in many crops and also of promoting plant growth. The objective of this work was to evaluate the efficacy of six pre-selected rhizobacteria isolates in controlling Ralstonia solanacearum and Fusarium oxysporum f. sp. lycopersici (FOL) under controlled conditions in a greenhouse, and to link such capacity to the "in vitro" production of selected biologically active compounds. The ability of these rhizobacteria isolates to produce chitinases, amylases, lipases, antibiotic compounds was investigated. Additionally, their ability in solubilizing phosphate was also checked. Microbiolization of seeds with one rhizobacterium DFs1421 (Pseudomonas sp.) reduced the tomato wilt AUDPC in both assays (36.6 and 91.7% in the first and second assays respectively). Such efficacy in wilt control is likely to be linked with the production of antibiotics as observed "in vitro". Streptomyces (DFs1296 and DFs1315) and Bacillus (DFs1414), and the chemical inducer (ASM) reduced significantly fusarium wilt ranging 22.5 to 76%. This may be owing to the observed chitinolytic activity and / or antibiosis in the presence of volatile compounds.