Soybean rust (SBR) is the most threatening fungal disease in the major soybean [Glycine max (L.) Merr.] production areas around the world. In spite of the availability of chemical control with fungicides, the increase of production costs as well as operational difficulties associated with fungicide use for disease management has prompted the search for resistant genes in the soybean germplasm. Five genes (Rpp1, Rpp2, Rpp3, Rpp4, and Rpp5) have been reported as capable of conferring SBR resistance in soybean. Here we report the genetic segregation of the SBR resistance in two populations derived from crossing the SBR resistance source PI 594760B with the breeding lines TMG06_0012 (Population 1 [POP‐1]) and TMG06_0011 (Population 2 [POP‐2]). In both populations the resistance segregated as a single gene, but the resistance gene was dominant in POP‐1 and recessive in POP‐2. Molecular mapping of the phenotype placed it in the vicinity of the Rpp1 locus in both POP‐1 and POP‐2. When the breeding lines TMG06_0011 and TMG06_0012 where crossed with several other sources of resistance at the Rpp1, Rpp2, Rpp4, and Rpp5 loci or other putative loci, the inversion of gene action type observed with PI 594760B occurred only for the putative Rpp1 genotypes. We propose that a dominant susceptible allele, present in TMG06_0011, is causing the inversion of dominance observed in each of these crosses.

Cultures of adventitious roots of Stevia rebaudiana (Bert.) Bertoni were performed in a roller bottle system for the production of both primary and secondary metabolites. Adventitious roots were induced from 1-cmlong root tip explants derived from in vitro regenerated plantlets on solid Murashige and Skoog (MS 1962) media supplemented with 10.7 lM of a-naphthaleneacetic acid. These cultures were successfully maintained in the same medium for 6 months with regular subcultures after 4 weeks. Thereafter, the roots were cut into 1.0-to 1.5-cmlong segments and transferred to the roller bottle system containing a fresh root tissue culture on liquid MS medium supplemented with 10.7 lM NAA. The apparatus consisted of a flask rolling system adjusted to 4g, and 3°of flask inclination. The roots were allowed to grow in the absence of light for adaptation and adventitious root formation. The best conditions for cultivation were investigated, considering culture volume (25 ml), culture period (4 weeks), salt concentrations in the nutrient medium (33%) and optimal initial inoculum (0.2 g) of S. rebaudiana roots. These results could give important information on how to improve the development of adventitious roots of S. rebaudiana for the production of primary and secondary metabolites.

Some biological and molecular properties of six potyvirus isolates (LSU-1, -2, -3, and -5; 95-2; and 95-6) from sweet potato (Ipomoea batatas) were evaluated. Isolates LSU-1 and -3 and 95-2 were transmitted by Aphis gossypii and Myzus persicae while LSU-2 and -5 were not transmitted by either aphid. The partial nucleotide sequence of the nuclear inclusion b (NIb) and the coat protein (CP) genes of these six isolates were compared with the corresponding sequences of 17 Sweet potato feathery mottle virus (SPFMV) strains and 18 other potyviruses. LSU-1 and -3 had high sequence similarity to the published sequences for Sweet potato virus G (SPVG), did not react with antisera to other known sweet potato viruses, and caused distinct symptoms. We propose to designate these two isolates as SPVG. This report documents the occurrence of this virus in the United States and provides the first characterization of its biological properties. LSU-2 and -5 were distinct in symptomatology; partial Nib, CP nucleotide, and derived amino acid sequence; and serology to other viruses. We propose to call this virus (LSU isolates 2 and 5) Ipomoea vein mosaic virus. The present study revealed a high degree of sequence similarity between 95-6 and the common strain of SPFMV, and between 95-2 and the russet crack strain of SPFMV. Results from this study suggest not only that at least two strains of SPFMV occur in the United States, but that two other potyviruses also are present.

Resumo -O objetivo deste trabalho foi avaliar a resistência à ferrugem causada pelo fungo Phakopsora euvitis, em genótipos de videira, e a efi ciência da infecção de acordo com a idade das folhas e concentração de inóculo. A avaliação foi feita em 15 genótipos, com base nos seguintes componentes de resistência: número de pústulas (urédios) por cm 2 ; tamanho das pústulas; número de esporos produzidos por pústula; e período latente. Os componentes de resistência, com exceção do período latente, apresentaram grande variação quantitativa. A análise multivariada desses componentes diferenciou cinco grupos de genótipos. Os genótipos mais resistentes foram as cultivares porta-enxertos IAC313, IAC572 e IAC766, em que a efi ciência da infecção foi baixa, com pústulas menores e menor produção de urediniósporos, além de reação de hipersensibilidade no tecido em torno das pústulas. O grau de infecção aumenta com o aumento na concentração do inóculo. A ferrugem coloniza, indiscriminadamente, folhas jovens e folhas maduras de videira.Termos para indexação: Phakopsora euvitis, Vitis, análise multivariada, reação de hipersensibilidade, resistência genética. Genetic resistance of grape genotypes to rustAbstract -The objective of this work was to evaluate the genetic resistance of grape genotypes to rust, caused by the fungus Phakopsora euvitis, and the infection effi ciency in relation to leaf age and inoculum concentration. The evaluation was carried out on 15 genotypes, based on the following resistance components: number of pustules (uredia) per cm 2 , size of pustules; number of urediniospores produced per pustules; and latent period. The resistance components, except for the latent period, presented considerable quantitative variation. The multivariate analysis of resistance components discriminated fi ve groups of genotypes. The more resistant genotypes were the rootstocks cultivars IAC313, IAC572, and IAC766, in which the infection effi ciency was low, with small pustule sizes, and less urediniospores production, besides hypersensivity response on tissue surrounding the pustules. The infection increases with increasing of inoculum concentration. The rust colonizes young and mature grape leaves.

Para avaliar a resistência de híbridos experimentais e comerciais de milho-pipoca à Exserohilum turcicum, agente causal da helmintosporiose do milho, implementou-se um ensaio em delineamento de blocos completos com tratamentos ao acaso, com quatro repetições, em Maringá, Paraná, na safra 2007/2008. O objetivo adicional foi comparar a eficiência de discriminação da resistência utilizando apenas uma das avaliações ou uma série de avaliações. Incidência e a severidade, avaliadas em quatro avaliações, foram usadas para estimar a área abaixo da curva de progresso da incidência (AACPI) e da severidade (AACPS). Os dados de incidência e severidade na última avaliação, mais a AACPI e AACPS foram submetidos à análise de variância e teste de Scott-Knott para comparar a resistência dos genótipos. A análise de correlações de postos de Spearman foi utilizada para verificar qual o grau de associação entre os dados de severidade, de incidência, AACPS e AACPI. Foram constatadas diferenças significativas (P≤0,001) de resistência entre os genótipos avaliados, permitindo a formação de três agrupamentos de resistência. Os híbridos UEM129, UEM145, UEM140, UEM116 e UEM101 apresentaram menores índices de intensidade da doença, e foram considerados os genótipos mais resistentes. Estes híbridos superaram os híbridos UEM109, UEM153 e IAC 112, classificados como resistentes, e Zélia e Jade, considerados susceptíveis. Pelas correlações constatou-se que a avaliação de incidência e severidade no estádio de grão pastoso não proporcionou dados equivalentes à AACPS e AACPI para a discriminação da resistência à E. turcicum.