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Soybean Asian rust and white mold stand out to cause great problems to soybean producing regions in Brazil. The aim of this study was to evaluate the partial resistance of soybean lines to Asian rust and white mold. In order to assess the resistance of soybean to Asian rust, 19 early maturing soybean lines were used in an experiment in a greenhouse. Four severity evaluation were carried and the area under the disease progress curve was calculated. The productivity of those lines was evaluated in the field. In a second experiment, the resistance to Sclerotinia sclerotiorum was assessed under greenhouse conditions. When the plants were in the V2 stage, the inoculation was carried by cutting the main stem and inserting a ferrule containing the fungal mycelium. Seventeen soybean lines and the controls Emgopa 316 and Nidera RR 7255 were evaluated. The averages were grouped by the Scott Knott test by using the software Assistat. The lines L203 and L279 showed partial resistance to Phakopsora pachyrhizi and good productivity. The inoculation method was efficient in assessing the resistance to S. sclerotiorum. The lines L203, L268, L266, L226, L144 and L267 were resistant to the infection of S. sclerotiorum.

The genetic control of rust resistance was studied using the Caiapônia x IAC-100 and Luziânia x Potenza crosses. The F2 and F3 generations were evaluated. Rust severity was quantified through visual assessment of the middle third of three leaflets per plant and performed by three different evaluators; the average score was calculated foreach individual plant. From these data, we estimated the mean and variance of the genetic components by employing the weighted least squares method. The estimated number of genes and broad- and narrow-sense heritabilities were also obtained. It was concluded that rust resistance is a characteristic controlled by 2 to 23 genes that are predominantly dominant. The estimate of narrow-sense heritability was greater than 70% for the Caiapônia x IAC-100 cross, and the wide-sense heritability was greater than 60% for the Luziânia x Potenza cross; thus, it is possible to successfully select resistant individuals in early generations.

This research work was carried out to verify the adaptability and phenotypic stability of soybean inbred lines of semi early cycle, using rust severity as the selection trait for partial resistance. The strains were evaluated during the growing seasons of 2007/08 and 2008/09, in the locations of Uberlândia and Uberaba, MG, Campo Alegre de Goiás and Senador Canedo, GO, using a randomized complete block design with three replications. Rust severity was evaluated by visual assessment of the leaflets at the medial third of five plants in each plot. By using disease severity, it was estimated: the mean absolute rate of disease progress (r), the area under the disease progress curve (AUDPC) and the partial resistance factor (PRF). Adaptability and stability of the strains were estimated by the methods proposed by Eberhart and Russell, as well as by the AMMI method. It was found that the strains which were the most resistant to rust, in general, also showed the best adaptability and stability.

O objetivo deste trabalho foi avaliar a resistência parcial de genótipos de soja ao fungo Phakopsora pachyrhizi. Calcularam-se o número médio de pústulas, a severidade e a área abaixo da curva de progresso da doença. Foram encontradas diferenças significativas entre os genótipos quanto ao número médio de pústulas e severidade, aos 12 dias após a inoculação. A análise de agrupamento permitiu a discriminação de genótipos parcialmente resistentes. Os genótipos G4, G41 e G42, referentes aos parentais Cristalina e IAC 100, foram detectados como os de maior resistência parcial à ferrugem da soja.The objective of this work was to evaluate the partial resistance of soybean genotypes against Phakopsora pachyrhizi. Resistance characteristics were: average number of pustules, rust severity and the area under the disease progress curve. Significant differences were found among the genotypes for the average number of pustules and rust severity. Multivariate analysis allowed the discrimination of partially resistant genotypes. Three genotypes (G4, G41, and G42), referring to parents Cristalina and IAC 100, presented greater partial resistance to soybean rust.