Com o objetivo de se identificar fontes de resistencia em sorgo a Colletotrichum graminicola, agente causal da antracnose, foram avaliadas em casa de vegetacao, as reacoes de 28 introducoes e 4 racas de patogeno. As inoculacoes foram realizadas em plantas com 30 dias de idade, sendo utilizada a concentracao de inoculo de 10/6 conidios/ml. Os genotipos SC 36, TX 2737, SC 224, SC 418-14 e 79HW 207 apresentaram resistencia as 4 racas de Colletotrichum graminicola.

SUMMARY Analysing the stability and adaptation of cultivars to different environments is always necessary before recommending them for planting on large areas. Additive main effects and multiplicative interaction (AMMI) models have been used to analyse genotype-by-environment interactions (G × E). AMMI models require data with homogeneous variance, normal errors and additive effects. However, agronomic data do not always conform to these statistical assumptions. The objective of the present study was to analyse G × E interactions for severity and incidence of grey leaf spot, a foliar disease in maize caused by Cercospora zeae-maydis , using a generalized AMMI model. Data were collected and evaluated for 36 maize cultivars from experiments carried out in nine Brazilian regions in 2010/11 by the Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA – Milho e Sorgo). Only two of three stable genotypes defined by a quasi-likelihood model with a logistic link function could be recommended for their desirable agronomic characteristics. Four growing locations in which the genotypes were stable were identified, but in only one of these was stability associated with very severe grey leaf spot disease. Cultivars adapted to specific locations with low percentage disease severity were also identified.

The aim of this study was to evaluate the use of genotype rotation as a sustainable management strategy for the control of foliar anthracnose of sorghum. Three grain sorghum hybrids, one susceptible (BR 304) and two resistant to anthracnose (1G150 and DAS740) were tested in continuous planting and genotype rotation during seven growing seasons. The area under disease progress curve (AUDPC) of sorghum anthracnose severity was significantly lower in the genotype rotation than in the continuous planting. The disease severity in the susceptible genotype BR 304 in rotation with the resistant genotypes 1G150 or DAS740 decreased about 42% and 70% respectively, compared to its continuous planting. A significant reduction of leaf blight disease severity caused by Exserohilum turcicum in DAS740 planted rotated with BR 304 was also observed. The grain yields of the three genotypes were significantly higher in the rotation system compared to continuous planting. The genotype rotation can be considered a practical management strategy for reducing the impact of anthracnose and other diseases in sorghum.

Anthracnose caused by the fungus Colletotrichum graminicola (Ces.) Wilson is the most important disease of maize in Brazil, especially in no-tillage without crop rotation. In this system, maize debris from earlier plantings increases the fungal inoculum potential over time. The use of genetic resistance is the most appropriate and advantageous strategy for anthracnose control. However, the effectiveness and durability of this practice depends on knowledge concerning the genetic variability of C. graminicola. In this study, fifteen maize genotypes were tested against 190 single spore of C. graminicola collected from infected leaves of maize plants cultivated in seven different Brazilian ecogeographic areas. Five races of C. graminicola were identified, and eleven maize genotypes were susceptible to all isolates. Results indicated that both the number of pathogen isolates and the number of genotypes to be tested are pivotal for an accurate identification of C. graminicola races. This is the first study showing the occurrence of C. graminicola races in Brazil. (C) 2013 Elsevier Ltd. All rights reserved.

Mancha-branca-do milho (MBM), tambem conhecida como mancha-de-feosferia (MF), tornou-se uma das mais importantes doencas do milho no Brasil. A etiologia da MBM/MF permanece objeto de controversia e debate. Este estudo teve como objetivo testar o fungo Phaeosphaeria maydis e a bacteria Pantoea ananatis como agentes causadores da doenca MBM/MF. As identidade dos isolados bacterianos foi confirmada por primers especificos da especie P. ananatis. O fungo P. maydis foi isolado a partir de plantas do hibrido comercial DAS657 sensivel a MBM/MF. Plantas de DAS657 foram inoculadas com P. ananatis (HR+) e P. maydis em casa de vegetacao. Plantas inoculadas com P. ananatis reproduziram sintomas tipicos da doenca MBM/MF e P. ananatis foi consistentemente reisolada das lesoes. Para P. maydis, dois procedimentos diferentes foram testados: suspensoes com 104 pseudotecios/ml e discos miceliais (1 cm de diâmetro) inoculados em plantas no estadio de 8 a 10 folhas. Varias tentativas para cumprir os postulados de Koch com P. maydis falharam. Estes resultados reforcam as evidencias de que a bacteria Pantoea ananatis e o agente causador da doenca MBM/MF do milho.

The aims of the present study were to assess the efficiency of hybrid sorghum mixtures for the management of anthracnose and analyze the virulence diversity and structure in the pathogen populations developed in response to these mixtures. Proportions of 25%, 50% and 75% of the susceptible BRS304 hybrid in relation to the resistant IG150 hybrid were evaluated. Six weekly evaluations of severity were performed. The data were transformed into area under disease progress curve (AUDPC). The isolates of Colletotrichum sublineolum were sampled from hybrid mixtures cultivated in Sete Lagoas and Indiancpolis (Brazil) as well as sorghum fields in Rio Verde and Parauna (Brazil). The increase in the proportion of the resistant hybrid in the mixtures led to a reduction in anthracnose severity. The most effective proportions were those with 25% and 50% of the susceptible variety blended with the resistant variety. Complex breeds of C. sublineolum predominated in the populations and a reduction in phenotype diversity was observed. This reduction in diversity was attributed to deviations in the degree of polymorphism in relation to virulence. However, the increase in complex breeds did not imply lesser efficiency on the part of the resistant hybrid in conferring protection to the susceptible hybrid.

Os objetivos deste trabalho foram avaliar a reacao de linhagens-elites de sorgo a diferentes populacoes de C. sublineolum e identificar combinacoes de linhagens restauradoras e macho-estereis capazes de gerar hibridos de alta resistencia a antracnose.

Maize white spot disease (MWSD) has become most important in Brazil. With this study the susceptible maize hybrid DAS657 was artificially inoculated under greenhouse conditions with the bacterium Pantoea ananatis and the fungus Phaeosphaeria maydis, the two most likely candidate etiological agents of MWSD. Plants inoculated with P. ananatis reproduced the symptoms typical of MWSD, while several attempts to fulfill Koch's postulates with P. maydis failed. The epidemiological variables associated with maize resistance to MWSD was assessed with eight simple hybrids, one double hybrid, one triple hybrid and five inbred lines evaluated in two trials in a randomized block design with three replicates in two planting times. The area under disease progress curve (AUDPC) and disease severity at the end of the epidemic (Y-max) were the epidemiological variables that better differentiated maize genotypes resistant to MWSD. One inbred line and three simple hybrids were highly resistant. Two inbred lines were identified as new sources of resistance and may be used in maize breeding programs.

The anthracnose stalk rot of corn (ASR), caused by Colletotrichum graminicola, is a major disease of this crop and occurs in most Brazilian regions where corn is grown. Despite its widespread occurrence, there are no estimates of the effect of ASR on the yield of corn under the Brazilian conditions. In this study, we evaluated the effect of ASR on corn hybrids yield. Two experiments were conducted (first crop 2007/2008 and second crop, 2009) in areas with a history of occurrence of leaf anthracnose and ASR. Five hybrids were evaluated in the first and second crops: AG1051, BRS 1001, BRS 1010, BRS 1035, P30F80 and BRS 1010, 2B710, P30F80, DKB390, BRS 1035, respectively. At harvest, we evaluated the incidence of plants with anthracnose stalk rot (IPASR), and we selected pairs of healthy and diseased plants to quantify the effect of ASR in the ear weight (EW), grain weight (GW) and the weight of a sample containing 100 kernels (W100). The IPASR was higher in the hybrid BRS 1010 (21.87 and 45.28%, first and second crops, respectively). The EW, GW and W100 were lower in diseased plants in all hybrids. The mean weight loss in the first season was EW 29.03%, GW 27.83% and W100 17.08%, and the second season was EW 27.75%, GW 25.60% and W100 16.99%. The most affected hybrids with weight loss in the first crop were AG1051 (EW 34.31%, GW 33.05%, W100 19.96%) and BRS 1035 (EW 34.74%, GW 34.65%, W100 22.31%). In the second crop, were P30F80 (EW 30.72%, GW 30.92%, W100 19.24%), DKB390 (EW 30.61%, GW 29.81%) and 2B710 (W100 19.27%). Corn yield was strongly affected by ASR.

The objective of this work was to evaluate the efficiency of dynamic multilines, using genetic mixing in populations of three-way hybrids, in the management of sorghum anthracnose, caused by the fungus Colletotrichum sublineolum. Eighteen three-way hybrids were obtained from seven different lines containing genes for resistance to the disease. The 25 genotypes of hybrids and lines were evaluated in field conditions. In some hybrids, a higher resistance level was observed when compared to that of the more resistant line used in the crosses, indicating an additive effect of the resistance genes of the different lineages in the composition of the final resistance of hybrids. The use of dynamic multilines reduced the disease intensity in field and increased productivity. This strategy makes it possible to use lineages that have desirable agronomic characteristics, but are susceptible to anthracnose.

A study was carried out to investigate the inheritance of resistance to anthracnose, caused by Colletotrichum sublineolum, in sorghum. Crosses between resistant and susceptible parents and backcrosses between F1 plants and the susceptible parents were carried out under field conditions. The F1 generations and the segregant populations were evaluated under artificial inoculation conditions in the greenhouse. In the F1 generation of all crosses with the respective isolates, all of the plants presented a resistance reaction except for the F1 plants resulting from the BR009 × SC283 cross. In the F2 generation, the frequencies of resistant and susceptible plants conformed to the hypothesis that one gene with two alleles controls host resistance, except in one cross. Out of the eight backcrosses, six presented segregation that corresponded to the hypothesis formulated. For most crosses, resistance was dominant, and the proportions of resistant and susceptible plants in the segregant populations conformed to the frequencies expected under the hypothesis of gene‐for‐gene resistance and dominant gene action.

O hibrido simples de milho BRS 1055 foi desenvolvido para lavouras de alto/medio investimento e historicos de alta/media produtividade.