No abstract

No abstract

RESUMO

No abstract

(4) e Léo Duc Haa Conceição (5) Resumo -A mancha-foliar de feosféria tem causado expressiva redução no rendimento de grãos de milho, no Brasil, principalmente, em decorrência da crescente amplitude da data de semeadura, conjugada com o uso de áreas irrigadas e de plantio direto. É importante o desenvolvimento de genótipos resistentes a essa moléstia; porém a realização de uma seleção eficiente depende do entendimento da variabilidade genética e da herança da resistência. Com o objetivo de determinar a capacidade combinatória e o modo de herança do caráter, foram cruzadas sete linhagens de milho, para a realização das análises dialélica e média de gerações. Os experimentos foram conduzidos no Município de Xanxerê, SC, sendo avaliada a porcentagem de tecido foliar afetado pela moléstia 30 dias após o florescimento. Os genótipos apresentaram amplitude de 4,3% a 67,0% de área foliar afetada pela moléstia, na qual a linhagem LA06 e seus híbridos demonstraram elevada resistência. Os resultados indicaram que a seleção de genótipos resistentes à feosféria pode ser realizada com sucesso em programas de melhoramento do milho, visto que a manifestação do caráter é controlada por, pelo menos, dois genes independentes e com uma efetiva participação de efeitos aditivos.Termos para indexação: Phaeosphaeria maydis, teste de progênie, variação genética, melhoramento vegetal. Inheritance of the resistance to phaeosphaeria leaf spot in maizeAbstract -Phaeosphaeria leaf spot (PLS) has caused an expressive reduction in the corn grain yield in Brazil. The increment in sowing date amplitude, conjugated with the use of irrigated areas and zero tillage, had major contribution in the increase of phaeosphaeria leaf spot (PLS) incidence and severity. For this reason, it is important to develop resistant genotypes to this disease; however, an efficient selection depends upon the understanding of the genetic variability and inheritance of the resistance. Aiming to determine combining ability and the mode of inheritance for PLS, seven corn inbreds were crossed for diallel and generation mean analysis. The experiments were conducted in Xanxerê, SC. Percentage of foliar area affected by the disease was evaluated 30 days after flowering. The genotypes presented amplitude of 4.3% to 67.0% of foliar area affected by PLS. The LA06 and its hybrids showed high level of resistance. Results indicated that selection for PLS resistant genotypes could be successfully accomplished in corn breeding programs. At least two major independent genes were identified with a preponderant participation of addictive effects in the inheritance of the trait.

RESUMO Este estudo teve o objetivo de reconhecer as espécies de moscas frugívoras em mirtáceas:

No abstract

Phaeosphaeria leaf spot (PLS) is a major foliar maize disease in Brazil, with reports of up to 60% yield reduction (Dourado & Fancelli, 2000). The cause has been attributed to Phaeosphaeria maydis (Fantin, 1994), although alternative suggestions have been made (Cervelatti et al ., 2002). The first symptoms appear as chlorotic leaf spots, later developing into straw-coloured elliptical lesions.Leaves with typical PLS lesions from 1 to 10 mm were examined, from different sites in Rio Grande do Sul (RS) and Goiás (GO) states in 2001, 2002 and 2003. Disinfected samples (1 min in 70% ethanol, 2 min in 1% NaOCl) were placed in a humid chamber for 96 h. Fungal sporulating structures were picked off and placed on potato dextrose agar (PDA) with 0·02% w/v streptomycin sulphate. Typical colonies were sent to CABI Bioscience, Egham, UK, for species identification, which was done based on colony, pycnidia and spore morphology. Phoma sorghina , a minor pathogen recorded on sorghum in Brazil (Pinto, 2002), was found in 70% of all samples. Phaeosphaeria maydis was obtained from only 7% of the samples from RS.Conidial suspensions (adjusted to 1 × 10 6 conidia mL − 1 in sterile distilled water) of either P. sorghina or P. maydis were sprayed onto three maize plants each of two cultivars: AS-3466 (resistant to PLS) and AS-32 (a susceptible cultivar). Plants were kept under a plastic cover for 72 h after inoculation. Control plants were sprayed with sterile distilled water alone. Plants inoculated with P. sorghina were kept in a glasshouse at 70% relative humidity (RH) at an average temperature of 25 ° C. Phaeosphaeria maydistreated plants were kept in a growth chamber at 80% RH, 21 ° C and a 12-h photoperiod.Plants inoculated with either Phaeosphaeria maydis or Phoma sorghina developed similar symptoms. Both sets of treated plants showed chlorotic lesions after 10 days on AS32 and 15 days on AS3466, both becoming necrotic and straw-coloured after 20 days. These lesions were smaller than the ones observed in the field. Both fungi were reisolated from these lesions, confirming their pathogenicity on maize. The pathogenicity tests were repeated with the same results. This is the first report of Phoma sorghina in the aetiology of leaf spot on maize in Brazil.