No abstract

ABSTRACT. Maize landraces derived from tropical germplasm represent an important source of genetic variability, which is currently poorly understood and under-exploited by Brazilian crop breeding programs. The aims of our study were to a) estimate the genetic diversity across 48 varieties of maize landraces cultivated at different locations in the States of Rio Grande do Sul (RS) and Paraná (PR) by means of random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and amplified fragment length polymorphism (AFLP) markers; b) cluster these varieties based on their genetic similarity estimates, and c) establish possible correlations between genetic similarity and germplasm collection sites. Maize landrace accessions were genotyped through the 30 RAPD, 47 SSR, and 25 combinations of AFLP primers. The results revealed high levels of variability across landraces within and between collection sites. AFLP analysis resulted in amplification of 762 polymorphic fragments and a polymorphic index of 40.3%, followed by RAPD with 335 fragments (81.9%) and SSR with 105 fragments (78.3%). The genetic similarity estimates of the investigated landraces ranged from 41 (SSR) to 74% (AFLP), and the amplitudes of these indices were notably similar between RAPD and SSR, as well as between AFLP and joint analysis. Regarding the RAPD and AFLP dendrograms, groups comprising accessions from RS prevailed, whereas SSR comprised varieties from both collection sites. Groups exclusive to RS or PR support the hypothesis that divergence between groups is possible owing to the fixation of regional adaptation alleles and to spatial barriers hindering genetic flow between locations.

RESUMO -As cultivares de aveia-branca (Avena sativa L.) cultivadas no sul do Brasil até princípios da década de 80 eram provenientes do Uruguai e da Argentina, apresentando problemas de adaptação ao ambiente de cultivo. A partir dos anos 70, programas de melhoramento começaram a produzir suas próprias populações segregantes, possibilitando o lançamento em escala comercial de cerca de 35 cultivares. Com o objetivo de estimar o progresso genético nos programas de melhoramento de aveia-branca do sul do Brasil, foi realizado um experimento envolvendo 15 cultivares lançadas em diferentes épocas, em dois locais, com quatro diferentes condições de manejo. Os resultados obtidos indicaram progresso genético linear para os caracteres ciclo vegetativo, rendimento de grãos, peso de grão e peso do hectolitro; a inexistência de efeitos quadráticos significativos sugeriram a possibilidade de ganhos posteriores a partir da seleção de novos genótipos. Os programas de melhoramento genético de aveia-branca do sul do Brasil, embora ainda não tenham atingido o patamar máximo, têm sido eficientes em produzir novas cultivares com maiores rendimento e qualidade de grãos e com caracteres agronômi-cos superiores.Termos para indexação: Avena sativa, ganho genético, métodos de melhoramento, adubação nitrogenada, fungicidas, características agronômicas, rendimento de grãos. GENETIC PROGRESS IN OAT BREEDING IN SOUTHERN BRAZILABSTRACT -The oat (Avena sativa L.) cultivars cultivated in Southern Brazil up to the beginning of the 80's were introduced from Uruguay and Argentina. They presented adaptation problems to the new environment. Starting from the 70's, oat breeding programs began to produce their own segregant populations. These programs already released 35 cultivars. Aiming to estimate the genetic progress in oat breeding programs from southern Brazil, an experiment with 15 cultivars released in different times was conducted in two locations using four different cultural practices. The results indicated linear genetic progress for days to flowering, grain yield, grain weight and test weight. The non significance of quadratic effects suggested the possibility of additional gains through selection of new genotypes. The oat breeding programs in southern Brazil have been efficient in producing new cultivars with higher grain yield, good grain quality, and with superior agronomic traits. However, a maximum breeding plateau was not reached for this species.

In this work we describe the cytogenetic analyses performed in specimens of Astylus variegatus (Germar, 1824) collected in two localities: one area of natural vegetation and one of agricultural crops, where agrochemical products were used. Astylus variegatus had karyotypes with 2n(male) = 16+Xy p and 2n (female) = 16+XX p , with exclusively metacentric chromosomes. Pachytene spermatocytes showed synapsed autosomal bivalents and non-associated sex chromosomes. In diplotene, the autosomal bivalents exhibited one or two terminal chiasmata and the Xy p had a typical parachute configuration. In meiotic cells of some specimens, an extra chromosome, interpreted as a B chromosome, was observed. C-banding showed constitutive heterochromatin in the pericentromeric region of all chromosomes, with the exception of the y p . Silver nitrate staining revealed one nucleolus organizer region (NOR) on the terminal region of the short arm of the second autosome pair. Silver staining of meiotic cells confirmed the NOR pattern detected in mitotic cells and revealed an argentophilous material on the Xy p . A cytogenetic comparison between the two populations of A. variegatus showed a statistically significant divergence (χ 2 = 117.10; df = 1) in the number of aneuploid cells and a higher frequency of B chromosome in the population exposed to agrochemicals.

Biological control consists of using one organism to attack another that may cause economic damage to crops. Integrated Pest Management (IPM) is a very common strategy. The white mold produced by Sclerotinia sclerotiorum (Lib.) causes considerable damage to bean crops. This fungus is a soil inhabitant, the symptoms of which are characterized by water-soaked lesions covered by a white cottony fungal growth on the soil surface and/or the host plant. Possible biological control agents taken from plants are being investigated as phytopathogen inhibitors. These are endophytic microorganisms that inhabit the intercellular spaces of vegetal tissues and are often responsible for antimicrobial production. The objective of the present study was to select endophytic fungi isolated from comfrey (Symphytum officinale L.) leaves with in vitro antagonist potential against the phytopathogenic fungus S. sclerotiorum. Twelve isolates of endophytic fungi and a pathogenic strain of S. sclerotiorum were used in the challenge method. With the aid of this method, four endophytes with the best antagonistic activity against S. sclerotiorum were selected. Pathogen growth inhibition zones were considered indicative of antibiosis. The percentages of pathogenic mycelia growth were measured both with and without the antagonist, resulting in growth reductions of 46.7% to 50.0% for S. sclerotiorum. These analyses were performed by evaluating the endophytic/pathogenic mycelia growth in mm/day over an eight-day period of antagonistic tests.