F. F. Teixeira

Effect of Baculovirus spodoptera isolates in Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) larvae and their characterization by RAPD

Foram utilizados 22 isolados de virus amostrados em diferentes regioes produtoras de milho do Brasil. Os virus foram purificados e suas suspensoes fornecidas a lagartas sadias do 3o e 4o instar de Spodoptera frugiperda (J.E. Smith). A mortalidade foi avaliada diariamente, e as lagartas infectadas foram congeladas logo apos sua morte, o que em geral ocorreu do 5o ao 7o dia apos ingestao do virus. Os isolados foram usados em seis concentracoes (103 a 108 poliedros/ml) e uma testemunha (agua). Os percentuais de mortalidade, duracao do periodo larval e periodo pupal, peso de pupa e a concentracao letal (CL50) foram determinados para todos os isolados. Foram observadas diferencas significativas entre todos os isolados e concentracoes testadas para todos os parâmetros avaliados, e tambem foi constatada a presenca da interacao isolado x concentracao, exceto para periodo pupal. Os padroes de amplificacao de 54 marcadores RAPD, sendo 41 polimorficos, foram utilizados para avaliar a distância genetica e a sua correlacao com os indices de mortalidade das lagartas. A divergencia genetica calculada pelo coeficiente Jaccard utilizando os dados moleculares permitiu dividir os isolados em dois grupos, com um elevada confiabilidade. O agrupamento nao apresentou associacao com a taxa de mortalidade causada pelos isolados ou com sua distribuicao geografica. No entanto, um fragmento de RAPD OPW04.2280 apresentou-se altamente associado com a mortalidade das lagartas e com a CL50, explicando 23% e 65% da variacao fenotipica para essas caracteristicas entre os isolados virais, respectivamente.

ANALYSES OF GENETIC VARIABILITY IN LENTINULA EDODES THROUGH MYCELIA RESPONSES TO DIFFERENT ABIOTIC CONDITIONS AND RAPD MOLECULAR MARKERS

The growth of thirty-four Lentinula edodes strains submitted to different mycelial cultivation conditions (pH and temperature) was evaluated and strain variability was assessed by RAPD molecular markers. The growth at three pH values (5, 6 and 7) and four different temperatures (16, 25, 28 and 37oC) was measured using the in vitro mycelial development rate and water retention as parameters. Mycelial cultivation was successful at all pH tested, while the ideal temperature for mycelial cultivation ranged between 25 and 28oC. The water content was lower in strains grown at 37oC. Among 20 OPA primers (Operon Technologies, Inc.) used for the RAPD analyses, seventeen presented good polymorphism (OPA01 to OPA05, OPA07 to OPA14, OPA17 to OPA20). The clustering based on similarity coefficients allowed the separation of strain in two groups with different geographic origins.

Evaluation of maize core collection for drought tolerance

The maize genebank (GBmaize) preserves nearly 4,000 accessions for conservation and use. The use is however restricted because the accessions do not perform as well as the elite genotypes. This problem can be reduced by pre-breeding, i.e., by extending the information on germplasm and introgressing useful alleles. Since irregular rainfall distribution and drought induce maize yield losses, drought tolerance is a main breeding target. In this study, the GBmaize accessions were evaluated for drought tolerance. Environmental factors, genotypes and the respective interactions influence the phenotypic expression. There was however no interaction genotype - irrigation level, so no accessions with different performance under the two water regimes could be identified. The performance of the following accessions was promising for a number of traits: SP154, BA166, MG099, CE002, SE025, BA154, BA194, BA085, MG076, PR053, Roxo Macapa, SE016, and AL018.

Genetic diversity assessed by microsatellite markers in sweet corn cultivars

Information on genetic diversity is essential to the characterization and utilization of germplasm. The genetic diversity of twenty-two sweet corn cultivars (seventeen open-pollinated varieties, OPV, and five hybrids, H) was investigated by applying simple sequence repeat markers. A total of 257 primers were tested, of which 160 were found to be usable in terms of high reproducibility for all the samples tested; 45 were polymorphic loci, of which 30 were used to assess the genetic diversity of sweet corn cultivars. We detected a total of 86 alleles using 30 microsatellite primers. The mean polymorphism was 82 %. The highest heterozygosity values (Ho = 0.20) were found in the PR030-Doce Flor da Serra and BR427 III OPVs, whereas the lowest values (0.14) were recorded in the MG161-Branco Doce and Doce Cubano OPVs. The polymorphism information content ranged from 0.19 (Umc2319) to 0.71 (Umc2205). The analysis of molecular variance revealed that most of the genetic variability was concentrated within the cultivars of sweet corn (75 %), with less variability between them (25 %). The consensus tree derived from the neighbor-joining (NJ) algorithm using 1,000 bootstrapping replicates revealed seven genetically different groups. Nei’s diversity values varied between 0.103 (Doce do Hawai × CNPH-1 cultivars) and 0.645 (Amarelo Doce × Lili cultivars), indicating a narrow genetic basis. The Lili hybrid was the most distant cultivar, as revealed by Principal Coordinates Analysis and the NJ tree. This study on genetic diversity will be useful for planning future studies on sweet corn genetic resources and can complement the breeding programs for this crop.

Pré-melhoramento de milho quanto à resistência a enfezamentos

The objective of this work was to select maize families derived from backcrossing between the composite NAP Corn Stunt (donor parent) and inbreed lines (recurrent parents), as to grain yield and resistance to corn stunt, and to evaluate the efficiency of the use of molecular markers in the phenotypic evaluation for the selection of genotypes with high grain yield. One hundred genotypes were evaluated in five environmental conditions in the 2009/2010 crop season. We selected RC1F2 families, which combine high grain yield present in the recurrent parents to resistance to corn stunt present in the donor parent. The selected maize families for agronomic performance and resistance to corn stunt were: L228-3-324-S, L228-3-237-R, L228-3-109-R, which were indicated for crosses with lines of the flint heterotic group; and L3-422-R and L3-586-R, which were indicated for crosses with lines of the dent heterotic group. For selecting genotypes with high grain yield, the molecular marker-assisted selection is not efficient for the recovery of the recurrent parent genotype, when compared to the phenotypic evaluation.

Genetic control of maize resistance to corn stunt spiroplasma

The corn stunt spiroplasma (CSS) is transmitted by Dalbulus maidis leafhopper. The disease causes severe losses on maize production. One complete diallel genotype of two corn stunt resistant maize lines, and two corn stunt susceptible maize lines were tested by spiroplasma inoculation under insect-proof screenhouse condition, in order to elucidate the maize genetic control to this disease. The percentage of reduction on plant dry weight caused by the spiroplasma inoculation in relation to the dry weight average of the healthy plants, was calculated for each plant spiroplasma inoculated, to express maize resistance. The disease incidence for each treatment was represented by the percentage of plants with CSS symptoms. The disease severity was scored based on CSS symptoms severity, for each plant. Reductions on the dry weight were caused by the disease; the disease severity data showed a positive and strong correlation (r = 0.80). The statistical analyses indicated that genetic control of maize resistance to spiroplasma includes genes with additive effects and genes with dominance or epistatic effects, suggesting complex resistance inheritance. One line was better performing than all the others, reducing the disease damage, as well per se as in crosses.

BRS Cipotânea and BRS Diamantina: maize varieties

The maize cultivars BRS Cipotânea and BRS Diamantina were developed from accessions of the Maize Germplasm Bank of Embrapa Maize and Sorghum. The evaluation was participative, performed by scientists and end-users. The varieties were developed to provide farmers with maize varieties suitable for corn-husk crafts.