Kátia Regiane Brunelli

First Report of Colletotrichum boninense Causing Anthracnose on Pepper in Brazil

Colletotrichum boninense was isolated from pepper (Capsicum annuum) fruits (cv. Amanda) with preharvest anthracnose symptoms collected in the Brazilian states of Rio Grande do Sul and São Paulo in July of 2005. In the field, the disease affected mature fruits and leaves with an incidence near 25%. Typical symptoms in fruits were circular, sunken lesions with orange spore masses in a dark center. Three single conidia isolates were obtained from infected fruits. When grown on potato dextrose agar at 25°C with a 12-h photoperiod, these isolates produced white colonies with a cream-to-orange color in the opposite side, but no sclerotia. Conidia were cylindrical, had obtuse ends and a hilum-like low protuberance at the base, and measured 13.5 to 15.5 × 4.6 to 5.1 μm. Conidial length/width ratio was 2.8 to 3.0. These morphological characteristics are consistent with the description of C. boninense (1). To confirm pathogen identity, the internal transcribed spacer rRNA region was sequenced (GenBank Accession Nos. FJ010199, FJ010200, and FJ010201) and compared with the same region of C. boninense (GenBank Accession No. DQ286160.1). Similarity between these sequences was 98 to 99%. The pathogenicity of the three isolates was determined on pepper fruits cv. Amanda. Attached as well as detached fruits from potted plants were inoculated. Inoculation was performed by depositing 40-μl droplets of a suspension (105 conidia per ml) on the surfaces of nonwounded (detached n = 5; attached n = 5) and wounded (detached n = 5; attached n = 5) fruits with a sterilized hypodermic needle. Incubation took place in a moist chamber for 12 days at 25°C with a 12-h photoperiod. Inoculation of control fruits was similar in procedure and number to that of test fruits, except sterile distilled water was used instead of the conidial suspension. Symptoms, observed in wounded and nonwounded test fruits 3 to 5 days after inoculation, were characterized by necrotic, sunken zones containing acervuli, black setae, and orange spore masses. Control fruits presented no symptoms. Pathogens reisolated from infected fruits showed the same morphological and molecular characteristics of the isolates previously inoculated. To our knowledge, this is the first report of C. boninense infecting pepper in Brazil. Reference: (1) J. Moriwaki et al. Mycoscience 44:47, 2003.

Efeito do meio de cultura e do regime de luz na esporulação de Cercospora zeae-maydis

Some fungal species, like Cercospora zeae-maydis, causal agent of maize gray leaf spot, do not satisfactorily produce spores in artificial media. The conidial production of C. zeae-maydis was evaluated on seven culture media (V8, tomato juice, coconut water, oat, PDA, maize leaf extract and maize leaf extract plus CaCO 3 ) under two light exposure regimens (12-hours photoperiod or six days under continuous light followed by three days of continuous darkness). The experiment was

MAPEAMENTO DE GENES DE RESISTÊNCIA QUANTITATIVA A Puccinia polysora EM MILHO

The objectives of this study were to identify microsatellite markers linked to resistance gene of resistance to Puccinia polysora and to estimate the phenotypic effect of these genes on two monocyclic variables lesion, number and length. Two inbreed lines with different degrees of resistance (Z-95 and Z-93), the hybrid (Z-95 X Z-93) and F2 plants derived by selfing this hybrid were phenotyped for disease resistance, in two field trials and genotyped for 142 microsatellite markers using bulked segregant analysis (BSA). The molecular markers putatively linked to the disease resistance genes identified by this method were used to genotype 165 segregant individuals and to confirm linkage. Two markers, Phi 65 and Phi 28, both located on chromosome nine, were significantly associated (p<0.000001 and p<0.000078) with a QRL (quantitative resistance loci) to P. polysora. The association explained 12.9 and 5.10% of the phenotypic variance in resistance for Phi 65 and Phi 28, respectively. In a third trial performed in the greenhouse, 94 plants were inoculated with a uredospore suspension and evaluated 15 days after inoculation for the total number of lesions and the length of ten lesions. These plants were genotyped with Phi 65 and Phi 28. Only Phi 65 showed a significant association with lesions number (p<0.000032). No marker showed significant association with lesion length. It is suggested that the QRL identified in the field trials is the same identified in the greenhouse experiment, since they are linked to the same marker.

Controle genético da antracnose foliar em milho

Variability in resistance to corn (Zea mays) leaf anthracnose caused by Colletotrichum graminicola was detected among four lines and two hybrids for the variables: total area of lesion (ATL), average lesion area (AML), total lesion length (CTL), average lesion length (CML) and lesion number (NL). No differential interaction was detected among isolates of C. graminicola and inbred lines and hybrids. In studies about the mode of resistance to foliar anthracnose, the inbred lines L186 and L64 were susceptible and resistant, respectively, whereas the hybrid L184 x L64 were resistant. The observed frequency of susceptible and resistant F2 plants derived from selfing of F1 plants from the cross L186 x L64 indicated monogenic and dominant control of resistance

Controle genético da resistência à mancha-de-Phaeosphaeria em milho

The Phaeosphaeria leaf spot, of ample occurrence in Brazil, has been causing an expressive reduction in the corn yield in the country. Thus, the development of resistant hybrids to this disease is one of the main objectives of corn breeding programs. Information about the genetic control of resistance to the disease is necessary so that the programs can be efficient. The main goal of this study was to determine the genetic control of resistance to the Phaeosphaeria leaf spot in maize through the assessment of the generation means from two crossing between a resistant inbred line (DAS95 or DAS72) with a susceptible line (DAS21) under natural infection conditions of the disease. The experiment was carried out in Indianopolis (MG) in two sowen dates, October and November, 2000. The randomized blocks design with three repetitions was utilized. The evaluation to resistance was performed thirty days after the flowering using a diagrammatic scale of percentage of the total foliar tissue of the plant affected by the disease. Disease severity means of parental lines and generations F1, F2, RCP1 and RCP2 were analysed according to the model by MATHER & JINKS (1971). Genetic variation due to additive effects varied from 73% to 84% whilst dominant effects ranged from 13% to 23%. In both studied population, the predominance of gene additive over dominant effects was evidented. The inheritance values were high, varying from 61% to 88%. These results indicate favourable conditions to develop new resistance lines to Phaeosphaeria leaf spot with the studied populations.

Sensibilidade dos microssatélites para determinar a pureza varietal em sementes de milho

Genotype contamination in seed production of maize inbred seed lots is not tolerated, i.e. the presence of only one seed from another genotype in a lot is sufficient to discard this lot. Many procedures have been studied to detect genotype purity in different crops, including molecular markers based on DNA polymorphism. This research aimed to evaluate the sensitivity of the microsatellite technique to detect the contaminating seeds in maize inbred lines. Four inbred lines (L1, L2, L3 and L4) were used. Samples of 100 seeds each of L1 were prepared considering L2 as a contaminant while seeds of L4 were contaminants in L3 seed lots. To simulate different contamination levels, 0, 1, 2, 5 and 10 seeds of the foreign genotype were mixed with the inbred line and then DNA was extracted from each treatment. Successive DNA samples dilutions of 0.01; 0.013; 0.02; 0.04; 0.1; 0.2; 1; 2; 5; 10 and 100% were also realized with to simulate low contamination levels. For both analysis microsatellites amplifications were performed with the primers BNLG125 for L1+L2 and BNLG240 for L3+L4. The results showed that the microsatellite technique is efficient to determine the varietal purity of inbred maize used in this research. The sensitive technique is able to detect a 0.01% DNA contaminant level. Standardization and intensity were better when a polyacrylamide matrix was used. The presence of foreign DNA in the contaminated lots was efficiently detected with the microsatellite technique, indicating the usefulness of this procedure to detect the presence of foreign seeds within maize inbred lots.

Inheritance of resistance to anthracnose stalk rot (Colletotrichum graminicola) in tropical maize inbred lines

applied into the stalk. Internal lesion length was directly measured by opening the stalk thirty days after inoculation. Results indicated contrasting modes of inheritance. In one population, dominant gene effects predominated. Besides, additive x dominant and additive x additive interactions were also found. Intermediate values of heritability indicated a complex resistance inheritance probably conditioned by several genes of small effects. An additive-dominant genetic model sufficed to explain the varia tion in the second population, where additive gene effects predominated. Few genes of major effects control disease resistance in this cross. Heterosis widely differed between populations, which can be attributed to the genetic background of the parental resistant lines.

Comparison of yield damage of tropical maize hybrids caused by anthracnose stalk rot

The objective of this study was to estimate the reduction in yield caused by Colletotrichum graminicola in resistant and susceptible maize hybrids inoculated at different stages of development. Two trials were conducted in different environmental conditions in a randomized block design with treatments arranged as a 2 × 5 factorial scheme and three replications. Treatments consisted of two hybrids (H8664, resistant and H8621, susceptible) inoculated at three growing stages (8-leaf, 12-leaf and tasseling stage). Internal lesion length, adjusted yield, and yield components (length, diameter and ear weight) were evaluated 120 days after emergence. Significant differences in yield and ear weight were detected in the susceptible hybrid inoculated at the earliest stage: yield was reduced by 16.1 and 20.2% in the first and second experiment, respectively. Although lesion length in the susceptible hybrid was approximately three times greater than in the resistant, there were no significant differences in lesion length among treatments for each hybrid. However, there were differences in the number of dead plants and ear weight. It is suggested that damage caused by early infection with C. graminicola results mainly from plant death and reduction in ear weigh rather than from the extent of colonization of the stalk.

Natural occurrence of Colletotrichum coccodes (Wallr.) Hughes causing anthracnose on pepper (Capsicum annuum L.) in Brazil.

, already reported in Brazil ontomato (Lopes & Avila, Doencas do tomateiro, 2005, 151p.) andpotato (Mendes et al., Fungos em plantas no Brasil, 1998, 569p.).The pathogen was isolated through collecting conidia directlyfrom the lesions and plating them on PDA medium. Ripe fruitswere inoculated by a small drop (20µL) of 10

Germinação e penetração de Stenocarpella macrospora em folhas de milho

The success of a parasitic relationship between fungal pathogens and their host plants depends on pre-infectional events. In this work scanning electron microscopy was used to study the events that occur between germination and penetration of the fungus Stenocarpella macrospora on maize (Zea mays) leaves. Plants of the hybrid Das-8492 were cultivated in greenhouse, and inoculated at the five-six leaves stage with 300 µl of a conidial suspension of 105 conidia/ml. Disk samples of leaf tissue were collected at different times after inoculation and prepared for analysis by scanning electron microscopy. It was verified that 86% of the conidia germinated between 12-15 h whereas apressoria formation occurred 18 h after inoculation. The presence of an extra cellular matrix also was observed during germination and penetration, suggesting that it may have a role in pathogenesis.