Variability of root traits in common bean genotypes at different levels of phosphorus supply and ontogenetic stages

Selection of common bean (Phaseolus vulgaris L.) cultivars with enhanced root growth would be a strategy for increasing P uptake and grain yield in tropical soils, but the strong plasticity of root traits may compromise their inclusion in breeding programs. The aim of this study was to evaluate the magnitude of the genotypic variability of root traits in common bean plants at two ontogenetic stages and two soil P levels. Twenty-four common bean genotypes, comprising the four growth habits that exist in the species and two wild genotypes, were grown in 4 kg pots at two levels of applied P (20 and 80 mg kg-1) and harvested at the stages of pod setting and early pod filling. Root area and root length were measured by digital image analysis. Significant genotype × P level and genotype × harvest interactions in analysis of variance indicate that the genotypic variation of root traits depended on soil nutrient availability and the stage at which evaluation was made. Genotypes differed for taproot mass, basal and lateral root mass, root area and root length at both P levels and growth stages; differences in specific root area and length were small. Genotypes with growth habits II (upright indeterminate) and III (prostrate indeterminate) showed better adaptation to limited P supply than genotypes of groups I (determinate) and IV (indeterminate climbing). Between the two harvests, genotypes of groups II and III increased the mass of basal and lateral roots by 40 and 50 %, respectively, whereas genotypes of groups I and IV by only 7 and 19 %. Values of the genotypic coefficient of determination, which estimates the proportion of phenotypic variance resulting from genetic effects, were higher at early pod filling than at pod setting. Correlations between shoot mass and root mass, which could indicate indirect selection of root systems via aboveground biomass, were higher at early pod filling than at pod setting. The results indicate that selection for root traits in common bean genotypes should preferentially be performed at the early pod-filling stage.

SPATIAL VARIABILITY OF SOIL PROPERTIES IN AN AGRARIAN REFORM SETTLEMENT

ABSTRACT The study of soil chemical and physical properties variability is important for suitable management practices. The aim of this study was to evaluate the spatial variability of soil properties in the Malhada do Meio settlement to subsidize soil use planning. The settlement is located in Chapadinha, MA, Brazil, and has an area of 630.86 ha. The vegetation is seasonal submontane deciduous forest and steppe savanna. The geology is formed of sandstones and siltstones of theItapecuru Formation and by colluvial and alluvial deposits. The relief consists of hills with rounded and flat tops with an average altitude of 67 m, and frequently covered over by ferruginous duricrusts. A total of 183 georeferenced soil samples were collected at the depth of 0.00-0.20 m inPlintossolos, Neossolo andGleissolo. The following chemical variables were analyzed: pH(CaCl2), H+Al, Al, SB, V, CEC, P, K, OM, Ca, Mg, SiO2, Al2O3, and Fe2O3; along with particle size variables: clay, silt, and sand. Descriptive statistical and geostatistical analyses were carried out. The coefficient of variation (CV) was high for most of the variables, with the exception of pH with a low CV, and of sand with a medium CV. The models fitted to the experimental semivariograms of these variables were the exponential and the spherical. The range values were from 999 m to 3,690 m. For the variables pH(CaCl2), SB, and clay, there are three specific areas for land use planning. The central part of the area (zone III), where thePlintossolos Pétricos and Neossolos Flúvicos occur, is the most suitable for crops due to higher macronutrient content, organic matter and pH. Zones I and II are indicated for environmental preservation.

Genetic variability of Brazilian phytoplasma and spiroplasma isolated from maize plants

The objective of this work was to characterize the genetic variability of phytoplasma and Spiroplasma kunkelii isolated from maize plants showing symptoms of stunt collected from different Brazilian geographic regions. A DNA fragment of 500 base pairs (bp) was amplified from the spiralin gene in S. kunkelii and one fragment of 1,200 bp was generated from 16S rDNA gene in phytoplasma. The partial sequences of the spiralin gene showed similarity of 98% among the isolates of S. kunkelii analyzed. These sequences were compared with the sequence of the spiralin gene from other Spiroplasma species deposited in the GenBank, resulting in a similarity varying from 76.9% to 88.1%. The 16S rDNA sequence from the phytoplasma were completely similar within the Brazilian isolates and showed up to 98% of the similarity with sequences already found from other phytoplasmas. A very narrow genetic variability was detected by these gene fragments within phytoplasma and Spiroplasma analyzed. However, other genomic regions with higher polymorphic levels shall be identified in order to better evaluate the genetic diversity within these microorganisms population.

Genetic variability of the Brazilian hair sheep breeds

The objectives of this work were to investigate the genetic structure of the Brazilian hair sheep breeds and to determine the origin of the Santa Inês breed. Molecular similarity was determined using Randomly Amplified Polymorphic DNA - Polymerase Chain Reaction markers in 238 individuals from five naturalized sheep breeds: Santa Inês (48 animals), Rabo Largo (48), Somali (48), Morada Nova (48) and Bergamasca (46), collected in Goiás, Sergipe, Bahia, and Ceará States as well as in the Federal District. Fifty-four loci were selected from 19 primers, after a pilot test using 140 primers. Qualitative analyses indicate diagnostic markers for all breeds. All breeds were significantly different from each other. Interbreed differences were explained by 14.92% of the total variation. Santa Inês clustered with Bergamasca (97% bootstrap) and with Rabo Largo, composing the third member of the group (81% bootstrap) while Morada Nova and Somali breeds clustered separately. Each breed should be considered as a separate management and conservation unit, and special care should be taken with Rabo Largo, Morada Nova and Somali breeds, represented by small herds in Brazil.

Genetic variability of Brazilian rice landraces determined by SSR markers

The objective of this study was to evaluate the genetic variability of rice (Oryza sativa) landraces collected in Brazilian small farms. Twelve simple sequence repeat (SSR) markers characterized 417 landraces collected in 1986, 1987 and 2003, in the state of Goiás, Brazil. The number of landraces with long and thin grain type increased in the evaluated period, probably due to market demand. Based on the molecular data, the genetic variability increased during this period and, as per to the factorial correspondence analysis, most of the accessions were grouped according to the year of collection. The incorporation of modern rice cultivars in landrace cultivation areas and the selection carried out by small farmers are the most probable factors responsible for increasing landrace genetic variability, during the evaluated period. Genotype exchange between farmers, selection practice and local environmental adaptation are able to generate novel adapted allele combinations, which can be used by breeding programs, to reinitiate the process.

Variability of ricin content in mature seeds of castor bean

The objective of this work was to evaluate ricin concentration in castor bean seeds (Ricinus communis) of 20 accessions from the Banco de Germoplasma de Mamoneira of the Embrapa Algodão, Campina Grande, PB, Brazil, using the Enzyme Linked Immunosorbent Assay. Significant differences were observed among accessions. BRA 3271 had the highest ricin concentration in seeds (32.18 ng µg-1), and BRS Paraguaçu had the lowest (3.53 ng µg-1). There is the possibility of selecting genotypes with different ricin concentrations, which can be used according on the interest of the breeding programs.

Genetic variability of rice recurrent selection populations as affected by male sterility or manual recombination

The objective of this work was to determine the effect of male sterility or manual recombination on genetic variability of rice recurrent selection populations. The populations CNA-IRAT 4, with a gene for male sterility, and CNA 12, which was manually recombined, were evaluated. Genetic variability among selection cycles was estimated using14 simple sequence repeat (SSR) markers. A total of 926 plants were analyzed, including ten genitors and 180 individuals from each of the evaluated cycles (1, 2 and 5) of the population CNA-IRAT 4, and 16 genitors and 180 individuals from each of the cycles (1 and 2) of CNA 12. The analysis allowed the identification of alleles not present among the genitors for both populations, in all cycles, especially for the CNA-IRAT 4 population. These alleles resulted from unwanted fertilization with genotypes that were not originally part of the populations. The parameters of Wright's F-statistic (F IS and F IT) indicated that the manual recombination expands the genetic variability of the CNA 12 population, whereas male sterility reduces the one of CNA-IRAT 4.

Genetic variability of marine shrimp in the Brazilian industry

The objective of this work was to estimate the genetic variability level and distribution in Brazilian broodstocks of marine shrimp (Litopenaeus vannamei). Nine of the country's largest hatcheries were evaluated using codominant and highly polymorphic microsatellite markers. The results obtained from genotyping of ten microsatellite loci are indicative of genetic variability that is compatible with that found in wild populations of L. vannamei in Mexico and Central America. A possible explanation is the highly diversified and relatively recent origin of the available broodstocks. Bayesian analysis detected a signal for five founding populations. The distribution of genetic distances partially reflects geographical location, and this information will be useful for the creation of new broodstocks. Therefore, L. vannamei genetic variability among nine of the largest national hatcheries can be considered high.

Genetic variability of hull-less barley accessions based on molecular and quantitative data

The objective of this work was to characterize and quantify the genetic, molecular, and agronomic variability of hull-less barley genotypes, for the selection of parents and identification of genotypes adapted to the irrigated production system in the Brazilian Cerrado. Eighteen hull-less barley accessions were evaluated, and three covered barley accessions served as reference. The characterization was based on 157 RAPD molecular markers and ten agronomic traits. Genetic distance matrices were obtained based on molecular markers and quantitative traits. Graphic grouping and dispersion analyses were performed. Genetic, molecular, and agronomic variability was high among genotypes. Ethiopian accessions were genetically more similar, and the Brazilian ones were genetically more distant. For agronomic traits, two more consistent groupings were obtained, one with the most two-rowed materials, and the other with six-rowed materials. The more diverging materials were the two-rowed CI 13453, CN Cerrado 5, CN Cerrado 1, and CN Cerrado 2. The PI 356466, CN Cerrado 1, PI 370799, and CI 13453 genotypes show agronomic traits of interest and, as genetically different genotypes, they are indicated for crossing, in breeding programs.

Intraspecific variability of Holostylis reniformis: concentration of lignans, as determined by maceration and supercritical fluid extraction (SFE-CO2), as a function of plant provenance and plant parts

Maceration and supercritical fluid extraction were used to prepare extracts from parts of plants (Holostylis reniformis) collected in two different regions of Brazil. ¹H NMR, HPLC-DAD-ESI/MS, HPLC-DAD, GC-MS, and chemometric techniques were used to analyse lignans in the extracts and showed that yields of SFE-CO2 were less than or equal to those of hexane maceration extracts. These analyses, in conjunction with the concentrations of aliphatic hydrocarbons, fatty acids and their methyl and ethyl derivatives in the extracts, also allowed the chemical composition of parts and provenance of the plant to be differentiated.

Molecular and pathogenic variability of Drechslera isolates from oats

Severe epidemics of leaf blotch and black leaf spot of oat (Avena sativa) caused by Drechslera avenae and Drechslera sp., respectively, are frequently observed in the State of Paraná, Brazil. Although some morphological differences between the isolates causing two different symptoms were noticed, the genetic relationship between them was not clear. Twenty-four isolates of D. avenae and Drechslera sp, collected between 1996-98, were assessed for the genetic variability by molecular and pathogenic analyses. The amplification products using primer pair ITS4/ITS5 showed a fragment length of approximately 600 bp for all the isolates except for one black spot isolate, where the fragment length was approximately 550 bp. Restriction enzymes Hinf I and Taq I, that cut in the ITS region, produced similar restriction patterns for all the isolates, whereas four others produced variable restriction patterns. RAPD analysis also showed distinctive patterns for some isolates. No clear difference between the black spot and the leaf blotch isolates was observed either by the molecular or by the pathogenicity analysis. Nonetheless, the rDNA analysis suggests that Drechslera probably comprises at least three distinct taxa. The results indicate that the difference observed between the isolates originating from two types of symptoms is due to intra-specific variants of D. avenae.

Variability of the anthracnose fungus Colletotrichum graminicola in sorghum genotype mixtures

This paper reports partial results obtained on the variability of Colletotrichum graminicola developed in response to the host diversity generated by three-line combination of sorghum (Sorghum bicolor) genotypes. Nine sorghum lines were used in this study: CMSXS210B, CMSXS112B, CMSXS215B, CMSXS221B, CMSXS169R, CMSXS180R, CMSXS182R, CMSXS227R, and CMSXS116R. A total of 39 treatments on mixtures and pure stands of the component lines were evaluated in the field for the development of anthracnose, as a natural epidemic. Samples of the single spore isolates of the pathogen of each treatment indicated a reduction in the phenotypic diversity and an increase in the frequency of more complex races in genotype mixtures in relation to the pure stands of each genotype.

Variability of the 3' terminal of the polymerase gene of Grapevine leafroll-associated virus 3 isolates from Vale do São Francisco, Brazil

Many viral diseases, including leafroll, which is of great economic importance, affect grapevines (Vitis spp.). A complex of eight viruses [Grapevine leafroll-associated virus (GLRaV) -1 to 8] is associated with this disease. The objective of this study was to compare the variability of the 3' terminal region of the polymerase gene of three isolates of GLRaV-3 (Grapevine leafroll-associated virus-3), from Submédio do Vale do Rio São Francisco (Petrolina-PE) with that of other isolates available at the GenBank, including an isolate from North America and another from Southern Brazil. The viral RNA was extracted from three infected ELISA reactive plants and a fragment of 340 bp was amplified, by RT-PCR, using primers that recognize that portion of the polymerase gene found between nucleotides 8267 and 8606. The three isolates from Vale do Rio São Francisco named Pet-1, Pet-2 and Pet-3, showed similarities ranging from 98% and 94%, respectively to the isolates from North America (AF037268) and Southern Brazilian (AF438411). Considering the whole genome, the main variation found was one amino acid change at position 2766 (F2766Y). These preliminary data indicate the existence of a natural variation among GLRaV-3 isolates from grapevines. This could be due to the vegetative propagation and long cycle of the plant, associated with the error-prone nature of RNA-dependent RNA polymerase.

Variability of the wheat powdery mildew pathogen Blumeria graminis f. sp. tritici in the 2003 crop season

Wheat (Triticum aestivum) powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases attacking this crop, reducing grain yields by 10% to 62% in Brazil. The disease can be controlled by genetic resistance of the host, but the pathogen has physiological specialization, which enables it to infect wheat cultivars that have remained resistant for years. The objective of this work was to evaluate the variability of pathogenic strains of B. graminis f. sp. tritici collected in Brazil and the effectiveness of wheat resistance genes to powdery mildew in the 2003 crop season. Plants of a differential series were inoculated with each monopustular isolate. Thirty-one combinations of effective and ineffective resistance genes were identified. Only the gene Pm4a+... remained totally effective to all isolates, and gene Pm6 was highly effective (below 10% of susceptibility), whereas genes Pm3a and Pm8 were totally ineffective (susceptible to all isolates). Genes Pm3c, D1, and D2 showed low effectiveness (above 50% of susceptibility), and genes Pm1, 2, 4a, 1+?, and 2+Mld had mean effective results to most strains (susceptibility between 10% and 49%). The virulence formula Pm1, 3c, 4a, 6, 1+?, 2+Mld, 4a+..., D2 (effective genes) / 2, 3a, 8, D1 (ineffective genes) was most frequently found, accounting for 15% of the occurrences. The most frequent number of ineffective genes was seven, ranging from three to ten.

Variability of the coat protein gene of Grapevine leafroll-associated virus 3 in Brazil

Leafroll is an economically important disease affecting grapevines (Vitis spp.). Nine serologically distinct viruses, Grapevine leafroll-associated virus-1 through 9, are associated with this disease. The present study describes the coat protein gene sequence of four GLRaV-3 isolates occurring in the São Francisco River basin, Northeastern Brazil. The viral RNA was extracted from GLRaV-3 ELISA-positive plants and the complete coat protein gene was amplified by RT-PCR. Sequences were generated automatically and compared to the complete coat protein sequence from North American (NY1) and Chinese (Dawanhong Nº2 and SL10) GLRaV-3 isolates. The four studied isolates, named Pet-1 through 4, showed deduced amino acid identities of 98-100% (Pet-1 through 3) and 95% (Pet-4) with North American and Chinese isolates. A total of seventeen amino acid substitutions was detected among the four characterized isolates in comparison to the NY1, Dawanhong No.2 and SL10 sequences. The results indicated the existence of natural variation among GLRaV-3 isolates from grapevines, also demonstrating a lack of correlation between sequence data and geographic origin. This variability should be considered when selecting regions of the viral genome targeted for reliable and consistent virus molecular detection.