João Flávio Veloso Silva

Identification of a new major QTL associated with resistance to soybean cyst nematode (Heterodera glycines)

Abstract Resistance of soybean [Glycine max (L.) Merr.] to cyst nematode (SCN) (Heterodera glycines Ichinohe), one of the most destructive pathogens affecting soybean, involves a complex genetic system. The identification of QTLs associated with SCN resistance may contribute to the understanding of such system. The objective of this work was to identify and map QTLs for resistance to SCN Race 14 with the aid of molecular markers. BC3F2:3 and F2:3 populations, both derived from an original cross between resistant cv. Hartwig and the susceptible line BR-92–31983 were screened for resistance to SCN Race 14. Four microsatellite (Satt082, Sat_001, Satt574 and Satt301) and four RAPD markers (OPAA-11795, OPAE-08837, OPR-07548 and OPY-072030) were identified in the BC3F2:3 population using the bulked segregant analysis (BSA) technique. These markers were amplified in 183 F2:3 families and mapped to a locus that accounts for more than 40% of the resistance to SCN Race 14. Selection efficiency based on these markers was similar to that obtained with the conventional method. In the case of the microsalellite markers, which identify homozygous resistant genotypes, the efficiency was even higher. This new QTL has been mapped to the soybean linkage group D2 and, in conjunction with other QTLs already identified for SCN resistance, will certainly contribute to our understanding of the genetic basis of resistance of this important disease in soybean.

Validação de marcadores microssatélites para a seleção assistida de resistência de soja ao nematóide-de-cisto raças 3 e 14

O objetivo deste trabalho foi validar marcadores microssatelites associados a resistencia as racas 3 e 14 do nematoide-de-cisto (Heterodera glycines Ichinohe) da soja (Glycine max L.), para serem utilizados em programas de selecao assistida por marcadores moleculares (SAM). Microssatelites dos grupos de ligacao A2, D2 e G da soja foram testados em duas populacoes, e suas eficiencias de selecao foram determinadas. As populacoes foram 65 familias F2:3, do cruzamento Msoy8001 (resistente) x Conquista (suscetivel), e 66 familias F2:3, do cruzamento S5995 (resistente) x Renascenca (suscetivel), avaliadas para a resistencia as racas 3 e 14, respectivamente. Familias com indice de femeas de ate 30% foram consideradas moderadamente resistentes. Marcadores dos grupos de ligacao A2 e G apresentaram associacao com a resistencia a raca 3. Os marcadores Satt309 e GMENOD2B explicaram a maior proporcao da variância fenotipica nos diferentes grupos. As combinacoes Satt309+GMENOD2B e Satt309+Satt187 apresentaram eficiencia de selecao de 100%. A resistencia a raca 14 foi associada com marcadores do grupo de ligacao G, e a eficiencia de selecao da combinacao Satt309+Satt356 foi de 100%. Os diferenciais de selecao fenotipica e de selecao assistida mostraram que os dois tipos de selecao podem proporcionar ganhos similares.

INFLUÊNCIA DE BACILLUS SUBTILIS NA ECLOSÃO, ORIENTAÇÃO E INFECÇÃO DE HETERODERA GLYCINES EM SOJA

The utilization of microorganisms for biological control of plant diseases has been studied in the world. In soybean cyst nematode (Heterodera glycines), an important diseases in soybeans, biological control strategies are important tools mostly because the lack of an efficient chemical control. The effect of Bacillus subtilis on H. glycines was studied on greenhouse and laboratory experiments. The presence of B. subtilis reduced the number of appeared H. glycines eggs when under stimulus of soybean exudes. Also, treatment of soybean roots with B. subtilis inhibited the juvenile larvae of H. glycines migration towards the soybean roots. In greenhouse experiments using soil infested with eggs of H. glycines, a reduction in the number of females was observed in the soybean root when both soil and seeds were previously treated with either wettable powder or solution containing B. subtilis. Considering the results of this research, and that H. glycines depends on plant exude for show up and orientation of larvae, it can be assumed that B. subtilis might interfere in the nematode life cicle.

Seleção de isolados de Paecilomyces lilacinus (Thom.) Samson para controle de Meloidogyne paranaensis em tomateiro

Paecilomyces lilacinus is a fungal species used in biological control of nematodes. It is considered one of the most frequently evaluated fungus under field conditions. The present study aimed to select P. lilacinus isolates with regard to their capacity in controlling Meloidogyne paranaensis in tomato. Santa Clara tomato plants were grown in pots and inoculated with M. paranaensis under greenhouse conditions. The tomato plants were replaced 45 days after inoculation with 50 grams of autoclaved rice colonized with P. lilacinus. Forty-five days after fungus inoculation the number of galls, egg masses, number of eggs in root system, aerial part mass weight, root mass weight and P. lilacinus survival in the soil were evaluated. All treatments involving P. lilacinus incorporation reduced the population of M. paranaensis in tomato roots. UEL pae 05, 08, 09, 13, 20, 21, 38, 41, 44, 54, ESALQ 831 e 832 were the best in the control of M. paranaensis, affecting reproduction of the nematodes and showing a high survival rate in the soil.

Size of AT(n) insertions in promoter region modulates Gmhsp17.6-L mRNA transcript levels.

During earlier experiments, an SSR molecular marker (176 Soy HSP) showing high correlation (70%) with resistance/susceptibility to javanese root-knot nematode Meloidogyne javanica was identified in soybean. After being sequenced, results indicated that the SSR 176 Soy HSP marker was inserted in the promoter region of Gmhsp17.6-L gene. It was also detected in this region that resistant genotypes presented insertions between AT(31) and AT(33) in size and susceptible genotypes, AT(9). Gmhsp17.6-L gene coding region presented a perfect match in amino acid sequence in all soybean genotypes. A ribonuclease protection assay showed that Gmhsp17.6-L gene mRNA transcripts were present in all genotypes. A real-time relative quantification (qPCR) indicated in the resistant individuals higher mRNA transcripts levels, which presented in the sequencing more AT(n) insertions. These results suggest that the number of AT(n) insertions inside this promoter region could modulate up or down gene levels. Those findings can lead to the possibility of manipulating, between some limits, the mRNA transcripts levels using different sizes of AT(n) insertions.

Parâmetros genéticos da resistência da soja aonematóide de cisto raça 1

This study aimed at verify the behavior of Recombinant Inbreed Lines, resulting of a cross between Hartwig (resistant parental) and EMGOPA-316 (susceptible parental) to NCS soybean nematode (race 1) and to estimate genetic parameters and those of selection progress. Estimated parameters used the mean female index (IF) obtained through the evaluation of 176 F6 lines for NCS resistance. The genotypes were evaluated in greenhouse. The frequency distribution and the variance analyses were performed to estimate the number of segregating loci involved in the resistance to NCS. The selection progress was estimated (i = -2,154) among the lines evaluated using different numbers of repetitions, as well the herdability (h2). It was concluded that: a) The normality distribution of the average IF, as well the estimated herdability and the number o segregation loci indicated the resistance to NCS (race 1) is poligenic; b) Promising NCS resistant lines were found. However, as the resistance test is difficult a larger number of F6 lines and a larger number of repetitions should be evaluated; c) The necessity of correction due to macroenvironment effects increased the bias of the estimatives.

Inheritance of resistance to soybean cyst nematode races 3 and 14 in soybean RIL and F2 populations

The objective of this work was to evaluate the soybean inheritance of resistance to cyst nematode races 3 and 14. The following populations where evaluated: one population of recombinant inbred lines (RILs) [Hartwig (resistant) x Y23 (susceptible line)] for races 3, 14 and 9; one population of families F2:3 [M-SOY 8001 (resistant) x MB/BR 46 - Conquista (susceptible)] for race 3; and one population of families F2:3 [(S5995 (resistant) x BRSMG Renascenca (susceptible)] for race 14. In RIL populations, four epistatic genes were identified which conditioned resistance to race 14, and three epistatic ones for resistance to races 3 and 9. The lack of one gene provided moderate resistance under all situations. The highest number of genes for resistance to race 14 points out that genes responsible for lower effects might be involved. In population F2:3 from M-SOY 8001 x MB/BR 46 - Conquista, one recessive gene for moderate resistance and two recessive genes complete resistance to race 3 were identified. Two recessive genes conditioning moderate resistance to race 14 were identified in population F2:3 from the crossing S5995 x BRSMG Renascenca. These results will be useful in designing crossings, involving these parentals, with higher possibility to accumulating genes that provide resistance to several SCN races.

Relação entre atributos de solo, população de nematoide das lesões radiculares e crescimento de plantas de soja

Root-lesion nematode (RLN) ( Pratylenchus brachyurus ) is an important challenge to soybean production in Central Brazil due to its widespread occurrence, along with the absence of resistant cultivars and strategies for its management. The aim of this research was to evaluate the relationship among soil properties, RLN populations, and soybean crop growth using geostatistical analysis. The experiment was conducted in a soybean field located in the northern half of Mato Grosso state, in Brazil, with a history of damages by RLN. The results suggest a positive correlation between plant height and values of pH, Ca, Mg, and base saturation. On the other hand, RLN population was positively correlated with organic carbon, cation exchange capacity, and soil potential acidity. Moreover, our findings also indicate that soybean plant growth is reduced under acidic soil conditions, as susceptibility to RLN increases. Thus, the correction of soil acidity to suitable levels for soybean crop becomes an important strategy to minimize damages by RLN.

Intervalo de confiança "bootstrap" como ferramenta para classificar raças do nematóide de cisto da soja

Bootstrap estimates of arithmetic mean of Pickett, Peking, PI88788 and PI90763 soybean genotypes and the confidence intervals obtained through normal theory and bootstrap distribution of this estimator, like the percentile bootstrap and the BCa (bias-corrected and accelerated) of the differentiation parameter of the standard cultivar Lee for susceptibility, are utilized to classify races of soybean cyst nematode. The confidence intervals obtained from bootstrap distribution showed smaller amplitude and were very similar. Therefore, the lower limit of the bootstrap percentile confidence interval was taken as reference level in the bootstrap distribution of the arithmetic mean estimator of the differential genotypes allowing to estimate the empirical probability of a positive or negative reaction and, consequently, to identify the most probable race under specific test.