Sugarcane is one of the most important agricultural crops in the world. However, pathogen infection and herbivore attack cause constant losses in yield. Plants respond to pathogen infection by inducing the expression of several protein types, such as glucanases, chitinases, thaumatins, peptidase inhibitors, defensins, catalases and glycoproteins. Proteins induced by pathogenesis are directly or indirectly involved in plant defense, leading to pathogen death or inducing other plant defense responses. Several of these proteins are induced in sugarcane by different pathogens or insects and have antifungal or insecticidal activity. In this review, defense-related proteins in sugarcane are described, with their putative mechanisms of action, pathogen targets and biotechnological perspectives.
ABSTRACT. The use of genetically resistant cultivars is the best method to reduce losses caused by white mold (Sclerotinia sclerotiorum (Lib.) de Bary). As the best known resistance sources are not adapted, the genetic control of white mold in the common bean must be understood to guide breeding more efficiently. The objective of the present study was to identify the genetic control of the resistance of common bean to white mold by an indirect method using oxalic acid. For this, the descendents of the VC3 cross (susceptible) x G122 (resistant) were used. The trait was assessed by a descriptive key of scores after treatment with oxalic acid. The assessments were made on individual plants (P 1 , P 2 , F 1 , F 2 populations and within F 2:3 families) in a complete randomized design and on family means where the randomized block design was used with two replications. The oxalic acid method was efficient in detecting genetic differences. The additive effects dominated and genetic control was characterized by partial dominance (d/a = 0.47). At least one resistance gene is involved, although the trait is greatly influenced by the environment. The broad sense heritability at the family mean level (0.47) was greater than that obtained at the individual plant level (0.33), indicating that selection should be more efficient based on progeny mean assessments.
Peptidase inhibitors (PIs) are essential proteins involved in plant resistance to herbivorous insects, yet many insect species are able to escape the negative effects of these molecules. We compared the effects of acute and chronic ingestion of soybean peptidase inhibitors (SPIs) on Spodoptera frugiperda and Diatraea saccharalis, two Lepidoptera species with different sensitivities to SPI ingestion. We analyzed the trypsin and chymotrypsin gene expression profiles in both species. Acute exposure of S. frugiperda to the inhibitors activated seven genes (SfChy5, SfChy9, SfChy19, SfChy22, SfTry6, SfTry8, and SfTry10), whereas chronic exposure activated 16 genes (SfChy2, SfChy4, SfChy5, SfChy8, SfChy9, SfChy11, SfChy12, SfChy15, SfChy17, SfChy21, SfChy22, SfTry6, SfTry8, SfTry9, SfTry10, and SfTry12). By contrast, the challenge of D. saccharalis with SPIs did not differentially induce the expression of trypsin- or chymotrypsin-encoding genes, with the exception of DsChy7. Bayesian phylogenetic analysis of S. frugiperda trypsin protein sequences revealed two gene clades: one composed of genes responsive to the SPIs and a second composed of the unresponsive genes. D. saccharalis trypsin proteins were clustered nearest to the S. frugiperda unresponsive genes. Overall, our findings support a hypothesized mechanism of resistance of Noctuidae moths to SPIs, involving gene number expansion of trypsin and chymotrypsin families and regulation of gene expression, which could also explain the variable susceptibility between S. frugiperda and D. saccharalis to these plant inhibitors.
seleção fenotípica e de seleção assistida por marcadores moleculares (SAM). Foram avaliadas 394 famílias, de quatro populações, e seus seis genitores, no Município de Lavras, em dois experimentos: um na geração F 3:4 , na safra das águas de 2005/2006, em látice simples 20x20; e outro na geração F 3:5 , na safra da seca de 2006, em látice triplo 20x20. Foram estimados parâmetros genéticos e fenotípicos, e foi realizada a genotipagem das famílias, com marcadores microssatélites associados a QTL controladores da produção de grãos, previamente identifi cados. Também foram realizadas análises de associação por marcas simples, entre os marcadores e a produção de grãos, e foi obtido um índice para a SAM. A ampla variabilidade entre famílias e as altas estimativas de herdabilidade possibilitaram obter elevados ganhos com a seleção fenotípica. Os marcadores explicaram pequena percentagem da variação fenotípica e apresentaram alta interação QTL x ambiente e QTL x população. A SAM gerou baixos ganhos e a coincidência de famílias selecionadas pelas duas metodologias foi baixa, o que evidencia, neste caso, a inefi ciência da SAM, principalmente pela pouca disponibilidade de marcadores ligados a QTL.Termos para indexação: Phaseolus vulgaris, QTL, locos de características quantitativas, associação por marcas simples, ganho genético, herdabilidade, microssatélites. Phenotypic and marker-assisted selection of common bean families with high grain yieldAbstract -The objective of this work was to select common bean families with high grain yield, using phenotypic and marker-assisted selections (MAS). Evaluations were made for 394 families of four populations and their six parents, in Lavras county, Minas Gerais, Brazil. Two fi eld experiments were conducted: one in the F 3:4 generation, in the rainy season of 2005/2006, using a 20x20 simple lattice design; and other in the F 3:5 generation, in the dry season of 2006, using a 20x20 triple lattice design. Genetic and phenotypic parameters were estimated, and the families were genotyped with microsatellite markers for grain yield quantitative trait loci (QTL), that had been identifi ed previously. Simple marker association analysis was performed between markers and grain yield, and an index was estimated for MAS. The high variability between families and the heritability estimates made high genetic gains possible through phenotypic selection. The markers explained a small percentage of phenotypic variation, and presented high QTL x environment and QTL x population interactions. The MAS achieved small gains, with low coincidence of families selected by both methodologies, showing, in this case, that the MAS ineffi ciency was mainly due to the low number of available markers.Index terms: Phaseolus vulgaris, QTL, quantitative trait loci, simple marker association analysis, genetic gain, heritability, microsatellites. IntroduçãoEm programas de melhoramento de feijoeirocomum, grande atenção deve ser dada à seleção de famílias segregantes promissoras, que darão origem a novas linhagens e cu...
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