The use of resistant genotypes is the preferred method to control orange rust of sugarcane (Saccharum spp) caused by Puccinia kuehnii. This approach has been adopted in Brazil but outbreaks of the disease on previously resistant varieties showed that the efficacy of this method is limited and requires a better understanding of pathogen diversity. Nevertheless, adequate molecular markers for examining pathogen diversity at population level are not available, which limits the success of orange rust control by genetic resistance. Therefore, two independent investigations were conducted to examine genetic diversity of P. kuehnii from São Paulo state, the most important sugarcane growing state of Brazil. First, simple‐sequence repeat (SSR) markers were developed in the present work and genotypic diversity of orange rust isolates from different locations investigated. Second, phenotypic diversity was examined by the single‐pustule inoculation technique on P. kuehnii isolates retrieved from three susceptible commercial sugarcane cultivars. A total of 96 SSR markers were generated and tested for this species. Subsequently, 29 isolates of P. kuehnii were fingerprinted with nine SSR markers to estimate the genotypic diversity by neighbour‐joining and 3D principal coordinates. The 29 isolates of the pathogen clustered into four main groups, which were identified by three SSR markers (NPRL_PK_108a, NPRL_PK_162_spka and NPRL_PK_221_spka). Phenotypic data at 21 days after the single‐pustule inoculation showed that P. kuehnii from highly susceptible commercial cultivars harboured a small proportion of variants capable of causing disease on resistant cultivars. A differential reaction was demonstrated for the most virulent variant in a repeated experiment confirming the existence of races within P. kuehnii in Brazil.
The use of resistant varieties is the ideal method to control rusts. Nevertheless, knowing the pathogen’s diversity is fundamental to the success of this measure. Diversity can be analyzed phenotypically and/or genotypically. For phenotypic diversity, the reaction of genotypes is assessed by means of inoculations of the pathogen generally obtained from several uredinia. One handicap of this technique is its impossibility to detect diversity among these uredinia, assuming that they are all homogenous. Therefore, the aim of the present study was to develop a single uredinium technique for Puccinia kuehnii to be used in studies of rust diversity in sugarcane. The comparison between the two inoculation methods was done by employing urediniospores from SP89-1115 on the varieties SP89-1115 (susceptible) and RB975201 (resistant). The adopted design was completely randomized with five and seven replicates, respectively, examining incubation, latency, disease score, and injured area at 14 and 21 days. The two inoculation techniques were significantly equal for the susceptible variety, considering all evaluated parameters. For the resistant genotype, a significant difference was identified in the injured area and such difference did not interfere in the classification of the reaction of the material since values were below 1%. The single uredinium technique developed in this study showed to be reliable since the genotypic profile of the inoculated fungus was similar to that of pathogens from the produced lesions.
RESUMO A ferrugem alaranjada (Puccinia kuehnii) tem prejudicado a produtividade da cana-de-açúcar no Brasil. O uso de variedades resistentes é o melhor método de controle da doença. No entanto, o sucesso dessa medida está intimamente ligado à correta avaliação da reação do material e diversidade do patógeno. Escalas de notas da doença e porcentagem de área lesionada são os parâmetros mais empregados para estudar resistência de cana-de-açúcar. Já a diversidade do patógeno é examinada por um conjunto de variedades diferenciadoras, o que ainda não está estabelecido para esse patossistema. Portanto, o presente trabalho estudou diferentes parâmetros para avaliar a reação de variedades comerciais de cana-de-açúcar à P. kuehnii. Três isolados do patógeno foram inoculados uma única vez em cinco variedades de cana-de-açúcar e sua reação examinada aos 21, 28, 35 e 42 dias após, empregando-se escala de notas. A quantidade e viabilidade de esporos também foram investigadas em dois diferentes ensaios, 42 dias depois da inoculação: primeiro, urediniósporos da RB855156 oriundos de lesões com classificação distintas: nota 2 (resistente) e nota 3 (suscetível); segundo: urediniósporos advindos de lesões com mesma classificação de doença, mas de variedades diferentes: RB855156 (suscetível) e RB975201 (resistente). Dados do presente estudo mostraram que a reação da RB855156 variou em função da época da avaliação, sendo resistente na primeira e suscetível na última. Além disso, viabilidade de urediniósporos foi o parâmetro que conseguiu diferenciar genótipos resistentes dos suscetíveis, sendo superior aos outros parâmetros que vem sendo empregados, como tamanho, abertura de pústulas e quantidade de urediniósporos.
A considerable part of fresh plant-based food has been discarded as waste, although it could be used to make organic compost for growing plants, retaining nutrient that would be discarded without any control in the environment. The aim of this study was to produce an organic compost using fresh vegetable food discarded from restaurants and mowed grass and to evaluate it for production of lettuce. The compost was produced and mixed with the commercial substrate Tropstrato HT Hortaliças® to occupy 0, 5, 10, 15, 20 or 25% of the volume of the mixture, which was used to grow Imperial and Imperial Roxa cultivars in the first experiment, and Camila and Red Star lettuce cultivars in the second one. The experiments were conducted under protected environment, organized in a 6x2 factorial scheme, following completely randomized design with three replicates. Chemical analyses of the substrate and compost and measurements of plant size and mass were carried out. The addition of compost caused an increase in all measurements of the plant traits, with the maximum estimated increase ranging from 1.7 to 9.0 times that estimated for the absence of compost in the plant growth substrate. Maximum estimated values for size and mass were observed with compost concentrations ranging from 20.1 to 26.7% of the mixture volume. The production of organic compost and its mixture with a commercial substrate proved to be an alternative for lettuce production, giving a better destination to the organic residues and promoting a reduction in the use of industrial inputs.
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