Avaliação visual e do potencial fotossintético para quantificação da ferrugem do milheto pérola e correlações com a produção Costa, Antonio C.T. da(Universidade Estadual do Oeste do Paraná Centro de Ciências Agrárias); Oliveira, Leandro B. de(Universidade Federal Rural do Rio de Janeiro Instituto de Agronomia Departamento de Fitotecnia); Carmo, Margarida Goréte F. do(Universidade Federal Rural do Rio de Janeiro Instituto de Agronomia Departamento de Fitotecnia) ...
Tropical plant pathology,
10/2009, Letnik:
34, Številka:
5
Journal Article
Recenzirano
Odprti dostop
O presente trabalho teve como objetivo a quantificação da ferrugem, causada por Puccinia substriata var. penicillariae em milheto e avaliar suas correlações com os componentes de produção. A ...quantificação da ferrugem foi realizada por meio de avaliações visuais com auxílio de duas escala descritivas de notas, em cinco plantas por parcela, em três tipos amostras: planta inteira e na quinta e segunda folhas. Com os dados de severidade calcularam-se os valores de área abaixo da curva de progresso da doença (AACPD) e em seguida as correlações residuais (r e) e genéticas (r g) entre os estes valores e a produção de grãos, massa seca total e massa seca da palhada. A avaliação da severidade da ferrugem na segunda folha, a partir do estádio de florescimento do milheto, foi o método mais eficiente para quantificação da doença, pois apresentou melhores correlações com a produção de biomassa e de grãos. Um segundo experimento foi instalado em casa de vegetação para quantificação indireta da ferrugem através da medida do potencial fotossintético (Fv/Fm), por emissão de fluorescência da clorofila "a", em folhas de seis genótipos: HKP, Guerguera, Souna III, BRS 1501, ENA 1 e o composto ENA 2. Neste ensaio, ficou demonstrado que a ferrugem afetou o potencial fotossintético de folhas de milheto e a medição da fluorescência da clorofila "a", que é rápida e independe do avaliador, poderá vir a ser uma variável fisiológica para a seleção de genótipos resistentes à ferrugem.
The aim of the present study was to quantify rust disease caused by Puccinia substriata var. penicillariae in pearl millet and its correlations with yield components. The rust quantification was done by visual evaluations using two scales based on visual description, in five plants per plot in three different kinds of samples: entire plant and fifth and second leaves. Using these values of the area under the disease progress curve (AUDPC) the residual correlation (r e) and genetic correlations (r g) were calculated between the values of AUDPC and production of grain, total dry matter and stover dry weight. The evaluation of rust severity on the second leaf, from the flowering stage of pearl millet, was the most efficient method to quantify the disease because of the higher correlation with biomass and grain production. A second assay was conducted in a greenhouse to quantify rust disease indirectly by measuring photosynthetic potential (Fv/Fm), by chlorophyll "a" fluorescence emission, in leaves of six genotypes: HKP, Guerguera, Souna III, BRS 1501 and ENA 1 and bulk ENA 2. In this assay, it was demonstrated that rust affected the photosynthetic potential of pearl millet leaves and that the measurement of chlorophyll "a" fluorescence, which is rapid and independent of evaluator, would be a physiological parameter for selection of rust-resistant genotypes.
The identification of sources of resistance to Fusarium head blight (FHB) in bread wheat is key to the sustainable management of the disease. An accurate characterization of resistance is critical; ...however, the experimental designs commonly used disregard germplasm variability in anthesis date (moment of highest disease susceptibility). Here, an accurate methodology for assessing type II resistance to FHB in the field was developed. Individual spikes of 126 RILs were point-inoculated at their optimum moment. The effect of anthesis date and environmental conditions on the prediction of bread wheat lines' performance was established. Anthesis date explained 26% of the total phenotypic variation for Severity at 21 days post-inoculation (dpi). Including this factor in the model increased the accuracy of the best linear unbiased predictors through a reduction of the residual and genotype by environment interaction variances. In addition, the genotypic variance and heritability of FHB severity at 21 dpi were increased. In summary, including the anthesis date effect in the model lead to a more precise and objective characterization of the level of genetic type II resistance to FHB under field conditions.
•Accurate assessment of resistance to Fusarium head blight in wheat is critical.•Anthesis date variation between genetic materials leads to confounding effects.•Considering anthesis date variation improves model prediction of type II resistance.•Precise field phenotyping can improve QTL mapping and generation of resistant lines.
Citrus huanglongbing (HLB), associated with 'Candidatus Liberibacter asiaticus' (Las), disseminated by Asian citrus psyllid (ACP), has devastated citrus in Florida since 2005. Data on HLB occurrence ...were stored in databases (2005 to 2012). Cumulative HLB-positive citrus blocks were subjected to kernel density analysis and kriging. Relative disease incidence per county was calculated by dividing HLB numbers by relative tree numbers and maximum incidence. Spatiotemporal HLB distributions were correlated with weather. Relative HLB incidence correlated positively with rainfall. The focus expansion rate was 1626 m month
, similar to that in Brazil. Relative HLB incidence in counties with primarily large groves increased at a lower rate (0.24 year
) than in counties with smaller groves in hotspot areas (0.67 year
), confirming reports that large-scale HLB management may slow epidemic progress.
Soybean (
L. Merr.) production is influenced by planting date, but its impact on yield in fields infested with
(Tassi) Goid. is unknown. A 3-year study was conducted in
-infested fields to assess the ...effects of planting date (PD) on disease severity and yield using eight genotypes, four of which are reported to be susceptible to charcoal rot (S), and four reported with moderate resistance (MR) to charcoal rot (CR). The genotypes were planted in early April, early May, and early June under irrigated and nonirrigated conditions. There was planting date by irrigation interaction for area under the disease progress curve (AUDPC) where May PD was significantly lower compared to April and June PDs in irrigated environments but not in nonirrigated environments. Correspondingly, yield in April PD was significantly lower than that of May and June. Interestingly, yield of S genotypes increased significantly with each subsequent PD, while yield of MR genotypes remained high across all three PDs. The interaction of genotypes by PD on yield revealed that the MR genotypes DT97-4290 and DS-880 had the greatest yields in May compared to April. While May PD had a decreased AUDPC and an increased yield across genotypes, the result of this research suggests that in fields infested with
, early May to early June planting coupled with appropriate cultivar selection provides maximum yield potential for western Tennessee and mid-southern soybean growers.
Shade effects on coffee rust are controversial, possibly because shade helps to prevent high fruit loads, which decreases leaf receptivity to the pathogen but, at the same time, might provide a ...better microclimate for germination and colonization. These two probable antagonistic pathways are combined under natural conditions. In order to clarify their individual effects, we dissociated the two factors by manually homogenising fruit loads under two light exposure situations, under shade and in full sunlight. The trial was set up in Turrialba, Costa Rica at 600 m of elevation, in a coffee plot initially under shade provided by the tree legume Erythrina poeppigiana. The plot was subdivided into two subplots: one was maintained under shade, whereas shade was eliminated in the second subplot. In each subplot, we removed fruiting nodes from 40 coffee plants in order to obtain the following four levels: none, 150, 250, and 500 fruiting nodes per coffee plant. Coffee rust incidence and severity, along with plant growth and defoliation, were assessed on these coffee plants over a period of two years. Air and leaf temperatures, leaf wetness and relative humidity were also monitored. As expected, the intensity of the coffee rust epidemic increased in line with fruit load. We quantified a 28.9% increase in coffee rust incidence and a 129.2% increase in severity on plants with 500 fruiting nodes as compared to plants with no fruits. With the homogenised fruit load, the intensity of the coffee rust epidemic was greater in the shaded subplot, with a 21.5% increase in incidence and a 22.4% increase in severity. Two mechanisms were suggested. Firstly, we highlighted a dilution effect due to host growth which was 25.2% and 37.5% greater in full sunlight when considering new leaves or new leaf area respectively. Secondly, the microclimate was more conducive to coffee rust under shade, with lower intra-day temperature variations, due to lower maxima, and a higher leaf wetness frequency. We concluded that shade has antagonistic effects on coffee rust. Coffee rust is reduced by shade because shade reduces the fruit load. However, with an equivalent number of fruiting nodes, coffee rust incidence and, to a lesser extent, severity were greater under shade. The service provided by shade in controlling coffee rust is necessarily associated with a disservice that consists in reducing yield in the short term.
► Shade effects on coffee rust were studied under several fruit load conditions. ► The intensity of the coffee rust epidemic increased in line with fruit load. ► The intensity of the coffee rust epidemic was greater under shade. ► Dilution effect due to host growth was greater in full sunlight. ► Microclimate was more propitious to coffee rust growth under shade.
ABSTRACT Phytophthora infestans is the most important disease in potato crops. Its control is based on the use of chemical products that have developed pathogen resistance and high economic and ...environmental impacts. To reduce these effects, the use of plant varieties or cultivars resistant to this pathogen has been proposed. The aim of this study was to evaluate the heritability of resistance to this pathogen in a population of elite Solanum phureja genotypes. In this study, 1,355 clones with three replicates from 20 families were included in the evaluation. Heritability was assessed in the broad and narrow senses. Results of the relative area under the disease progress curve varied between 0.08 and 0.64, indicating that the population contains genes that code for resistance. Heritability in both directions (narrow 0.022 and broad 0.255) showed significant differences, indicating an influence of dominance genetic effects and environmental effects. Thus, to use these genotypes in potato breeding programs, hybridization methods should be used instead of selection methods.
Verticillium dahliae
Kleb., the causal agent of Verticillium wilts, is a devastating plant disease affecting many plant species. Fungus
V. dahliae
was detected in a partially artificially established
...Acer pseudoplatanus
L. forest stand in central Slovenia. This finding incited further study about the risk of different sources of
V. dahliae
isolates for maples in forests and the pathogenicity of three
V. dahliae
isolates of different origins was tested on saplings of
A. pseudoplatanus
,
A. platanoides
L., and
A. campestre
L. The inoculated saplings exhibited disease symptoms, i.e., leaf necrosis and wilting. At the end of the pathogenicity test, typical xylem browning was visible on the cross-sections, and the pathogen was successfully re-isolated. The isolates showed significant differences in their pathogenicity to specific maple hosts, with the agricultural isolate (originated from bell pepper) being the most aggressive on all three maple species. The disease severity index (DSI) and relative area under the disease progress curve (rAUDPC), as well as the success of re-isolation, indicate that
A. platanoides
is the most susceptible to inoculation with
V. dahliae
. In addition, significant differences in sapling biomass were observed between treated and control plants. These results suggest that maples in forest stands are threatened by
V. dahliae
, and biosecurity measures should be considered and implemented in forest management to reduce the transmission and potential spread of the pathogen.
Because of its known anti-bacterial properties, we explored the potential of
Xanthium strumarium
, an invasive, enormous mass-producing weed, for the control of
Ralstonia solanacearum
which causes ...bacterial wilt (BW) of tomato. Both in-vitro and
in-planta
experiments were conducted, using different concentrations of the dried powders of the plant parts applied to infested soil at different times. Addition of a 20% (w/v) aqueous extract of leaf powder or succulent shoot powder to wells cut in nutrient agar inhibited growth of
R. solanacearum
. In
in-planta
experiments, 4.5% (w/w) leaf powder applied to artificially infested soil 10 days before transplant (DBT), produced the best effect and enhanced root length, shoot length, and plant fresh bio-mass by 64%, 37%, and 42%, respectively, as compared to inoculated control. Leaf powder also lowered the area under disease progress curve (AUDPC) by 38%, and the pathogen counts (g
−1
dry soil) by 1.202 log
10
units. Succulent shoot powder (4.5% w/w) applied 20 DBT proved to be better than other application times and increased root length, shoot length, and plant fresh bio-mass by 55%, 42%, and 57%, respectively, as compared to inoculated control. Succulent shoot powder also decreased AUDPC by 35%, and the pathogen counts (g
−1
dry soil) by 1.294 log
10
units. Our data strongly suggest that 4.5% (w/w) of leaf or succulent shoot powder, applied 20 DBT, can be an effective component of the integrated disease management (IDM) against BW.
The severity and temporal dynamics of sorghum anthracnose on six and nine sorghum genotypes were evaluated on field plots during 2014 and 2015 cropping years in Southwestern Ethiopia, respectively. ...Anthracnose severity was assessed as the proportion of leaf area affected by the disease. 12 consecutive time point anthracnose severity assessments and their mean severity, disease progress rate, AUDPC, grain yield and yield related components were used to evaluate the response of the genotypes. In the year 2014 and 2015, the mean anthracnose severity was varying from 65 to 79 PSI and 54–82 PSI among six and nine sorghum genotypes, respectively. AUDPC varied from 5063 to 6113%-day and 4171 to 6383%-day in the year 2014 and 2015, respectively. BRC-378 and BRC-245 genotypes consistently had the lowest disease levels and highest grain yields during the two experimental years. The disease pressure was reduced, whereas grain yield and 1000-seed weight of the genotypes were increased in 2015 cropping year. Anthracnose severity was strongly correlated with weather variables and showed strong negative associations with grain yield of all tested sorghum genotypes.
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