High Disease Intensity Research Articles

Field Evaluations of Leaf Spot Resistance and Yield in Peanut Genotypes in the United States and Bolivia.

Field experiments were conducted in 2002 to 2006 to characterize yield potential and disease resistance in the Bolivian landrace peanut (Arachis hypogaea) cv. Bayo Grande, and breeding lines developed from crosses of Bayo Grande and U.S. cv. Florida MDR-98. Diseases of interest included early leaf spot, caused by the fungus Cercospora arachidicola, and late leaf spot, caused by the fungus Cercosporidium personatum. Bayo Grande, MDR-98, and three breeding lines, along with U.S. cvs. C-99R and Georgia Green, were included in split-plot field experiments in six locations across the United States and Bolivia. Whole-plot treatments consisted of two tebuconazole applications and a nontreated control. Genotypes were the subplot treatments. Area under the disease progress curve (AUDPC) for percent defoliation due to leaf spot was lower for Bayo Grande and all breeding lines than for Georgia Green at all U.S. locations across years. AUDPC for disease incidence from one U.S. location indicated similar results. Severity of leaf spot epidemics and relative effects of the genotypes were less consistent in the Bolivian experiments. In Bolivia, there were no indications of greater levels of disease resistance in any of the breeding lines than in Bayo Grande. In the United States, yields of Bayo Grande and the breeding lines were greater than those of the other genotypes in 1 of 2 years. In Bolivia, low disease intensity resulted in the highest yields in Georgia Green, while high disease intensity resulted in comparable yields among the breeding lines, MDR-98, and C-99R. Leaf spot suppression by tebuconazole was greater in Bolivia than in the United States. This result indicates a possible higher level of fungicide resistance in the U.S. population of leaf spot pathogens. Overall, data from this study suggest that Bayo Grande and the breeding lines may be desirable germplasm for U.S. and Bolivian breeding programs or production.

RESISTANCE TO LEAF RUST IN COFFEE CULTIVARS

All the Coffea arabica L. cultivars developed by the IAPAR4 were resistant to rust ( Hemileia vastatrix ) when registered. However, with the appearance of new races these cultivars now present different resistance levels. The aim of this work was to assess the resistance to rust in coffee cultivars developed by the IAPAR. Resistance to the local leaf rust races was assessed in high disease intensity field conditions in August 2007. Twelve coffee cultivars, from IPR 97 to IPR 108, were evaluated. ‘IAPAR 59’ and ‘Catuai Vermelho IAC 81’ were used as resistance and susceptibility standards, respectively. The experimental design was in randomized blocks with nine replications and plots with seven plants. A scale from 1 to 5, based on rust severity, was used to evaluate resistance. Yield evaluation was based on the harvest carried out in June 2007. The cultivars IAPAR 59, IPR 97, IPR 98, IPR 104 and IPR 105 were almost 100 % rust resistant, while IPR 99, IPR 101, IPR 102 and IPR 107 presented approximately 75% of plants with complete resistance. Thus, the resistance gene(s) is probably in heterozygous condition. The cultivars IPR 103 and IPR 108 may present incomplete resistance, while the IPR 100 presented similar susceptibility to ‘Catuai Vermelho IAC 81’ and IPR 106 may also be susceptible.

Herd immunity against new influenza A (H1N1) in pre-vaccinated residents aged over 5 years in Beijing

To explore the herd immunity against influenza A (H1N1) in pre-vaccinated residents aged over 5 years, and therefore to provide data for vaccination policies in high risk populations. From October to December 2009, Beijing CDC conducted a serum survey of the novel influenza A (H1N1) in the local residents, stratified in 10 age groups between 5 years to over 60 years, without H1N1 vaccination history and disease history. Hemagglutination inhibition (HI) assays were performed at Beijing CDC. Statistical significance was determined with geometric mean titer (GMT). 3499 serum samples were tested for HI antibody. The average level of HI antibody was 1:8.03, and 11.06% (387/3499) were sero-positive (HI antibody level ≥ 1:40). In the group aged from 5 to 19 years, the level of HI antibody and the sero-positive rate were higher (HI antibody > 1:8.9, sero-positive rate > 12%). The antibody levels in different groups were affected by age specific morbidity, and the higher antibody level of the school-age group was correlated with higher disease intensity in this population. The data showed that the herd immunity in Beijing was under the optimal level, but influenza A (H1N1) would probably become prevalent in the short coming future.

Dinâmica temporal da mancha foliar da 'Gala' em macieiras conduzidas sob os sistemas de produção convencional e orgânico

Este trabalho objetivou avaliar a dinâmica temporal da Mancha Foliar da 'Gala' em macieira nos sistemas convencional e orgânico de produção, em condições edafo-climáticas do Planalto Catarinense. A incidência e severidade foram quantificadas quinzenalmente, em 100 folhas, distribuídas em quatro ramos da cultivar 'Royal Gala' com 12 repetições, gerando 16 mapas em cada sistema de produção. A severidade foi avaliada de acordo com escala diagramática específica. Com os dados obtidos, foram plotadas curvas de progresso da doença, e as epidemias foram comparadas em relação à a) início do aparecimento dos sintomas (IAS); b) tempo para atingir a máxima incidência e severidade da doença (TAMID e TAMSD); c) valor máximo de incidência e severidade da doença (Imax e Smax); e d) área abaixo da curva de progresso da incidência e severidade da doença (AACPID e AACPSD). Os dados de incidência e severidade foram analisados por meio de análise de regressão linear simples, sendo ajustados para três modelos empíricos, Logístico, Monomolecular e Gompertz. A cultivar 'Royal Gala' foi suscetível ao Colletotrichum sp., e as maiores intensidades de doença foram registradas no sistema de produção orgânico. O modelo mais apropriado para descrever o progresso da doença foi o Logístico e, por meio do uso da incidência, não foram detectadas diferenças significativas entre os sistemas de produção, porém a taxa de progresso da severidade da doença foi significativamente maior no sistema de produção orgânico do que no convencional.

Elaboration and Validation of a Diagrammatic Scale for Epidemiological Studies of Cercospora Leaf Spot of Castor Bean

The castor bean cercospora leaf spot (Cercospora ricinella Sacc. & Berl.) is a common disease in castor bean crop (Ricinus communis L.), causing defoliation and losses. In spite of this, the evaluation of disease severity is an important decision support for adoption of strategies and tactics for disease control. Therefore the objective of this work was to elaborate and to validate a diagrammatic to evaluate cercospora leaf spot severity in the castor bean. The scale was developed based on six treatments with different irrigation depths plus the control treatment without irrigation. Based on disease incidence analysis, it was possible to select different severity levels per treatment, which were used to define the percentage intervals of foliar diseased area of the diagrammatic scale. In view of the inexistence of standardized methods for the quantification of cercospora leaf spot in the field, the levels of 0%, 0.1 to 1%, 1.1 to 10%, 10.1 to 20% and 20.1 to 45% of lesioned foliar area were established, pointing out the observation that in the interval of 20 to 45% leaf fall started to occur. The scale was tested according its accuracy, precision and reproducibility. For that, 40 leaves with different disease severity levels were appraised by 10 users, without and with the scale, with an interval of seven days between evaluations of the same users. The appraisers obtained better results under utilization of the scale. The scale proposed in this work presented appropriate applicability for cercospora leaf spot evaluation in castor bean. Higher disease intensity was observed in the control and in treatments with higher irrigation depth and lower irrigation frequency.

Blast fungus inoculation reduces accumulation and remobilization of pre-anthesis assimilates to rice grains

The importance of stored assimilates for grain development in cereals has been widely recognized, particularly in cereals exposed to stress during the grain filling period. This study was conducted to investigate the effect of the blast fungus Magnaporthe grisea on dry matter accumulation, remobilization and utilization in rice ( Oryza sativa L.) under field conditions. Four rice varieties with various levels of susceptibility to rice blast were grown in 2003 and 2004 under high and low disease intensity, caused by early inoculation and natural infection respectively. High disease intensity reduced plant height, dry matter accumulation, the harvest index and grain yield. Plants grown under high disease intensity translocated fewer stored assimilates to the grain than plants grown under low disease intensity. Dry matter translocation from the vegetative parts to the grain was significantly correlated with dry matter at anthesis (r=0.65, P l). High stress from early leaf blast caused by inoculation with the blast fungus affected overall plant growth and lowered the production of pre-anthesis assimilates, as well as causing severe levels of neck blast that resulted in a low translocation rate during the filling period, and therefore a lower grain yield than in naturally infected plants.

PATOGENISITAS JAMUR KARAT (PUCCINIA PHILIPPINENSIS Syd.), PADA GULMA TEKI (CYPERUS ROTUNDUS L.)

The pathogenicity of a rust fungus (Puccinia philippinensis Syd.), on purple nutsedges (Cyperus rotundus L.). A research aimed at understanding the pathogenicity of a rust fungus (Puccinia philippinensis Syd.), a potential biological control agent of purple nutsedges (Cyperus rotundus L.) had been conducted in a glasshouse of Faculty of Agriculture the University of Mataram. These factorial experiments designed according to Randomized Completely Design (CRD) and consisted of spore density and time of application. Spore density treatments consisted of 0, 5000, 10 000, 15 000, 20 000, 25 000, or 30 000 spore/mL applied either in the morning or in the afternoon. The results showed that the higher the spore density, the higher the number of pustules formed, the higher the disese intensity, and the faster the disease progressed. Urediniospores applied in the afternoon produced more pustules, higher disease intensity, and faster disease progression compare to those applied in the morning.

Estimation of Annual Mortality Rates for Eastern Oysters (Crassostrea virginica) in Chesapeake Bay Based on Box Counts and Application of Those Rates to Project Population Growth of C. virginica and C. ariakensis

In an effort to restore the ecological role of oysters in Chesapeake Bay and the economic benefits of a commercial fishery, the states of Maryland and Virginia are considering introducing the nonnative Asian oyster (Crassostrea ariakensis) into the Bay. As part of an ecological risk assessment (ERA) to evaluate the proposed action and alternatives, demographic modeling is being used to project the change in populations of both the Asian and the native eastern oyster (C. virginica) in the Bay across space and time. Annual mortality rates are vital input to the demographic model. We present two approaches for parameterizing mortality rates for C. virginica by salinity ranges and disease-intensity categories and discuss how these rates could be applied to project population growth for the Asian oyster. We estimated mortality rates from empirical data collected during annual dredge surveys of oyster beds in Maryland. We compared counts of recent boxes (dead oysters without fouling or sedimentation on the inner valve surfaces, including “gapers” of one or two weeks old with tissue remaining in the shell), old boxes (dead oysters without tissue remnants but with fouling, sedimentation or both on the inner valve surfaces), and live oysters in market-size and small classes. Our mortality estimates based on counts of recent boxes consistently differentiated between years with high disease intensity and those with low disease intensity, between wet and dry years, and between salinity zones. In contrast, traditional estimates of yearly mortality based on total box counts often were out of phase with measured levels of disease intensity and weather (dry or wet). To model populations of C. ariakensis, we propose to adjust the mortality rates for C. virginica based on research results that provide estimates of differences between the two species' resistance to MSX and dermo and to other mortality factors, such as predation.

Effect of Sclerotinia minor Infection Loci on Peanut Production Parameters

Fungal diseases of peanut, such as Sclerotinia blight caused by Sclerotinia minor, are responsible for increased production costs and yield losses of up to 50% for peanut producers in the Southwestern U.S., North Carolina, and Virginia. The literature is replete with information on the pathology, epidemiology, and control of S. minor infection of peanut, however little is known about the physical location of infection on the plant and its effect on plant production. In a 2-yr field trial, the susceptible peanut cultivar Okrun was subjected to high disease intensity without fungicide application for control of S. minor. Location of initial S. minor infection was noted to occur either on the ‘‘crown’’ or ‘‘limb’’ of infected plants, and the date of initial onset was recorded. In general, plants with initial crown infections had reduced yield and seed quality compared to those with initial limb infections. Initial infections occurring in early- and mid-season were more detrimental to plant productivity than those infections occurring late in the season. Mid-season onset of a crown infection had the greatest impact on plant productivity, causing a severe decrease in seed quality and pod yield. This study demonstrates that both infection location and date of disease onset affect plant productivity, and the results may be used to improve Sclerotinia blight management strategies.

Previsão da requeima da batateira

Com o objetivo de adequar um sistema de previsão para uso criterioso do controle químico da requeima da batateira (Solanum tuberosum), foram instalados ensaios em condição de campo, seguindo-se o delineamento experimental em blocos ao acaso, com sete tratamentos e quatro repetições, com a cultivar Bintje. Os fungicidas dimetomorfe, cimoxanil, mancozeb e clorotalonil foram associados com diferentes esquemas de pulverização baseados no sistema de previsão modificado de Wallin (1962) e no sistema tradicional de controle da requeima. Os tratamentos consistiram de : 1) aplicação de dimetomorfe de acordo com VSD-12 + clorotalonil semanalmente; 2) aplicação de dimetomorfe de acordo com VSD-14 + clorotalonil semanalmente; 3) aplicação de dimetomorfe de acordo com VSD-16 + clorotalonil semanalmente; 4) aplicação dos fungicidas protetores mancozeb, clorotalonil e oxicloreto de cobre alternados a cada sete dias; 5) aplicação dos fungicidas mancozeb, dimetomorfe, clorotalonil e cimoxanil, alternados a cada sete dias; 6) aplicação de dimetomorfe + clorotalonil de acordo com VSD-12; e 7) testemunha (sem aplicação). O uso do sistema de previsão conforme os tratamentos 1, 2 e 3 apresentou eficiência comparável ao calendário semanal (tratamento 5) de pulverização no controle da requeima da batateira. Os tratamentos baseados no acúmulo de 12 e 14 VSD's apresentaram maior eficiência em prever a ocorrência de epidemias da requeima. Apenas o sistema de previsão 2, permitiu reduzir o número de pulverizações com fungicida sistêmico, sem que houvesse perda significativa na produção.

Influence of inoculum density of races 0 and 5 of Fusarium oxysporum f. sp. ciceris on development of Fusarium wilt in chickpea cultivars

Artificial inoculation experiments were carried out at 25°C to determine the effects of inoculum density of Fusarium oxysporum f.sp. ciceris races 0 (Foc-0) and 5 (Foc-5) and susceptibility of chickpea cultivars P-2245 and PV-61 on development of Fusarium wilt. Foc-5 proved much more virulent than Foc-0. Increasing the inoculum density of F. oxysporum f.sp. ciceris caused an exponential reduction in disease incubation period and a monomolecular increase of disease incidence and the area under the disease intensity progress curve. The extent of these effects was highest in the most conducive ‘P-2245’/Foc-5 combination and decreased in the less susceptible ‘PV-61’ and for the less virulent Foc-0, in that order. For ‘P-2245’/Foc-5, the highest disease intensity was attained with 6 chlamydospores g−1 of soil, the lowest inoculum density in the study. One thousand chlamydospores g−1 of soil of the same race were needed to attain a comparable disease intensity in ‘PV-61’. Twenty thousand chlamydospores g−1 of soil of Foc-0 were required for maximum disease intensity in ‘P-2245’.

Interaction of Ht and Partial Resistance to Exserohilum turcicum in Maize.

Components of northern leaf blight resistance in maize due to race-specific resistance controlled by the Ht gene, partial resistance derived from inbred H99, and a combination of the two kinds of resistance, were studied subsequent to inoculation with Exserohilum turcicum race O. Lesion types, number of lesions (lesion number), percent leaf area affected (severity), and area under the disease progress curve (AUDPC) based on lesion number and severity were assessed in field studies conducted at two locations in Uganda and one location in Ohio in 1993. Lesion types observed were consistent for genotypes across locations. In general, significant differences among genotypes for data based on lesion number and severity were consistent for AUDPC based on lesion number and severity, respectively, at all locations. In Ohio, both Ht and partial resistance were effective in limiting disease development. In Uganda, susceptible inbreds (A619, A635, and B73) generally had higher severity than genotypes with partial resistance (H99, Mo17, and Babungo 3). However, there was a difference in response among genotypes depending on disease intensity at each location. Ht resistance and moderate partial resistance did not greatly affect lesion number at the higher disease intensity location, compared with the susceptible inbreds, but at the lower disease intensity location genotypes with partial resistance had fewer lesions than susceptible inbreds or the Ht conversions of the susceptible inbreds. At both plot locations, genotypes with partial resistance had lower severity than the susceptible inbreds or Ht conversions of the susceptible inbreds. Hybrids derived from crossing H99 with genotypes with moderate levels of partial resistance (Mo17 and Babungo 3) did not have significantly lower lesion numbers than hybrids of susceptible inbreds crossed with H99, but severity was significantly lower on these hybrids at the high disease intensity location. Results indicate that the level of partial resistance in H99 would be as effective in controlling northern leaf blight as using Ht resistance, or a combination of Ht resistance and moderate levels of partial resistance as found in Mo17.