Area Under The Disease Progress Curve Values Research Articles

Field Based Assessment of Spot Blotch (Bipolaris Sorokiniana) Disease of Wheat (Triticum Aestivum L.)

Wheat, the third major staple crop of Nepal has suffered from many diseases. Various diseases are the major limiting factors of considerable wheat production, one of them is Spot blotch. Spot blotch caused by Bipolaris sorokiniana is a major disease of wheat in warm and humid regions of Nepal. The fungus has a worldwide distribution but as a pathogen, it is the most aggressive under the conditions of high relative humidity and temperature associated with the low fertility of soils in South Asia, South America, Africa, and Australia. The yield loss due to the disease is very significant in Nepal. This experiment was conducted to identify the genotypes having a good level of resistance against spot blotch. The experiment set was received from CIMMYT comprises 52 entries and arranged in alpha lattice design with two replications in 2017/18 at Regional Agricultural Research Station, Parwanipur, Bara, Nepal. Each plot size was 8 rows of 2 meters long. Three times disease scoring was done in the double-digit method and calculated the Area under the disease progress curve (AUDPC). Heading days, days to maturity, plant height, number of grains per spike (NGPS), number of tillers per meter square (NTPM), mean AUDPC, thousand-grain weight (TGW), and grain yield were found highly significant. The genotype 8HLBSN24 was found the highest yielder (4999kg/ha) with a 208 mean AUDPC value. The grain yield and mean AUDPC was a strong negative correlation (-0.96). However, NGPS and NTPM found a positive correlation to grain yield. Keywords: Foliar blight, AUDPC, Wheat, Genotype

Seleção de genótipos de vinagreira tolerantes/resistentes à mancha foliar induzida por Corynespora cassiicola em Guerrero, México

ABSTRACT Roselle spot caused by Corynespora cassiicola affects calyx production in Mexico. The aim of the present study was to evaluate twenty-two roselle genotypes against C. cassiicola under greenhouse conditions. The area under the disease progress curve (AUDPC) was used to detect susceptible, tolerant and resistant genotypes. Considering the incidence in leaves, susceptible genotypes were Conpoz, Sudlaz, Morcot and Sudigua (AUDPC values of 7379.2 to 5891.7); tolerant genotypes were Conayu and Chinxal (AUDPC 1341.6 and 1313.2). Based on the severity in leaves, susceptible genotypes were Sudigua, Conpoz and Morena2 (AUDPC from 788.4 to 436.3); tolerant genotypes were Almatech, Crioxal, Rojatec and Conayu (37.7 to 28.76 AUDPC). Assessment of the incidence in calyces indicated that susceptible genotypes were Morena2, Morena, Conpoz, Descop and Chinayu (AUDPC from 6572.1 to 2319.4); for the severity in calices, susceptible genotypes were Morena2, Descop, Morena, Cabxal, Chinayu and Conpoz (AUDPC from 3355.4 to 779.2). Incidence and severity on calyces evidenced resistant genotypes, which were Almatech, Criolaz2, Criocot, Criolaz, Rojatec, Criopoz, Crioxal, Chinxal and Conayu (0.0 AUDPC). In the present study, tolerant and resistant genotypes were detected to leaf and calyx spot caused by C. cassiicola in roselle.

Identification of mung bean germplasm for resistance against Cercospora canescens and to study the association of biochemical parameters with defense mechanisms

AbstractSizable loss in crop yields resulting from Cercospora leaf spot (CLS), caused by Cercospora canescens and is a major disease in mung bean [Vigna radiata (L.) R. Wilczek] crops, demands a thorough evaluation of various parameters dealing with the infection. Determination of components for CLS resistance is associated with leaf spot intensity in the field, which is estimated from the area under the disease progress curve (AUDPC). The present study showed that out of 261 genotypes screened in the field for CLS, 88, 89, 51 and, 33 genotypes were found to be resistant, moderately resistant, moderately susceptible, and susceptible, respectively, on the basis of the AUDPC values. Further, five resistant and five susceptible genotypes were selected from the screened genotypes for bioassay analysis and were subjected to artificial inoculation with three different isolates of Cercospora canescens to study the effectiveness in polyhouse. The morphological data along with disease incidence, chlorophyll content, proline content, phenol content and enzymatic activities of phenylalanine ammonia‐lyase (PAL), peroxidase (POX), and superoxide dismutase (SOD) were estimated. The findings showed that there was a significant increase in the enzymatic activities, total phenol, and proline contents in inoculated resistant and susceptible genotypes vs. control (without inoculation). However, the total chlorophyll content reduced in both resistant and susceptible genotypes after inoculation. Moreover, higher enzyme activities were marked in the resistant genotypes than the susceptible genotypes. This study will help to identify the resistant and susceptible mung bean genotypes against Cercospora canescens for further agronomic study as well as breeding programs.

Chemotype and Aggressiveness Evaluation of Fusarium graminearum and Fusarium culmorum Isolates from Wheat Fields in Wisconsin.

Fusarium graminearum commonly causes Fusarium head blight on wheat, barley, rice, and oats. F. graminearum produces nivalenol (NIV) and deoxynivalenol (DON) and forms derivatives of DON based on its acetylation sites. The fungus is profiled into chemotypes based on DON derivative chemotypes (3 acetyldeoxynivalenol [3ADON] chemotype; 15 acetyldeoxynivalenol [15ADON] chemotype), and/or the NIV chemotype. This study assessed the Fusarium population found on wheat and the chemotype profile of the isolates collected from 2016 and 2017 in Wisconsin. F. graminearum was isolated from all locations sampled in both 2016 and 2017. Fusarium culmorum was isolated only from Door County in 2016. Over both growing seasons, 91% of isolates were identified as the 15ADON chemotype, while 9% of isolates were identified as the 3ADON chemotype. Aggressiveness was quantified by area under the disease progress curve (AUDPC). The isolates with the highest AUDPC values were from the highest wheat-producing cropping districts in the state. Deoxynivalenol production in grain and sporulation and growth rate invitro were compared with aggressiveness in the greenhouse. Our results showed that 3ADON isolates in Wisconsin were among the highest in sporulation capacity, growth rate, and DON production in grain. However, there were no significant differences in aggressiveness between the 3ADON and 15ADON isolates. The results of this research detail the baseline frequency and distribution of 3ADON and 15ADON chemotypes observed in Wisconsin. Chemotype distributions within populations of F. graminearum in Wisconsin should continue to be monitored in the future.

Pathogenic Variability of the Jackfruit-Bronzing Bacterium Pantoea stewartii Subspecies stewartii Infection to Jackfruit Varieties and Its Pivotal Plant Hosts in Malaysia

Infection with Pantoea stewartii subspecies stewartii, which causes jackfruit-bronzing disease, is a huge problem faced by the jackfruit industry in Malaysia. This study was carried out to assess the disease ratings and aggressiveness performance of 28 Pantoea stewartii subspecies stewartii isolated from jackfruit-bronzing diseased jackfruits from four collection areas (Jenderam in Selangor State, Maran and Muadzam Shah in Pahang State, and Ipoh in Perak State) in Peninsular Malaysia, inoculated into jackfruit varieties (Tekam Yellow J33, Hong J34 and Subang Chap Boy J39), the sweetcorn variety, Mas Madu (two-week-old seedlings and nine-week-old seedlings), the cucumber variety, Rocky, and the pineapple variety, MD2. The results revealed that Pantoea stewartii subspecies stewartii produced symptoms upon all inoculations in the pathogenicity testing, thus fulfilling Koch’s postulates, except in the case of J39 and sweetcorn (two-week-old seedlings). No disease symptoms (disease rating 0) were observed in J39 and sweetcorn (two-week-old seedlings) within 14 days post-inoculation (14 dpi). The disease progression (based on disease ratings) proved that the jackfruit variety J39 was the most resistant, whereas J33 and J34 were susceptible to jackfruit-bronzing disease. The disease ratings of the 14-dpi period revealed a variability of disease progression among the 28 bacterial isolates, where the isolate JEN-14 had the fastest and highest disease ratings when inoculated into J33, J34, nine-week-old sweetcorn seedlings, cucumber, and pineapple. Likewise, the AUDPC value, based on disease rating, across the 28 isolates indicated that JEN-14 is the most aggressive and significant of the isolates (J33, J34, nine-week-old sweetcorn seedlings, cucumber, and cucumber pineapple inoculation; p < 0.05). Even though isolates from Jenderam (other than JEN-14) and Maran had better disease ratings and the area under the disease progress curve (AUDPC) values than isolates from Muadzam Shah and Ipoh, no significant differences were found among the isolates (p < 0.05). Based on our findings, we identified the isolate JEN-14 as the best potential candidate to assist in jackfruit-bronzing disease resistance breeding in the future. Last but not least, the methods, disease ratings, and variations of the aggressiveness profiles among the isolates from this study may be beneficial and significant by providing disease-rating references and appropriate screening approaches when selecting the most appropriately aggressive isolates for evaluating the defense response in the disease resistance breeding program.

IdeTo: Spreadsheets for Calculation and Analysis of Area Under the Disease Progress Over Time Data

When disease ratings are obtained over time, area under the disease progress metrics such as area under the disease progress curve (AUDPC) and area under the disease progress stairs (AUDPS), which allow integration of these measures into a single value, have found use for both survey or replicated experiment data. IdeTo, an Excel-based calculator, computes AUDPC, AUDPS, and their standardized and relative values for up to 200 individuals evaluated at 200 timepoints. In addition to the areas, descriptive statistics are provided for the group of individuals (e.g., accessions and replicates), and both Pearson and Spearman correlation coefficients between the areas and other traits of interest. Graphs are provided to visualize the progression of disease scores over time, distribution of AUDPC and AUDPS values in the dataset, and their linear correlation with the traits of interest. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2021.

Evaluation of Geranium Cultivars and Biorational Products to Control Botrytis Blight in the Greenhouse

Botrytis blight caused by the fungus Botrytis cinerea is an important disease of geranium, affecting leaves, stems, and flowers, and decreasing the crop’s marketability. Our objectives were to evaluate (i) susceptibility of geranium cultivars to B. cinerea and (ii) efficacy of biorational products for control of Botrytis blight on geranium. Disease assessment included the number of blighted leaves, foliar lesions, and leaves with B. cinerea sporulation. The area under the disease progress curve (AUDPC) was calculated. Among the 10 geranium cultivars evaluated, ‘Pinto Premium Orange’, ‘Horizon Coral Spice’, and ‘Ivy Tornado White’ had significantly less disease than ‘Ringo 2000 Violet’ and ‘Maverick Scarlet Picotee’ for all measured parameters. When 11 treatments were compared in the efficacy trial of biorational products, Botector (Aureobasidium pullulans) and Prestop (Gliocladium catenulatum) effectively controlled the disease according to AUDPC for blighted leaves and leaves with sporulating B. cinerea in both Ringo 2000 Violet and Pinto Premium Orange. Zio (Pseudomonas chlororaphis), Serifel (Bacillus amyloliquefaciens), Serenade Opti (B. subtilis), and LifeGard (B. mycoides) were also effective when combined with the geranium cultivar Pinto Premium Orange, one of the least susceptible cultivars in our study based on AUDPC values for all measured parameters. AUDPC for leaves with sporulating B. cinerea showed that all biorational products included in the study effectively limited B. cinerea except Actinovate (Streptomyces lydicus) in Pinto Premium Orange geranium. A sustainable management approach could combine one of the least Botrytis-susceptible geranium cultivars identified with biorational controls for effective Botrytis blight control.

Screening Rice Genotypes for Brown Spot Disease Resistance

A field experiment was conducted to screen 20 rice genotypes against brown spot disease caused by Bipolaris oryzae under natural epiphytotic field conditions at Bangaun, Dang, Nepal, from June 2018 to March 2019. The experiment was carried out in a randomized complete block design with 3 replications. Sawa Mansuli was taken as susceptible check and Sabitri as a resistant check in the experiment. Disease assessment was done by calculating disease severity and Area Under the Disease Progress Curve (AUDPC). Among the evaluated genotypes, disease severity and AUDPC varied in the field experiments. Rice genotypes showed the resistance to highly susceptible reactions based on AUDPC value which ranged from 88.51 to 260.65. Among the evalauted rice genotypes in the field experiment, the highest mean AUDPC value was recorded with Basmati (260.65) followed by Radha-13 (172.80) and the lowest was recorded with Kathe Jhinuwa (88.51). Similarly, the highest severity rate was recorded with Basmati (25.91) followed by Radha-13 (21.00) and Tilki (20.75) and the lowest was recorded with Kathe Jhinuwa (11.03) which was at par with Radha-4 (11.11) followed by Sukhadhan-1 (12.02) and Sabitri (12.06). The highest grain yield was recorded with Sarju-52 (4.32 t/ha) followed by Sabitri (4.19 t/ha). Grain yield was negatively correlated with mean AUDPC by 14.77%. Kathe Jhinuwa, Radha-4, and Sabitri can be used for higher grain yield purposes under similar field conditions and also can be utilized as the source of resistance in a plant breeding program.

Rootstock and Plastic Mulch Effect on Watermelon Flowering and Fruit Maturity in a Verticillium dahliae–Infested Field

Separately, grafting and the use of plastic mulch can increase yield, quality, and early harvest of watermelon (Citrullus lanatus), especially when plants are under biotic and/or abiotic stress. A 2-year field study was conducted to evaluate the combination of four different rootstocks and two types of plastic mulch (black and clear) on date of watermelon first flowering, fruit ripening, yield, and fruit quality when plants were exposed to Verticillium dahliae. Seedless watermelon cv. Secretariat was grafted onto rootstocks Lagenaria siceraria cv. Pelop, Benincasa hispida cv. Round, and two interspecific hybrid squash rootstocks Cucurbita maxima × C. moschata cvs. Super Shintosa and Tetsukabuto, with nongrafted ‘Secretariat’ as the control. Fruit were harvested 0, 7, and 14 days after both the leaflet and tendril attached to the fruit pedicel were completely dry (fruit considered to be physiologically mature). The area under the disease progress curve (AUDPC) values for verticillium wilt were not different for mulch type in either year, although the overall AUDPC value was greatly reduced in the four grafted treatments (227) compared with nongrafted (743). There was no difference in days to male or female flowering due to mulch type or year, and rootstock did not affect first flowering of male flowers. Female flowering was 14 and 11 days later in 2018 and 2019, respectively, for ‘Secretariat’ grafted onto bottle gourd ‘Round’ compared with ‘Secretariat’ grafted onto ‘Tetsukabuto’. Female flowering of ‘Secretariat’ on ‘Round’ was also 7 days later compared with nongrafted ‘Secretariat’ both years. However, days to first harvest was not different with mulch or rootstock and was 92 days after transplanting (DAT) in 2018 and 114 DAT in 2019. There was no difference in yield (fruit number and weight) due to year, harvest date, or mulch, but there was a difference due to grafting. ‘Secretariat’ grafted onto ‘Super Shintosa’ had the greatest total number and weight of fruit per plant (3.7 and 14.8 kg, respectively), and nongrafted ‘Secretariat’ had the lowest (0.7 and 3.2 kg, respectively). Fruit quality attributes hollow heart formation (rating 3.2/5 on average), hard seed count (6 on average), total soluble solids (11% on average), and lycopene content were not different among mulch type, rootstock treatment, or harvest date; however, lycopene content did differ due to year (52.44 and 32.51 µg·g−1 in 2018 and 2019, respectively). Flesh firmness was highest for watermelon grafted onto ‘Super Shintosa’ rootstock (6.7 N) and lowest for nongrafted watermelon (4.3 N). Overall, rootstocks reduced verticillium wilt severity and increased fruit yield whereas mulch had no effects, and 5 V. dahliae colony forming units (cfu)/g of soil may be the minimum level for impact on watermelon fruit yield.

Field validation of TOMCAST modified to manage Septoria leaf spot on tomato in the central-west region of Brazil

Septoria leaf spot, caused by Septoria lycopersici, is a devastating disease on tomato in Brazil. In order to rationalize the chemical control, we validated the TOMCAST system to manage Septoria leaf spot on fresh market tomato in the State of Goiás, Brazil. Three field experiments were performed in a randomized complete block with five treatments and four replications. The first experiment was carried out from October 2017 to February 2018, the second from October 2018 to February 2019, and the third from November 2018 to March 2019. The treatments evaluated were: 1. Weekly calendar application of fungicides (WCA); 2 to 4. Disease severity values (DSV) 15, 20, and 25; 5. Control: plants not treated with fungicides. The values of the average air temperature and leaf wetness were used to calculate the DSV. The environmental conditions were favorable to the disease in experiments. The lowest values of the area under the disease progress curve (AUDPC) were recorded in WCA (809), DSV 20 (837), and DSV 15 (842) in the first experiment. Disease rates (r) of 0.010 were estimated in these treatments. Highest AUDPC (1325) and r (0.013) were detected in the control. In the second and third experiments, the highest AUDPC values were 638 and 59 in the control, respectively. The lowest AUDPC values were recorded in DSV 15 and WCA which were 325 and 28, 349 and 26, in the second and third experiments, respectively. No differences of r were detected in the second and third experiments. The highest number of fruits by plant (15) was estimated in DSV 15 in the second experiment. There were no differences on tomato yield in other experiments. As the number of fungicides applications was the highest in DSV 15, the TOMCAST system is not a useful tool for controlling Septoria leaf spot on tomato in the State of Goiás and other Brazilian regions with similar climatic characteristics.

Temporal Progress of Candeia Rust Caused by Puccinia velata in Clonal Candeia Plantation (Eremanthus erythropappus (DC.) McLeisch)

The temporal progress of candeia rust, caused by the fungus Puccinia velata, was monitored in an experimental field at Lavras municipality, Southern Minas Gerais state, Brazil. A plantation with 17 Eremanthus erythropappus clones was set at the site, and the temporal disease progress was analyzed based on visual assessments of disease severity on leaves. The disease was monitored monthly between September 2016 and August 2017. Progress curves based on disease severity were constructed and empirical models were fitted. The area under the disease progress curve (AUDPC) was calculated, and the means test was applied to select clones resistant to the disease. The Pearson coefficient was used to assess correlations between disease severity and environmental variables. The model that best described disease progress over the assessment period was the Gompertz model. The mean AUDPC values were grouped into four groups of resistance levels according to the Scott–Knott test. There was a negative correlation between air temperature and disease severity. Considering that the disease occurred in all clones and that the climatic conditions of Southern Minas Gerais are favorable to the candeia rust, it is important to adopt measures for the selection of clones resistant to this disease.

Genotype by environment interaction for area under the disease-progress curve (AUDPC) value in spring barley using additive main effects and multiplicative interaction model

The objective of this study was to assess genotype by environment interaction for area under disease progress curve values in spring barley grown in South-West Poland by the additive main effects and multiplicative interaction model. The study comprised of 25 spring barley genotypes (five cultivars: Basza, Blask, Antek, Skarb and Rubinek as well as all possible 10 two-way mixtures and 10 three-way mixtures combinations), evaluated at two locations in 4 years (eight environments) in a randomized complete block design, with four replicates. Area under disease progress curve (AUDPC) value of the tested genotypes ranged from 75.3 to 614.3, with an average of 175.3. In the AMMI analyses, 13.43% of the AUDPC value variation was explained by environment, 37.85% by differences between genotypes, and 18.20% by genotype by environment interaction. The mixture Basza/Skarb is recommended for further inclusion in the breeding program due to its low average AUDPC value (98.8) and is stable (AMMI stability value = 6.65).

Controlling Cucumber Powdery Mildew using Cow Milk and Whey under Greenhouse Conditions

The role of raw cow's milk and whey (40 and 50% dilution in water) and number of sprays against cucumber powdery mildew caused by Sphaerotheca fuliginea was studied in greenhouse experiments during 2017/18 and 2018/19. As a result of number of sprays, the disease severity percentage and area under the disease progress curve (AUDPC) were affected by the number of sprays with raw milk and whey. The number of sprays played an important role in controlling powdery mildew, and significant differences have occurred among all applied sprays. Four sprays with intervals of one week was the effective treatment in reducing disease severity, AUDPC values, compared to other treatments, i.e., two and three sprays in comparison to the fungicide as well as a control treatment. Additionally, treated plants showed a significant increase in plant growth and yield parameters in case of spraying four times. Also, the activity of defense-related enzymes (catalase, peroxidase, and polyphenoloxidase) and amino acid proline was high in response to increasing the number of sprays at four times compared with untreated plants. Light and scanning electron microscopic observations showed a clear change in the morphology of S. fuliginea spores, in addition to hyphae degradation and loss the vitality of conidia as well as rupturing the content of conidia. The results obtained also indicated that cow's milk and whey dilution effectively reduced the powdery mildew signs and symptoms on infected cucumber plants at 50% with the four sprays treatment being the most effective treatment.

Biofungicides evaluation in two coffee cultivars for Hemileia vastatrix control

El objetivo del presente estudio fue evaluar el efecto de biofungicidas elaborados con <em>Azadirachta indica</em>, <em>Melaleuca alternifolia</em> y la combinación de<em> Bacillus subtilis</em> con <em>A. indica</em> y <em>Syzygium aromaticum</em>, en el control de la roya causada por <em>Hemileia vastatrix</em>, en las variedades Garnica y Typica. Se establecieron experimentos en condiciones de campo en tres localidades: Lipuntahuaca, Chilocoyo y Cinco de Mayo, con plantas de cinco meses de edad. Se encontraron diferencias significativas entre biofungicidas y el testigo para la incidencia (P=0.04), área bajo la curva del progreso de la severidad (ABCPE) (P=0.04) y tasa de infección aparente (P=0.03). No se encontraron diferencias en severidad excepto en la última evaluación. <em>M. alternifolia</em> indujo los valores más bajos de incidencia (34.4 %), ABCPE (61.8) y tasa de infección aparente (0.028), con porcentajes de reducción con respecto al testigo de 20.9, 14.2 y 39.1%, respectivamente. No se presentaron diferencias significativas entre las variedades Typica y Garnica para incidencia y severidad. Las plantas de la localidad de Lipuntahuaca tuvieron menor incidencia (26.9%) y severidad (2.3%) en comparación con Chilocoyo y Cinco de Mayo con 51.5 y 44.5 % (incidencia) y 4.2 y 3.4% (severidad), respectivamente (P<0.0001). Los biofungicidas no suprimieron la infección, pero los resultados sugieren que debe continuarse la investigación en este patosistema.

Aggressiveness and Deoxynivalenol Production of Nebraska Isolates of Fusarium boothii and F. graminearum

Significant losses in wheat result from Fusarium head blight (FHB) and its associated mycotoxin deoxynivalenol (DON). The predominant FHB pathogen in North America is Fusarium graminearum. F. boothii was recently confirmed for the first time in the United States as a causal agent of FHB in Nebraska wheat fields. This greenhouse study compared the aggressiveness and DON production in wheat among 13 F. graminearum and three F. boothii isolates from Nebraska. Spikes of the susceptible spring wheat cultivar Wheaton at anthesis were spray-inoculated with spores of the isolates. Severity data were used to calculate the area under the disease progress curve (AUDPC). DON concentration in the grain was quantified by gas chromatography/mass spectrometry. F. graminearum isolates were more aggressive and produced more DON than F. boothii isolates. Mean AUDPC values were 1,171 and 885 percent days for F. graminearum and F. boothii, respectively. Mean DON values were 41.0 and 13.6 µg/g for F. graminearum and F. boothii, respectively. Although only three available F. boothii isolates were used, the results are in agreement with previous studies that found F. graminearum be more aggressive and toxigenic in wheat than F. boothii.

Winter pruning: option for management against alternaria brown spot (Alteraria alternata f. sp. citri) in Honey Murcott tangor [Citrus reticulata Blanco x C. sinensis (L.) Osbeck

Alternaria brown spot (ABS), caused by Alternaria alternata f. sp. citri, is the main fungal disease plaguing tangerines. The main symptoms are falling leaf and fruit, resulting in the loss of production and quality. The initial symptoms in leaves are characterized by small brown or black spots, surrounded, or not, by yellowish halos. In the fruit, dark cortical patches appear that can easily break. In this study, the winter pruning of the plants was investigated to complementary control of ABS. The experiment was conducted in 10-year-old Honey Murcott tangor plants, where two treatments were applied: pruning in winter and no pruning, using a randomized block design with ten replicates. The treatment of winter pruning was performed before the flowering of the plants (September in Brazil), where the branches were cut close to the trunk, the thicker branches were removed. The chemical control was performed in both treatments. Evaluations of disease severity in fruit were performed using a diagrammatic scale; the disease incidence and area under the disease progress curve (AUDPC) were also calculated. The fruit drop and yield (t ha-1) of the plants were quantified, and the temperature and humidity inside the canopy of the plants were measured. Winter pruning had a positive effect on ABS management since it provided a decrease in incidence, severity, and AUDPC values. Fruit fall was reduced, resulting in greater productivity for Honey Murcott tangor plants. The results confirmed the positive effect of winter pruning on the management of alternaria brown spot.

Determination of the most susceptible phenological stage of rice panicles to infection by species of Fusarium graminearum

ABSTRACT Occurrence of rice seeds infected by Fusarium graminearum has shown the importance of identifying the most favorable phenological stage of panicles to grain infection. The experiments were conducted in two crop seasons under greenhouse conditions, using the rice hybrid INOV CL. The phenological stages during inoculation were complete booting, full heading and flowering. All plots were inoculated using two isolates of Fusarium graminearium species complex 15A (F. graminearium - 15-ADON) and FmNiv (F. meridionale - Nivalenol). Disease severity was estimated at weekly intervals and was used to calculate the area under the disease progress curve (AUDPC), while panicles were collected to determine the percentage of spotted grains and Fusarium incidence. Percentage of spotted grains and incidence of F. graminearum and F. meridionale were greater when inoculation was made during flowering stage, significantly differing from heading and booting stages. Rice flowering stage is more susceptible to infection by F. graminearum and F. meridionale, inducing higher disease severity and incidence of spotted grains, as well as presence of fungi in the grains. Flowering was the most susceptible stage in the two crop seasons for both isolates, and the complete booting stage presented the lowest values of AUDPC.

Inhibition of Alternaria stem canker on tomato by essential oils from Baccharis species

The toxicity of four essential oils extracted from Baccharis articulata, Baccharis ochracea, Baccharis psiadioides and Baccharis trimera was tested against the phytopathogen Alternaria alternata, which causes Alternaria stem canker on tomatoes. Diseases caused by Alternaria fungi are responsible for great economic losses in terms of production and are controlled by synthetic fungicides; however, essential oils offer an alternative, since they have been proven to be effective for controlling against various plant pathogens. In this way, the antifungal activity of Baccharis essential oils was tested using potato dextrose agar medium with concentrations ranging from 0.1 to 20.0 µL mL−1. Baccharis trimera and Baccharis ochracea essential oils presented 100% mycelial growth inhibition of A. alternata and were also able to control Alternaria stem canker disease under greenhouse conditions. Tomato plants treated with these essential oils exhibited area under the disease progress curve (AUDPC) values of 230.10 and 241.42, differing from the control condition, which showed an AUDPC value of 268.92. The essential oils of B. trimera and B. ochracea can be an alternative for controlling Alternaria stem canker disease of tomatoes and should be formulated as a potential fungicide against the A. alternata pathogen.

REACTION OF POTATO CULTIVARS AND CLONES TO Phytophthora infestans

ABSTRACT The in vitro and field reactions of 23 potato cultivars and clones to two isolates of Phytophthora infestans were tested. The in vitro test used the detached potato leaflets method, and disease severity was evaluated 6 days after inoculation. Field experiments were conducted in autumn of 2013, in two locations in Pelotas City, Rio Grande do Sul State, Brazil. Seven evaluations of the disease severity were performed. From the severity values, the area under the disease progress curve (AUDPC) was calculated. Tubers were harvested to determine the yield (g plot-1). The A2 mating type isolate was the most aggressive for the majority of the potato genotypes. It was possible to group the different reactions of the potato genotypes based on the AUDPC values. Clones C2553-1-06, C2573-4-06, C2550-4-06, C2551-2-06, and CIP392,617.54 showed moderate-to-high resistance to the two isolates of P. infestans. The values of severity and AUDPC obtained in vitro and field tests were positively correlated for both P. infestans isolates, but in some interactions, inconsistencies were observed. Tuber yield was negatively correlated with AUDPC.

Detection of Ralstonia solanacearum phylotype II, race 2 causing Moko disease and validation of genetic resistance observed in the hybrid plantain FHIA-21

Vascular wilt of banana and plantains, also known as Moko disease, is caused by Ralstonia solanacearum (Rs) phylotype II, and is the main bacterial disease affecting these crops in the Americas. Upon comparative sequence analysis of 44 Rs genomes we developed an improved PCR protocol based on the nucleotide sequence of a gene coding for a hypothetical DUF3313 domain protein. Next, we tested the detection protocol with two Rs inoculation methods to validate field resistance reported in the hybrid plantain genotype FHIA-21, previously identified as susceptible to Moko disease in greenhouse experiments in which wounds were caused to the roots prior to inoculation. By using an inoculation method without causing wounds to the roots, we confirmed resistance of FHIA-21 to Moko disease (no Rs was detected by PCR in inoculated plants). In contrast, the field-susceptible genotype Dominico Harton developed severe symptoms of Moko disease, regardless of the inoculation method used. FHIA-21 showed an area under the disease progress curve (AUDPC) close to zero, while Dominico Harton plants showed AUDPC values ranging from 65.8 to 88.4. The availability and analysis of genomic data facilitates the development of improved pathogen detection tools that together with the availability of improved inoculation methods and tolerant genotypes to Moko disease will be of great use in Musa breeding programs.