Apparent Infection Rate Research Articles

Effect of Weather Parameters on Disease Severity and Progression of Fusarium Wilt in Chilli (Capsicum anuum L.)

Fusarium wilt incited by Fusarium oxysporum is an economically damaging disease of chilli (Capsicum anuum L.). Field experiments on epidemiological studies were conducted using susceptible variety (Pusa Jwala) to study the effect of weather parameters on the progression of the disease. The study revealed that transplanting chilli during the first half of July reduced the disease severity compared to earliest transplant dates. The area under disease progress curve (AUDPC) and the apparent infection rate were lowest in the crop transplanted on 15th July, 2022 while they were highest in the crop transplanted on 15th June, 2022. The correlation analysis showed a positive correlation between disease severity and bright sunshine hours, and a negative correlation with the other weather parameters. The R2 value obtained from multiple regression equations revealed that the combined effect of weather parameters could explain the prediction of a disease level of 83-86 per cent at all three transplant dates.

Effect of Environmental Factors in the Development of Powdery Mildew in Okra [Abelmoschus esculentus (L.) Moench

In order to study the effect of environmental factors in the development of powdery mildew in okra [Abelmoschus esculentus (L.) Moench] an experiment was carried out at the College of Agriculture, IGKV, Raipur, Chhattisgarh during kharif (2019-20). The correlation analysis revealed that the age of the crop was significantly, positively correlated and T max, T min and morning RH were significantly, negatively correlated with the disease severity. In addition to this by linear regression analysis, it was observed that plant age (69%), maximum temperature (62%), minimum temperature (60%) and morning relative humidity (46%) contributed in percent disease severity. Based on the proportional measures of extent of infection at different times the apparent rate of infection was found maximum during 70-84 DAS. At this time when the disease progress the average maximum temperature was 29.3℃, minimum temperature 14.9℃, morning relative humidity 87.6% and evening relative humidity 38.33%.

Epidemiological Dynamics of Xanthomonas xonopodis pv. phaseoli in French bean (Phaseolus vulgaris): Unraveling the Factors Governing Bacterial Blight Pathogenesis

The study was conducted during May, 2020 to June, 2021 in the Department of Plant Pathology Laboratory of Dr. Y.S Parmar University of Horticulture and Forestry, Nauni, located in Solan district of Himachal Pradesh, India to study the role of various epidemiological parameters on the development of common bacterial blight of French bean. The diseased samples were collected and the pathogen was isolated and purified on Luria Bertani (LB) agar plates. The pathogenicity test was performed on the potted plants as well as on the detached leaves using carborundum abrasion and pin prick method of inoculation. The incubation period on potted plants using carborundum abrasion and pin prick method revealed the initial symptoms after 117.60 h and 120.30 h, respectively, while on detached leaves they were visible after 72.30 h and 84.50 h of inoculation, respectively. Further to study the effect of different epidemiological factors on disease development, the leaves inoculated using carborundum abrasion were subjected to four temperature levels, five relative humidity levels and five different durations of leaf wetness under controlled conditions in relative humidity cum temperature control cabinet. The observations were recorded at different intervals and the data revealed that the pathogen caused severe symptoms on the leaves with high apparent rate of infection under 30°C temperature, 100% RH and a maximum of 24 h of leaf wetness. It was observed that the severity of disease decreased as the temperature raised from 30°C and increased with the rise in RH levels and leaf wetness duration.

EVALUATION OF WHEAT GENOTYPES FOR SPOT BLOTCH (Bipolaris sorokiniana Sacc.) RESISTANCE AT KHAIRAHANI, CHITWAN

Wheat (Triticum aestivum L.) is the third most important cereal crop of Nepal in terms of area and production. Spot blotch caused by Bipolaris sorokiniana Sacc. is one of the major diseases reducing the productivity and quality of wheat in Nepal, which is favored by high temperature and relative humidity. The experiment was conducted at research farm of Rampur Campus, Khairahani, Chitwan from 18th Nov 2021 to 29th Mar 2022, to identify the genotypes resistance against spot blotch. It was laid out in Randomized complete block design (RCBD) with twelve genotypes as treatments and three replications. Double digit scoring method was used to assess the disease five times from 90 DAS at the interval of 7 days and Area under disease progress curve (AUDPC) was calculated. Statistically, significant difference was obtained in all the observed traits except for plant height, spike weight, harvest index, and straw yield. The highest AUDPC value was recorded in RR-21 (2074) yielding 4.0 tonha-1 whereas the lowest AUDPC value was recorded in NL 1437 (781) yielding 6.1 tonha-1, suggesting it to be more resistant than other genotypes. NL 1447 was the highest yielder (6.5tonha-1) with a 985.185 mean AUDPC value followed by NL1437 (6.1 tonha-1) while RR-21 was the lowest yielder (4.0 tonha-1). The lowest apparent infection rate was detected for BL 4951 (0.018). Correlation studies indicated that total grains and grain weight per spike as well as the grain yield were negatively and significantly correlated with AUDPC.

EVALUATION OF WHEAT GENOTYPES FOR SPOT BLOTCH (Bipolaris sorokiniana Sacc.) RESISTANCE AT KHAIRAHANI, CHITWAN

Wheat (Triticum aestivum L.) is the third most important cereal crop of Nepal in terms of area and production. Spot blotch caused by Bipolaris sorokiniana Sacc. is one of the major diseases reducing the productivity and quality of wheat in Nepal, which is favored by high temperature and relative humidity. The experiment was conducted at research farm of Rampur Campus, Khairahani, Chitwan from 18th Nov 2021 to 29th Mar 2022, to identify the genotypes resistance against spot blotch. It was laid out in Randomized complete block design (RCBD) with twelve genotypes as treatments and three replications. Double digit scoring method was used to assess the disease five times from 90 DAS at the interval of 7 days and Area under disease progress curve (AUDPC) was calculated. Statistically, significant difference was obtained in all the observed traits except for plant height, spike weight, harvest index, and straw yield. The highest AUDPC value was recorded in RR-21 (2074) yielding 4.0 tonha-1 whereas the lowest AUDPC value was recorded in NL 1437 (781) yielding 6.1 tonha-1, suggesting it to be more resistant than other genotypes. NL 1447 was the highest yielder (6.5tonha-1) with a 985.185 mean AUDPC value followed by NL1437 (6.1 tonha-1) while RR-21 was the lowest yielder (4.0 tonha-1). The lowest apparent infection rate was detected for BL 4951 (0.018). Correlation studies indicated that total grains and grain weight per spike as well as the grain yield were negatively and significantly correlated with AUDPC.

Efficacy of indigenous Trichoderma isolates of West Timor, Indonesia, as biocontrol agents of brown spot (Drechslera oryzae) on two upland rice varieties

BackgroundBrown spot disease is one of the most destructive foliar diseases of rice. Biological control of this disease is considered more environmentally safe, but the biological control agents have limited availability. The fungus Trichoderma can be used as a biocontrol agent for various plant diseases, including brown spots. Indigenous Trichoderma species from West Timor were evaluated in this study to reveal their effectiveness in reducing brown spot disease of upland rice. The study was conducted under a screen house condition using a factorial treatment design laid out in a completely randomized design. The two factors were the brown spot disease control method (T. viride, T. harzianum, T. hamatum, fungicide Trivia 73 WP, and a control treatment) and upland rice genotype (Inpago 7 and Breun Senaren 2).ResultsThe results showed that Trichoderma spp. and the fungicide Trivia 73 WP caused significantly lower AUDPC and apparent infection rate than the control treatment. The total phenol content and agronomic characters (number of reproductive tillers per plant, number of filled grains per panicle, grain yield per plant) were higher in the Trichoderma and fungicide treatments than the control treatment. Meanwhile, tannin and saponin levels were non-significantly different among treatments. Trichoderma and the fungicide Trivia treatments effectively suppressed brown spot disease of upland rice, and the efficacy was dependent on the rice variety, with a mean efficacy range over the two varieties of 27.05–36.42%. The Trichoderma and the fungicide Trivia treatments increased the grain yield per plant differentially in the 2 rice varieties, with a mean grain yield increase over the 2 varieties of 13.0% (T. viride), 23.5% (T. harzianum), 35.0% (T. hamatum), and 19.9% (Trivia 73 WP).ConclusionEfficacy of local Trichoderma of West Timor and the fungicide Trivia treatments were varietal dependent with T. hamatum being the most effective in reducing the brown spot disease and producing the highest grain yield increase over the 2 rice varieties. The local Trichoderma species of West Timor have a future potential as biocontrol agents of upland rice brown spot disease, but it is necessary to further evaluate their effectiveness against the disease in replicated field trials.

Epidemiology of Late Blight of Potato, Its Progress and Apparent Rate of Infection

Late blight of potato caused by Phytophthora infestans is one of the most destructive diseases of potato world over. The devastation of the disease is very much related with climatic factors like temperature, relative humidity, fog or dew deposition and also sunshine hours. An experiment was conducted in Indo-Gangetic plains of West Bengal to know the effect of weather parameters on initiation and severity of the disease as well as progress and pattern of development of disease which will ultimately help to develop the effective spray schedule to manage the disease. From the experiment it is observed that 7 days prior to first appearance of late blight disease of potato the average maximum and minimum temperature varied between 24-26˚C and 7-8˚C respectively; average maximum and minimum relative humidity varied between 90-93% and 41-44% respectively; average sunshine hours per day varied between 6-8 hours. Correlation study of late blight disease severity with different weather parameters were also carried out. Maximum and minimum temperature as well as maximum and minimum relative humidity found to be positively correlated with late blight disease build up. While sunshine hour found to be negatively correlated with the disease build up. But only minimum temperature was significant at 0.01 level in all the planting dates and maximum temperature was significant at 0.01 level in two dates of planting. Apparent rate of infection of the disease and area under disease progress curve were calculated for different planting dates of potato. From the results it is evident that late blight of potato progressed almost in an exponential fashion starting from its first appearance. As the crop approached towards maturity and weather became unfavourable for the pathogen the rate of progress declined. This may be due to non-availability of healthy tissue.

Downy Mildew Disease Severity on Different Dates of Sowing Under Variable Weather Conditions in Different Varieties of Isabgol

The downy mildew incited by Peronospora plantaginis Underwood is one of the economically important diseases of Isabgol. It is important to study and understand the role of different dates of sowing on the development of diseases and their eco-friendly management. The downy mildew symptoms appeared in four different varieties viz. GI-2, Niharika, H1-5, and HI-2009 sown on 28th October (1st DOS) on 74-76 DAS whereas it was 52-54 days when sown on 12th November (2nd DOS) and 51-52 days on the crop sown on 28th November (3rd DOS). The maximum disease intensity of 62.77% was observed during the second date of sowing and the least disease intensity was recorded on the third date of sowing (27.77%). The maximum average disease progression (7.50 cm) was observed on the first date of sowing and a minimum of 6.49 cm on the third date of sowing. As the disease intensity increased AUDPC values also increased and these values were almost similar for all four varieties with the date of sowing. The apparent infection rate increased to a greater extent from the first date of sowing to the second date of sowing thereafter, decreased during the third date of sowing.

Genetic variation of infection degrees to blast disease among rice genotypes

AbstractThe blast of rice caused by Pyricularia oryzae is a disease prevalent throughout the world. The pathogen overwintering in rice straw and stubble for many years makes disease mitigation difficult. Among all available methods of managing disease, the use of resistant varieties is an economical approach. The objective of this study was to identify genotypes with slow‐blasting that could be used in breeding resistant hybrids. A total of 25 rice genotypes with different combinations of resistance genes were tested in 2013 and 2014 for rice blast resistance. The reactions of genotypes varied from highly resistant to highly susceptible. Of the 25 genotypes tested in 2013, only three were highly resistant to leaf blast (disease score: 1), while Rasi and RamanadStr3 were resistant (disease score: 2). Genotypes Co39 and HR12 were highly susceptible recording a disease score of 8 and the remaining genotypes were classified as susceptible with scores ranging from 5 to 7. In 2014, only Tetep genotype was found highly resistant to leaf blast with disease score ‘1’, and genotypes NILA57, RamanadStr3, Shia‐tia‐tsao, IR64, Rasi, and Tadukan were resistant with disease scores ranging from 2 to 3. The remaining genotypes were susceptible to leaf blast with disease scores of 4–7 and two genotypes Co39 and HR12 were highly susceptible to leaf blast (disease scores: 8–9). For neck blast, all genotypes were resistant (disease scores: 0–3) in both years except for CO39 and HR12, which were recorded as moderately resistant in 2013 and resistant in 2014. Based on 2 years of data on the apparent rate of infection, area under the disease progress curve, and components of slow‐blasting, the genotypes viz., IR64, Tadukan, Rasi, Tetep, and RamanadStr3 were identified as slow‐blasting types. Hence, these genotypes can be harnessed to develop blast‐resistant varieties in rice breeding programmes.

Influence of weather parameters on powdery mildew of mango inflorescence in humid tropics of South Gujarat

The influence of environmental parameters on the development of powdery mildew caused by Oidium mangiferae Berthet on mango inflorescence was studied for seven consecutive years (2012-18) in humid tropics climatic conditions of South Gujarat. The disease incidence and severity (DIS), area under disease progress curve-AUDPC (A-value) and apparent infection rate (r-value) were recorded at panicle and fruit setting stages of the tree at weekly intervals. The correlation studies showed that incidence and severity of powdery mildew significantly negative relationship with morning relative humidity (r = -0.631; p<0.05 and r = -0.721; p<0.01) and average relative humidity (r = -0.766 and r = -0.787; p<0.01). Temperature (maximum and average) and evaporation showed positive relationship with incidence and severity of powdery mildew. Further, stepwise linear regression model indicated that average relative humidity as single predictor independent variable had the strongest relationship disease incidence and severity, which explained 59 percent disease incidence and 62 percent for disease severity variability. This forewarning model can be useful for efficient management of powdery mildew disease of mango and as well as agro advisory services to farmers.

Evaluation of 20 enset (Ensete ventricosum) landraces for response to Xanthomonas vasicola pv. Musacearum infection

Xanthomonas wilt, caused by Xanthomonas vasicola pv. musacearum (Xvm), formerly X. campestris pv. musacearum, is the most threatening and economically important disease of enset (Ensete ventricosum), the multipurpose food security crop orphan in south and southwestern Ethiopia. Xvm has also had a major impact on banana and plantain production in east Africa following its detection in Uganda in 2001 and subsequent spread. The only current effective control of this disease relies on integrated disease management strategies including minimizing field pathogen inoculum and deployment of wilt-resistant enset landraces. Identifying landraces with stable and durable Xvm resistance will greatly accelerate breeding programmes. While previous reports have identified landraces with varying degrees of tolerance to Xvm, no systematic study has collectively assessed their relative resistance. Here we undertook a detailed “common garden” analysis of 20 enset landraces previously reported to exhibit lower susceptibility to Xvm using an aggressive Xvm inoculum isolated from a disease hotspot area. Detailed longitudinal and survival analyses were applied to each landrace, using a combination of area-under-disease progress stairs, disease index and apparent infection rate to capture disease metrics as well as disease progression symptoms. Considerable variation was observed among the 20 landraces; however, none exhibited full immunity to Xvm infection. Landraces Haella, Mazia and Lemat showed the lowest susceptibility to Xvm as evidenced by reduced disease units and higher survival rates compared to the susceptible control landrace Arkiya, which exhibited the highest infection level and lowest survival rate, consistent with a high degree of susceptibility to Xvm. Thus, we have in this controlled experiment identified new material suitable for incorporation into future breeding programmes to develop Xvm-resistant enset varieties.

Yield loss assessment due to Alternaria blight disease in rapeseed and mustard: Yield loss due to alternaria Blight in rapeseed and mustard

Alternaria blight disease in rapeseed-mustard caused by Alternaria brassicae and A. brassicicola is the important disease of rapeseed-mustard crop in India. The experiment was conducted to assess the yield losses due to Alternaria blight in different released cultivars of rapeseed-mustard during Rabi 2016-17 and 2017-18 at Student’s Instructional Farm of the A. N. D. University of Agriculture and Technology, Kumarganj, Ayodhya by planting 15 varieties of the rapeseed-mustard namely RH-749, Pusa gold, KBS-3, GSL-5, GSL-2, Pusa mustard-27, Jhumka, Anuradha, PT-30, T-27, PM-25, Pusa aditya, PT-303, Sheetal, TMLC-2 in six replications (three protected and three unprotected under natural conditions). Seed of each variety were treated with Apron @ 6g/kg and three spray of Trifloxystrobin 25% + Tebuconazol 50% (Nativo) @ 0.08% in protected replication. The minimum disease severity on leaves and pods were recorded in protected and unprotected conditions in the variety GSL-5 (2.65% and 16.26%), (1.75% and 6.32%) followed by GSL-2 (3.20% and 19.72%), (1.89% and 6.75%) Pusa aditya (6.91% and 19.89%), (2.18% and 7.20%) and Sheetal (7.99% and 23.13%), (3.21% and 7.43%), respectively. On the basis of mean values the minimum infection rate on pods was recorded GSL-2 (0.083 and 0.042) followed by Pusa aditya (0.089 and 0.045), respectively. The minimum AUDPC on leaf under protected and unprotected was recorded on cultivar GSL-5 (76.40 and 496.20) followed by GSL-2 (88.80 and 596.85), Pusa aditya (205.35 and 588.25), Sheetal (241.70 and 717.30) and RH-749 (244.95 and 950.85), respectively. Whereas the minimum AUDPC on pod was recorded with variety GSL-5 (32.10) and Pusa aditya (200.25) followed by [GSL-2 (34.65) and Sheetal (206.65)], [Pusa aditya (39.35) and RH-749 (566.41)] and [Sheetal (60.95) and Pusa mustard-27 (741.75)], respectively. The maximum yield avoidable loss (%) was recorded T-27 (46.67%) followed by Jhumka (44.53%, Anuradha (40.00%), KBS-3 (38.77%) and Pusa gold (34.13%), respectively. Minimum avoidable loss (%) was recorded on cultivar GSL-5 (11.09%) followed by Anuradha (14.36%), GSL-2 (17.73%), RH-749 (17.90%) and Pusa aditya, respectively. In present investigation out of 15 genotypes examined for blight resistance, GSL-5, Pusa Aditya, Sheetal and GSL-2 exhibited good level of partial resistance i.e. moderately resistance. Other 11 varieties RH-749, Pusa gold, Pusa mustard-27, Jhumka, Anuradha, PT-30, PT-303, T-27, KBS-3, TMLC-2 and PM-25 were susceptible based on the mean basis severity (PDI), reduced apparent infection rate and lesser value of AUDPC.

Identification of Source of Resistance to Horse Gram Yellow Mosaic Disease (HgYMD) in French Bean (Phaseolus vulgaris L.)

Background: Horse gram yellow mosaic disease (HgYMD) is one of the major limiting factor for legumes production in India as it can cause economic loss up to 100%. Till date, horse gram yellow mosaic virus was rare to infect french bean, but now-a-days, it has become the major causal agent for yellow mosaic epidemics in the southern part of India. Few bush type varieties, resistant to yellow mosaic disease are released but not specifically resistant to HgYMD. So, systemic breeding work has been initiated to identify the resistant source for HgYMD in french bean. Methods: Seventyone genotypes of french bean were screened in a randomized complete block design (RCBD) with three replications under natural epiphytotic as well as artificial condition during Summer, 2018 at ICAR-IIHR, Bengaluru, India. Result: The genotypes varied for percent disease index (PDI), area under disease progress curve (AUDPC) and the apparent rate of infection per unit time period (r). Two varieties i.e., Jade-5058 and Arka Arjun were showing less PDI of 13.33 and 14.44, least average rate of infection of 0.64 and 0.65 and lowest AUDPC value of 350.54 and 359.16 respectively, compared to other genotypes. Average PDI of Arka Arjun and Jade-5058 were 13.33 and 12.22 under artificial screening, which were much lesser than susceptible check Arka Komal (PDI 92.22) and Arka Anoop (PDI 90.00). Resistant genotypes identified from this experiment can be used for breeding HgYMD resistant french bean lines.

Diversity within and among Ethiopian barley (Hordeum vulgare L.) landraces in resistance to barley net blotch (Pyrenophora teres F. teres (Ptt))

In this study, we evaluated a collection of 585 barley landraces along with 10 checks at Sinana Agricultural Research Center (SARC) and Bale-Goba research sites in 2018/19 and 2019/20 cropping seasons for resistance to net blotch (Pyrenophora teres F. teres (Ptt)). The experiments were laid out in an augmented complete block design. Data on agronomic performance and disease response were recorded. Analysis of variance showed highly significant variations between and within the landraces and cultivars in net blotch percent severity index (PSI), area under the disease progress curve (AUDPC), apparent infection rate, days to heading, plant height, number of fertile tillers per plant, seeds per spike, spike length and thousand seed weight. The overall mean net blotch epidemics varied from area under disease progress curve (AUDPC) of 86 to 1835. The disease was as high as AUDPC of 1378 on the susceptible check ‘Abdanie’. Similarly, the variations between and within barley landraces in terms of regions of origin, altitude classes and ear-types were significant. Out of the 585 barley landraces evaluated, 198 (33.85%) had significantly lower disease than the susceptible check, of which 12 (2.05%) and 186 (31.79%) landraces, respectively showed resistant (R) and moderately resistant (MR) infection types. The frequency of resistant landraces was more in third (2000-2500 m) and fourth (>2500 m) altitude classes and six-rowed and irregular barley types than in lower altitude areas and two-rowed ear-types. Furthermore, the correlation analysis among PSI and some yield components revealed adverse effect of the disease on grain yield of barley.

Crown rust on oat genotypes with different levels of resistance: damages and losses

ABSTRACT: The evolution in virulence of Puccinia coronata f. sp. avenae has challenged the genetic resistance to crown rust in oat genotypes. New resistance sources are constantly required for yield stabilization and costs reduction. This study aimed to characterize the crown rust resistance of oat genotypes and the disease´s productive and economic impact. Experiments were conducted in two environments, with and without chemical control. Resistance was measured by disease progress, apparent rate of infection, final severity and pustule size. Damages were based on reduction of yield, 1000 grain mass and hectoliter mass. UFRGS16Q6030-2 was immune. In both environments, UFRGS166091-2 and URS Brava exhibited the greatest level of resistance and the smallest grain yield reduction, while URS 22 was highly susceptible, reducing more than 70% of its grain yield. These results surpass the negative impacts of the disease previously reported in oats, particularly related to grain yield. The data presented in this paper highlighted the importance of genetic resistance, particularly partial resistance, for maintaining oat genetic yield potential, reducing environmental contamination with less fungicides, and increasing economic gains with oat cultivation.

Screening of rose genotypes for resistance against powdery mildew disease

A total of fifty five rose genotypes were screened against natural incidence of powdery mildew disease caused by Podosphaera pannosa, under a naturally ventilated polyhouse. Evaluation trial was conducted for two seasons during 2015-16 and 2016-17 to screen rose genotypes for their reaction to powdery mildew. The pooled apparent infection rate (r) of disease calculated for both seasons has showed a wide variation among genotypes. Based on per cent disease index (PDI), genotypes were categorized into different classes as tolerant (0-10 PDI), moderately tolerant (10.1-20 PDI), moderately susceptible (20.1-30 PDI) and highly susceptible (>40 PDI) to powdery mildew. Further, it was found that the accumulation of disease was low in case of moderately susceptible varieties compared to highly susceptible ones as indicated by the area under disease progression curve (AUDPC).

Screening of sesame genotypes against powdery mildew disease caused by Erysiphe cichorecearum

Powdery mildew disease of sesame occurs on epidemic scale in areas of high rainfall and humidity coupled with low night temperature causing considerable yield losses. Use of host plant resistance is the practical approach to manage this disease, but proper resistance sources with combining ability for the trait are unknown. Hence, an experiment was conducted to determine resistance in sesame genotypes against powdery mildew disease. Among the twenty four genotypes screened, none was found resistant while, nine genotypes exhibited moderately resistant to tolerant reaction and 15 genotypes exhibited susceptible reaction. Apparent rate of infection value varied and at times they did not remain consistent for given genotype and also did not show a particular trend which is attributed to genetic character of the genotype. The AUDPC values differed considerably for different genotypes. The values of AUDPC and apparent rate of infection of susceptible varieties were high as compared to moderately susceptible varieties. Genotype ‘JLS-302-11’ and ‘JLT-7’ having minimum AUDPC and apparent rate of infection value showed lowest intensity of powdery mildew while, genotype ‘JLT-408’ having maximum AUDPC and apparent rate of infection value showed highest intensity of powdery mildew.

Epidemiological Criteria to Support Breeding Tactics Against the Emerging, High-Consequence Wheat Blast Disease.

Plant disease epidemiology can make a significant contribution for cultivar selection by elucidating the principles of an epidemic under different levels of resistance. For emerging diseases as wheat blast (WB), epidemiological parameters can provide support for better selection of genetic resources. Field experiments were conducted at two locations in Bolivia in 2018-2019 to characterize the temporal dynamics of the disease on 10 cultivars with different levels of reaction to WB. Logistic models best (R2 = 0.70-0.96) fit the disease progress curve in all cultivars followed by Gompertz (R2 = 0.64-0.94), providing additional evidence of a polycyclic disease. Total area under disease progress curve (tAUDPC), final disease severity (Ymax), and logistic apparent infection rates (rL*) were shown to be appropriate epidemiological parameters for describing resistance and cultivar selection. Cultivars that showed a high spike AUDPC (sAUDPC) showed a high leaf AUDPC (lAUDPC). tAUPDC, Ymax, and rL* were positively correlated among them (P < 0.01) and all were negatively correlated with grain weight (P < 0.01). Based on the epidemiological parameters used, cultivars that showed resistance to WB were Urubó, San Pablo, and AN-120, which were previously reported to have effective resistance against the disease under field conditions. The information generated could help breeding programs to make technical decisions about relevant epidemiological parameters to consider prior to cultivar release.

Biofungicides evaluation in two coffee cultivars for Hemileia vastatrix control

El objetivo del presente estudio fue evaluar el efecto de biofungicidas elaborados con &lt;em&gt;Azadirachta indica&lt;/em&gt;, &lt;em&gt;Melaleuca alternifolia&lt;/em&gt; y la combinación de&lt;em&gt; Bacillus subtilis&lt;/em&gt; con &lt;em&gt;A. indica&lt;/em&gt; y &lt;em&gt;Syzygium aromaticum&lt;/em&gt;, en el control de la roya causada por &lt;em&gt;Hemileia vastatrix&lt;/em&gt;, 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. &lt;em&gt;M. alternifolia&lt;/em&gt; 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&amp;lt;0.0001). Los biofungicidas no suprimieron la infección, pero los resultados sugieren que debe continuarse la investigación en este patosistema.

Screening brown spot resistance in rice genotypes at the seedling stage under water stress and irrigated conditions

The nursery resistance of 95 rice genotypes to brown spot (BS) was evaluated under water stress and irrigated conditions during 2017 and 2018. Disease assessment was done by calculating the final brown spot index, area under the disease progress curve and apparent infection rate. Susceptible genotypes demonstrated high disease indices at both the hydrological treatments in comparison to resistant genotypes. Water shortage at the seedling stage caused an increasing rate of disease severity in rice genotypes; however, the responses varied among genotype. These findings suggest that the evaluation of resistance to brown spot disease could be done under water stress conditions. Among genotypes tested, 13 genotypes, i.e. Gharib-Siyah-Reihani, Ghashangeh, Gerdeh, Shahpasand, Neda, Sange-Tarom, Hasani, Dasht, Gohar, Kanto 51, Khazar, Koohsar and Mohammadi-Chaparsar exhibited seedling resistance to brown spot disease at both hydrological conditions which could be recommended for cultivation and further breeding utilization to develop promising resistant lines in management of the brown spot disease.