Area Under Disease Progress Curve Values Research Articles

Screening of onion (Allium cepa) genotypes to find out novel resistant source against purple blotch (Alternaria porri)

Purple blotch caused by Alternaria porri (Ellis) Cif., 1930 causes huge losses to bulb crop and seed crop of onion (Allium cepa L.). This is a major disease affecting successful onion production in majority of the onion growing areas. To identify resistant source against purple blotch, 34 onion genotypes with good marketable yield based on field evaluation trial in 2017 and allied species Pusa Soumya were screened under protected conditions during kharif, 2018 at insect proof net house facility of ICAR-Indian Agricultural Research Institute, New Delhi. The pure culture of Alternaria porri, isolated from infected leaf samples of onion crop raised under natural epiphytotic conditions during kharif, 2017. Highest change of disease severity index was observed between 1–2 weeks post inoculation (WPI) while highest disease severity index was recorded at 5 WPI suggesting that preventive measures must be employed as soon as disease symptoms appear in the field. The disease severity index ranged from 0.10–33.33 at 1 WPI, which increased to 9.33–89.33 at 5 WPI. The cultivated allied species Pusa Soumya was identified as novel resistance source with DSI value less than 10.0% at 5 WPI. Four genotypes exhibited moderately susceptible reaction, while 20 genotypes were susceptible and 10 genotypes were highly susceptible. The area under disease progress curve (AUDPC) value ranged from 22.33–240.17. Pusa Soumya had the lowest value and among onion lines Arka Kirtiman was found promising. Three onion genotypes had low relative AUDPC value and can effectively be utilized in resistance breeding programme. The average daily temperature between 20–25°C and relative humidity above 75% was found ideal for disease development.

Partial Resistance Components and Morphological Traits Aid Selection of Resistant Wheat Genotypes against Spot Blotch

Spot blotch caused by Bipolaris sorokiniana results substantial yield losses (15-80%) in an Indian subcontinent. Wheat varietal improvement through breeding followed by evaluation of elite germplasms against a particular disease is crucial method to manage diseases. Fifty diverse wheat genotypes and two susceptible checks viz., Sonalika and Nepal 297 were evaluated under artificial epiphytotic condition against spot blotch at NWRP, Bhairahawa, Nepal in 2017-18 and 2018-19. Evaluation was based on partial resistance components viz., lesion sizes, lesion types (chlorotic/ necrotic), lesion characteristics (sporulating/ non-sporulating) and area under disease progress curve (AUDPC) and morphological traits viz. lesion mimic, leaf angle, leaf tip necrosis and plant height. Statistical analysis revealed that genotypes with smaller lesion size (<1 cm), small dark brown to black lesions with or without chlorosis/ necrosis and non sporulating lesions had lower AUDPC (<225). Similarly genotypes with erect to semi erect leaf (leaf angle 1-2), medium to high leaf tip necrosis (2-4), low percentage of lesion mimic (0-22.5%) were found resistant (AUDPC<225) to moderately resistant (AUDPC value 226-315). Moreover AUDPC showed strong and positive correlation with lesion sizes (0.76), lesion types (0.84) and lesion characteristics (0.54). Twenty genotypes were found resistant (AUDPC<225), could be used as new resistance sources in breeding program. However genotypes viz., KACHU/BECARD//WBLL1*2/BRAMBLING/3/ATTILA*2/PBW65//MURGA, FRET2*2/SHAMA//TNMU/3/FRET2*2/SHAMA/4/UP2338*2/KKTS*2//YANAC/5/FRET2*2/SHAMA//PARUS/3/FRET2*2/KUKUNA, KACHU#1//PI610750/SASIA/3/KACHU/4/MUU#1//PBW343*2/KUKUNA/3/MUU/5/KACHU#1//PI610750/SASIA/3/KACHU, BORL14//KFA/2*KACHU and KFA/2*KACHU//QUELEA were found excellent based on partial resistance components and morphological traits. These genotypes could be further evaluated for yield potential in multi environment and better performing genotypes could be released as resistant varieties for spot blotch.

Cultivar and Fungicide Evaluations for Cercospora Leaf Spot Control in Organic and Conventional Table Beet Production

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive foliar disease of table beet (Beta vulgaris ssp. vulgaris) in Wisconsin, USA, and globally. Under conducive conditions, symptomatic lesions on the leaf expand and coalesce forming large necrotic areas that can ultimately lead to complete defoliation. This damage reduces productivity and threatens the ability to mechanically harvest. CLS damage also detracts from the visual appeal of fresh market bunched beets to such an extent that growers risk buyer rejection if CLS severity is observed to be greater than 5%. Fungicide use for CLS control is threatened by the emergence of resistant C. beticola strains, and the application of host resistance is constrained by limited knowledge of cultivar reaction to CLS in table beet. This study aimed to address the knowledge gaps of fungicide efficacy and cultivar reaction by conducting replicated field trials in multiple table beet growing environments across Wisconsin. Broad variation for resistance to CLS was observed among the 10 included cultivars. The mean area under disease progress curve (AUDPC) across environments for the most susceptible cultivar was 267% greater than the most resistant cultivar. Spearman correlations between environments for mean cultivar AUDPC value ranged from 0.71 to 0.99, revealing consistent cultivar CLS reactions across environments. Although susceptible cultivars surpassed 5% severity in all environments, the resistant cultivars remained below this threshold in six of the 10 environments. By comparison with resistant sugar beet (Beta vulgaris ssp. vulgaris) cultivars, however, all tested table beets appeared susceptible to CLS, highlighting the potential for a CLS breeding effort in table beet. Neither of the evaluated Organic Materials Review Institute–listed treatments were effective at limiting CLS disease progress, whereas both tested conventional fungicides significantly reduced disease severity over the nontreated plots. These findings may provide helpful guidance to table beet growers affected by CLS in Wisconsin and beyond.

Wheat Genotype Evaluation for Spot Blotch Disease Resistance: Unveiling Resilient Varieties

Spot blotch, caused by Bipolaris sorokiniana (Sacc.) Shoemaker is a major disease of wheat (Triticum aestivum L.), in all the six agro climatic zones of India. Estimation of losses due to this disease vary from location to location, due to diverse environmental conditions. The use of resistant cultivars is the most effective, long-lasting, cost-effective, and environmentally friendly technique for sustainable disease control. The experiment was conducted at Crop Research Centre, Chirodi farm of Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (U.P.). Among the tested varieties, disease index and AUDPC values varied significantly for both years’ data viz. 2021-22 and 2022-23. In this experiment 32 wheat varieties were screened against B. sorokiniana under artificial epiphytotic conditions in the field. Each variety were sown in two row of three-meter length with three replications, two line of susceptible check RAJ 4015 was sown at every ten genotypes of interval. Among 32 wheat varieties, two varieties were found to be resistant, eleven varieties were found moderately resistant, fourteen varieties were found moderately susceptible and five varieties were found susceptible, none of the variety was found immune and highly susceptible against spot blotch disease. Area Under Disease Progress Curve (AUDPC) calculated for the thirty- two wheat varieties on the basis of disease index. AUDPC varies from 212.90 to 1143.9 and 198.80 to 1144.90 during the 2021-22 and 2022-23 years’ data. The pooled mean, Area Under Disease Progress Curve varied from 205.85 to 1144.40, showing the fast progress of disease in all genotypes. It was observed that different wheat varieties expressed varied type of disease response against B. sorokiniana.

Host resistance by sowing date interaction reduced Fusarium wilt pressure and improved grain yield of chickpea (Cicer arietinum L.) in North Shoa, Ethiopia

AbstractChickpea Fusarium wilt is seriously damaging chickpea productivity. To determine the integrated effects of three sowing dates and four chickpea varieties on epidemics of Chickpea Fusarium wilt and grain yield, field experiments were conducted in naturally infested soils at Alem Ketema and Enewari, Ethiopia, during 2018. Treatments were factorial arranged in a randomized complete block design with three replications. Results showed that variety Mastewal recorded relatively low mean Fusarium wilt incidence at Alem Ketema (15.344%) and Enewari (38.19%) compared with the other test varieties. Variety Mastewal also produced high grain yield over others at Alem Ketema (1155.14 kg ha−1) and Enewari (1120.91 kg ha−1). Related trends were observed for infection rate, area under disease progress curve (AUDPC), and yield components at both locations. Late August sowing resulted in higher stand count at harvest (132.08 and 102.08), number of pods (50.28 and 40.62), grain yield (1030.86 and 1122.08 kg ha−1), and lower AUDPC value (321.30%‐days and 540.34%‐days) than early August sowing in that order at Alem Ketema and Enewari. Interaction of variety Mastewal by late August sowing gave relatively high grain yield (1341.36 and 1331.85 kg ha−1), and it had low AUDPC (196.58%‐days and 483.36%‐days) at Alem Ketema and Enewari, respectively. Conversely, early planting caused up to 25.32% (Alem Ketema) and 193.67% (Enewari) yield reductions in chickpea varieties over late planting. Therefore, delaying sowing date and growing variety Mastewal found to maximize chickpea yield and minimize effect and progression of Fusarium wilt, and hence, recommended for the study areas.

Secondary metabolites of the granular form of Pseudomonas fluorescens P60 and its applications to control tomato bacterial wilt

Abstract. Soesanto L, Saputra DA, Sastyawan MWR, Mugiastuti E, Suprapto A, Rahayuniati RF. 2023. Secondary metabolites of the granular form of Pseudomonas fluorescens P60 and its applications to control tomato bacterial wilt. Biodiversitas 24: 2475-2482. Bacterial wilt is one of the important diseases of tomatoes caused by Ralstonia solanacearum (Smith 1896) Yabuuchi et al. 1996. Its control can be achieved by applying secondary metabolites of Pseudomonas fluorescens Migula 1895 P60 in granular form. The study aimed to determine the shelf life of the secondary metabolites P. fluorescens P60' in granular form and its application to manage bacterial wilt and the performance of tomatoes. The study was conducted for five months at the Plant Protection Laboratory and Experimental Farm, Faculty of Agriculture, Universitas Jenderal Soedirman. A randomized block design was used with four replicates and six treatments, consisting of R. solanacearum (control), R. solanacearum + 1, 5, 10, or 15 g, and bactericide (a.i. agrimycin sulphate 20%). Variables observed were inhibition zone, incubation period, disease intensity, the area under disease progress curve (AUDPC), crop height, crop fresh and dry weight, root fresh and dry weight, and phenolic compounds qualitatively. Results of the research showed that the granular formula until the 4th week still had an inhibition zone between 21.67-23.34%. However, the granules stored for as much as 15 g for four weeks effectively reduced disease intensity by 75.00%, decreased AUDPC value by 74.72%, and increased plant height, root dry weight, and fresh crop weight as well 44, 62.5, and 65.65 %, respectively. In addition, the granular formula increased the content of tomato phenolic compounds qualitatively.

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.

Distribution of Bipolaris maydis in southern Khyber Pakhtunkhwa (KP) – Pakistan and estimation of yield losses in maize crop

Maydis leaf blight, is an important disease of maize in Khyber Pakhtunkhwa (KP) – Pakistan. Knowledge about distribution pattern of a disease in an area is helpful for adoption of appropriate disease management strategy. Therefore, an extensive survey of the disease was conducted in southern districts of the province in 2020. Four union council in each district and five fields per union council were assessed in “X” shaped pattern. The highest disease incidence was found in district Bannu (78.05%) while least was detected in district Tank (39.84%). Similarly, the isolates of Bannu and Kohat districts exhibited larger colony diameter and spore size than other isolates. Yield losses were also assessed based on attainable and actual yield. The highest value of area under disease progress curve (AUDPC) was observed for cultivar Azam (229.7). Regression analysis indicated that a unit (1%) increase in AUDPC value increased yield loss by 7.6%.

Information on disease resistance patterns of grape varieties may improve disease management.

Resistance to downy mildew (DM) and powdery mildew (PM) contributes to sustainable vineyard management by reducing the diseases and the need for fungicide applications. Resistant varieties vary in their degree of resistance to DM and PM, and in their susceptibility to other diseases. As a consequence, fungicide use may differ among varieties depending on their "resistance patterns" (i.e., the resistance level of a variety toward all of the diseases in the vineyard). The resistance patterns of 16 grapevine varieties to DM, PM, black rot (BR), and gray mold (GM) were evaluated over a 4-year period under field conditions. Disease severity was assessed on leaves and bunches, and the AUDPC (Area Under Disease Progress Curve) was calculated to represent the epidemic progress. GM was found only on bunches and only at very low levels, irrespective of the year or variety, and was therefore excluded from further analyses. The varieties were then grouped into four resistance patterns: i) low resistance to DM and PM, intermediate resistance to BR; ii) high resistance to DM, intermediate resistance to PM, low resistance to BR; iii) intermediate resistance to DM and BR, low resistance to PM; and iv) high resistance to DM, PM, and BR. AUDPC values on leaves were positively correlated with AUDPC values on bunches for susceptible varieties but not for resistant ones, with the exception of PM. Therefore, bioassays with leaves can be used to predict the resistance of bunches to DM and BR for susceptible varieties but not for resistant ones. These results may facilitate both strategic and tactical decisions for the sustainable management of grapevine diseases.

English

Production of wheat in Ethiopia is under danger from wheat stem rust, which is brought on by the disease Puccinia graminis f.sp. tritici and has resulted in a yield loss of 100%. An investigation was conducted in a hotspot area (Debere Zeit, Ethiopia) to evaluate the status of Ethiopian durum wheat cultivars for their level of stem rust resistance in the field. During the main seasons of 2017, 2020, and 2021, 34 durum wheat varieties with three susceptibility checks were examined. Terminal Rust Severity (TRS), Coefficient of Infection (CI) and Area under Disease Progress Curve (AUDPC) were used to measure stem rust field resistance. Analysis of all disease parameters was carried out using R studio. Due to their low levels of AUDPC, ACI, and TRS values combined with MR infection type, two commercial varieties (Oda and Tob-66) may have a significant resistance gene(s) and seven varieties (Boohie, Kilinto, Ginchi, Robe, Toltu, Lelisso, and Bekelcha) showed a moderate level of field resistance with MR to MRMS responses and may have adult plant resistance mediated by minor resistance genes. Stem rust was found to affect 73.5% of the Ethiopian durum cultivars. Therefore, this study suggests that the national breeding effort should focus on local durum cultivars rather than the ones that were imported. Key words: Field resistance, durum wheat, stem rust, Puccinia graminis f.sp tritici.

Management of powdery mildew and aphid in organically grown Indian mustard (Brassica juncea L.) through different oils

All the cultivated Brassica species exhibited powdery mildew severity with highest (43.2%) on Brassica juncea followed by B. rapa (28.0%) which is widely cultivated in India. Yield losses from 10-90 per cent with reduction in 6.47 per cent oil content have been estimated from different Brassica species. Hence, the present study was carried out to evaluate different oils to manage powdery mildew disease and aphids in an organically grown mustard crop. Five oils (castor, groundnut, sunflower, neem and mustard oil) and ghee were evaluated against powdery mildew (Erysiphae cruciferarum) and aphid (Lipaphis erysimi) of Indian mustard (Brassica juncea). Castor oil 50 EC, neem oil 50 EC and mustard oil 50 EC and deshi ghee 50 EC (@ 100 ml/10 litre water) were effective over untreated control in reducing powdery mildew disease severity when applied as foliar spray (@ 5 ml/litre) in the experiment carried out in organic field (plot No. B-2 at Agronomy Instruction Farm, S. D. Agricultural University, Sardarkrushinagar). Maximum reduction in germinated conidia (66.0%) over control, disease severity (50.0%), area under disease progress curve (AUDPC) values (51.8%) and maximum increase over control in 1000 seed weight (16.7%) and seed yield (10.3%) was observed with neem oil. This was followed by the application of ghee which exhibited reduced disease severity (22.9%) and AUDPC values (30.6%) and increased seed yield (8.1%) and the application of castor oil 50 EC which exhibited an increased in seed yield (8.0%) and reduced powdery mildew severity (20.8%). Shortest log phase was observed with neem oil during 10th std. week. All the oils tested (castor, groundnut, sunflower, neem and mustard oil) and deshi ghee were effective in reducing aphid population (39.5 to 65.9%) and damage index (6.1 to 25.1%). A maximum reduction in aphid population (65.9%) over control and lowest aphid damage index (3.70) was observed with neem oil 50 EC 6 days after 2nd spray. Application of neem oil, castor oil and deshi ghee resulted in increased seed yield (8.1 to 10.4%). This information could be useful in devising strategies for powdery mildew and aphid management in organic cultivation, eco-friendly management and IPM of mustard.

Close-Range Thermography and Reflectance Spectroscopy Support InVitro and InVivo Characterization of Colletotrichum spp. Isolates from Mango Fruits.

Colletotrichum causing anthracnose in mango is known for its variable virulence that may have an effect on disease development and efficacy of management strategies. In this study, we characterized Colletotrichum spp. isolated from mango fruits under invitro and invivo conditions using close-range thermography and reflectance spectroscopy. Twenty-six isolates were phylogenetically characterized to ascertain species using the internal transcribed spacer sequence. Virulence, spectral (invivo and invitro), and thermographic responses (invivo) of these isolates were analyzed. Isolates were grouped into the Colletotrichum gloeosporioides species complex and classified into eight morphotypes. Mycelial growth, conidia production, sporulation abundance, and area under disease progress curve (AUDPC) varied largely among isolates. Disease symptoms were observed 4 days after inoculation (dai), and, for most morphotypes, changes in tissue temperature were registered at 11 dai, with the greatest decrease at 14 dai with pathogen sporulation. In vitro and invivo morphotypes shared changes in the spectrum range, and main variations were found in the number of informative spectral bands. In vivo average gross reflectance was higher in disease-inoculated tissue than in healthy uninoculated tissue. Morphotype responses varied depending on AUDPC values and postinoculation time. Discriminant analysis of the spectral response using principal component analysis and partial least squares regression explained 94 to 96.3 and 98 to 99.9% of the variance from invitro and invivo tests, respectively. Spectral markers were obtained for four distinct morphotype groups. We found three (550 to 650, 650.1 to 790, and 1,300 to 1,400 nm) and two (520 to 830 and 1,100 to 1,450 nm) regions with highly (P < 0.05) discriminant spectral bands for diseased fruits and morphotype characterization.

Phenotypic Screening of F3 Rice (Oryza sativa L.) Population Resistance Associated with Sheath Blight Disease

The experiment was conducted during July–December, 2019 in the Agricultural Research Farm Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India. One hundred and twenty-two F3 rice populations from the cross made between IC277332 (susceptible parent)×IC277275 (moderately resistant parent) were evaluated against sheath blight disease under field conditions. The area under disease progress curve (AUDPC) values categorized rice population into four groups viz., moderately resistant (24), moderately susceptible (38), susceptible (40), and highly susceptible (20). A moderate resistance level to the disease was identified during the study in 24 lines (19.6%) with a mean Percentage Disease Index (PDI) of 12.22%−36.6%. Furthermore, 38 individuals showed moderate susceptibility with AUDPC values (1012−1446 day-1). The maximum PDI and AUDPC value were 76.11 and 2325.56, and the minimum PDI and AUDPC values were 22.78 and 622.22, respectively. The principal component (PCA) biplot analysis showed 71.62% and 12.05% variation, respectively. Unweighted Pair Group Method of Arithmetic Means (UPGMA) cluster analysis grouped the 122 individuals into two major clusters, A and B and sub-clusters. These findings indicated that no rice line resistant to sheath blight had been identified. However, few population lines exhibited moderate resistance, which can be utilized as donor lines to generate sheath blight-resistant rice cultivars. These findings will provide a solid basis for our future breeding and screening activities at the institution.

Evaluation of F2:3 rice population resistant to Rhizoctonia solani Kuhn inciting sheath blight disease

Rice sheath blight caused by the soil-borne fungal pathogen Rhizoctonia solani Kuhn is an economically important disease in rice resulting in enormous yield losses worldwide. In the present investigation, a population constituting F3 lines resulted from the cross made between IC277332 (susceptible parent) and Tetep (resistant parent) were evaluated for sheath blight resistance and other agronomic traits over a season. The rice population lines were categorized into four groups viz., moderately resistant (11), moderately susceptible (63), susceptible (24), and highly susceptible (8), based on area under disease progress curve (AUDPC) values. During the study, nine moderate resistant lines showed, less AUDPC values in comparison to Tetep. Furthermore, 63 individuals (60%) exhibited moderate susceptibility with AUDPC values (677-987 per day). The principal component biplot analysis PC1 and PC2 showed 47.08% and 13.19% variation, respectively. The employment of Unweighted Pair Group Method of Arithmetic Means (UPGMA) cluster analysis led to the grouping of the 106 individuals into 2 major clusters A and B. The results suggested that none of the rice lines was resistant to sheath blight disease. However, few lines showed moderate resistance to the disease which can be exploited for the development of sheath blight-resistant cultivars.

Genetic Studies and Response of Rice Germplasm (Oryza sativa L.) to Brown Spot Incidence in Aerobic Condition

The present investigation was carried out with 150 rice genotypes and three check varieties namely Rajshree, Pankaj and Rajendra Neelam with the view of assessing the variability in traits related to productivity and studying the response of these varieties towards brown spot resistance under the aerobic condition. These genotypes were evaluated for brown spot incidence and yield potential by recording observation for 11 quantitative traits by using augmented randomized complete block design at Rice research farm of RPCAU, Pusa, Bihar, during Kharif season of 2019. Analysis of variance revealed significant differences amongst the genotypes for all the eleven traits studied. Based on the mean performance, 14 genotypes out of 150 genotypes were significantly superior to the best check, Rajendra Neelam, for three traits viz., grain yield/ plant, Percent Disease Intensity (PDI) and area under disease progress curve (AUDPC), which are considered key traits for the assessment of brown spot incidence. The genotypes viz., VLD 16 entry no. -5, Udyagiri entry no.-9, and SKL 6 entry no.-94 significantly exhibited high mean for majority of the traits under study. Based on the AUDPC values, genotypes Satabdi, PS-4, Haryana Basmati and SKL6 were resistant for brown spot incidence. For most of the traits studied, moderate to low value of phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) was recorded. Higher magnitude of broad sense heritability and genetic advance as per cent of mean (GAM) were perceived for days to 50% flowering, plant height, no. of tillers per plant, no. of panicles per plant, filled grains per panicle, grain yield per plant, PDI, AUDPC signifying that direct selection by these traits can be rewarding for achieving yield improvisation and resistance to brown spot disease

Epidemiology of potato late blight disease and other major postharvest biotic stressesin Malawi

The epidemiology of Potato Foliar Late Blight (PFLB) disease (Phytophthora infestans) was quantified in major potato production areas of Malawi. Seed multiplication fields, tests clones and local farmers’ fields were sampled basing on Area Under Disease Progress Curve (AUDPC). The determined severity values were transformed into AUDPC coefficients characterizing rate of disease spreading across the crop. Results indicate minimum and maximum AUDPC values of 0 and 1050 respectively, with an average value of 233.57. The results show significant statistical differences in PLB disease across seed multiplication fields, test clones and local farmers’ fields. AUDPC values differed significantly (p &lt; 0.001) among potato growing districts, as well as sources of seed (aeroponics, sandponics, and vendors). Post-harvest survey targeting potato tubers showed that tubers that were sampled from Mzimba district had the highest likelihood of being infected with Potato Tuber Late Blight (PTLB), followed by potatoes that were sampled from Lilongwe (coefficients, b= 1.89, t = 6.11, p-value&lt;0.001) while the potatoes tubers that were sampled from Ntcheu did not vary in the severity with those that were sampled in Dedza. Susceptibility to potato PTLB among potato varieties were varied, with Rosita likelihood to PTLB disease, while there were no other significant differences to PTLB in the rest varieties (b=1.12, t=4.23, p-value&lt;0.001). An extended study on bacterial wilt (PBW) revealed that disease was influenced by the district where the tubers were sampled (x2= 9.26, p-value &lt; 0.001) while the type of variety sampled did not have any significant difference on PBW (x2= 3.59, p-value = 0.268). The presence of potato tuber moth which varied among the sampled districts, was not influenced by variety sampled. The paper has documented and quantified increasing epidemic spread of late blight disease and the consequent effect on sustainable potato production and clean seed systems in Malawi.

Screening global set of barley germplasm for resistance to spot blotch disease in the warm-humid plains of Nepal

Spot blotch disease (SB) caused by Bipolaris sorokiniana (teleomorph: Cochliobolus sativus ) is a major disease of barley and causes a significant yield loss under favorable conditions in the warm and humid areas. A global set of 340 barley germplasm obtained from ICARDA were evaluated for SB resistance under natural epiphytotic conditions along with two local checks (Bonus and Solu Uwa) at the research field of Nepal Agricultural Research Council, Rampur, Chitawan, Nepal for three consecutive years (2016-2018). Analysis of variance showed significant variation in Area Under Disease Progress Curve (AUDPC) of the studied genotypes in all the three years’ experiments. The check varieties were susceptible to SB (AUDPC value ≥ 750) in all the experiments. In the first-year experiment, 28, 105, 98 and 109 genotypes had resistant (R, AUDPC &lt;250), moderately resistant (MR, AUDPC 250-499), moderately susceptible (MS, AUDPC 500-749), and susceptible (S, AUDPC≥750) type of disease reaction, respectively. In the second year, 1, 42, 136 and 161 genotypes showed R, MR, MS, and S type of disease reaction. In the third-year, 69 genotypes had MR, 132 MS and 139 S type of disease reaction. Summarized across the years, about 27 % genotypes had MS to MR or R type of SB reaction. The study identified barley lines that can be a potential source of SB resistance for barley breeding programs.

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.

Isolate-Dependent Inheritance of Resistance Against Pseudoperonospora cubensis in Cucumber

Six wild accessions of Cucumis sativum were evaluated for resistance against each of the 23 isolates of the downy mildew oomycete Pseudoperonospora cubensis. The isolates originated from Israel, Europe, USA, and Asia. C. sativum PI 197088 (India) and PI 330628 (Pakistan) exhibited the highest level of resistance against multiple isolates of P. cubensis. Resistance was manifested as reduced lesion number, lesion size, sporangiophores and sporangia per lesion and enhanced encasement of haustoria with callose and intensive accumulation of lignin in lesions of both Plant Introductions (PIs) compared to the susceptible C. sativum SMR-18. In the field, much smaller AUDPC (Area Under Disease Progress Curve) values were recorded in PI 197088 or PI 330628 as compared to SMR-18. Each PI was crossed with SMR-18 and offspring progeny plants were exposed to inoculation with each of several isolates of P. cubensis in growth chambers and the field during six growing seasons. F1 plants showed partial resistance. F2 plants showed multiple phenotypes ranging from highly susceptible (S) to highly resistant (R, no symptoms) including moderately resistant (MR) phenotypes. The segregation ratio between phenotypes in growth chambers ranged from 3:1 to 1:15, depending on the isolate used for inoculation, suggesting that the number of genes, dominant, partially dominant, or recessive are responsible for resistance. In the field, the segregation ratio of 1:15, 1:14:1, or 1:9:6 was observed. F2 progeny plants of the cross between the two resistant PI’s were resistant, except for a few plants that were partially susceptible, suggesting that some of the resistance genes in PI 197088 and PI 330328 are not allelic.