Apparent Infection Rate Research Articles

Graft response of Capsicum chinense-Capsicum annuum var. glabriusculum to Begomovirus in field

Uno de los problemas fitosanitarios en el cultivo de chile es la mosca blanca, transmisor de begomovirus. Ante la necesidad de alternativas, se planteó el objetivo de evaluar la tolerancia de injertos de <em>Capsicum chinense-Capsicum annuum</em> var. glabriusculum a begomovirus bajo condiciones de campo. Se utilizaron dos materiales criollos para portainjerto (amashito y muela) y chile habanero como injerto (criollo y jaguar). Se empleó la injertación de “púa terminal” y se generaron seis tratamientos. Se registraron cada 10 días las poblaciones de mosca blanca, la incidencia y severidad de la enfermedad, con esta última se calcularon ABCDE, tasa de infección aparente y Yfinal. En etapa de producción, se determinó rendimiento, longitud y diámetro de frutos. A los 130 días después del trasplante, la menor población de mosca blanca, se cuantificó en los tratamientos injertados (muela + habanero jaguar, amashito + habanero jaguar, muela + habanero criollo y amashito + habanero criollo) que osciló entre 5.5 a 14.5 insectos por planta. La mayor incidencia y severidad promedio de virosis fue en habanero jaguar con 100 y 62%. La menor ABCPE, tasa de infección aparente y Yfinal se estimaron en muela + habanero criollo con 746.6 (% por día), 0.005 (% por día) y 23.4%, en su orden; asociado con la fortaleza genética del portainjerto. Los injertos amashito + habanero jaguar, amashito + habanero criollo y muela + habanero criollo mostraron mejor comportamiento agronómico y productividad del cultivo.

Identification of new sources of resistance to stem rust race Ug99 (TTKSK) in wheat genotypes

Stem rust disease which caused by Puccinia graminis f. sp. tritici is one of the major wheat production constraints in the high lands of central, south eastern and north western part of Ethiopia. The disease had caused up to 100% yield loss on the unprotected wheat farms. This study was conducted to identify new sources of resistance to stem rust disease. After the removal of genotypes that showed a major gene (race specific) resistance expression at seedling test, 60 selected genotypes were evaluated for their adult plant resistance to stem rust and agronomic traits across three locations (Debrezeit, Adet and Kulmsa) using a 5 × 12 alpha lattice design with three replications. Genotypes showed a highly significant difference (p = 0.001) on the traits of final rust severity (FRS), area under disease progress curve (AUDPC), coefficient of infection (CI) and apparent infection rate (r) at different locations. Moreover, combined analysis of variance also showed the presence of highly significant effects of genotypes, environments and GE interaction on the magnitude of FRS, AUDPC, CI, r, days to maturity (DM), plant height (PH), hectoliter weight (HLW), thousands kernel weigh (TKW) and grain yield (GY) across testing locations. The correlation analysis revealed the presence of positive highly significant (p<0.001) relationship of FRS with both CI (r=0.894) and AUDPC (r=0.877). A positive and highly significant (p<0.001) correlation was also observed between CI and AUDPC (r=0.996) of the tested genotypes. Principal component analysis indicated that only the first four principal components (PCs) explained 86.58% of the total variation among the tested genotypes. Cluster analysis also confirmed the presence of variation among the tested genotypes by dividing them into five major groups. In this study, four bread wheat genotypes (G12, G60, G31 and G52) were found to be resistant to stem rust disease across the three locations and could be used as source of stem rust resistance in future wheat improvement program.

English

Angular leaf spot caused by Phaeoisariopsis griseola is one of the most destructive diseases on common bean in Southern and Southwestern parts of Ethiopia. However, systematic and focus studies were lacking to this important disease. Therefore, greenhouse study was conducted to test aggressiveness of P. griseola isolates and evaluate resistance reactions of bean varieties to pathogenic isolates. 55 leaf samples were collected and seven isolates were recovered, but three isolates namely Dolla1, Dolla2 and Dorebafano1 were successfully multiplied and tested to evaluate their pathogenicity and aggressiveness on susceptible variety Dinknesh. Dolla1 and Dolla2 isolates were collected from Bolloso Sore district, while Dorebafano was from Hawassa Zuria. 21 days old plants were inoculated with spore concentration of 2 × 104 conidia ml-1. The study was factorial arranged in a completely randomized design in four replications. All tested isolates were found aggressive to susceptible check with PSI value ranging from 83.34 to 93.52%. 75% of tested varieties showed susceptible reaction to isolates, but overall aggressiveness was higher on varieties Dimtu, Babile, KATB1, KATB69 and Dinknesh. PSI values ranged from 87.96 to 100% in most varieties. The apparent infection rate was faster on susceptible varieties. The disease progress curve attained sigmoid shape in most varieties. Varieties SER125, SER119 and Nasir were identified as a good source of resistant gene to develop ALS resistance. However, further studies on identification of genes and genetic diversity of the pathogen should capture research priority. Varieties evaluated under greenhouse conditions should also be tested under field conditions. Key words: Aggressiveness, angular leaf spot, common bean, incidence, reaction, severity. &nbsp

Avaliação de sistemas de previsão para a septoriose do tomateiro tutorado em Caçador, SC, Brasil

A septoriose, causada pelo fungo Septoria lycopersici, é uma das mais importantes doenças do tomateiro tutorado em Caçador, SC, Brasil. A doença é geralmente controlada pela aplicação preventiva de fungicidas. Experimentos de campo foram realizados com o objetivo de avaliar sistemas de previsão dessa doença: um com base no sistema TomCast (10, 15 e 20 valores de severidade – VSD), outro pelo período de molhamento foliar (limiar ≥ 12 horas), ambos comparados com a aplicação semanal de fungicidas. O TomCast utiliza a duração do molhamento foliar e a temperatura média deste período para calcular o valor de severidade diário da doença (VSD). Não houve diferença significativa entre o tratamento semanal e os previsores em relação a produtividade, severidade final, área abaixo da curva do progresso da doença e taxa de infecção aparente (r). Entretanto, com o tratamento 20-VSD houve redução de 12,5 a 70% das pulverizações em relação ao tratamento semanal. Termos para indexação: Solanum lycopersicum; sistema de alerta; TomCast; Septoria lycopersici; método de controle

Differential development of wilt and stem rot diseases in grafted bell pepper (Capsicum annuum, L.)

In bell pepper production, diseases caused by soil-borne pathogens are a serious problem. The use of chemicals remains the main method for the control of soil-borne pathogens, with poor results in many cases. However, grafting has been proposed as an alternative which can also improve control. The present study analyses and compares the development of diseases caused by soil-borne pathogens in grafted and non-grafted sweet bell pepper plants. Plots of cultivars Fascinato and Janette non-grafted and grafted on Terrano rootstock were established on a farm managed under the shaded greenhouse system. Phytophthora capsici and Rhizoctonia solani AG4 were identified causing wilt. Fusarium solani was identified causing stem rot. Terrano resisted wilt by reducing the apparent infection rate and the final incidence in the Fascinato variety by 92% and 89%, respectively, and in the Janette variety by 99% and 98%, respectively. However, Terrano was not resistant to stem rot. Compared to non-grafted plants, Terrano had a higher apparent infection rate and final incidence, which in Fascinato were 56% and 60%, respectively, and in Janette were 97% and 99%, respectively. Terrano also affected the spatial patterns of both wilt and stem rot. These results show that it is necessary to supplement the use of Terrano with other strategies. This complicates the goal of reducing the use of chemicals, environmental pollution and the costs of control in the production of sweet bell pepper.

Infection of Wildlife by Mycobacterium bovis in France Assessment Through a National Surveillance System, Sylvatub

Mycobacterium bovis infection was first described in free-ranging wildlife in France in 2001, with subsequent detection in hunter-harvested ungulates and badgers in areas where outbreaks of bovine tuberculosis (TB) were also detected in cattle. Increasing concerns regarding TB in wildlife led the French General Directorate for Food (DGAL) and the main institutions involved in animal health and wildlife management, to establish a national surveillance system for TB in free-ranging wildlife. This surveillance system is known as “Sylvatub.” The system coordinates the activities of various national and local partners. The main goal of Sylvatub is to detect and monitor M. bovis infection in wildlife through a combination of passive and active surveillance protocols adapted to the estimated risk level in each area of the country. Event-base surveillance relies on M. bovis identification (molecular detection) (i) in gross lesions detected in hunter-harvested ungulates, (ii) in ungulates that are found dead or dying, and (iii) in road-killed badgers. Additional targeted surveillance in badgers, wild boars and red deer is implemented on samples from trapped or hunted animals in at-risk areas. With the exception of one unexplained case in a wild boar, M. bovis infection in free-living wildlife has always been detected in the vicinity of cattle TB outbreaks with the same genotype of the infectious M. bovis strains. Since 2012, M. bovis was actively monitored in these infected areas and detected mainly in badgers and wild boars with apparent infection rates of 4.57–5.14% and 2.37–3.04%, respectively depending of the diagnostic test used (culture or PCR), the period and according to areas. Sporadic infection has also been detected in red deer and roe deer. This surveillance has demonstrated that M. bovis infection, in different areas of France, involves a multi-host system including cattle and wildlife. However, infection rates are lower than those observed in badgers in the United Kingdom or in wild boars in Spain.

Screening of bitter gourd germplasm and advanced breeding lines against powdery mildew

Powdery mildew caused by Podosphaera xanthii is a devastating fungal disease in bitter gourd growing areas of India inflicting more than 70% losses. Resistance sources were identified among 31 genotypes of Momordica charantia, M. charantia var. muricata and M. balsamina based on screening under natural field and artificial epiphytotic condition at seedling stage. The genotypes varied with respect to percent disease index (PDI), area under disease progressive curve (AUDPC) and the apparent rate of disease spread in unit time period (r). The mean PDI under natural and artificial screening ranged from 0.0 to 100.0 and 0.0 to 94.4, respectively. The genotypes, IIHR-80-1-2 and IIHR-80-1-3 (M. balsamina) were free from disease, whereas, IIHR-144-1 (M. charantia var. muricata) showing mild symptoms with PDI of 1.8 and 4.3 under natural and artificial screening, respectively at later stage were also resistant. Genotypes IIHR-40-1 and IIHR-49-34-5 were moderately susceptible (PDI ˂ 40) PDI was highly correlated with AUDPC under both natural and artificial screening (r = 0.99, 0.95; P ˂ 0.01). Also PDI under natural field screening was highly correlated with the artificial screening under controlled conditions. The highest apparent infection rate (r) was recorded in the genotype, Arka Harit (1.29), whereas, it was the least in IIHR-80-1-2 and IIHR-80-1-3 (0.00). Statistical analysis of disease severity over time using non linear growth model revealed that 97% of variability in disease progression over time was captured by nonlinear logistic model. The rate of disease severity was maximum at t = 2–3 weeks in susceptible and t = 4.24 in moderately susceptible genotype IIHR-40-1, inferring that management strategies may be undertaken within the period identified to avoid loss. The newly identified resistant sources may be used for developing powdery mildew resistant bitter gourd varieties/hybrids.

Evaluation of field pea germplasm against rust disease caused by Uromyces viciae fabae De Bary in glass house and field conditions

Seventy three germplasm of field pea were tested under glasshouse and field condition against rust disease caused by Uromyces viciae fabae (Pers.) de Bary. Among screened germplasms, 30 susceptible, 40 highly susceptible and 3 belonged to moderately resistance group. The susceptible germplasm showed leaf area with symptoms (LAS) ranged from 30 to 65% with area under disease progressive curve (AUDPC) values from 77.5 to 1290 and apparent infection rate from 0.0134 to 0.1698 and highly susceptible germplasm showed LAS ranged from 60 to 95% with AUDPC values ranged from 1075 to 2179. Apparent infection rate ranged from 0.0616 to 0.6950 while moderately resistance germplasm showed LAS ranged from 20 to 24% with AUDPC values ranged from 350 to 438 and apparent infection rate ranged from 0.1180 to 0.1198 in field as well as glasshouse conditions. The moderate resistance germplasm JPF 99025, KPMR 615 and KPMR 551showed lowest LAS, AUDPC value and apparent infection rate, hence, these germplasms could be used in breeding programme.

Weather-based coffee leaf rust apparent infection rate modeling.

Brazil is the major coffee producer in the world, with 2 million hectares cropped, with 75% of this area with Coffea arabica and 25% with Coffea canephora. Coffee leaf rust (CLR) is one of the main diseases that cause yield losses by reducing healthy leaf area. As CLR is highly influenced by weather conditions, this study aimed to determine the best linearization model to estimate the CLR apparent infection rate, to correlate CLR infection rates with weather variables, and to develop and assess the performance of weather-based infection rate models to be used as a disease warning system. The CLR epidemic was analyzed for 88 site-seasons, while progress curves were assessed by linear, monomolecular, logistic, Gompertz, and exponential linearization models for apparent infection rate determination. Correlations between CLR infection rates and weather variables were conducted at different periods. From these correlations, multiple linear regressions were developed to estimate CLR infection rates, using the most weather-correlated variables. The Gompertz growth model had the best fit with CLR progress curves. Minimum temperature and relative humidity were the weather variables most correlated to infection rate and, therefore, chosen to compose a CLR forecast system. Among the models developed, the one for the condition of high coffee yield at a narrow row spacing was the best, with only 9.4% of false negative occurrences for all the months assessed.

Screening of mango germplasm under natural epiphytotic conditions against anthracnose (Colletotrichum gloeosporioides)

Thirty cultivars of mango growing at Regional Horticulture Research and Training Station, Jachh, Nurpur, Kangra and 18 cultivars of mango growing at Regional Horticulture Research and Training Station, Dhaulakuan, Sirmour were evaluated for their resistance/susceptibility against mango anthracnose (Colletotrichum gloeosporioides) under natural epiphytotic conditions for two consecutive years i.e., 2014 and 2015. None of the cultivar showed resistant disease reaction against the anthracnose disease in both districts on fruits and leaves. At Jachh, five cultivars viz., Pusa Peetamber, Pusa Shreshth, Pusa Surya and Apple Mango showed moderately susceptible reactions to anthracnose and rest of the cultivars were either susceptible or highly susceptible. At Dhaulakuan two cultivars viz., Pusa Arunima and Pusa Surya exhibited susceptible reaction and rest of the cultivars were highly susceptible. Apparent infection rate of cv. Pusa Pratibha at Jachh was the lowest with 0.08 per unit per day with minimum area under disease progress curve of 6.45.

Respuesta de diez cultivares de mango amarillo al daño por cenicilla (Erysiphe quercicola) en México

<p>La cenicilla del mango (<em>Erysiphe quercicola</em>)<em> </em>causa pérdidas de producción de hasta 90%, por lo que es necesario estimar la tolerancia a este patógeno en el nuevo germoplasma introducido o generado recientemente para incrementar el potencial de exportación de México. El objetivo de este estudio fue determinar la respuesta al daño por cenicilla mediante una técnica de inoculación optimizada para inducir la enfermedad en hojas adheridas de 10 cultivares de mango amarillo nuevos para México. Se evaluaron dos métodos de inoculación. El mejor fue por aspersión de conidios a concentración de 4.6 × 10<sup>5</sup> esporas mL<sup>-1</sup>, en las superficies adaxial y abaxial de las hojas, a ± 300–450 lux y suspendidos en polisorbato 20 + surfactante a base de alcoholes etoxilados al 2%. La prueba de inoculación mostró que el cv. Alphonso fue moderadamente tolerante y Neelum y Fairchild ligeramente tolerantes. En contraste, Nam Doc Mai, Rosigold, Ataulfo Zafiro, Cotaxtla y Kesar fueron susceptibles y Mallika e Ivory altamente susceptibles. Los cultivares más tolerantes presentaron valores menores de incidencia, severidad máxima, área bajo la curva del progreso de la enfermedad, tasa de infección aparente y densidad de conidios por cm<sup>2</sup> de área foliar dañada (LSD, P ? 0.05).</p>

Status and management of banded leaf and sheath blight of Little Millet caused by Rhizoctonia solani Kühn with chemicals

Mean disease incidence and frequency of occurrence ranging from 6.9 to 18.8% and 26.1 to 75.4%, respectively were recorded during survey. Highest average BLSB incidence (13.7%) and disease frequency (61.1%) were recorded in the farmers field of Satna district, whereas lowest values were recorded at Anuppur district of Madhya Pradesh. Foliar spray of two non-conventional chemicals salicylic acid (SA) and sodium fluoride (SF) in 100, 150 and 200 ppm along with one fungicide Validamycin (0.2%) were evaluated against BLSB during 2012–13 and 2013–14. Lowest relative lesion height (19.0%) and highest grain yield (967.5 kg ha−1) were recorded in the treatment of Validamycin. Average apparent infection rate varied 0.081 to 0.201%/day in all the treatments. Both the non-conventional chemicals were found to reduce the severity of the disease, infection rate and enhancing the grain yield possibly due to induction of resistance in host plant against the pathogen. Maximum reduction in relative lesion height (50.5%) and highest grain yield (937.5 kg ha−1) was recorded in foliar spray of salicylic acid (200 ppm) followed by sodium fluoride (200 ppm).

Wilt Disease of Tara (<i>Caesalpinia spinose</i> Molina Kuntz) in Nursery in the Inter Andean Valley of Cochabamba, Bolivia

Tara (Caesalpinia spinose Molina Kuntz) is a native plant of the Bolivian Andes. A number of projects have promoted the cultivation of this species over the last 20 years, in efforts to make use of its medicinal, food and industrial properties. However, as tara plantations have grown, so too has the incidence of disease affecting the species, leading to economic losses. The aim of the present work was to identify the causal agent of wilting in tara, and to determine the incidence of the disease in nursery-grown plants. Three experimental plots (R1-R3) were established in plantlet production bedsat the ESFOR nursery in order to assess the incidence of wilting. Plant spacing was 1 × 1 m. At the two leaf stage, samples of diseased and apparently healthy plants were taken to the laboratory for the isolation of pathogens. Both the apparently healthy and diseased plants gave rise to the same kinds of fungal colony on PDA. Microscopic examination revealed microconidia, macroconidia, phialides and chlamydospores suggesting the causal agent to be Fusarium oxysporum. Over the (up to) 84-day period following thinning, the incidence of wilting for 2010 was R1 = 2.56%, R2 = 3.15% and R3 = 2.22% per 14 days, and for 2013 it was R1 = 1.24%, R2 = 2.45% and R3 = 2.13% per 14 days; the apparent infection rates for 2010 were rR1 = 0.0003/day, rR2 = 0.0003/day and rR3 = 0.0003/day, and for 2013 they were rR1 = 0.0003/day, rR2 = 0.0004/day and rR3 = 0.0003/day. These values are characteristic of monocyclic epiphytic fungi such as F. oxysporum.

Effect of cultivar susceptibility and planting date on narrow brown leaf spot progression in rice

Narrow brown leaf spot (NBLS) of rice (Oryza sativa L.) is caused by Cercospora janseana (Racib). O. Const. (Synonyms: Cercospora oryzae Miyake, Passalora janseana Racib. U.). Experimental studies were conducted in Louisiana to study NBLS progression in resistant to very susceptible cultivars at different planting dates. The very susceptible cultivars CL131 and Cheniere, susceptible CL111, moderately susceptible CL151, and resistant cultivars, Della and Presidio were planted in mid-April and mid-May plantings. Weekly disease assessments began at 45 days after sowing (DAS) and the final disease assessments were done at 109 DAS. Results revealed that AUDPC and final NBLS severity were greater in very susceptible and susceptible cultivars as compared to resistant cultivars. The AUDPC for mid-May plantings were greater for all cultivars. AUDPC increased with increasing susceptibility rating in the mid-April planting. Early onset of NBLS was observed in very susceptible and susceptible cultivars regardless of planting date. Significant interactions were detected between cultivar and planting date for AUDPC and final disease but were non-significant for apparent infection rate. Apparent NBLS infection rate was greatest in the highly susceptible Cheniere and CL131 in the mid-May planting. Apparent infection rates were less in the susceptible and moderately susceptible cultivars and least for the resistant cultivars in both plantings.

Resistance status of cultivated potatoes to early blight (Alternaria solani) in Denmark

Field experiments were conducted in 2015 and 2016 to classify the resistance level to early blight of the main potato cultivars in Denmark. A total of 38 cultivars were used. The experiment was designed as a randomized complete block design (RCBD) with four replicates. The potatoes were inoculated by spreading barley (Hordeum vulgare) kernels infested with Alternaria solani and A. alternata. Disease assessment was done at weekly intervals starting from the onset of the first symptoms. The disease progress curves (DPC) of early blight on the cultivars were compared to that of Bintje. A multivariate analysis was performed with the apparent infection rate, the relative area under the disease progress curve, the time to reach 50% severity, the daily defoliation, the disease severity in the middle of the epidemic and the duration of the epidemic to classify the resistance level of the cultivars. The analysis of the DPC of the cultivars showed that none of the cultivars was completely resistant to early blight. However, the epidemic development differed between the different cultivars. The resistance levels of the cultivars were thus classified into classes I, II, III and IV interpreted as ‘very susceptible’, ‘susceptible’, ‘moderately slow blighting’ and ‘slow blighting’, respectively. All the late maturity cultivars were classified as class IV, and the earlier maturing cultivars were either class I or class II.

Screening St. Augustinegrass Genotypes for Brown Patch and Large Patch Disease Resistance

Two diseases of St. Augustinegrass (SAG) [Stenotaphrum secundatum (Walt.). Ktze.] are caused by different anastomosis groups (AGs) of Rhizoctonia solani. Brown patch (BP) is a foliar disease of little economic importance, and large patch (LP) causes leaf sheath rot and death of affected turfgrass shoots and stolons. St. Augustinegrass genotypes were inoculated with an isolate that causes BP and an isolate that causes LP in repeated experiments. Three disease severity parameters were calculated from data recorded from each genotype, including final disease severity (Y), area under the disease progress curve (AUDPC), and the apparent infection rate (r L ). The inoculation protocol reliably produced symptoms, and both r L and AUDPC provided statistically significant separations between genotypes for their susceptibility to BP and LP. A significant interaction between isolate and genotype was observed, and some genotypes that were very susceptible to LP were among the least susceptible to BP. These data suggest that differences in resistance to LP can be quantified in SAG genotypes, but genotype response may be isolate dependent.

High rates of infection by blood parasites during the nestling phase in UK Columbids with notes on ecological associations.

Studies of blood parasite infection in nestling birds rarely find a high prevalence of infection. This is likely due to a combination of short nestling periods (limiting the age at which nestlings can be sampled) and long parasite prepatent periods before gametocytes can be detected in peripheral blood. Here we examine rates of blood parasite infection in nestlings from three Columbid species in the UK. We use this system to address two key hypotheses in the epidemiology of avian haemoparasites: first, that nestlings in open nests have a higher prevalence of infection; and second, that nestlings sampled at 14 days old have a higher apparent infection rate than those sampled at 7 days old. Open-nesting individuals had a 54% infection rate compared with 25% for box-nesters, probably due to an increased exposure of open-nesting species to dipteran vectors. Nestlings sampled at 14 days had a 68% infection rate compared with 32% in nestlings sampled at 7 days, suggesting that rates of infection in the nest are high. Further work should examine nestlings post-fledging to identify rates of successful parasite infection (as opposed to abortive development within a dead-end host) as well as impacts on host post-fledging survival and behaviour.

Slow mildewing in Pumpkins: an opportunity to reduce Pumpkin yield losses caused by Erysiphe cichoracearum

<p class="Normal1"><span>Pumpkin powdery mildews, a disease caused by fungus <em>Erysiphe cichoracearum</em>, is one of the major diseases that reduce yield and quality of pumpkins. A field screening study involving fifty two pumpkin accessions was carried out at three powdery mildew hot spot sites in Malawi. The main objective was to assess the reactions of pumpkin accessions to <em>E. cichoracearum</em>. The experiment was laid out in a randomized complete block design replicated three times. Plot size was 3m x 3. 7m. There were statistically significant differences in apparent infection rates (P<0.001), area under disease progress curve, AUDPC (P<0.001), percent disease index, PDI (P<0.001) among the accessions across all sites. Pumpkin accessions 6 and 42 consistently showed slow rate of powdery mildew development at 4<sup>th</sup>, 6<sup>th</sup>, and 8<sup>th</sup> week after germination. A strong positive correlation (R= 0.7 at 8<sup>th</sup> week, and 0.97 at 12<sup>th</sup> week after germination) was observed between the number of rotten fruits and AUDPC. This study showed that out of the fifty two pumpkin accessions tested, none was immune to <em>Erysiphe cichoracearum</em>. However the accessions that recorded very slow rate of powdery mildew development showed high potential to maintain viable vines and support their fruits up to physiological maturity. We concluded that promoting slow mildewing pumpkin genotypes is appropriate solution to fruit yield and quality losses caused by<em> E. cichoracearum</em>.</span></p>

Evaluation of Ugandan Cowpea Germplasm for Yield and Resistance to Scab Disease

Aims: This study was conducted to identify cowpea (Vigna unguiculata) cultivars with high yield potential and resistance to scab disease caused by Sphaceloma sp. in Uganda. 100 cowpea genotypes were evaluated at two locations (Kabanyolo and Serere) in Uganda between April and July, 2014 using a 10 × 10 alpha lattice design. Place and Duration of Study: Makerere University Agriculture Research Institute Kabanyolo (MUARIK) and the National Semi Arid Resources Research Institute (NaSARRI) – Serere between April to July, 2014. Study Design and Methodology: Hundred cowpea lines (69 landraces, 25 inbred lines at F7, 1 local and 5 improved cultivars) were grown at each location in a 10 × 10 alpha lattice design with 3 replications to assess their reaction to the scab disease and yield potential (grain yield and yield related traits). Results: The cowpea lines differed significantly (P = .05) in their response to natural disease Original Research Article Afutu et al.; AJEA, 12(2): 1-18, 2016; Article no.AJEA.25138 2 pressure as determined by disease incidence, apparent infection rate (r) and severity indicated by area under disease progress curve (AUDPC). Analysis of variance showed that there was highly significant differences (P < .001) in genotypes, locations, AUDPC and other traits and genotype by location (G×L) interaction on AUDPC. The correlation analysis revealed a positive relationship of scab disease incidence with AUDPC (0.8; P < .001) but a significant (P < .001) negative relationship with grain yield (-0.8), number of pods per plant (-0.5), number of seeds per pod (-0.5) and 100 seed weight (-0.5). Cluster analysis based on only scab disease indexes produced 4 main clusters while cluster analysis based on disease and yield traits produced 3 main clusters. However, the two different clusters revealed similar grouping patterns in which cowpea lines with similar resistance ratings were shown to form unique clusters. R-mode principal component analysis yielded 4 principal components explaining 62.28% of the variation observed. Conclusion: The study revealed that the use of apparent infection rate “r” alone as an index for rating a genotype for scab reaction was not decisive. One line (NE 15) was found to be resistant to the scab disease at both locations and high yielding and could be used in the cowpea improvement programme to breed for resistance to the scab disease.

Evaluation of finger millet genotypes for partial resistance to leaf blast caused by Pyricularia grisea

Blast of finger millet (ragi) caused by Pyricularia grisea is disastrous disease to limit the potential yield levels in the farmers field. The pathogen affects the crop at all growth stages and the most susceptible stage for leaf blast is seedling stage. Use of resistant cultivars for minimizing losses due to leaf blast at early stage of crop growth is a viable and economical alternative. In the present study, partial resistance to leaf blast in fourteen genotypes of finger millet was assessed under field conditions. None of the genotypes were highly resistant to leaf blast. However, two genotypes namely PR 10-30 and VL 368 were shown resistance. Seven genotypes namely VR 988, VL 353, VL 348, TNAU 1214, GPU 45, VL 369, KOPM 942 were found moderately resistant, three namely PPR 2773, KRI 007-01, VR 708 were susceptible and two namely TNAU 1226 and REC 69 were highly susceptible. The correlation coefficients between leaf blast severities (LBS) with different components of partial resistance of slow blasting were significant. Low value of coefficient of infection (CI), apparent infection rate (r), area under disease progress curve (AUDPC), lesion number (LN), lesion area (LA), lesion circumference (LC) and high value of incubation period (IP) were recorded in resistant genotypes of finger millet, whereas, higher values of CI, r, AUDPC, LN, LA, LC and low values of IP were recorded in highly susceptible genotypes. A significant positive correlation was found in leaf blast severity with CI (r=0.948*), r (r=0.829*), AUDPC (r=0.998*), LN (r=0.967*), LA (r=0.957*), LC (r=0.976*) whereas IP (r=-0.825*) was negatively correlated with blast resistance. PR 10-30 and VL 368 showed higher degree of partial resistance or slow blasting resistance against P. grisea infection on finger millet.