AUDPC Values Research Articles

Characteristics of superior soybean breeding lines tolerance to rust (Phakopsora pachyrhizi Syd.)

<p>Soybean rust caused by Phakopsora pachyrhizi is one of the most important diseases which limits soybean production. The aim of this study was to evaluate the resistance of 28 superior soybean lines and their tolerance to rust. The study was conducted at a screen house and arranged in a completely randomized design (CRD); three replications. All genotypes tested were artificially inoculated with P. pachyrhizi, and a set of un-inoculated genotypes was planted as a comparison. Number of pustules was recorded weekly, and resistant criteria was rated based on the International working group on soybean rust IWGSR method. Lesion color (LC), sporulation level (SL), number of uredia (NoU), frequency of pustule which had uredia, and yield were also recorded. Among 28 genotypes tested, only one was categorized as resistant and 2 genotypes were susceptible. Resistant genotypes had few pustules, lower AUDPC values, low disease severity, and Reddish Brown lesion type. Soybean rust affected yield components, i.e. number of intact pods and yield per plant. Yield loses due to rust in this study varied from 5-89%, and the average was 51%. The set of lines from Tanggamus pedigree showed more resistant to rust but less tolerant compared to Sinabung pedigree.</p><p><strong>How to Cite</strong></p><p>Inayati, A., & Yusnawan, E. (2016). Characteristics of superior soybean breeding lines tolerancet to rust (Phakopsora pachyrhizi Syd.).<em> Biosaintifika: Journal of Biology & Biology Education</em>, 8(1), 47-55.</p>

English

Chocolate spot (Botrytis fabae Sard.) is one of the major diseases menacing faba bean (Vicia faba L.) production and restraining its productivity in Ethiopia and other African countries. The yield losses reach up to 100% on susceptible cultivars. Although a number of faba bean varieties with good yield potential have been released, their reaction to this major disease and yield performance are little understood in southwest Ethiopia. Thus, chocolate spot epidemics on 13 improved faba bean varieties were studied under natural infections at three sites varying in altitudes from 1805 to 2660 m in the Dawuro zone of southwest Ethiopia. The field experiments consisted of 14 treatments (13 varieties and a local cultivar) are laid out in a randomized complete block design (RCBD) with three replications (40 plants/plot) during the 2011/2012 crop season. The onset and progress of chocolate spot severity was assessed (with a 1-9 scale) every seven days until the epidemic attained peak and then grain yield and 100-seed weight were recorded and statistically analysed. The varieties varied significantly (P < 0.001) in disease severity index, AUDPC and infection rates (r) values, grain yield and 100-seed weight. CS20DK, Degaga, Nc-58, Bulga-70, Tesfa and Kasa exhibited high to moderate resistance to chocolate spot with consistently slow progression and terminal disease severity, AUDPC- and r-values at all testing sites. The yield performance of CS20DK and Degaga were also superior at Tocha and Turi while Nc-58 (2027 kg/ha) and Moti (1973 kg/ha) that showed susceptible reaction gave good yield only at Tocha. This study indicated that improved faba bean varieties reacted differently to chocolate spot infection and yield potentials across varying localities, and thus better performing varieties such as CS20DK, Degaga and Nc-58 are recommended for faba bean production in southwest Ethiopia.   Key words: Botrytis fabae, evaluation, improved varieties, Vicia faba.

Exploring Durable Genetic Resistance against Leaf Rust through Phenotypic Characterization and Lr34Linked STS Marker in Wheat Germplasm

Present study was aimed to screening the population of 25 wheat genotypes from Baluchistan region of Pakistan along with five commercial cultivars for leaf rust adult plant resistance (APR) through gene postulation using natural inoculation of Puccinia triticina Erikss local pathotype. Infection severity was recorded on scale in comparison with susceptible control “Morroco” cultivar. On the basis of phenotypic score, seven accessions and four varieties (Zardana-89, Sariab-92, Zarlashta-99 and Raskoh-05) with AUDPC values up to 20% were characterized as resistant genotypes. Coefficient of infection (CI) score ranged from 0-10 for some accessions and cultivars showing high level of adult plant resistance. Furthermore, bi-allelic STS marker csLV34 having close linkage with Lr34 (0.4cM). This marker amplified one gene specific allele of 150bp in 21 genotypes, including 19 accessions and two commercial varieties (Sariab-92 and Zarghoon-79) which confirmed presence of Lr34 gene conferring adult plant resistance against leaf rust. The rust pathogenicity scale varied for accessions from resistant to moderately susceptible. However, beside Lr34 , phenotypic gene postulation, in combination with marker assisted selection for leaf rust resistance, has revealed presence of some other unknown resistance genes in local wheat germplasm which signified its use in wheat improvement programs both locally and abroad.

Screening of Rice Varieties against Brown Leaf Spot Disease at Jyotinagar, Chitwan, Nepal

A field experiment was conducted on fourteen rice varieties to determine the level of resistance against brown leaf spot (Bipolaris oryzae)disease at Karma Research and Development Center, Jyotinagar, Chitwan during summer in 2013. Design used was randomized completeblock design with three replications. Disease severity, total AUDPC value, thousand grain weight and grain yield were highly significant amongthe rice varieties. Disease severity and total AUDPC value ranged from 21.73% to 58.07% and 614.8 to 1827 respectively. None of thesevarieties were found either resistant or highly resistant to disease. Only HJ-G1 and HJ-G2 were moderately resistant with grain yield of 5.10t/ha and 4.25 t/ha respectively. HJ-G1 variety had the highest grain yield 5.10 t/ha and lowest disease severity (21.73%) as well as total AUDPCvalue (6148). From this experiment, it can be concluded that HJ-G1 variety can be used for higher grain yield purpose under similar fieldcondition because it has highest yield and also tolerant to disease.DOI: http://dx.doi.org/10.3126/ijasbt.v3i1.12014 Int J Appl Sci Biotechnol, Vol. 3(1): 56-60

Leaf Rust Resistance and Molecular Identification of Lr 34 Gene in Egyptian Wheat

Twenty six wheat genotypes were evaluated for their levels of adult plant resistance to leaf rust at two different locations i.e. Shibin El-Kom and Itay El-Baroud during two successive growing seasons, i.e., 2011/12 and 2012/13. The wheat varieties Sids 12, Sids 13, Misr 1 and Misr 2, Shandweel 1, Beni Sweif 4 and Beni Sweif 5 have race-specific resistance. While, the wheat genotypes Lr 34, Giza 165, Giza 168, Sakha 8, Sakha 94, Sakha 95, Gemmeiza 5, Gemmeiza 7, Gemmeiza 9, Gemmeiza 10, Gemmeiza 11 and Sohag 3 showed high levels of slow rusting resistance. On the other hand, the other tested varieties were highly susceptible or fast rusting ones i.e. Giza 160, Giza 163, Giza 164, Sakha 69, Sakha 93, Sids 1 and Giza 139. These varieties showed higher values of final rust severity (%) and AUDPC compared to the other varieties under the same field conditions. SSR marker i.e. cslv34b allele (150 bp) for Lr 34 was used to confirm the presence of the adult plant resistance gene Lr 34 in the tested genotypes.

Dissection of wheat spot blotch disease resistance QTLs in to single Mendelian genes

Two QTLs imparting spot blotch resistance and located on chromosomes 2BS and 5BL were dissected in to a single Mendelian gene using 341 single seed descent (SSD) derived F3 and F4 lines of YS102 × Sonalika and 335 F3, F4 and F5 lines of YS116 × Sonalika cross. The resistant parental lines YS102 and YS116 were selected on the basis of phenotypic and genotyping data of base mapping population (Yangmai 6 × Sonalika in F12 generation) used for QTL mapping. Both the populations were tested for spot blotch resistance under artificial epiphytotic conditions in the field. Disease severity (%) and AUDPC values of each line were calculated. The parent YS116 was known to possess a single major QTL on chromosome 5BL, while YS102 possess QTL on chromosome 2BS. The test for goodness of fit (1: 2: 1 in F3, 3: 2: 3 in F4 and 7: 2: 7 in F5 generations) confirmed segregation at one locus in both the crosses. These SSD derived lines from both the crosses may further be used for fine mapping and map based cloning of the QTLs of spot blotch resistance OTLs.

Recovery of Verticillium dahliae from commercially available potato seed lots planted in Turkey and characterization of isolates by vegetative compatibility and aggressiveness

A total of 105 seed samples collected from commercially available potato seed lots in Turkey were assayed for Verticillium dahliae. V. dahliae was successfully isolated from 29 of the 105 seed lots tested. The frequency of infected lots was nearly 28%. Vegetative compatibility of the isolates was assessed through complementation tests using nitrate non-utilizing mutants. Of the 110 isolates obtained, 63 were assigned to VCG4A, 24 to VCG4B, 19 to VCG2A and one to VCG2B, while the three remaining isolates could not be assigned to any of the identified VCGs. All 36 of the isolates tested in the greenhouse on potato cv. ‘Russet Burbank’ were pathogenic to potato. As a group, AUDPC values were significantly higher (P <0.05) for VCG4A than for VCG4B and VCG2 isolates. These data suggest that (i) commercial potato seed lots are commonly infected with V. dahliae, and that this is a primary method by which the pathogen can be introduced into production fields; (ii) potato isolates of V. dahliae belong to VCG4A, 4B and 2A and these isolates are widely distributed via seed lots; and (iii) VCG4A and VCG4B are distinct pathotypes of V. dahliae that vary in their aggressiveness to potato. The present study is the first report of natural infections of potato by VCG4A and VCG2A in Turkey.

Field Management of Anthracnose (&lt;i&gt;Colletotrichum lindemuthianum&lt;/i&gt;) in Common Bean through Foliar Spray Fungicides and Seed Treatment Bioagents

Common bean anthracnose is a major production constraint in bean growing regions of Ethiopia. This study aimed to determine whether foliar sprays of mancozeb, folpan and mancolaxyl or antagonistic bioagents; Trichoderma harzianum, Trichoderma viride and Pseudomonas fluorescens could reduce anthracnose symptoms and consequently, increase yield and yield components. A total of seven treatments were arranged in a randomized complete block design with three replications. Statistical analysis showed significant differences among treatments. Anthracnose incidence, severity, infected pods per plant and the area under disease progress curve were highest in the control plots compared to the fungicide sprayed and bioagent treated seed plots. The highest percentage of infected pods per plant, 78.9 and 55 were recorded on the control and mancozeb sprayed plots respectively. The highest AUDPC value resulted in the lowest yield of 1.01 t/ha in the control plots compared to a highest yield of 3.33 t/ha from the sprayed plots with folpan and 1.79 t/ha from plots treated with Pseudomonas fluorescens. Relative yield losses of 69.67, 46.25 and 22.82% were recorded from the control, seed treated plots with P. fluorescens and sprayed plots with mancolaxyl respectively. Economic analysis revealed that the highest rate of return of 8,740 was obtained from Pseudomonas fluorescens seed treatment and the highest net benefit; 43,154 on folpan foliar spray treatment. The results of the present study support the novel possibility of using folpan foliar spray and Pseudomonas fluorescens seed treatments to decrease anthracnose symptoms in bean plants and consequently, achieve greater yield.Keywords: Bioagents; Folpan; Pseudomonas fluorescens; Mancolaxyl; seed treatment

VCG diversity and virulence of Verticillium dahliae from commercially available cotton seed lots in Turkey

Samples of seeds collected from commercially available cotton seed lots in Turkey were assayed for Verticillium dahliae. V. dahliae was successfully isolated from 67 of 104 seed lots tested, a successful isolation rate of nearly 65 %. Vegetative compatibility of the isolates was assessed through complementation tests using nitrate non-utilizing mutants. Of the 188 isolates obtained, 105 were classified as VCG1A, 17 as VCG2A, 64 as VCG2B and two as VCG4B. All 50 of the isolates tested in the greenhouse on cotton cv. DP 15–21 and Acala SJ-1 were pathogenic on both cultivars. As a group, AUDPC values were significantly higher (P < 0.05) for VCG1A than for VCG2 and VCG4B isolates. These data suggest that: (1) commercial cotton seed lots are commonly infected with V. dahliae and thus may serve as primary sources of the pathogen; (2) cotton isolates of V. dahliae belong to VCG1A, 2A, 2B and 4B and these strains are widely distributed via seed lots; and (3) VCG1 and VCG2 are distinct pathotypes of V. dahliae that vary in their virulence to cotton.

Response of Tunisian Durum and Common Wheat Cultivars to Powdery Mildew under Natural Infection

Cereal production is an important component of agriculture. Powdery mildew (Erysiphe graminis f. sp tritici Em. Marchal), caused by Blumeria graminis (DC.) E.O Speerf. sp. tritici (Bgt), which is one of the most worldwide devastating diseases of durum and common wheat specially in Tunisia. Several works have discussed plant resistance to mildew and its potential risks but, it was neglected or no study was reported for that in Tunisia. There is an increasing need for studies that address the potential side effects of mildew to different wheat cultivars and their outcome and behave via disease criteria. This study focuses to compare the behave of ten Tunisian wheat cultivars to powdery mildew under field conditions during two successive cropping seasons 2011-2013. Using the 5 disease criteria (infected leaf number, pustules per stem and per leaf, number of spores produced per pustule and AUDPC “Area Under the Disease Progress Curve”, based on pustules per leaf) to investigate the plant disease resistance, specially the AUDPC parameter, durum wheat showed susceptibility to natural infection of powdery mildew specially the cultivar Souabaa Eljia with mean AUDPC value of 583.8, while common wheat, the cultivar Hydra, showed resistance with mean AUDPC value of 52.1,while, the improved durum cultivars Nasr and Karim showed an intermediate reaction. Principal Components Analysis (PCA) showed that the variables were grouped in two principal components that explained 76.65% of the total variance. The projection of the point-cloud representing the populations on the plan formed by the principal components «Fact.1» (49.65%), in abscissa, and «Fact.2» (27%) in ordinate, permitted to distribute the accessions in several groups. Two common wheat cultivars (Hydra and Bysra) showed on one hand a high level of resistance to Bgt and on other hand this fungus behaves differently on these cultivars via the conidia production. The cluster analysis suggested that these two cultivars are genetically similar, but the PCA distribute each one in a distinct single group. Hydra affect all the component of resistance tested and seems more efficient than Bysra

Field Management of Anthracnose (Colletotrichum lindemuthianum) in Common Bean through Fungicides and Bioagents

Common bean anthracnose is a major production constraint in bean growing regions of Ethiopia. This study aimed to determine whether foliar sprays of mancozeb, folpan and mancolaxyl or antagonistic bioagents; Trichoderma harzianum, Trichoderma viride and Pseudomonas fluorescens could reduce anthracnose symptoms and consequently, increase yield and yield components. A total of seven treatments were arranged in a randomized complete block design with three replications. Statistical analysis showed significant differences among treatments. Anthracnose incidence, severity, infected pods per plant and the area under disease progress curve were highest in the control plots compared to the fungicide sprayed and bioagent treated seed plots. The highest percentage of infected pods per plant of 78.9 and 55.0 recorded on the control and mancozeb sprayed plots, respectively. The highest AUDPC value resulted in the lowest yield of 1.01 t/ha in the control plots compared to a highest yield of 3.3 t/ha from the sprayed plots with folpan and 1.8 t/ha from plots treated with Pseudomonas fluorescens. Relative yield losses of 69.7, 46.3 and 22.8% were recorded from the control, seed treated plots with P. fluorescens and sprayed plots with mancolaxyl, respectively. Economic analysis revealed that the highest rate of return of 8,740 was obtained from Pseudomonas fluorescens seed treatment and the highest net benefit value of 43,154 calculated on folpan foliar spray treatment. The results of the present study support the novel possibility of using folpan foliar spray and Pseudomonas fluorescens seed treatments to decrease anthracnose symptoms in common bean and consequently, achieve greater yield.

Morpho-physiology of wheat genotypes under different sowing dates as affected by Helminthosporium leaf blight and leaf rust in Chiwan, Nepal

An experiment was conducted at the Agronomy farm of the Institute of Agriculture and Animal Science (IAAS), Rampur, Nepal in 2008/09. The experiment was laid out in factorial design in spit plot arrangement consisting of date of sowing as main factor and wheat genotypes as sub factor. Wheat genotypes were sown in 22 November for normal sowing and 29 December for late sowing condition. These were assessed against Helminthosporium leaf blight and leaf rust severity in a naturally inoculated environment. Result showed that wheat genotypes differed significantly with respect to flag leaf area, flag leaf duration and plant height. Genotype BL-3064 showed the lower decline (624.9 to 615.1) in chlorophyll content whereas RR-21 showed highest decline (471.2 to 360.4) in chlorophyll content from normal to late sowing, possibly contributing to resistant to the disease. The AUDPC value revealed that genotypes BL-3625 and BL-3623 had increased level of resistance due to lower AUDPC value and higher flag leaf duration. The results of this study suggest that genotypes BL-3623, BL-3625, BL-3063 and BL-3064 could be the option in warm and humid regions of Terai condition so far as resistant to Helminthosporium leaf blight and leaf rust are concerned. Agronomy Journal of Nepal (Agron JN) Vol. 3. 2013, Page 109-116 DOI: http://dx.doi.org/10.3126/ajn.v3i0.9012

Instrata Fungicide Evaluated for Control of Cercospora Leaf Spot on Crapemyrtle

Efficacy of Instrata™ 3.61E at rates of 0.54, 0.74, and 1.11 g ai·liter−1 was compared with recommended rates of the its component fungicides Daconil Ultrex 82.5WDG (chlorothalonil), Banner MAXX 1.3MEC (propiconazole), and Medallion 50W (fludioxonil) as well as Eagle 40W, Heritage 50WDG, and 3336 4.5F fungicide standards for the control of Cercospora leaf spot (Cercospora lythracearum) on field grown ‘Byer's Wonderful White’ crapemyrtle (Lagerstroemia indica) in 2007 and 2008. Efficacy of Instrata 3.61E for the control of Cercospora leaf spot on crapemyrtle was significantly impacted by application rate. Cercospora leaf spot intensity and defoliation AUDPC values as well as final disease ratings usually were lower for the 1.11 compared with the 0.54 g ai·liter−1 rates of Instrata 3.61E, while those of the 0.74 g ai·liter−1 rate were intermediate. The 1.11 g ai·liter−1 but not lower rates of Instrata 3.61E gave superior Cercospora leaf spot control in both study years when compared with the Daconil Ultrex 82.5WDG, Banner MAAX 1.3MEC, and Medallion 50W component fungicides with the two former fungicides providing some control in one of two years and the latter failing to reduce disease intensity or defoliation. Eagle 40W, Heritage 50WDG, and 3336 4.5F proved equally effective as the 1.11 g ai·liter−1 rate of Instrata 3.61E in controlling Cercospora leaf spot in 2007 but only Eagle 40W gave comparable disease control in 2008, while Heritage 50WDG and 3336 4.5F were generally less efficacious than all rates of Instrata 3.61E. In one of two years, better disease control was obtained with Eagle 40W when compared with the 3336 4.5F and Heritage 50WDG standards. Overall, efficacy of the 1.11 g ai·liter−1 rate of Instrata 3.61E for the control of Cercospora leaf spot on crapemyrtle was superior to not only the label rate of each component fungicide but also to the fungicide standards in one of two study years.

Assessment on early blight of potato in order to compare the two methods&amp;lt;i&amp;gt; in vitro &amp;lt;/i&amp;gt;using pathogenic fungi &amp;lt;i&amp;gt;Alternaria solani&amp;lt;/i&amp;gt;

Potato (Solanum tuberosum) early blight, caused by Alternaria solani is one of the most destructive fungal foliar diseases. This research was done in order to study methods comparison of evaluation by culture filtrate of A. solani in in vitro condition for selecting resistance cultivars to early blight. Plantlets of potato viruse free were obtained from the National plant gene bank of Iran, and were inoculated in vitro methods with a culture filtrate of A. solani. In in vitro selection by droplet of culture filtrate method, leaflet received a 10 μl droplet of the A. solani culture filtrate and in in vitro selection by direct using of culture filtrate method, plantlets were placed in test tubes that include 5 μl A. solani culture filtrate. The experimental design was factorial on basis of completely randomized design (CRD) with two factors, three replications and six genotypes. During droplet method assay, the A. solani symptoms appeared 1 - 2 days until 6 days and during direct method they appeared 2 - 3 days until 6 days. The AUDPC values were submitted to the analysis of varience (ANOVA) and AUDPC means were compared by using Duncan test (α = 0.01%). In each method, significant difference among potato cultivars was observed for disease to early blight (p in vitro methods experiment had the same result.

Standardizing resistance screening to Pseudomonas fuscovaginae and evaluation of rice germplasm at seedling and adult plant growth stages

Sheath lesions, grain sterility and grain discolouration of rice caused by Pseudomonas fuscovaginae can cause yield losses of up to 100 %. The most sustainable method of managing this disease is the use of host plant resistance. To identify sources of resistance an inoculation method that is practical, rapid and reliable is needed. We compare three different inoculation methods. Results showed that the pin-prick method is appropriate for identifying sources of resistance to P. fuscovaginae, while the spray method could be useful for mass screening of rice genotypes. The seed-soaking method was also evaluated and has showed potential in detection of early disease resistance. A total of 16 Multiparent Advanced Generation Inter-Crosses and 20 OryzaSNP set varieties from the International Rice Research Institute were evaluated using the pin-prick and seed-soaking methods. All growth stages were susceptible to the pathogen and the 107 cfu mL−1 inoculum concentration was optimal for discriminating between resistant and susceptible genotypes. For the pin-prick method, a single point assessment of disease severity at 14 days post-inoculation could be used instead of the AUDPC values to classify genotypes. An index of reduction in seedling height 10 days after seed soaking was established for the classification of the genotypes reaction to the disease. Resistant varieties identified using both the pin-prick and seed-soaking methods could be verified for use in disease resistance breeding programs. Of the 36 genotypes evaluated 22 were found to be resistant at the late booting or early panicle exsertion stage by pin-prick method, while 25 were resistant at the seed to germination stage. No correlation was found between the resistance classification of varieties between the two inoculation methods, indicating that there could be different mechanisms of resistance to P. fuscovaginae in rice.

Reduced fungicide use on a new Australian peanut cultivar, highly resistant to the late leaf spot and rust pathogens

Rust (caused by Puccinia arachidis) and late leaf spot (LLS, caused by Mycosphaerella berkeleyi) can cause significant yield losses in Australian peanut crops. Until recently, all commercial peanut varieties were highly susceptible to these pathogens, but the new Australian cultivar Sutherland has significantly higher levels of resistance than the older cultivars. Field trials were conducted at two sites in Queensland to (a) confirm the improved resistance of cv. Sutherland over another commercial cultivar, Menzies, (b) study the effects of timing of first spray, spray interval and cultivar on disease severity and yield, and (c) develop a suitable fungicide management program for cv. Sutherland. In the 2006 and 2007 trials, rust and LLS developed slower and had lower final disease ratings and AUDPC values on unsprayed plots of cv. Sutherland than on cv. Menzies. The timing of the first spray is critical in managing both rust and late leaf spot, with the results demonstrating that the first fungicide spray on cv. Sutherland should be applied as soon as rust and LLS are first seen on cv. Menzies. In most trials spray intervals of 14 days or 21 days were suitable to effectively control rust and LLS. In years with low disease pressure, few, if any, fungicide applications will be needed to manage the diseases, but in other years up to four sprays may be necessary.

Field assessment of calcium, copper and zinc ions on plant recovery and disease severity following infection of Huanglongbing (HLB) disease

The effect of Ca, Cu and Zn ions on plant recovery and disease severity following infection of huanglongbing disease was carried out at a commercial citrus orchards belonging to Lembaga Pertubuhan Peladang (LPP) Terengganu, situated at Durian Mentangau, Dungun, Terengganu. Application of Zn or Cu ions in combination with Ca was able to delay disease incidence and severity of hunglongbing disease. These treatments (C/Ca/Cu and C/Ca/Zn) also showed slightly reduction of AUDPC value on infected citrus trees. In general, analysis of macronutrients and micronutrients content in citrus leaves showed significantly different at the beginning of the study (0 to 6 months after treatment) but no significant different were observed at the end of the study period (6-9 months after treatment) as noted on Mg, P, Ca and Zn analysis. Results for specific leaf area showed no significant different among treatment as observed in leaf area, total leaf length and total leaf width. However, specific leaf area was increased gradually in all treatments over the period of the study. The overall results of field trial showed that infected citrus trees treated with combination of Ca and Zn ions at 600 and 10 ppm, respectively resulted in significant increase (P≤0.05) in terms of fruit production and total soluble solid (TSS) content only. Key words: Huanglongbing, candidatus liberibacter asiaticus, field assessment, micronutrients and macronutrients.

Effect of Phytophthora infestans on potato yield in dependence on variety characteristics and fungicide control

The epidemiology of potato late blight (Phytophthora infestans) was observed over the three-years with 110 potato varieties from various maturity groups treated or not treated with fungicides. The determined severity values were transformed into AUDPC coefficients characterizing rate of disease spreading across the crop in connection with varietal characteristics, fungicide application and year effects. The analysis of the pathogen population for the distribution of races virulent to usually used resistance genes indicated non-efficiency of these genes; resistance could only be increased by breeding for polygenically determined horizontal resistance. There were important yearly variations observed for the epidemiology of P. infestans. A correlation was detected between increasing AUDPC value and yield reduction in both fungicide treated and non-treated variants. AUDPC value of the treated variant is to a certain extent positively correlated with the value of the non-treated variant. However, particular interaction between potato genotype and applied fungicide program was shown, which could positively or negatively affect disease course in dependence on the variety.

Evaluation of Advance Wheat Lines for Slow Yellow Rusting (Puccinia striiformis f. sp. Tritici)

Stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici is one of the most damaging diseases ofwheat in Pakistan. Lack of durable resistance in local wheat varieties is the main reason for stripe rust epidemicwhich could limit yields. The use of genetically resistant wheat varieties is the most economic way of controllingthe disease. Evaluation of 135 advance wheat lines for slow yellow rusting was conducted during croppingseason 2008-2009 under natural epidemics at field locations of Ayub Agriculture Research Institute, Faisalabadand Cereal Crops Research Institute, Pirsabak (Northwest), Pakistan. Resistance level based on final diseaseseverity (FDS) along with other slow rusting parameters relative area under disease progress curve (rAUDPC)and relative infection rate (RIR) was assessed. A total of 25 wheat lines were identified to potentially havedurable resistance with low frequency of disease severity (10-30%) and lower relative AUDPC values (2-66%).Based on the slowing rusting data, RAPD (random amplified polymorphic DNA) primers were used in order toevaluate genetic diversity among 25 lines. Of 20 OPA (Operon series) primers tested, 4 (20%) primers werepolymorphic that showed amplification differences among 25 genotypes. OPA-06 and OPA-04 revealed thehighest polymorphism (67% and 50%) while OPA-02 and OPA-17 exhibited the lowest polymorphism (33% and25%) respectively. From the amplification profile, a total of five RAPD markers were obtained in this study. Asimilarity matrix data depicted that most of these genotypes are genetically very close (60-100%). The 25advance lines identified from slow rusting evaluation with five RAPD markers may have partial resistance genesand can be used as slow yellow rusting lines with longer field life in Pakistan breeding program.

Reação em campo à murcha bacteriana de cultivares de tomate em Roraima

A murcha bacteriana causada por Ralstonia solanacearum (Smith) é a doença bacteriana mais importante do tomateiro na Região Norte do Brasil. Os objetivos deste trabalho foram avaliar o nível de resistência de cultivares de tomate, avaliar o progresso da murcha bacteriana nesses genótipos a fim de conhecer o comportamento da doença nos diferentes estádios de desenvolvimento da cultura, para auxiliar no manejo da epidemia, e determinar a época crítica para o desenvolvimento da doença nessas cultivares nas condições de Roraima. Os experimentos foram conduzidos em um campo naturalmente infestado com a biovar 1 de Rasltonia solanacearum, por dois anos. A área tinha um histórico de quatro anos de plantios sucessivos com plantas de tomate suscetíveis à murcha bacteriana, e as perdas alcançando até 100%. Para condução do experimento foram utilizadas mudas das cultivares Majestade, Nemonetta, Carmen, Liliane, Santa Clara, Sensação, San Vito, Gaúcho Melhorado, Hector e Laura. Foram feitas seis avaliações do número de tomateiros que apresentavam murcha irreversível e/ou morte durante o ciclo da cultura. Foram determinadas as variáveis área abaixo da curva de progresso da doença (AACPD) e a taxa de progresso da doença (r), incidência média (Y50), incidência máxima (Ymáx) e a incidência final da doença. Os valores de AACPD e da variável r para a cultivar Majestade foram menores que para as demais, demonstrando que houve menor incidência de plantas doentes nesta cultivar, indicando resistência. Embora o nível de resistência apresentado por esta cultivar não seja muito elevado, o cultivo da mesma é recomendável e viável para o plantio no Estado de Roraima, especialmente considerando-se os altos preços do tomate, que são adquiridos de outras regiões produtoras no país, embora somente esta resistência não garanta, sozinha, o controle adequado da doença, sendo necessárias outras medidas de controle associadas.