Percentage Of Infected Leaf Area Research Articles

Study of southern leaf blight (Bipolaris maydis) on maize genotypes and its effect on grain yield

Southern maize leaf blight is known to be the foremost harmful disease of maize crop which causes significant yield loss. In present investigation, 20 maize genotypes were selected for the test against Southern Leaf Blight (SLB) in the prevailing field conditions at Prithu Technical College, Bangaun, Dang, Nepal with an objective to find the new sources of resistance against southern leaf blight disease. Randomized Complete Block Design (RCBD) was used with three replications as the experimental design. The total percentage of infected leaf area per plant was studied for the disease scoring. It was conducted consequently 5 days of interval, for 5 times after 60 days after sowing and disease severity, mean AUDPC were estimated and yield recorded. The tested 20 maize genotypes differed significantly in mean AUDPC values and based on AUDPC values, genotypes were categorized as highly susceptible, susceptible, moderately resistance and resistance category. Maize genotype Rampur-S03F08 (AUDPC value 65) appeared most resistant followed by Across-0091(AUDP value 67.08) and TLBRSO7F16 (AUDPC value 70.41). Significantly highest yield (1.8 t/ha) was found on genotype Rampur-SO3FO8 (1.8 t/ha) followed by Across-0091 (1.65 t/ha) and TLBRSO7F16 (1.63 t/ha). Thus indicating the high yielding and resistance maize genotypes Rampur- S03F08, Across-0091 and TLBRSO7F16 could be developed as the resistant varieties to southern leaf blight disease.

Bivariate analysis of barley scald resistance with relative maturity reveals a new major QTL on chromosome 3H

The disease scald of barley is caused by the pathogen Rhynchosporium commune and can cause up to 30–40% yield loss in susceptible cultivars. In this study, the Australian barley cultivar ‘Yerong’ was demonstrated to have resistance that differed from Turk (Rrs1 (Rh3 type)) based on seedling tests with 11 R. commune isolates. A doubled haploid population with 177 lines derived from a cross between ‘Yerong’ and the susceptible Australian cultivar ‘Franklin’ was used to identify quantitative trait loci (QTL) for scald resistance. A QTL on chromosome 3H was identified with large effect, consistent with a major gene conferring scald resistance at the seedling stage. Under field conditions, a bivariate analysis was used to model scald percentage of infected leaf area and relative maturity, the residuals from the regression were used as our phenotype for QTL analysis. This analysis identified one major QTL on chromosome 3H, which mapped to the same position as the QTL at seedling stage. The identified QTL on 3H is proposed to be different from the Rrs1 on the basis of seedling resistance against different R. commune isolates and physical map position. This study increases the current understanding of scald resistance and identifies genetic material possessing QTLs useful for the marker-assisted selection of scald resistance in barley breeding programs.

Identification of QTL conferring resistance to stripe rust (Puccinia striiformis f. sp. hordei) and leaf rust (Puccinia hordei) in barley using nested association mapping (NAM).

The biotrophic rust fungi Puccinia hordei and Puccinia striiformis are important barley pathogens with the potential to cause high yield losses through an epidemic spread. The identification of QTL conferring resistance to these pathogens is the basis for targeted breeding approaches aiming to improve stripe rust and leaf rust resistance of modern cultivars. Exploiting the allelic richness of wild barley accessions proved to be a valuable tool to broaden the genetic base of resistance of barley cultivars. In this study, SNP-based nested association mapping (NAM) was performed to map stripe rust and leaf rust resistance QTL in the barley NAM population HEB-25, comprising 1,420 lines derived from BC1S3 generation. By scoring the percentage of infected leaf area, followed by calculation of the area under the disease progress curve and the average ordinate during a two-year field trial, a large variability of resistance across and within HEB-25 families was observed. NAM based on 5,715 informative SNPs resulted in the identification of twelve and eleven robust QTL for resistance against stripe rust and leaf rust, respectively. Out of these, eight QTL for stripe rust and two QTL for leaf rust are considered novel showing no overlap with previously reported resistance QTL. Overall, resistance to both pathogens in HEB-25 is most likely due to the accumulation of numerous small effect loci. In addition, the NAM results indicate that the 25 wild donor QTL alleles present in HEB-25 strongly differ in regard to their individual effect on rust resistance. In future, the NAM concept will allow to select and combine individual wild barley alleles from different HEB parents to increase rust resistance in barley. The HEB-25 results will support to unravel the genetic basis of rust resistance in barley, and to improve resistance against stripe rust and leaf rust of modern barley cultivars.

A nested association mapping population identifies multiple small effect QTL conferring resistance against net blotch (Pyrenophora teres f. teres) in wild barley.

The net form of net blotch caused by the necrotrophic fungus Pyrenophora teres f. teres is a major disease of barley, causing high yield losses and reduced malting and feed quality. Exploiting the allelic richness of wild barley proved to be a valuable tool to broaden the genetic base of resistance of modern elite cultivars. In this study, a SNP-based nested association mapping (NAM) study was conducted to map QTL for P. teres resistance in the barley population HEB-25 comprising 1,420 lines derived from BC1S3 generation. By scoring the percentage of infected leaf area followed by calculation of the average ordinate (AO) and scoring of the reaction type (RT) in two-year field trials a large variability of net blotch resistance across and within families of HEB-25 was observed. Genotype response to net blotch infection showed a range of 48.2% for AO (0.9–49.1%) and 6.4 for RT (2.2–8.6). NAM based on 5,715 informative SNPs resulted in the identification of 24 QTL for resistance against net blotch. Out of these, six QTL are considered novel showing no correspondence to previously reported QTL for net blotch resistance. Overall, variation of net blotch resistance in HEB-25 turned out to be controlled by small effect QTL. Results indicate the presence of alleles in HEB-25 differing in their effect on net blotch resistance. Results provide valuable information regarding the genetic architecture of the complex barley-P. teres f. teres interaction as well as for the improvement of net blotch resistance of elite barley cultivars.

Seedling resistance to Stagonospora nodorum blotch in wheat genotypes

In two independent experiments set up in the greenhouse the seedling resistance to Stagonospora nodorum blotch was investigated in 92 varieties, breeding lines and genotypes with a known genetic background. The greatest area under the disease progress curve calculated from lesion type was 37.06, while in the case of the most resistant genotype this value was 0.38. Many of the lines and varieties bred in Martonvásár proved to have excellent resistance in terms of both percentage of infected leaf area and lesion type. Observations indicate that, depending on the aim of the experiment, the efficient selection of breeding lines is possible in the seedling stage either on the basis of the area under the disease progress curve calculated for lesion types, or on the basis of lesion types scored 7, 11 or 14 days after inoculation.

Occurrence of Downy Mildew Caused by Peronospora belbahrii on Sweet Basil in Hungary.

Sweet basil (Ocimum basilicum L.) is an important medicinal and aromatic plant in Hungary that is cultivated over a large area. During field surveys conducted in 2010, significant incidence of downy mildew was observed in two plant stands at Budapest-Soroksár and Tordas. In 2003, the disease occurred in a greenhouse at Albertirsa as well. By the end of September, on full-grown leaves of two sweet basil cultivars, the frequency of disease occurrence and the percentage of infected leaf area reached 80 to 90% and 17 to 20%, respectively, at Budapest-Soroksár. Symptoms appeared mainly on cvs. Genovese and Milita among others. On leaves, large chlorotic lesions with soft margins developed, followed by necrotization from the middle. Chlorosis often involved the entire leaf surface. Necrotic spots were irregular, variable in diameter, and limited by the main veins. A typical grayish white furry growth could be observed mainly on abaxial leaf surfaces both in chlorotic and necrotic regions. Most abundant growth developed on the leaves of cv. Genovese. Premature leaf fall on diseased plants occurred as well. The fungus was identified as Peronospora belbahrii Thines on the basis of morphological investigation suggested by Thines et al. (4). Sporangiophores were colorless with a long, straight trunk and monopodially branched five to seven times with a length of 416 to 784 μm (average 572 μm). Sporangiophores ended with two slightly curved acute branchlets, the longer one measured 12.5 to 25.0 μm (average 17.1 μm) and the shorter one measured 5.0 to 18.8 μm (average 9.5 μm) long. Ratio of longer to shorter branchlets was 0.7 to 3.0, the average ratio was 1.9. Sporangia were rounded or slightly ovoid, olive to dark brown, and measured 29.3 × 25.6 (23.8 to35.0 × 20.0 to 31.3 μm). Length/width ratio was 1.2 (1.0 to 1.4). Molecular investigation of two isolates was performed. DNA extraction from sporangiophores was followed by PCR using ITS5 and ITS4 primers. The obtained sequence (GenBank Accession No. HQ702191) showed 99.8 to 100.0% similarity with sequences of P. belbahrii (e.g., Accession Nos. FJ394335 and HN462241) and Peronospora sp. (e.g., Accession Nos. AY884605, AY919301, and FJ346561) isolated from sweet basil. In Europe, the disease was reported from Italy (2), France (3), Germany (4), and Switzerland (1). To our knowledge, this is the first report of downy mildew on sweet basil in Hungary.

Soybean cultivar performance in the presence of soybean Asian rust, in relation to chemical control programs

Soybean rust is caused by an obligate parasite (Phakopsora pachyrhizi) which has spread in Brazil in each new season since 2001 and, despite the efforts to control the disease, losses have occurred every year. Its control demands several tactics amongst which chemical control with fungicides is the main method and remains indispensable. Control strategies such as the use of cultivars with partial resistance are desirable, but are not yet commercially available. The present study analyzed the existing differences in the reactions of short, medium and long cycle soybean cultivars against Asian rust and their responses to fungicide sprays. The experiment was conducted at Uberlândia-MG, Brazil, under field conditions from December 2007 to May 2008, in the Syngenta Seeds Experimental Station. The high pressure of the disease in the experiment simulated the natural pressure that the disease often reaches in Brazil. The studied variables were: visual severity (percentage of infected leaf area), percentage defoliation and productivity (kg ha−1). Disease severity was expressed as AUDPC (area under disease progress curve). Variance analysis and comparison of means by the Tukey test (5% significance) were done for all variables studied. Significant differences were observed between cultivar effects and chemical control programs. The results obtained here indicate that the cultivars M-Soy 8199RR and Emgopa 315RR were less susceptible to disease, and that a control program termed “monitoring” (in which the appearance of new pustules of the pathogen were monitored to make the decision at each fungicide spray) was the most effective.

Greenhouse Method for Assessing Spot Blotch Resistance in Barley

Department of Molecular Biology and Biotechnology, AECS, P. O. Box 6091, Damascus, Syria(Received on July 27, 2010; Accepted on November 3, 2010)New sources of barley (Hordeum vulgare L.) resistant tospot blotch, caused by Cochliobolus sativus, are neededto provide effective resistance because of the rapidchange pathotype patterns of C. sativus in fields. Thepurposes of our study were to develop a method toscreen barley for resistance to spot blotch disease andthen use this methodology to screen barley genotypesfor resistance to the major virulent pathotype Pt4 inbarley populations in Syria. A transparent tape method,in which a conidial suspension of C. sativus was droppedonto transparent tape and placed, treated-side down, onthe second leaf surface of barley plants. Disease symp-toms of fungus were easily detected on the leaves coveredby the transparent tape after 48h of inoculation. Thetransparent tape method was repeatable and the diseasescores obtained were correlated ( r = 0.91, P = 0.001) withthose obtained by the seedling assay. This method maybe beneficial in various plant pathology breeding prog-rams. Keywords : Cochliobolus sativus, Hordeum vulgare L.,resistance test, spot blotchCochliobolus sativus (Ito & Kurib.) Drechsl. ex Dast.[anamorph: Bipolaris sorokiniana (Sacc. in Sorok.) Shoem.],the cause of spot blotch (SB), is a common foliar pathogenof barley (Hordeum vulgare), a disease responsible forheavy crop losses (Wilcoxon et al., 1990; Kumar et al.,2002). Although fungicides can be effective in reducing SBseverity (Kiesling, 1985), the most effective and environ-mentally sound means of control is the use of resistantcultivars. However, development of stable forms resistantto foliar diseases depends upon identification of resistanceseffective against the prevalent isolates in barley growingareas (Gupta et al., 2001). A fast, accurate, and precise screening method that can beused to identify sources of tolerant, partially resistant, andpathotype specific resistant barley germplasm would aid inthe development of cultivars for optimal control of C.sativus. Resistance in barley to SB is often evaluated at theseedling and adult plant stages by determining the visibledisease symptoms as a percentage of infected leaf area(Fetch and Steffenson, 1999; Ghazvini and Tekauz, 2008).This method is time-consuming and several environmentalinteractions make it impossible to obtain error-free esti-mates (Gilchrist et al., 1995). Recently, a detached seedlingfirst leaf technique (Arabi and Jawhar, 2007) has been usedfor evaluating barley resistance to SB. However, this methodbased on testing detached leaves in vitro far away from themother plant, and the assessment should be done duringshort time using artificial media, antibiotics and Petri dishes.In classifying the disease reactions of barley lines forbreeding purposes or for studies on host parasite genetics, itis important to have a reliable screening technique forreducing the inconvenience of field tests. The objectives ofour research were to develop a C. sativus screening methodfor barley and then screen barley genotypes for resistance tothe major virulent pathotype Pt4 in barley populations inSyria. Inoculum preparation. The major Syrian pathotype C.sativus (Pt4) used in the study was the most virulent of 117isolates collected in 1998 and 2004 from naturally infectedbarley in different regions of Syria, as described by Arabiand Jawhar (2003). The fungal mycelia were transferredfrom a stock culture into Petri dishes containing potatodextrose agar (PDA, DIFCO, Detroit, MI, USA) with 13mg/l kanamycin sulphate and incubated for 10 days at 21 ±1°C in the dark. Then, conidia were collected with 10 mLof sterile distilled water. The conidial suspension wasadjusted to 2 × 10

Anthracnose disease response in the Burundi sorghum germplasm collection

The United States National Plant Germplasm System maintains 151 sorghum accessions from Burundi of which 148 accessions were evaluated for resistance to Colletotrichum sublineolum at the Tropical Agriculture Research Station in Isabela, Puerto Rico in replicated evaluations during the 2007 and 2008 growing seasons. For the 2007 experiment, 120 accessions showed a resistant response with 89 of these accessions rated as resistant in 2008. The resistant accessions showed reddening of inoculated leaves with no acervuli development, whereas accessions rated as susceptible showed acervuli development on inoculated leaves. Mean infection severity based on the percentage of infected leaf area for the susceptible accessions was 2% in 2007 and 2.5% for the 2008 experiment. Only four accessions showed an infection severity more than 10% and eight accessions showed a susceptible response across replications and growing seasons. Results of this study indicate that sorghum germplasm from Burundi is an important source of anthracnose resistance for sorghum improvement and that germplasm from regions of high annual rainfall is frequently associated with anthracnose resistance.

DANOS CAUSADOS PELA INFECÇÃO DE OÍDIO EM DIFERENTES ESTÁDIOS FENOLÓGICOS DA SOJA

RESUMO Ainda não há estudos precisos que quantifiquem os prejuízos decorrentes de infecção por oídio e/ou outras doenças foliares, para a maioria das culturas de importância econômica no Brasil. O objetivo foi quantificar as perdas causadas por oídio (Microsphaera diffusa) infectando a cultura da soja em diferentes estádios fenológicos e relacioná-las ao desenvolvimento e produtividade da cultura. O experimento foi desenvolvido em ambiente protegido, e os tratamentos foram testemunha controlada, testemunha sem controle, infecção iniciada em R1 – R2, infecção iniciada em R – R, infecção iniciada em R – R e infecção iniciada em R – R. A avaliação foi feita 345.15.25.35.4 semanalmente, considerando a porcentagem da área foliar infectada. Os resultados mostraram que, no tratamento em que houve infecções iniciadas em R1-R2 e R3-R4, a porcentagem de área foliar afetada foi maior (41% e 38%, respectivamente), com consequente menor produtividade (1.186,6 e 1.309,5 kg.ha-1 respectivamente). No tratamento em que a infecção ocorreu em R – R, houve 5.35.4 a menor média de área foliar afetada pela doença (24%) e a produtividade teve queda de 26%. Os resultados mostraram que as perdas de produtividade pelo oídio na cultivar Embrapa 48 variaram ao redor de 26 a 50%, e que a recomendação oficial para o início de controle do oídio da soja, quando esta se apresentar entre 40 e 50% de severidade, deve ser questionada e outros trabalhos neste âmbito devem ser desenvolvidos para determinação das perdas ocasionadas por esta doença na cultura.

Selection strategies of segregant soybean populations for resistance to Asian rust

The objective of this work was to identify the best selection strategies for the more promising parental combinations to obtain lines with good resistance to soybean Asian rust (Phakopsora pachyrhizi). Two experiments were carried out in the field during the 2006/2007 and 2007/2008 growing seasons, to determine the percentage of infected leaf area of individual plants of five parents and their segregant F2 and F3 populations. The data obtained indicates that additive genetic variance predominates in the control of soybean resistance to Asian rust, and that the year and time of assessment do not significantly influence the estimates of the genetic parameters obtained. The narrow-sense heritability (h²r) ranged from 23.12 to 55.83%, and indicates the possibility of successful selection of resistant individuals in the early generations of the breeding program. All the procedures used to select the most promising populations to generate superior inbred lines for resistance to P. pachyrhizi presented similar results and identified the BR01-18437 x BRS 232 population as the best for inbred line selection.

Response to stripe rust (Puccinia striiformis Westend. f. sp.tritici) and its coincidence with leaf rust resistance in hexaploid introgressive triticale lines withTriticum monococcum genes

Triticale introgressive lines were developed by incorporating diploid wheat (Triticum monococcum [TM16]) genes into the hexaploid triticale genotype LT522/6. The synthetic allotetraploid T. monococcum cereale (A(m) A(m)RR) was used as a bridging form to introduce the genes. A group of 43 introgressive lines, parental stocks and a check cultivar were inoculated at the seedling stage (in the greenhouse) and at the adult plant stage (in the field) with four pathotypes of Puccinia striiformis f. sp. tritici to determine if the stripe rust resistance was derived from TM16 and to analyze the expression of the diploid wheat gene(s) at the hexaploid level. At the seedling stage, 14 triticale introgressive lines expressed resistance to some of the used pathotypes, showing introduction of a genetic material from the T. monococcum genome. Among them, 7 lines were resistant to all four stripe rust pathotypes applied at this stage. In the field, adult plant resistance and percentage of infected leaf area were scored and transformed into the coefficient of infection. Plant response to stripe rust was compatible at these two developmental stages with a high statistical probability showing the genetic dependence on the same genetic background. Also observed was a full concordance of the adult plant resistance to stripe rust with previously assessed resistance to leaf rust, as well as the highly significant linkage of the resistance to the both diseases at the seedling stage in the set of the tested introgression lines. This result strongly suggests that T. monococcum genes responsible for these characters are located in proximity.

Application of Rhizobacteria for Induction of Systemic Resistance to Bacterial Blight of Cotton Caused by Xanthomonas Campestris PV. Malvacearum Using Fluorescent Pseudomonads of Rhizosphere

The ability of fluorescent pseudomonads of cotton rhizosphere of induction of systemic resistance (ISR) against bacterial blight of cotton was investigated. Of the 21 isolates tested, 19 were observed to increase the resistance of plants. This was demon- strated by a lower percentage of infected leaf area. On the basis of growth promotion and ISR induction ability, isolates 148, 35Q, 16Q and 113 were selected for further investigations. All isolates increased the resistance of plants, and per cent of infected area on leaves of these treatments were lower than those control of plants. Levels of peroxidase (PO) and phenylalanine ammonia lyase (PAL) activ- ity in the leaves of bacterized plants with selected isolates were similar to that in control plants, but after inoculation of leaves with the pathogen, the amount of these enzymes increased in bacterized plants to high levels. The increase of enzyme activity in control plants was low after inoculation.

Interação entre resistência genética parcial e fungicidas no controle da ferrugem asiática da soja

O objetivo deste trabalho foi estudar a interação de diferentes cultivares de soja com fungicidas no controle da ferrugem asiática, em duas épocas de semeadura. O experimento foi realizado em condições de campo, de setembro de 2005 a maio de 2006. Foram analisadas as características: incidência, severidade (porcentagem de área foliar infectada e nota visual da parcela), número de pústulas por centímetro quadrado, peso de mil sementes e produtividade. A área abaixo da curva de progresso da doença (AACPD) foi calculada para os dados da doença. Foram observados efeitos significativos das cultivares, dos fungicidas, e da interação entre esses fatores, tanto nos valores de AACPD quanto no peso de mil sementes e produtividade. As cultivares IAC-100, Potenza e UFUS-Impacta apresentaram, em ambas as épocas de semeadura, a presença de resistência parcial à ferrugem asiática, evidenciada pelos valores baixos da AACPD. O fungicida do grupo dos triazóis (cyproconazole) e sua mistura com um fungicida do grupo das estrobilurinas (azoxystrobina e cyproconazole) apresentam controle eficiente sobre a ferrugem asiática.

Evaluation of barley doubled haploid and mutant lines for agronomic traits and scald resistance

Barley (Hordeum vulgare L.) is a major field crop grown worldwide. Field research was undertaken at ICARDA’s (International Center for Agriculture Research in Dry Area) main station in Northwest Syria to evaluate barley doubled haploid (DH) and mutants lines for agronomic traits (grain yield, plant height and days to heading) and resistance to scald (Rhynchosporium secalis) under natural infection conditions for two consecutive years. Significant differences were found among lines in the percentage of infected leaf area. However, they exhibited a continuous range of response from very susceptible to resistant. Seven lines had significantly lower percentage of infected leaf area with disease than did the other lines, which are associated with potential for grain yield and earliness. These lines could be considered as possible donors in further barley breeding programs.

Factors Affecting the Onset of Cercospora Leaf Spot Epidemics in Sugar Beet and Establishment of Disease-Monitoring Thresholds

ABSTRACT Severe Cercospora leaf spots epidemics in sugar beet during the late 1980s and early 1990s in southern Germany prompted us to initiate investigations on the epidemiology of the causal agent, Cercospora beticola. The data set involved 69 field trials (1993 to 2003) focusing on factors affecting the epidemic onset of this disease. Observations were made at weekly intervals, recording the calendar week when canopy closure occurred (growth stage according to BBCH scale = 39) and symptom development by assessing the percentage of infected leaf area on a single-leaf basis (n = 40 plants). These monitoring trials revealed that epidemic onset varied between early July and mid-September. Hence, the target was to identify the reasons for this variation in order to deduct the most suitable approach for predicting epidemic onset. Differences in cultivar resistance explained part of epidemic onset variability, as did different timings of canopy closure, presumably due to associated microclimate changes. Moreover, meteorological variables were considered as potential reasons for variation in epidemic onset. The weather-dependent infection probability was assessed by daily infection values (DIV) in the range from 0 to 1 using hourly weather data. For calculating DIVs, the temperature effect was quantified by the proportions of the latent period (LP) relative to the optimum at 20 to 25 degrees C, established by artificial inoculation of sugar beet plants in growth cabinets. Artificial infection experiments further established that air relative humidity (RH) >95% or leaf wetness was required for infection and subsequent lesion development. Under field conditions, the probability of leaf wetness was 75% at RH >90%. Therefore, DIVs were set to 0 for RH </=90% in the absence of precipitation (moisture index I). Alternatively, the effect of moisture was modeled with a sigmoidal function describing the occurrence of leaf wetness in dependence of RH in the field (moisture index II). Using this approach, DIV values were cumulated (c-DIV) for each of the 69 trials beginning either at fixed starting dates (1 May, 16 May, or 1 June) or the dates of canopy closure. Accumulation of DIV ended at the time of epidemic onset. The two different moisture index definitions had no significant influence on c-DIV; whereas, for starting time of summation of DIV, the date of canopy closure was more suitable. Values of c-DIV ranged from 7 to 19 in highly susceptible cultivars and 12 to 25 in cultivars with lower susceptibility. Given this variation, c-DIV values were insufficient to explain differences in the date of epidemic onset and thus were not considered suitable for making accurate and precise management decisions. However, a negative prognosis assessing the most likely periods of disease absence was possible by determining the minimum c-DIV as a threshold. This threshold was 7 c-DIV for highly susceptible cultivars and 12 c-DIV for cultivars with low susceptibility. Crop monitoring is recommended as soon as these threshold values are exceeded so that the exact epidemic onset time can be observed.

Diallel analysis of sooty stripe resistance in sorghum

Sooty stripe [Ramulispora sorghi (Ellis and Everhart) Olive and Lefebre] is a widespread foliar disease of sorghum [Sorghum bicolor (L.) Moench] in West Africa, responsible for grain yield losses up to 46%. We studied the inheritance of sooty stripe resistance in a 9 × 9 sorghum F2-population diallel grown together with parent lines and checks in1996 under natural disease pressure at two locations in Mali. The percentage of infected leaf area was determined twice over a two-week interval during the season. At the second evaluation, the mean sooty stripe severity amounted to 13% infected leaf area at Samanko and 12% at Cinzana. The frequency distribution of the entries was approximately normal for the mean disease severity, averaged across assessment dates and locations, pointing to the involvement of multiple genes. With the data combined across the two locations, genetic differences among lines and among F2 populations were highly significant. Genotype × location interaction variances were also significant but much smaller than the genetic variances. Broad-sense heritability estimates were 0.92 for lines and 0.94 for the F2 populations, for the mean percentage infected leaf area across the two assessment dates. General combining ability effects (GCA) determined most of the differences among the F2 populations. Specific combining ability effects (SCA), and the interactions of GCA or SCA with locations were also significant but less important. Line performance per se was highly correlated with GCA. Because of the high heritability and predominance of additive effects, prospects are good for the genetic improvement of resistance to sooty stripe in sorghum in Mali, using simple pedigree or recurrent selection procedures.

Components of Variation for Quantitative Adult-Plant Resistance to Powdery Mildew in Winter Rye

The genetics of quantitative resistance to powdery mildew (Erysiphe graminis f. sp. secalis) in winter rye (Secale cereale) was investigated by testing four sets of factorial crosses along with their parental inbred lines (53 crosses, 28 inbred lines in total) at two locations during 1988 and 1989. Genotypes were scored on a 0-9 scale for the percentage of infected leaf area at booting and heading stages on the upper three leaves of 10 randomly chosen main stems per plot. Estimates of heritability were high in all materials at both assessment stages (h 2 =0.65-0.95). High correlations were found among leaves (r=0.75-0.97; P=0.01) for all sets and between booting and heading pooled over leaves for three out of four sets (r=0.89-0.98; P=0.01) [...]

A Detached-Leaf Technique for Detecting Resistance to Phytophthora parasitica var. nicotianae in Tobacco

Leaves (7-9 cm long) from healthy tobacco plants were excised, surface-sterilized for 30 sec in a 0.05% NaOCl 3 solution and inoculated with four mycelial plugs of 2-day-old P. p. var. nicotianae cultures grown on oatmeal agar.(...) Genotype rankings for lesion development and percentage of infected leaf area were similar to known rankings of the same genotypes for field resistance