Percentage Of Leaf Area Research Articles

Assessing Soybean Cultivar Resistance to Target Spot Using a Detached Leaf Assay

Target spot (TS), caused by the fungus Corynespora cassiicola, is a foliar disease of increasing importance to soybean in the US. Identifying cultivar resistance to TS is challenging. The objective of this research was to determine the reactions of a diverse collection of soybean genotypes to target spot using a detached leaf inoculation method. A detached unifoliate leaf of each soybean genotype was placed in a Petri dish on moist filter paper, wounded at three locations, inoculated with 10 μl, of a 105 conidial suspension of C. cassiicola, and incubated at room temperature (23°C). The percent leaf area with TS symptoms (TSS) was measured digitally 7, 10, 14, and 17 days after inoculation (DAI) and the area under the disease progress curve (AUDPC) calculated. Thirty-seven soybean genotypes and three soybean cultivars were evaluated in three replicated trials. At 17 DAI, target spot symptoms ranged from 2 to 84% TSS. Significant differences occurred between soybean genotypes at each rating time in each trial. Across the three trials, the reaction of most soybean genotypes ranged from resistant to susceptible. These soybean genotypes were evaluated in the field with natural inoculum at two locations in 2022. Target spot developed late but differed significantly between genotypes averaging from 0.35 to 3.35% TSS. Field results were not significantly correlated to the detached leaf results. The detached leaf assay is another tool for screening soybean genotypes for resistance to TS but needs field validation.

Genetic mapping of loci affecting seedling and adult-plant resistance to powdery mildew derived from two CIMMYT wheat lines

Main conclusionPM3 and PM8 alleles carried by two CIMMYT wheat lines confer powdery mildew resistance in seedlings and/or adult plants. A stage-specific epistatic interaction was observed between PM3 and PM8.Powdery mildew is an important foliar disease of wheat. Major genes for resistance, which have been widely used in wheat breeding programs, are typically effective against only limited numbers of virulence genes of the pathogen. The main aim of this study was to map resistance loci in wheat lines 7HRWSN58 and ZWW09-149 from the International Maize and Wheat Improvement Center (CIMMYT). Doubled haploid populations (Magenta/7HRWSN58 and Emu Rock/ZWW09-149) were developed and grown in controlled environment experiments and inoculated with a composite of Blumeria graminis f.sp. tritici isolates that had been collected at various locations in Western Australia. Plants were assessed for powdery mildew symptoms (percentage leaf area diseased) on seedlings and adult plants. Populations were subjected to genotyping-by-sequencing and assayed for known SNPs in the resistance gene PM3. Linkage maps were constructed, and markers were anchored to the wheat reference genome sequence. In both populations, there were asymptomatic lines that exhibited no symptoms. Among symptomatic lines, disease severity varied widely. In the Magenta/7HRWSN58 population, most of the observed variation was attributed to the PM3 region of chromosome 1A, with the allele from 7HRWSN58 conferring resistance in seedlings and adult plants. In the Emu Rock/ZWW09-149 population, two interacting quantitative trait loci were mapped: one at PM3 and the other on chromosome 1B. The Emu Rock/ZWW09-149 population was confirmed to segregate for a 1BL·1RS translocation that carries the PM8 powdery mildew resistance gene from rye. Consistent with previous reports that PM8-derived resistance can be suppressed by PM3 alleles, the observed interaction between the quantitative trait loci on chromosomes 1A and 1B indicated that the PM3 allele carried by ZWW09-149 suppresses PM8-derived resistance from ZWW09-149, but only at the seedling stage. In adult plants, the PM8 region conferred resistance regardless of the PM3 genotype. The resistance sources and molecular markers that were investigated here could be useful in wheat breeding.

Grain Yield and Quality Losses Caused by Tan Spot in Wheat Cultivars in Australia

Tan spot (TS), known in Australia as yellow leaf spot, is caused by the fungal pathogen Pyrenophora tritici-repentis, a major foliar disease of wheat. Four experiments were conducted between 2016 and 2017 in two different climatic zones of southeastern Australia to determine the impact of TS on grain yield and quality in six wheat cultivars with different resistance ratings. In each experiment, high and low TS disease scenarios were applied to each cultivar. Disease severity was assessed as either whole-plot percentage leaf area affected (%LAA) or top three leaf (flag to flag-2) %LAA. Whole-plot %LAA was analyzed using both repeated measurements and area under the disease progress curve (AUDPC). For whole-plot %LAA, the repeated measurements identified differences in epidemic progression at key growth stages not identified through AUDPC. Both AUDPC and end-of-season flag to flag-2 %LAA were negatively correlated with grain yield and screenings. Increased rainfall impacting disease development and number of rain days above 5 mm increased TS severity across both climatic zones. Cultivar resistance ratings influenced grain yield loss, with moderately resistant, moderately susceptible, and susceptible cultivars losing up to 6, 18, and 24% grain yield, respectively. High disease significantly increased screenings by up to 1, 3, and 5% for moderately resistant, moderately susceptible, and susceptible cultivars, respectively. This study demonstrated that TS can cause significant grain yield losses in southeastern Australia, and a minimum cultivar rating of moderate resistance to moderate susceptibility was required to prevent severe TS and associated grain yield and quality losses. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Aggressiveness of Xanthomonas translucens pv. undulosa Isolates and Differential Reaction Among Spring Wheat Varieties Under a Controlled Environment

Xanthomonas translucens pv. undulosa causes bacterial leaf streak (BLS) in wheat that can lead to up to 40% losses globally. Understanding the aggressiveness of isolates from different locations in a state may help in screening for BLS resistance in wheat-breeding programs for that area. A greenhouse study to determine the aggressiveness of 17 isolates collected from South Dakota on spring wheat cultivar SY-Rockford and differential reactions of 21 spring wheat varieties grown in South Dakota to BLS under greenhouse conditions was conducted in 2021 and 2022. To assess BLS severity, one randomly selected plant per pot was rated based on the percentage of leaf area with BLS symptoms. Significant differences among the bacterial isolates were observed, with Xtpvu21OC (23.33%) being the most aggressive in causing BLS in SY-Rockford. Spring wheat varieties MN Washburn (25.0%) and ND Frohberg (22.5%) were found to be the most susceptible to BLS. It is suggested that the most aggressive Xanthomonas translucens pv. undulosa isolate available to researchers in their region be used in screening varieties and lines for BLS resistance.

Leaf defenses of subtropical deciduous and evergreen trees to varying intensities of herbivory.

Generally, deciduous and evergreen trees coexist in subtropical forests, and both types of leaves are attacked by numerous insect herbivores. However, trees respond and defend themselves from herbivores in different ways, and these responses may vary between evergreen and deciduous species. We examined both the percentage of leaf area removed by herbivores as well as the percentage of leaves attacked by herbivores to evaluate leaf herbivore damage across 14 subtropical deciduous and evergreen tree species, and quantified plant defenses to varying intensities of herbivory. We found that there was no significant difference in mean percentage of leaf area removed between deciduous and evergreen species, yet a higher mean percentage of deciduous leaves were damaged compared to evergreen leaves (73.7% versus 60.2%). Although percent leaf area removed was mainly influenced by hemicellulose concentrations, there was some evidence that the ratio of non-structural carbohydrates:lignin and the concentration of tannins contribute to herbivory. We also highlight that leaf defenses to varying intensities of herbivory varied greatly among subtropical plant species and there was a stronger response for deciduous trees to leaf herbivore (e.g., increased nitrogen or lignin) attack than that of evergreen trees. This work elucidates how leaves respond to varying intensities of herbivory, and explores some of the underlying relationships between leaf traits and herbivore attack in subtropical forests.

Exserohilum turcicum (Northern Corn Leaf Blight) Severity on Maize Hybrids and the Associated Crop Performance in O.R. Tambo District, Eastern Cape, South Africa

<i>Exserohilum turcicum</i> is a fungus that causes northern corn leaf blight (NCLB) and has deleterious effects on maize production globally. Therefore, it is prudent to mitigate the effects of NCLB using genetic diversity. The objective of this research was to assess the severity of NCLB disease on the growth and yield of various maize genotypes. A randomized complete block design field experiment, replicated three times, was conducted to evaluate the effect of <i>E. turcicum</i> on 10 maize hybrids. Percent disease index, plant height, and leaf area were recorded at the silk stage. Cob weight, grain fresh weight, and grain yields were determined at harvest maturity. All measured parameters were significantly different (<i>P</i><0.05) between the maize hybrids. Of the 10 genotypes, four (PAN 4R-528R, PAN 4R-728BR, PAN 3R-724BR, and P1788BR) were susceptible, five (DKC74-74BR, PAN 5R-582R, PAN 5R-890R, PAN 5R-854R, and PAN 5R-590R) were moderately susceptible, and one (DKC80-40BR) was moderately resistant. DKC80-40BR exhibited greater cob weight, while DKC74-74BR was superior in all other plant growth and yield components. Interestingly, although not significant (<i>P</i>>0.05) and high, maize growth and yield parameters had negative correlations with disease incidence, except for grain fresh weight. Therefore, DKC80-40BR may be selected for cultivation in areas prone to NCLB to reduce maize susceptibility to the disease, while DKC74-74BR may improve crop performance. These hybrids could be considered as potential sources of resistance or tolerance to NCLB for further validation by plant breeders.

Genome-Wide Association Study of Resistance to Pseudomonas syringae in the USDA Collection of Citrullus amarus.

Pseudomonas leaf spot (PLS), caused by Pseudomonas syringae pv. syringae, is an emerging disease of watermelon in the United States with the potential to severely reduce yield under humid conditions. The genetic basis of resistance to this disease is not known and no resistant germplasm is available. Because Citrullus amarus is an important reservoir of resistance genes for the cultivated watermelon, C. lanatus, we screened the United States Department of Agriculture plant introduction collection of C. amarus for resistance to PLS. Accessions (n = 117) were phenotyped for their level of resistance to PLS in two separate tests. Accession means of percent leaf area affected ranged from 1.5 to 99.4%. The broad-sense heritability for the trait was 0.51. Whole-genome resequencing generated 2,126,759 single-nucleotide polymorphisms (SNPs) which were used to perform a genome-wide association study (GWAS) aimed at discovering molecular markers for resistance. Three different models-BLINK, FarmCPU, and MLM-were included in the GWAS analyses. BLINK and FarmCPU, which are multilocus models, found eight SNPs, located on chromosomes Ca01, Ca05, Ca06, Ca08, and Ca10, that were significantly associated with resistance to PLS. Two of these SNPs were found by both BLINK and FarmCPU. The MLM model did not detect any significant associations. BLINK and FarmCPU estimated an explained phenotypic variance of 43.6 and 28.5%, respectively, for SNP S6_19327000 and 25.0 and 26.0%, respectively, for SNP S1_33362258, the two most significant SNPs found. In total, 43 candidate genes with known involvement in disease resistance were discovered within the genomic intervals of seven of the eight peak SNPs. Eleven of the candidate genes that were found have been reported to be involved in resistance to P. syringae in other plant species. Two significant SNPs were within resistance genes previously documented to play important roles of plant resistance specific to P. syringae in other pathosystems. The SNPs identified in this study will be instrumental in finding causal genes involved in PLS resistance in watermelon and developing resistant germplasm through breeding.

Resistance Breeding to Northern Corn Leaf Blight with Dominant Genes, Polygene, and Their Combinations—Effects to Yield Traits

Resistance breeding is the most economic method to control northern corn leaf blight (NCLB). The objectives of these studies were: To assess effects of dominant genes (Ht(s)), polygene (PG), and combinations on percent leaf area affected (PLAA), yield, kernel moisture, kernel number per ear, and 100-kernel weight; to understand genetic action of combinations; to predict losses and effects of resistant genes for yield traits with PLAA; and to assess yield under different NCLB epidemic conditions. Two experiments were conducted. E1 had 120 crosses, their parents, and ten hybrid checks, inoculated NCLB twice in 2015 and 2016; and E2 had 85 crosses and 10 hybrids, with none, one, and two inoculation treatments in 2015. E1 results showed the order of PLAA was Ht3 ≈ Ht2 ≈ PGHtm1 ≈ PGHt1< PGHt3 ≈ PGHt2 < PGHtn1 < PG < Ht1 < Htn1 ≈ Htm1. The order of Ht(s) effects for yield was Ht2 > Ht3 > Ht1 > Htm1 > Htn1. Gene effects of cross ≈ gene effects of (female + male) for all five traits. Predicted losses and predicted effects of resistant genes between yield traits with PLAA were determined. E2 results indicated resistant genes increased yield more efficiently under NCLB epidemic environments.

Genetic characterization of downy mildew resistance from the hop (Humulus lupulus L.) line USDA 64035M

AbstractDowny mildew (caused by Pseudoperonospora humuli) resistance (DMR) will facilitate the success of hop (Humulus lupulus L.) production in humid, temperate climates. However, DMR in hop has a narrow genetic base, and its genetic architecture is poorly understood. In this study, we characterized the genetic control of DMR using a biparental mapping population derived from a cross between a female, the susceptible cultivar ‘Comet,’ and a male plant, the resistant line USDA 64035M. Resistance was evaluated after inoculation with the downy mildew pathogen as disease severity and percent leaf area with sporulating lesions under greenhouse conditions. Significant (p value < 0.01) genotypic differences were observed for the traits. Broad‐sense heritability was 0.33 for disease severity and 0.72 for percent leaf area with sporulating lesions. Genome–phenome association between 4090 markers and 274 individuals identified three significant markers for disease severity and five for percent leaf area with sporulating lesions. Our study demonstrated that DMR was under polygenic control with small effect loci in this population. In addition, a pleiotropic locus on chromosome two was found to be associated with both disease severity and percent leaf area with sporulating lesions. Identifying the gene(s) underlying such a pleiotropic locus can help improve our understanding of hop response to pathogen infection.

Evaluation of Different Chemicals for Controlling Powdery Mildew of Black Gram

One of the major constraints of black gram production is Powdery mildew (Erysiphe polygoni) disease. This study was an attempt of assess the efficacy of different chemicals against powdery mildew disease. The Experimental design was RCBD with three replication and Binamash-1 variety was planted under natural field conditions. Four chemicals viz. salicylic acid (1g/L), copper shulphate (0.5g/L), chitosan (0.1g/L) and thiovit (2g/L) was evaluated against powdery mildew disease. Those chemicals were applied 3 times with 7days interval after the disease initiation. Disease incidence and percent leaf area infection data was recorded three time after the application of treatments and other agronomic data was recorded after harvest. All the treatments were performed better than control in reducing the incidence of powdery mildew disease and percent leaf area infection. During the experimental period (Khrif -2, 2020), there was no incidence of other fungal foliar disease. Results represent that thiovit @ 2g/L performed best in controlling powdery mildew disease incidence (41%), percent leaf are infection (33%) and highest seed yield (520.57 kg/ha) among the treatments. We can conclude this study that, Thiovit (80% sulphur fungicide @ 2g/L) was best for controlling powdery mildew of black gram among the treatments and it (applied 3 times with 7days interval after the disease initiation) can be used for controlling this disease.

Studies on Antimicrobial Effect of Botanicals on Leaf Blight of Indian mustard Caused By Alternaria brassicae

The present study was conducted at ANDU&T Kumarganj Ayodhya at student instructional form (SIF). As in the investigation it was observed that foliar spray with Carbendazim (0.1%), Neem oil (5%), followed by Neem leaf extract (5%) found to be more effective on growth parameters like Number of branches/plants, number of leaves/ plants, plant height (cm), number of pods/plants,) and increased the yield (1000-seed weight, per plant yield (g), per hectare yield) and also significantly reduced the Alternaria blight in Indian mustard. Carbendazim (0.1%), Trichoderma harzianum (2%) followed by garlic bulb extract (5%) was found most effective in reducing Alternaria blight, recorded maximum disease incidence i.e. percent Disease intensity, percent Leaf area disease (LAD), percent leaf infection, number of spots per pods, seed infection percent respectively.

Evaluation of Rapeseed Genotypes against Alternaria Blight under Field Conditions in Nawalparasi-West, Nepal

Alternaria blight disease causes both yield and quality loss in Brassica crops. A field evaluation of ten rapeseed genotypes against Alternaria blight disease was conducted during November 2018 to February 2019 in Parasi, Nawalparasi-west district. Experiment was laid out in a randomized complete block design with individual plot size of 2.25 m2 with three replications. Post-harvest in-vitro seed infection test was done in a completely randomized design with four replications. Disease scoring was done as percentage of leaf area and pod infection on individual 15 sample plants per plot at seven days intervals. Genotype ICT 2001-35 was found moderately resistant based on categorization of mean leaf AUDPC (308.52) and mean pod infection AUDPC values (391.48) with low seed infection (12.50%). Preeti, Bikash and Pragati showed highly susceptible reactions to both leaf blight and pod infection. Therefore, genotype ICT 2001-35 could be used in a varietal improvement program for disease resistance against Alternaria blight.

More than what they eat: uncoupled biophysical constraints underlie geographic patterns of herbivory

Herbivory rates have classically been hypothesized to decrease from the tropics towards higher latitudes because the more benign abiotic conditions in tropical systems foster greater ecosystem complexity including greater intensity of biotic interactions. However, attempts to quantify latitudinal patterns of herbivory often fail to support this hypothesis. While biases have been offered as explanations for null results, here, we argue that framing the question of latitudinal variation in herbivory around nutrient and energetic constraints of insect herbivores and plants may provide mechanistic explanations of latitudinal herbivory patterns. As a case study, we focused on sodium as an uncoupled nutrient between herbivore and plant communities: sodium is a key limiting micronutrient for herbivore neural and muscular development while present at orders of magnitude lower concentrations in plants. We compared sodium deposition with latitude, mean annual temperature (MAT) and actual evapotranspiration (measure of primary productivity, AET) in their ability to predict consumed percentage leaf area from published datasets. Leaf percent herbivory increased with sodium deposition and MAT and decreased with latitude but was unrelated to AET. Sodium had comparable effect size and predictive ability to either MAT or latitude. Additionally, herbivory was highest in locales with both high sodium deposition and high MAT. Our hypothesis that geographic variation in herbivory is driven by an interaction of unrestrictive temperature environments (high MAT) and limiting nutrient supply to herbivores (high sodium deposition) was strongly supported. We propose that greater generality, predictability and theoretical development on geographic variation in herbivory will arise from a refocus on the biophysical constraints (e.g. productivity, micronutrient availability, leaf mass consumed) that ultimately control consumer interactions rather than latitude per se. This refocus is likely to open new hypotheses for the evolution of defense syndromes across plant populations and communities based on the specific geography of limiting nutrients.

Stem portion and number of stakes influence on growth and yield of cassava variety in the South East, Nigeria

Investigations were conducted to study the effect of stem portion and number of stakes per stand on crop establishment, growth and yield of cassava variety NR 8082 in Umudike Southeastern Nigeria during the 2016/17 and 2017/18 cropping seasons. In each year, the experiment was laid out as a 3 × 3 factorial, in randomized complete block design with three replications. Treatments consisted of three stem portions of different physiological ages (top, middle and basal) and three numbers of stakes per stand (1, 2 and 3). The middle and basal stem portions significantly increased percent establishment, plant height and leaf area index at 3 months after planting (MAP) but had no effect on number of storage roots per plant. The best stem portion for storage root yield was, however, the top portion which produced the highest yield on average. Number of stakes per stand did not significantly affect stem girth, number of nodes per plant and leaf area index, but the use of 1 stake per stand increased number of storage roots per plant, root weight and storage oot yield in 2017/2018 cropping season. Number of stakes per stand did not significantly influence storage root yield across the two seasons of evaluation. Interactions between stem portion and number of stakes per stand did not significantly affect storage root yield of NR 8082 high cassava variety in both cropping seasons. Based on the findings, the use of 1 stake per stand is recommended for high root yields of NR 8082 cassava variety under conditions of low soil fertility in Umudike, South East Nigeria. Although the top portion enhanced root yield, farmers could use any of the stem portions, since the middle and basal parts gave satisfactory yields and had better establishment than the former.

Successional and Intraspecific Variations in Leaf Traits, Spectral Reflectance Indices and Herbivory in a Brazilian Tropical Dry Forest

Leaf traits are good indicators of ecosystem functioning and can affect herbivory and leaf reflectance patterns, allowing a better understanding of changes in environmental conditions, such those observed during forest natural regeneration. The aim of this study was to evaluate the intraspecific variation in leaf traits and their influence on the pattern of herbivory and leaf reflectance in three species distributed along a successional gradient (early, intermediate and late stages) in a tropical dry forest (TDF) in northern Minas Gerais, Brazil. We sampled individuals of the following abundant tree species that occurred in multiple successional stages: Cenostigma pluviosum, Handroanthus ochraceus, and Tabebuia reticulata. We collected 10 leaves from each tree to determine the contents of chlorophyll a, b, and total, carotenoids and water, as well as the percentage of leaf area removed by herbivores and leaf specific mass (LSM). We also measured five spectral reflectance indices (Normalized Difference Vegetation Index-NDVI, Simple Ratio-SR, modified Normalized Difference-nND, modified SR-mSR and Water Index-WI) using a portable spectrometer. Our results showed intraspecific differences in most leaf traits along the successional gradient, suggesting that local adaptation may play an important role in plant community assembly. However, herbivory only differed for H. ochraceus in early and intermediate stages, but it was not affected by the leaf traits considered here. Spectral reflectance indices also differed among successional stage for all species together and for each species separately, except for T. reticulata in intermediate and late stages. Thus, leaf spectral signatures may be an important tool to the remote detection of different successional stages in TDFs, with implications for forest management.

Isolate Virulence and Cultivar Response in the Winter Wheat: Pyrenophora tritici-repentis (Tan Spot) Pathosystem in Oklahoma.

Prevalence of tan spot of wheat caused by the fungus Pyrenophora tritici-repentis has become more prevalent in Oklahoma as no-till cultivation in wheat has increased. Hence, developing wheat varieties resistant to tan spot has been emphasized, and selecting pathogen isolates to screen for resistance to this disease is critical. Twelve isolates of P. tritici-repentis were used to inoculate 11 wheat cultivars in a greenhouse study in split-plot experiments. Virulence of isolates and cultivar resistance were measured in percent leaf area infection for all possible isolate x cultivar interactions. Isolates differed significantly (P < 0.01) in virulence on wheat cultivars, and cultivars differed significantly in disease reaction to isolates. Increased virulence of isolates detected increased variability in cultivar response (percent leaf area infection) (r = 0.56, P < 0.05) while increased susceptibility in cultivars detected increased variance in virulence of the isolates (r = 0.76, P < 0.01). A significant isolate × cultivar interaction indicated specificity between isolates and cultivars, however, cluster analysis indicated low to moderate physiological specialization. Similarity in wheat cultivars in response to pathogen isolates also was determined by cluster analysis. The use of diverse isolates of the fungus would facilitate evaluation of resistance in wheat cultivars to tan spot.

Occurrence of Volutella Blight Caused by Pseudonectria foliicola on Boxwood in Tennessee.

Boxwood (Buxus sp. L.) is a very popular evergreen shrub in the United States which is widely used as landscape plant and fresh greenery. Boxwood 'Green velvet' (B. sinica var. insularis x B. sempervirens) plants grown in field condition exhibiting Volutella blight symptoms were found in a commercial nursery in Warren Co., Tennessee in May 2019. Leaves appeared red, brown or tan color on affected plants. Waxy, salmon pink colored fruiting bodies (sporodochia) were observed underneath the affected leaves using a hand lens (Figure 1). Leaf drop was also observed on plants. Black lesions under the bark were observed in some of the plants. The disease severity (percentage leaf area diseased) was nearly 40% and the disease incidence was nearly 30% of 1,000 plants. Infected leaf and stem tissues collected from four symptomatic plants were surface sterilized with 70% ethanol and washed with sterile distilled water. Culturing the infected leaf and stem pieces, 5-mm in size, on potato dextrose agar (PDA) consistently yielded white fluffy aerial mycelium growth with scattered salmon-color slimy masses of conidia forming from sporodochia after 10 days incubation at 25°C in a 12-h fluorescent light and dark cycle. A total of two isolates (FBG2020_396 and FBG2020_405) were hyphal tip purified on PDA. The conidia (n = 50) were hyaline, aseptate, fusiform to ellipsoidal measuring average of 7.8 × 3.3 μm (range: 4.84 to 13.2 μm × 2.2 to 4.64 μm). To confirm the pathogen identity, total DNA was extracted using UltraClean Microbial DNA Isolation Kit (MO BIO Laboratories, Inc., Carlsbad, CA) directly from a 5-day old culture of isolates (FBG2020_396 and FBG2020_405) on PDA. The ribosomal DNA internal transcribed spacer region (ITS), β-tubulin (tub2) and part of 28S large ribosomal subunit (LSU) regions were amplified by PCR using the primer pairs ITS 5/ITS 4, T1/BTb2 and LR0R/LR5, respectively (Glass and Donaldson 1995; O'Donnell and Cigelnik 1997; Rehner and Samuels 1994; Vilgalys and Hester 1990; White et al. 1990). Newly generated sequences - GenBank/NCBI acc. nos. MW459251, MW465902 (ITS), MW464656, MW464657 (tub2) and MW459255, MW465903 (LSU) were 100% identical to Pseudonectria foliicola L. Lombard & Crous ex-type (CBS 123190) sequences KM231776, KM232035 and NG_058095, respectively. To complete Koch's postulates, six boxwood 'Green velvet' plants grown in 10 cm square pots (containing 40% coarse sand and 60% ground pine bark) were inoculated by spraying conidial suspension of P. foliicola [FBG2020_396 (1 × 105 conidia/mL)] obtained from 2-wk-old PDA cultures. Plants were covered with clear plastic humidity domes for 3 days and then they were maintained in a growth chamber at 25°C and 60% RH in a 12-h fluorescent light and dark cycle. Six control boxwood plants were maintained in the same environment without pathogen introduction. Pathogenicity test was conducted twice. After 10 days, typical symptoms of Volutella blight developed on the inoculated plants and microscopic examination revealed the same pathogen morphology as the original isolate. Pseudonectria foliicola was consistently re-isolated from leaves and stems. All control boxwood plants remained symptom-free and P. foliicola was not isolated from the leaves or stems. Pseudonectria foliicola causing Volutella blight has been reported on B. sempervirens in Czech Republic (Spetik et al. 2020), New Zealand (Lombard et al. 2015); Buxus sp. in Illinois, Maryland, Massachusetts, North Carolina and Washington (Salgado-Salazar et al. 2019). To our knowledge, this is the first report of Volutella blight of boxwood caused by P. foliicola in Tennessee. Pseudonectria foliicola is an opportunistic pathogen and infects weak, stressed, and injured boxwood plants/cuttings (Rivera et al. 2018). This pathogen could cause a serious economic loss to boxwood nursery growers, as it can significantly affect the ornamental value of boxwood plants and fresh greenery. Integration of sanitation practices with other disease management strategies such as biorational products and reduced-risk fungicides will be necessary for limiting the spread of pathogen and successful management of P. foliicola on boxwood in both field and postharvest conditions.

QTL Mapping of Seedling and Adult Plant Resistance to Septoria Tritici Blotch in Winter Wheat cv. Mandub (Triticum aestivum L.)

Septoria tritici blotch (STB) is one of the most devastating foliar diseases of wheat worldwide. Host resistance is the most economical and safest method of controlling the disease, and information on resistance loci is crucial for effective breeding for resistance programs. In this study we used a mapping population consisting of 126 doubled-haploid lines developed from a cross between the resistant cultivar Mandub and the susceptible cultivar Begra. Three monopycnidiospore isolates of Z. tritici with diverse pathogenicity were used to test the mapping population and parents’ STB resistance at the seedling stage (under a controlled environment) and adult plant stage (polytunnel). For both types of environments, the percentage leaf area covered by necrosis (NEC) and pycnidia (PYC) was determined. A linkage map comprising 5899 DArTSNP and silicoDArT markers was used for the quantitative trait loci (QTL) analysis. The analysis showed five resistance loci on chromosomes 1B, 2B and 5B, four of which were derived from cv. Mandub. The location of QTL detected in our study on chromosomes 1B and 5B may suggest a possible identity or close linkage with Stb2/Stb11/StbWW and Stb1 loci, respectively. QStb.ihar-2B.4 and QStb.ihar-2B.5 detected on chromosome 2B do not co-localize with any known Stb genes. QStb.ihar-2B.4 seems to be a new resistance locus with a moderate effect (explaining 29.3% of NEC and 31.4% of PYC), conferring resistance at the seedling stage. The phenotypic variance explained by QTL detected in cv. Mandub ranged from 11.9% to 70.0%, thus proving that it is a good STB resistance source and can potentially be utilized in breeding programs.

Susceptibility of several cotton varieties to the cotton flea beetle, Podagrica puncticollis Weise (Coleoptera: Chrysomelidae), in a hot dry tropical environment of Ethiopia

Field trials were conducted to determine the reaction of cotton varieties to cotton flea beetle infestation. The experiment was laid out in a Randomized Complete Block Design with three replications comprising twelve cotton varieties. The results showed significant (P &lt; 0.01) differences among varieties in the populations of adult beetle they hosted and the injury they sustained at 15, 22, 29, 36 and 43 days after sowing (DAS). At 15 DAS, the highest numbers of adult beetle per plant (6.3), percent leaf area damaged (60.32 %) and number of shot-holes per attacked leaf (53.4) was recorded in Cucurova variety, whereas the lowest in Bulk-202 (2.05 beetles, 26.15% leaf area damaged and 23.16 shot-holes). The rate of incidence and damages decreased with the increase of the age of the cotton plants. Significant differences were also observed among cotton varieties in some agronomic characteristics i.e. in number of plants counted per plot at harvest and seed cotton yield in terms of kilogram per hectare. Seed cotton yield obtained from all cotton varieties varied from 602.36 to 1644.71 kilogram per hectare and the highest was obtained from Bulk-202, while the lowest from Local variety. Based on these findings, Cucurova, Local, Ionia and Acala SJ-2 varieties showed highly susceptible response, while Candia, Sille-91 and Deltapine-90 were moderately susceptible to cotton flea beetle. However, Bulk-202, Delcero and Claudia were relatively more tolerant varieties followed by CCRI-12 and Cuokra. These results will be important for the most proper management of cotton flea beetle.

PREVALENCE ON THE INFESTATION OF FLEA BEETLE (Phyllotreta nigripes) AGAINST DIFFERENT VARIETIES OF MUNGBEAN

Mungbean is one of the important pulse crops in Bangladesh. More than 12 species of insect pests infest mungbean, among them flea beetle cause significant yield loss due to attack from seedling to vegetative stages. The experiment was conducted to find out tolerant and susceptible varieties of mungbean against flea beetle at the farmer’s field of Patuakhali, Bangladesh from January to April 2016. Results revealed that BARI Mung-4 had the lowest abundance of flea beetle while BINA Moog-7 and BARI Mung-6 had the highest flea beetle abundance. Among the tested all varieties, significantly the lowest number (1.33) of infested plant by flea beetle was recorded in BARI Mung-4 followed by BINA Moog-4 (1.51) and the highest number (2.54) of infested plant by flea beetle was in BARI Mung-6 followed by (2.42) BINA Moog-7. The lowest percentage of leaf area damaged was on BARI Mung-4 (5.37%) while the highest on BARI Mung-6 (11.33%). Population of flea beetle showed a positive correlation (R2= 0.019) with temperature and a negative correlation (R2= -0.01) with relative humidity. BARI Mung-6 produced highest yield while Patuakhali local Mung produced the lowest followed by BARI Mung-4. Among tested varieties BARI Mung-4 showed comparatively more tolerant against flea beetle and BARI Mung-6 produced maximum yield in spite of being susceptile to flea beetle.