Incidence Of Spot Research Articles

Genetic analysis of low-n traits in maize (Zea mays L) using triple test cross

Low-N maize variety is developed for its ability to tolerate low nitrogen soil environment. This experiment was conducted to study the genetic implication of Low-N maize variety for grain yield and related traits under low nitrogen soil conditions triple test cross analysis. Inbred lines used for the study were generated from twelve low nitrogen tolerance open pollinated maize varieties after six generations of selfing. Two inbred lines along with their F1 were used as testers for ten inbred lines in a triple test cross pattern to generate 30 crosses. The 30 crosses, their parents and the testers to State University, Ado-Ekiti during 2017 planting season. The experimental design was a Randomized Complete Block Design (RCBD). Data were collected on plant height, ear height, days to 50% anthesis, days to 50% silking, incidence of curvularia leaf spot, blight, plant aspect, ear aspect, ear rot, stay green, cob per plant, ear weight, grain moisture content and grain yield. All data were subjected to analysis of variance and complete genetic estimates. Additive and dominants were significant (P < 0.05) for all traits; however, epitasis estimates were not significant for all the traits tested. The degree of dominance component indicated partial dominance for all the traits. Correlation coefficients for days to 50% anthesis and 50% silking, plant height, ear height, number of cobs per plant and grain yield were positive and significant (P < 0.05). Since both additive and dominance gene actions were important for low-N traits, the use of reciprocal recurrent selection procedure can be adopted in incorporating the trait into elite maize varieties.

Effect of Nitrogen Nutrition on the Intensity of Cercospora Leaf Spot of Mulberry

Leaf spot (Cercospora moricola, Cooke) is a disease that negatively influences the yield of mulberry (Morus alba L.) plants. To determine the effect of nitrogen levels on the incidence and severity of leaf spot an experiment was carried out on mulberry plants. The nitrogen levels included 0, 100, 200 and 300 kg ha-1, which were applied in two splits coinciding with the two rainy seasons. The study design was randomized complete block design (RCBD) with three replications. Determination of disease intensity involved scoring for disease intensity on a 1-5 Manandhar scale and calculation of the disease incidence were performed by expressing the number of infected leaves as a percentage of the total number of leaves. The values were translated to area under disease progress stairs (AUDPS). The means for AUDPS were subjected to analysis of variance (ANOVA) using PRO GLM in SAS and Fisher’s least significant difference (LSD) used to partition the means at p≤0.05. The results showed that as the rate of nitrogen application was increased, there was a corresponding decrease in AUDPS for disease incidence and a decrease in AUDPS for disease severity. From the obtained results it can be concluded that nitrogen at an application rate of 200 kg ha-1 is an effective approach to suppress Cercospora leaf spot of mulberry and can be recommended to the farmers, where this disease is a problem for cultivation of mulberry.

Litchi anthracnose caused by Colletotrichum karstii in Guangxi, China.

Litchi (Litchi chinensis Sonn.), a native fruit tree from southern China, has been planted in many subtropical and tropical countries for its fruit which are considered delicious and of medicinal value (Anderson et al. 2013). Anthracnose, one of the most important diseases on litchi, can cause flower drop, fruit drop, and fruit rot. Infected leaves form dark brown spots which turn to reddish brown with gray-white edges. Infected fruits formed dark brown spots which developed eventually to entire black rotted fruits. On both tissues, small dots of acervuli appeared with high humidity (Lai et al. 2004). On 20 April 2019, two leaf spots samples of litchi from different plants were collected from a 2 ha litchi orchard in Xintang Town (N 22.38˚, E 108.61˚), Qinzhou City, Guangxi province. The incidence of leaf spots in the orchard was above 20%. Each sample was cut into multiple pieces targeting zone between symptomatic and healthy plant tissues, disinfected with 75% ethanol for 10 s and 1% sodium hypochlorite (NaClO) for 1 min, and then washed three times with sterilized distilled water. The sterilized leaf tissues were placed on potato dextrose agar (PDA) and incubated at 28°C in darkness for one week. The growing hyphae from each sample was transferred to fresh PDA. The pieces from each leaf yielded a similar fungal morphotype over 75% of the time, and a representative one from each leaf was retained and called LZ1-1 and LZ3-1. The resulting colonies were incubated on the PDA for 7 days with gray to white aerial tufted hyphae, and abundant colorless to pale orange conidia in center of colony. The conidia were smooth, apex obtuse, base truncate, straight, cylindrical, and the contents remained granular. The conidial size of LZ1-1 was 10.6 to 21.4 × 4.5 to 9.1 μm (n=100) and that of LZ3-1 was 12.7 to 16.7 × 5.5 to 8.0 μm (n=100). Appressoria of LZ1-1 (6.9 to 14.9 × 6.0 to 11.1 μm) (n=100) and LZ3-1 (6.5 to 15.4 × 5.4 to 11.4 μm) (n=100) were pale to medium brown, ovoid to bullet-shaped, not nodose, and smooth-walled to undulate. DNA was extracted from two isolates, followed by PCR amplification and sequencing using primers for the rDNA internal transcribed spacer (ITS), actin (ACT), calmodulin (CAL), chitin synthase (CHS-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and β-tubulin (TUB2) (Damm et al. 2012). The resulting sequences were deposited in GenBank (ITS: MW494453 and MW494454, ACT: MW495034 and MW495035, CAL: MW495036 and MW495037, CHS-1: MW495038 and MW495039, GAPDH: MW495040 and MW495041, TUB2: MW495042 and MW495043). The concatenated sequences comprised of six genomic regions of LZ1-1, LZ3-1 and other sequences of Colletotrichum obtained from GenBank were used to construct a Neighbor-Joining (NJ) tree with 1000 bootstrap replicates using MEGA4 (Tamura et al. 2007). The results revealed both LZ1-1 and LZ3-1 were clustered with type strain of C. karstii with high bootstrap value. The pathogenicity of the two isolates was determined by inoculating on leaves of 1-year-old litchi saplings in the greenhouse. Slight scratches were made on the surface of healthy leaves and 10 μL of spore suspension (106 conidia/mL) in 0.1% Tween 20 were inoculated onto each wounded spot. The blank control groups were inoculated with 10 μL 0.1% Tween 20. Each isolate was inoculated onto at least 27 leaves of three saplings, with each leaf wounded at spots. The inoculated saplings were placed in a greenhouse (12 h/12 h light/dark, 25 ± 2°C), and humidity maintained by covering plastic bags. The leaves inoculated with spore suspension showed reddish-brown spots after one week, while no symptoms were observed in the control. Each fungal isolate was consistently reisolated from inoculated leaves, thus fulfilling Koch's postulates. It was reported that members of the C. acutatum species complex and the C. gloeosporioides species complex could cause anthracnose on litchi (Ling et al. 2019), including C. gloeosporioides, C. siamense, C. fioriniae, and C. simmondsii (Ling et al. 2019; 2020). To our knowledge, this is the first report of anthracnose on litchi in China caused by C. karstii, a member of the C. boninense species complex. This study expands the understanding of the pathogen of anthracnose on litchi which can lead to improved management and control.

The Use of Coherent Laser Stimulation of Seeds and a Fungal Inoculum to Increase the Productivity and Health of Soybean Plants

The laser stimulation of seeds is regarded as a modern method of seed enhancement. Our study evaluated the productivity and health of soybean plants resulting from the coherent irradiation of seeds and irradiation of an arbuscular mycorrhizal fungi (AMF) inoculum. The two-factor pot experiment took into account (1) the type of irradiated biological material (seeds, AMF inoculum, and seeds and inoculum) and (2) the means of irradiation (red laser—LR, blue laser—LB, red and blue laser—LR + LB, and control). Seed weight per plant, pod number per plant, root weight, the Fv/Fm fluorescence parameters, and the health status of the aboveground and underground parts of the plants were assessed. Stimulation with a laser light was shown to have a positive effect on the productivity and health of soybean plants. Significantly better effects can be obtained by stimulating the seeds alone. The stimulation of seeds treated with AMF inoculum slightly reduced the productivity of the plants. However, with regards to the conditions of plants, the treatment of seeds with AMF inoculum and laser irradiation was shown to reduce the incidence of Septoria brown spots.

Model-based forecasting of twig canker incidence of bacterial spot of peach in Fukushima Prefecture

Model-based forecasting of twig canker incidence of bacterial spot of peach in Fukushima Prefecture

Development of a Sequential Sampling Plan using Spatial Attributes of Cercospora Leaf Spot Epidemics of Table Beet in New York

Sampling strategies that effectively assess disease intensity in the field are important to underpin management decisions. To develop a sequential sampling plan for the incidence of Cercospora leaf spot (CLS), caused by Cercospora beticola, 31 table beet fields were assessed in the state of New York. Assessments of CLS incidence were performed in six leaves arbitrarily selected in 51 sampling locations along each of three to six linear transects per field. Spatial pattern analyses were performed, and results were used to develop sequential sampling estimation and classification models. CLS incidence (p) ranged from 0.13 to 0.92 with a median of 0.31, and beta-binomial distribution, which is reflective of aggregation, best described the spatial patterns observed. Aggregation was commonly detected (>95%) by methods using the point-process approach, runs analyses, and autocorrelation up to the fourth spatial lag. For Spatial Analysis by Distance Indices, or SADIE, 45% of the datasets were classified as a random pattern. In the sequential sampling estimation and classification models, disease units are sampled until a prespecified target is achieved. For estimation, the goal was sampling CLS incidence with a preselected coefficient of variation (C). Achieving the C = 0.1 was challenging with <51 sampling units, and only observed on datasets with incidence >0.3. Reducing the level of precision, i.e., increasing C to 0.2, allowed the preselected C to be achieved with a lower number of sampling units and with an estimated incidence ([Formula: see text]) close to the true value of p. For classification, the goal was to classify the datasets above or below prespecified thresholds (pt) used for CLS management. The average sample number, or ASN, was determined by Monte Carlo simulations, and was between 20 and 45 at disease incidence values close to pt, and approximately 11 when far from pt. Correct decisions occurred in >76% of the validation datasets. Results indicated these sequential sampling plans can be used to effectively assess CLS incidence in table beet fields.

Crop Regulation in Pomegranate (Punica granatum L.) through Induced Water Stress and Ethrel Application

The present investigation was carried out at ICAR-CIAH, Bikaner, Rajasthan, India during 2017 to 2019 to regulate crop production in pomegranate at the desired period with higher number of bisexual flower for higher quality fruit yield and to minimize fruit splitting through water stress, pruning and ethrel application. Pooled data analysis revealed that horticultural interventions, chemical treatments and their interactions significantly improved plant volume, bisexual flower number, maturity index, fruit yield with significant reduction in fruit splitting, mite and fungal spot incidence. Among different treatment combinations, maximum canopy volume, number of bisexual flowers, maturity index, fruit yield and lower fruit splitting were recorded (8.56 m3, 85.11 plant-1, 47.81, 124.01 q ha-1 and 1.87 kg plant-1) in withholding irrigation during June+pruning+thinning+ethrel 2 ml l-1 as compared to absolute control (3.41 m3, 75.62 plant-1, 33.35, 85.66 q ha-1 and 2.41 kg plant-1), respectively. The mite and fungal spot incidence were recorded minimum (4.72 and 8.50%) in withholding irrigation during June+pruning+thinning+ethrel 3 ml l-1 application in comparison to maximum recorded in absolute control (29.73 and 33.68%), respectively. Therefore, it can be concluded that withholding irrigation during June+pruning+thinning with ethrel 2 ml l-1 treatment significantly improved quality fruit yield with higher number of bisexual flowers and reduced fruit splitting through induction of flowering and fruit growth during optimal climatic conditions.

Reaction of Sour Passion Fruit Lineages and Hybrids to Bacterial Spot Caused by Xanthomonas axononopodis pv. passiflorae Under Protected Cultivation and Field Conditions

Passion fruit is infected by many plant pathogens, including Xanthomonas axonopodis pv. passiflorae, causing bacterial spot disease. This disease has been impaired orchards all over Brazil, resulting in low yield and production. In addition, it results in premature death of plants in the field. This study aimed to analyze the reaction of sour passion fruit genotypes to bacterial spot in leaves under protected cultivation (Experiment 1) and the bacterial spot severity in fruits under field conditions (Experiment 2). Experiment 1 was carried out as a randomized block design (RBD) with subdivided plots, composed of 24 treatments (genotypes), three replications, five plants per plot, and five evaluation dates. Bacterial spot incidence and severity were evaluated using a 0 to 5 grading scale. Evaluations were carried out at a 7-day interval after disease symptoms first appeared. Genotypes differed for mean disease severity and incidence. The bacterial spot disease evaluations showed that genotypes MAR20#46 P3 R4 X Rosa Claro R4 and MD 16 P3 X MAR20#39 P1 R4 presented the lowest scores for the disease incidence in the leaves. S2L AP R1, MAR20#19 ROXO R4 X ECRAM P3 R3, and MD 16 P3 X MAR20#39 P1 R4 were the genotypes with the lowest disease severity scores. Experiment 2 consisted of a RBD with 24 treatments, three replications, and seven plants per plot. Severity assessments were monthly performed on five fruits per plot, totaling three evaluation dates. In this experiment, the percentage of total fruit area with necrotic lesions was measured using a 1 to 4 grading scale. Bacterial spot severity assessments in fruits identified interactions between genotypes and evaluation dates (p &amp;le; 0.05). The lineages S2L MAR 20#15 R4 and S2L MAR20#19 R2 showed the lowest mean severity scores of bacterial spot in fruit. The genotypes with the lowest mean scores were selected to continue the breeding program.

Performance of diploid and interploid hybrids of St. Augustinegrass under moderate shade

AbstractShadetolerance is an important factor for cultivar selection in urban areas. Diploid (2n = 2x = 18) cultivars of St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] with moderate to high shade tolerance have been popular choices for residential and commercial landscapes in the southern United States. This study evaluated 26 elite drought resistant diploid and interploid (polyploid × diploid) hybrids and four commercial cultivars under 75% continuous shade from 20 June 2017 through 30 Oct. 2018. Biweekly data were collected during the growing season for percent green cover, visual turfgrass quality, canopy color, shoot density, and daily leaf elongation rates (DER; mm d–1). Spring greenup was rated annually, and to gray leaf spot incidence was rated when naturally occurring. All genotypes lost green cover through 2017, and greenup was delayed transitioning into the summer of 2018 when most diploids struggled to recover from disease, shade, and winter injury whereas, on an average, interploid hybrids reached up to 84.0% green cover. Daily leaf elongation rates were lower for diploids than polyploids in both years. Turfgrass quality, color, and density generally declined under shade as expected. Overall, three interploid hybrids (DALSA 1329, 1404, and 1406) were the top performers demonstrating good retention of turfgrass performance traits and reduced DER under shade.

Use of Liming and Incidence of Diseases in Sugarcane

This study aimed to evaluate the incidence of red rot, brown leaf spot, and smut in ten sugarcane genotypes during two consecutive cycles, in the absence and presence of limestone. The experimental design consisted of randomized blocks with four replications, in the presence and absence of liming in the following sugarcane genotypes: G1 (RB002754), G2 (RB021754), G3 (RB041443), G4 (RB863129), G5 (RB93509), G6 (RB951541), G7 (RB962962), G8 (RB992506), G9 (SP79-1011), and G10 (VAT90-212) for genotype x environment interaction. The lowest incidences of red rot were observed in G3 (RB041443), G4 (RB863129), G8 (RB992506), and G9 (SP79-1011) for plant cane, and in G3 (RB041443), G4 (RB863129), G5 (RB93509), G8 (RB992506), and G9 (SP79-1011) for ratoon. All genotypes were susceptible to Colletotrichum falcatum, but limestone reduced its incidence in G3 (RB041443), G6 (RB951541), and G10 (VAT90-212) during the first growth cycle, and in G1 (RB002754), G2 (RB021754), G5 (RB93509), G6 (RB951541), G7 (RB962962), and G10 (VAT90-212) in the ratoon crop. Liming also reduced the incidence of brown leaf spot in G4 (RB863129), G6 (RB951541), and G9 (SP79-1011) in plant cane and G6 (RB951541) and G7 (RB962962) in the ratoon crop. Only the G9 genotype (SP79-1011) showed an incidence of smut. The genotypes had different incidence levels of red rot, brown leaf spot, and smut diseases, which varied in the presence of limestone. Limestone use reduced disease incidence as a function of genotype and cutting cycle.

Prospection of genotypes resistant to black spot in half‐sib families of papaya

AbstractPapaya (Carica papaya L.) breeding is a complex task; furthermore, Carica papaya has a sexual chromosome and is difficult to make crosses. One of the most critical papaya crop diseases is black spot, which is caused by Asperisporium caricae (Speg.) MaublSince . Therefore, we used half‐sib families to combine genetic gains on the yield and resistance traits to papaya black spot. In this scenario, the present study proposed to select papaya genotypes more resistant to black spot from half‐sib families. Five parents with superior attributes related to black spot resistance were pollinated with a pollen mixture from five parents considered “elite” for agronomic traits, thus generating five half‐sib families. The half‐sib families were evaluated for black spot resistance in a greenhouse with two control cultivars (‘Golden’ and ‘Maradol’), for 75 d, at 15‐d intervals, totaling five evaluations. The families exhibited genetic variability for all traits associated with disease resistance, surpassing even the Golden and Maradol controls. The traits associated with severity by papaya black spot are more efficient to distinguish resistance genotypes using principal components analysis, like mean incidence of black spot (MSBS) (cos² = 0.794) and area under the disease progress curve (AUDPC) (cos² = 0.697). The recommended progeny for resistance to black spot are M‐1.4, M‐1.5, M‐3.1, M‐3.3, M‐2.5, and M‐4.5, as they showed lower values of mean severity of black spot, MIBS, and AUDPC. These progenies from half‐sib families overcame the resistant control genotype Maradol as potential to combining resistance to papaya black spot with superior agronomic traits.

Potential biocontrol of endophytic fungi against Lasiodiplodia pseudotheobromae causal agent of cocoa dieback on cocoa seedling

Endophytic fungi associated with cocoa are one of the effective agents to control plant pathogens on cocoa, including the fungus Lasiodiplodia pseudotheobromae. L. pseudotheobromae cause a significant disease on cocoa, cocoa dieback. The disease is considered an emerged disease on cocoa in Sulawesi, Indonesia. The research aimed to determine the effect of the endophytic fungi on L. pseudotheobromae on cocoa seedlings. This study used a randomized block design consisting of 6 treatments and 3 replications. Five different fungi isolates were used that belong to Aspergillus genera. The treatment is three isolates of endophytes fungi (isolate T2S2LT, T245LT, T645LT), Aspergillus isolates combination, and control (with and without pathogen). The results showed that the combination of isolates and T645LT isolate was the best treatment for suppressing necrotic symptoms (leaf spot) incidence and severity. Also, T645LT isolate performed well to inhibit leaf blight symptoms incidence severity. Meanwhile, the chlorotic symptom was reduced by isolates combination, followed by T2S2LT, T645LT, and T245LT. Endophytic fungi can potentially be an important option to control cocoa dieback disease.

Novel action thresholds of a logistic regression model to forecast dollar spot on bentgrasses

AbstractDollar spot (Clarireedia jacksonii) susceptibility varies among bentgrasses (Agrostis spp.). This trial assessed the ability of five action thresholds of the risk index (RI) of a logistic regression model to forecast dollar spot incidence on bentgrass fairway turf grown on a sandy loam in North Brunswick, NJ. Dollar spot incidence was assessed over 128 observation periods (May to Nov. annually) over 3 yr and related to five action thresholds for prediction accuracy. Action thresholds included a RI threshold of 20% (RI 20%), interpreting the change in the RI over time (RI slope), adjusting the RI upwards to maximize accuracy (RImax), combining RI 20% with RI slope, and combining RImax with RI slope. The RI 20% accurately predicted disease on 63 to 66% of observation periods for highly susceptible creeping bentgrass (A. stolonifera L.) cultivars Shark, Penncross, and Independence; other action thresholds improved accuracy by only 10% or less for these cultivars. Prediction accuracy on lower susceptibility cultivars (007, Declaration, and colonial bentgrass Capri; A. capillaris L.) was substantially improved with four novel action thresholds by reducing over‐predictions compared to RI 20%. Accuracy was improved by as much as 32% when the RImax and RI slope were combined for Declaration compared to RI 20%. On low susceptibility cultivars, turf managers may be able to use action thresholds that incorporate a RI greater than 20% and/or RI slope to reduce fungicide inputs and maintain acceptable dollar spot control compared to RI 20%.

Molecular characterization of leaf spot caused by Alternaria alternata on buttonwood (Conocarpus erectus L.) and determination of pathogenicity by a novel disease rating scale.

The buttonwood (Conocarpus erectus L.) is a mangrove shrub belonging to Combretaceae family. It mostly grows on the shorelines of tropical and subtropical regions in the world. It was introduced to Lasbela University of Water, Agriculture & Marine Sciences (LUWMS), Uthal, Baluchistan as an ornamental plant as it grows well under harsh, temperate and saline conditions. During a routine survey, typical leaf spot symptoms were observed on the leaves of buttonwood plants. A disease severity scale for alternaria leaf spot of buttonwood was developed for the first time through this study. Disease severity according to the scale was 38.97%. The microscopic characterizations was accomplished for the identification of Alternaria alternata and Koch’s postulates were employed to determine the pathogenicity. For molecular identification, 650 bp internal transcribed spacer (ITS) regions (ITS1, 5.8s and ITS2) were amplified from three representative isolates (LUAWMS1, LUAWMS2 and LUAWMS3) through polymerase chain reaction (PCR). The nucleotide sequences from ITS regions of the isolates were submitted to NCBI with GenBank accession numbers MW585375, MW585376 and MW585377, respectively. The phylogenetic tree of 22 A. alternata isolates was computed and representative isolates exhibited 99.98% genetic similarity with mangroves ecosystem isolates. This study reports the incidence of alternaria leaf spot of buttonwood at LUWMS for the first time. It is suspected that the disease may spread further. Therefore, effective management strategies should be opted to halt the further spread of the disease.

Brown Spot and Stalk Rot Diseases of Maize (Zea Mays) and Susceptibility of Two Varieties to Physoderma Maydis in Far North Cameroon

Corn (Zea mays L.) is one of the most widely grown cereals in the world. However, in Cameroon, particularly in the Far North Region, yields remain low because of diseases increasing due to farming practices and climate change. This work aimed to characterize Brown Spot and Stalk Rot of corn and evaluate the susceptibility of two maize varieties to Physoderma maydis in field conditions. Two maize varieties, CMS9015, and CMS8704 were evaluated in a randomized block design. Disease symptoms were observed and described using identification keys. Microscopic characteristics of pathogens were performed using a microscope. Incidence, severity, and areas under disease curve progress (AUIPC and AUSiPC) were calculated. Brown spot occurred 3 or 4 weeks after sowing (WAS) at the growing stage in CMS8704 variety first, and stalk rot 7 WAS. Brown spot appeared in leaves and is characterized by oval yellowish spots in the leaf blade and brownish spots in the midrid. Stalk rot infects stem nodes and is characterized by brownish spots, leading to the broken stem. The incidence of brown spot increased with time and environmental conditions (rainfall). The highest incidence of Physoderma Brown Spot was recorded with CMS8704 variety 53.06 % against 51.72 % with CMS9015. Severity was respectively 54.40 % and 47.12 % with CMS8704 and CMS9015. The incidence and severity of stalk rot were almost identical in both varieties. AUIPC of PBS and PSR was higher in CMS9015 than in CMS 8704, 63 DAS. PBS and PSR infect maize production, and both varieties are susceptible to P. maydis.

Effects of Orthodontic Bonding Containing TiO2 and ZnO Nanoparticles on Prevention of White Spot Lesions: an In Vitro Study

Demineralization is a common problem following orthodontic treatments. Today using antibacterial nanoparticles in preventing white spot lesions is being discussed. Given that ZnO and TiO2 nanoparticles have direct antibacterial known properties, this study aims to evaluate these nanoparticles' antibacterial effects in orthodontic bondings' composition on preventing white spot lesions. In this in vitro experimental study, 43 sound human premolar teeth were divided into five groups according to the adhesive utilized for bracket bonding: None group consisting of 12 teeth bonded with Transbond XT, TiO2 Group consisting of 12 teeth with Transbond XT and TiO2 nanoparticles, ZnO group consisting of 12 teeth with Transbond XT and ZnO nanoparticles, a positive control group consisting of 5 teeth without brackets and negative control groups consisting of 5 teeth in a sterile medium. All teeth were stored in a medium consisting of 1cc brain heart infusion (BHI) + sucrose 1%+ 0.5 McFarland Streptococcus mutans bacteria for 28 days. The medium was replaced every 48 hours. All the samples were examined every week for 4 weeks using DIAGNOdent and photography to detect white spots. The results of this study revealed that adding TiO2 and ZnO nanoparticles to Transbond XT bonding caused a decrease in enamel lesions occurrence and incidence of white spots (p value= 0.00). The results did not reveal significant differences between TiO2 and ZnO groups. Novel bonding agents containing TiO2 and ZnO nanoparticles represent promising candidates in combating enamel white spot lesions.

Effects of botanical extracts and antibiotic on incidence and severity of bacterial blight of cotton incited by Xanthomonas axonopodis pv. Malvacearum

A multilocational field trial was conducted to investigate the effect of some plant extracts (Bolanite aegyptica, Eucalyptus camaldulensis and Citrus aurantium) and a synthetic antibiotic (Streptomycin) on the incidence and severity of angular leaf spot on five cotton geno-types namely SAMCOT-8, SAMCOT-9, SAMCOT-10, SAMCOT-11 and SAMCOT-12 in Yola and Jalingo, both located in the northern guinea savannah zone of Nigeria. The experiment was carried out on a split-plot design having three replications with cotton genotypes on the main plots and plant extracts on the sub-plots. Data collected on the incidence and severity of the disease were analysed using the Generalized Linear Model procedure and means separation at 5% level of probability by Duncan Multiple Range Test. Findings of the study revealed that Streptomycin and Bolanite aegyptiaca were able to reduce the disease incidence by 18.12% from 58.69% in Yola at 13 WAS. In Jalingo however, B. aegyptiaca was found to have re-duced the disease severity from 52.12% to 19.69% at 13 WAS. SAMCOT-8 consistently recorded lower incidence and severity means in Yola and Jalingo of 47.96%; 59.12% and 40.82%; 39.70% while SAMCOT-12 recorded higher means of 53.29%; 59.82% and 48.03%; 46.70% respectively.

Determining the presence of host specific toxin genes, ToxA and ToxB, in New Zealand Pyrenophora tritici-repentis isolates, and susceptibility of wheat cultivars

Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is an important disease of wheat worldwide, and an emerging issue in New Zealand. The pathogen produces host-specific toxins which interact with the wheat host sensitivity loci. Identification of the prevalence of the toxin encoding genes in the local population, and the susceptibility of commonly grown wheat cultivars to Ptr will aid selection of wheat cultivars to reduce disease risk. Twelve single spore isolates collected from wheat-growing areas of the South Island of New Zealand representing the P. tritici-repentis population were characterised for the Ptr ToxA and ToxB genes, ToxA and ToxB, respectively, using two gene specific primers. The susceptibility of 10 wheat cultivars to P. tritici-repentis was determined in a glasshouse experiment by inoculating young plants with a mixed-isolate spore inoculum. All 12 New Zealand P. tritici-repentis isolates were positive for the ToxA gene but none were positive for the ToxB gene. Tan spot lesions developed on all inoculated 10 wheat cultivars, with cultivars ‘Empress’ and ‘Duchess’ being the least susceptible and ‘Discovery’, ‘Reliance’ and ‘Saracen’ the most susceptible cultivars to infection by the mixed-isolate spore inoculum used. The results indicated that the cultivars ‘Empress’ and ‘Duchess’ may possess a level of tolerance to P. tritici-repentis and would, therefore, be recommended for cultivation in regions with high tan spot incidence.

First Report of Alternaria tenuissimain Causing Leaf Spot of Celery (Apium graveolens) in China.

Celery (Apium graveolens) is one of the most widely grown vegetables in the world. A survey in Anding District of Gansu Province in 2019 showed that the incidence of celery leaf spot was 25%-45%. The disease mainly occurs in late June and July. The leaf spot is conducive to the onset at high temperature and humidity environment. The initial symptoms were many small light brown, irregular-shaped on the leaves. The lesions gradually enlarged in the later stage of the disease, and multiple lesions coalesced to form large irregular brown spots, eventually the whole leaves died. A 3~4mm leaf tissue was cut from the junction of the diseased leaf and the healthy area, the leaf tisse was surface-sterilized in 1.5% NaClO for 1 min and washed with sterile water. Then, it was incubated on potato dextrose agar (PDA) and obtained the pure culture (Q1). After 5 days of cultivation at 25°C, the fungal colonies were olivaceous to dark olive with white margins and abundant aerial mycelia. The conidia were obclavate or ellipsoid, pale brown, with 3~4 longitudinal septa and 2~7 transverse septa, and measured 20.0 to 50.0 × 3.5 to 14.0μm (n=50). Conidiophores were septate, arising singly, and measured 3.5 to 40.0 × 2.5 to 4.5 μm (n=50). Based on morphological characteristics, the fungus was preliminarily identified as A.tenuissima (Simmons 2007). To further confirm the identification, the internal transcribed spacer region (ITS), translation elongation factor 1-α gene (TEF), RNA polymerase II second largest subunit (RPB2), major allergen Alt a 1 gene (Alt a 1), endopolygalacturonase gene (endoPG), anonymous gene region (OPA10-2) and glyceraldehyde 3-phos-phatedehydrogenase (GAPDH) were amplified and sequenced using primers ITS1/ITS4 (Peever et al. 2004), EF1-728F/EF1-986R (Carbone et al. 1999), RPB2-5F2/RPB2-5R (Sung et al. 2007), Alt-for/Alt-rev (Hong et al. 2005), EPG-specific/EPG-3b (Peever et al. 2004), OPA10-2R/OPA10-2L (Peever et al. 2004) and Gpd1/Gpd2 (Berbee et al. 1999) (GenBank accession no.MN046364, MW016001, MW016002, MW016003, MW016004, MW016005, MW016006). DNA sequences of TEF, RPB2, endoPG, OPA10-2 and GAPDH were 100% identical to those of A. tenuissima (MN256108, MK605866, KP789503, JQ859829 and MK683802), but ITS and Alt a 1 were 100% similarity with A. tenuissima (MN615420, JQ282277) and A. alternate (MT626589, KP123847). The ITS and Alt a 1 sequence did not distinguish A. tenuissima from the A. alternate complex. Maximum likelihood phylogenetic analyses were performed for the combined data set with TEF, RPB2, and endoPG using MEGA6 under the Tamura-Nei model (Kumar et al. 2016). The isolate Q1 clustered with type strain A. tenuissima CBS 918.96. The 20 celery plants of 4-7 leaf age were used test the pathogenicity of Q1, the ten plants were sprayed with 20ml of spore suspension (1×105 spores/ml), the control was sprayed with 20mL sterile water, which were placed in a growth chamber (25℃, a 14h light and 10h dark period, RH > 80%). Eight days after inoculation, 40% of the leaves formed lesions, which were consistent with the field observation，the control group was asymptomatic. The pathogen was reisolated from infected leaves to fulfill Koch's postulates. To our knowledge, this is the first report of A. tenuissima causing leaf spot on celery in China.

Plant and Weather Factors on Resistance of Saccharum officinarum Germplasm Against Ring Spot Disease

Ring spot caused by Leptosphaeria sacchari is a very common disease of sugarcane in humid tropical conditions. We have conducted a detailed study on status of disease resistance to the disease in our major Saccharum spp collections of Saccharum officinarum. All the S. officinarum clones exhibited ring spot disease with varying intensity as 70.14% clones showed resistant reaction, 24.3% clones showed intermediate reaction and 5.5% clones showed susceptible reaction. The disease appears in the month of June and remains until the harvest. Maximum average disease severity (29.33%) was observed in the July. The accessions analysed also showed significant difference with respect to origin. Multiple comparisons indicated that mean rank of Thailand accessions (682.50) was significantly highest as compared to those of other. Stalk height and leaf length showed significantly weak correlation with ring spot incidence, and other morphological factors were not significant. Disease severity with leaf colour and canopy type was found significant. Purple-leaved clones recorded lower disease incidence than other clones. Very strong positive correlation was observed with rainfall, evening relative humidity and rainy days, whereas maximum temperature showed significant negative correlation. This study clearly indicated the role played by the morphological factors, juice quality traits and weather factors in determining resistance in germplasm to ring spot disease in sugarcane.