Yield Loss in Sweet Corn Caused by Puccinia sorghi: A Meta-Analysis

Anthraquinones and their analogues as potential biocontrol agents of rust and powdery mildew diseases of field crops

BACKGROUND

Rusts and powdery mildews are severe fungal diseases of major crops worldwide, including cereals and legumes. They can be managed by chemical fungicide treatments, with negative consequences as environmental pollution and risk for human and animal health. Bioactive natural products could be the safest alternative for pest control. The family of anthraquinones, as well as analogue compounds containing an anthraquinone moiety or some modified anthraquinone rings, has been reported to exhibit certain antibiotic activity. Thus, the potential antifungal activity of some anthraquinones isolated from Ascochyta lentis, was assayed in this study for their effectiveness to reduce rust and powdery mildew diseases on pea and oat. Their effect on fungal development was macro- and microscopically assessed on inoculated leaves, and compared to the control achieved by the chemical fungicide (Tetraconazol 12.5% and Azoxystrobin 25%). In addition, the most promising compound was also tested at different concentrations in inoculated whole plants in order to evaluate its preventive and curative potential against fungal infection.

RESULTS

All metabolites studied strongly reduced the development of rust and powdery mildews in both pea and oat, being pachybasin and lentiquinone C the most effective ones in hampering fungal spore germination and appressoria formation. Some of them also affected post-penetration events reducing colony size and number of haustoria per colony. Results were confirmed for pachybasin in whole plants assays, showing an efficacy similar to the commercial fungicide to control fungal diseases, both in preventive and curative applications.

CONCLUSIONS

Some fungal anthraquinones and close metabolites, especially pachybasin, could be very promising molecules with effective potential as antifungal agents against both rust and powdery mildew of both pea and oat. Some structure activity-relationships feature have also been evaluated. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Uptake and Translocation of a Silica Nanocarrier and an Encapsulated Organic Pesticide Following Foliar Application in Tomato Plants

Pesticide nanoencapsulation and its foliar application are promising approaches for improving the efficiency of current pesticide application practices, whose losses can reach 99%. Here, we investigated the uptake and translocation of azoxystrobin, a systemic pesticide, encapsulated within porous hollow silica nanoparticles (PHSNs) of a mean diameter of 253 ± 73 nm, following foliar application on tomato plants. The PHSNs had 67% loading efficiency for azoxystrobin and enabled its controlled release over several days. Thus, the nanoencapsulated pesticide was taken up and distributed more slowly than the nonencapsulated pesticide. A total of 8.7 ± 1.3 μg of the azoxystrobin was quantified in different plant parts, 4 days after 20 μg of nanoencapsulated pesticide application on a single leaf of each plant. In parallel, the uptake and translocation of the PHSNs (as total Si and particulate SiO₂) in the plant were characterized. The total Si translocated after 4 days was 15.5 ± 1.6 μg, and the uptake rate and translocation patterns for PHSNs were different from their pesticide load. Notably, PHSNs were translocated throughout the plant, although they were much larger than known size-exclusion limits (reportedly below 50 nm) in plant tissues, which points to knowledge gaps in the translocation mechanisms of nanoparticles in plants. The translocation patterns of azoxystrobin vary significantly following foliar uptake of the nanosilica-encapsulated and nonencapsulated pesticide formulations.

Analysis of the transcriptomic, metabolomic, and gene regulatory responses to Puccinia sorghi in maize

Common rust, caused by Puccinia sorghi, is a widespread and destructive disease of maize. The Rp1-D gene confers resistance to the P. sorghi IN2 isolate, mediating a hypersensitive cell death response (HR). To identify differentially expressed genes (DEGs) and metabolites associated with the compatible (susceptible) interaction and with Rp1-D-mediated resistance in maize, we performed transcriptomics and targeted metabolome analyses of P. sorghi IN2-infected leaves from the near-isogenic lines H95 and H95:Rp1-D, which differed for the presence of Rp1-D. We observed up-regulation of genes involved in the defence response and secondary metabolism, including the phenylpropanoid, flavonoid, and terpenoid pathways. Metabolome analyses confirmed that intermediates from several transcriptionally up-regulated pathways accumulated during the defence response. We identified a common response in H95:Rp1-D and H95 with an additional H95:Rp1-D-specific resistance response observed at early time points at both transcriptional and metabolic levels. To better understand the mechanisms underlying Rp1-D-mediated resistance, we inferred gene regulatory networks occurring in response to P. sorghi infection. A number of transcription factors including WRKY53, BHLH124, NKD1, BZIP84, and MYB100 were identified as potentially important signalling hubs in the resistance-specific response. Overall, this study provides a novel and multifaceted understanding of the maize susceptible and resistance-specific responses to P. sorghi.

Identification and diversity of tropical maize inbred lines with resistance to common rust (Puccinia sorghi Schwein)

Common rust (CR) caused by Puccinia sorghi Schwein is one of the major foliar diseases of maize (Zea mays L.) in Eastern and Southern Africa. This study was conducted to (i) evaluate the response of elite tropical adapted maize inbred lines to Puccinia sorghi and identify resistant lines (ii) examine associations between CR disease parameters and agronomic traits, and (iii) assess the genetic diversity of the inbred lines. Fifty inbred lines were evaluated in field trials for three seasons (2017-2019) in Uganda under artificial inoculation. Disease severity was rated on a 1-9 scale at 21 (Rust 1), 28 (Rust 2), and 35 (Rust 3) days after inoculation. Area under disease progress curve (AUDPC) was calculated. The genetic diversity of the lines was assessed using 44,975 single nucleotide polymorphism markers. Combined ANOVA across seasons showed significant (P < .001) line mean squares for the three rust scores and AUDPC. Heritability was high for Rust 2 (0.90), Rust 3 (0.83), and AUDPC (0.93). Of the 50 lines, 12 were highly resistant to CR. Inbred lines CKL1522, CKL05010, and CKL05017 had significantly lower Rust 3 scores and AUDPC compared to the resistant check CML444 and are potential donors of CR resistance alleles. The genetic correlations between CR disease resistance parameters were positive and strong. A neighbor-joining (NJ) tree and STRUCTURE suggested the presence of three major groups among the lines, with lines highly resistant to CR spread across the three groups. The genetic diversity among the highly resistant lines can be exploited by recycling genetically distant lines to develop new multiple disease resistant inbred lines for hybrid development and deployment.

Potential occurrence of Puccinia sorghi in corn crops in Paraná, under scenarios of climate change

In the face of climate change scenarios, it is important to evaluate the possibility of an increase in the incidence of corn crop diseases and to promote studies aimed at creating mitigation measures. This paper aims to study the impacts that regional climate changes may have on the potential occurrence of corn common rust (Puccinia sorghi), in the region of Castro, Paraná (Brazil). The Eta climate model was driven by the global model CanESM2. We use the Historical simulation of the EtaCanESM2 model from 1981 to 2005, and future projections from 2046 to 2070 to simulate the occurrence of common rust. The criteria was adopted to simulate the common rust disease favored in environments with the minimum temperature lower than 8 °C, the maximum temperature higher than 32 °C, average temperature between 16 and 23 °C, and relative humidity higher than 95%. In Brazil, there are two different seasons for corn crop (Normaland Safrinha). Results show that relative humidity and minimum temperature simulated by the model presented good skills, approaching the observed data. Compared to the Historical simulation, the projections show a tendency to increase of maximum and minimum temperature in the future, and a tendency to decrease relative humidity. There is an increase in the number of days with the potential for the occurrence of the disease. The distribution of days with favorable conditions to rust disease tends to change in the future. In the Normaland Safrinhaseasons, there is a tendency to increase the number of days with favorable conditions to common rust occurrence. The influence of planting time is greater in Historical simulation when compared to future scenarios. The Safrinhaseason may present more days with the potential for the occurrence of common rust in the future than the Normalseason.

Peanut Yield Loss in the Presence of Defoliation Caused by Late or Early Leaf Spot

Late and early leaf spot, respectively caused by Nothopassalora personata and Passalora arachidicola, are damaging diseases of peanut (Arachis hypogaea) capable of defoliating canopies and reducing yield. Although one of these diseases may be more predominant in a given area, both are important on a global scale. To assist informed management decisions and quantify relationships between end-of-season defoliation and yield loss, meta-analyses were conducted over 140 datasets meeting established criteria. Slopes of proportion yield loss with increasing defoliation were estimated separately for Virginia and runner market type cultivars. Yield loss for Virginia types was described by an exponential function over the range of defoliation levels, with a loss increase of 1.2 to 2.2% relative to current loss levels per additional percent defoliation. Results for runner market type cultivars showed yield loss to linearly increase 2.2 to 2.8% per 10% increase in defoliation for levels up to approximately 95% defoliation, after which the rate of yield loss was exponential. Defoliation thresholds to prevent economic yield loss for Virginia and runner types were estimated at 40 and 50%, respectively. Although numerous factors remain important in mitigating overall yield losses, the integration of these findings should aid recommendations about digging under varying defoliation intensities and peanut maturities to assist in minimizing yield losses.

Combined linkage and association mapping reveal QTL for host plant resistance to common rust (Puccinia sorghi) in tropical maize

BACKGROUND

Common rust, caused by Puccinia sorghi, is an important foliar disease of maize that has been associated with up to 50% grain yield loss. Development of resistant maize germplasm is the ideal strategy to combat P. sorghi.

RESULTS

Association mapping performed using a mixed linear model (MLM), integrating population structure and family relatedness identified 25 QTL (P < 3.12 × 10- 5) that were associated with resistance to common rust and distributed on chromosomes 1, 3, 5, 6, 8, and 10. We identified three QTLs associated with all three disease parameters (final disease rating, mean disease rating, and area under disease progress curve) located on chromosomes 1, 3, and 8. A total of 5 QTLs for resistance to common rust were identified in the RIL population. Nine candidate genes located on chromosomes 1, 5, 6, 8, and 10 for resistance to common rust associated loci were identified through detailed annotation.

CONCLUSIONS

Using a diverse set of inbred lines genotyped with high density markers and evaluated for common rust resistance in multiple environments, it was possible to identify QTL significantly associated with resistance to common rust and several candidate genes. The results point to the need for fine mapping common rust resistance by targeting regions identified in common between this study and others using diverse germplasm.

Inhibition of early development stages of rust fungi by the two fungal metabolites cyclopaldic acid and epi-epoformin

BACKGROUND

Rusts are a noxious group of plant diseases affecting major economically important crops. Crop protection is largely based on chemical control. There is a renewed interest in the discovery of natural products as alternatives to synthetic fungicides for control. In this study we tested two fungal metabolites, namely cyclopaldic acid and epi-epoformin, for their effectiveness in reducing early stages of development of two major rust fungi from the genera Puccinia and Uromyces, P. triticina and U. pisi. Spore germination and appressorium formation were assessed on pretreated detached leaves under controlled conditions. Cyclopaldic acid and epi-epoformin were also tested in infected plants in order to evaluate the level of control achieved by treatments both before and after inoculation.

RESULTS

Cyclopaldic acid and epi-epoformin were strongly effective in inhibiting fungal germination and penetration of both rust species studied. This effect was not dose dependent. These results were further confirmed in planta by spraying the metabolites on plant leaves, which reduced fungal developmental of U. pisi and P. triticina at values comparable with those obtained by application of the fungicide.

CONCLUSION

Our results further demonstrate the potential of fungal metabolites as natural alternatives to synthetic fungicides for the control of crop pathogens of economic importance as rusts. © 2016 Society of Chemical Industry.

Inhibition of Spore Germination and Appressorium Formation of Rust Species by Plant and Fungal Metabolites

Eight fungal and plant metabolites belonging to different classes of naturally occurring compounds, a 24-oxa[14]-cytochalasan as cytochalasin B (1), a trisubstituted isocoumarin as 6-hydroxymellein (2), a tetracyclic pimarane diterpene as sphaeropsidin A (3), a chalcone as cavoxin (4), a pentasubstituted benzofuranone as cyclopaldic acid (5), a bicyclic-sesquiterpene as inuloxin A (6), a epipolythiopiperazine as gliotoxin (7) and a cyclohexene epoxide as epi-epoformin (8), were tested for their effectiveness in reducing early stages of development of several major rust fungi from the genera Puccinia and Uromyces. Spore germination and appressoria formation were assessed on pre-treated detached leaves, under controlled conditions. Among the various metabolites evaluated, compounds 5 and 8 were the most effective in inhibiting fungal germination and penetration of all rust species studied at values comparable with those obtained by fungicide application, while compound 4 was phytotoxic to plant leaves at any concentration tested.

Optimal Cotton Insecticide Application Termination Timing: A Meta-Analysis

The concept of insecticide termination timing is generally accepted among cotton (Gossypium hirsutum) researchers; however, exact timings are often disputed. Specifically, there is uncertainty regarding the last economic insecticide application to control fruit-feeding pests including tarnished plant bug (Lygus lineolaris (Palisot de Beauvois)), boll weevil (Anthonomus grandis), bollworm (Helicoverpa zea), tobacco budworm (Heliothis virescens), and cotton fleahopper (Pseudatomoscelis seriatus). A systematic review of prior studies was conducted within a meta-analytic framework. Nine publicly available articles were amalgamated to develop an optimal timing principle. These prior studies reported 53 independent multiple means comparison field experiments for a total of 247 trial observations. Stochastic plateau theory integrated with econometric meta-analysis methodology was applied to the meta-database to determine the shape of the functional form of both the agronomic optimal insecticide termination timing and corresponding yield potential. Results indicated that current university insecticide termination timing recommendations are later than overall estimated timing suggested. The estimated 159 heat units (HU) after the fifth position above white flower (NAWF5) was found to be statistically different than the 194 HU termination used as the status quo recommended termination timing. Insecticides applied after 159 HU may have been applied in excess, resulting in unnecessary economic and environmental costs. Empirical results also suggested that extending the insecticide termination time by one unit resulted in a cotton lint yield increase of 0.27 kilograms per hectare up to the timing where the plateau began. Based on economic analyses, profit-maximizing producers may cease application as soon as 124 HU after NAWF5. These results provided insights useful to improve production systems by applying inputs only when benefits were expected to be in excess of the respective costs.

Meta-analysis of the relationship between crop yield and soybean rust severity

Meta-analytic models were used to summarize and assess the heterogeneity in the relationship between soybean yield (Y, kg/ha) and rust severity (S, %) data from uniform fungicide trials (study, k) conducted over nine growing seasons in Brazil. For each selected study, correlation (k=231) and regression (k=210) analysis for the Y-S relationship were conducted and three effect-sizes were obtained from these analysis: Fisher's transformation of the Pearson's correlation coefficient (Zr) and the intercept (β0) and slope (β1) coefficients. These effect-sizes were summarized through random-effect and mixed-effect models, with the latter incorporating study-specific categorical moderators such as disease onset time (DOT) (70%, moderate=>40 and ≤70%, and low=≤40% S the check treatment), and growing season. The overall mean for r- (back-transformed Z-r) was -0.61, based on the random-effects model. DOT and DP explained 14 and 25%, respectively, of the variability in Z-r. Stronger associations (r-=-0.87 and -0.90) were estimated by mixed-effects models for the Zr data from studies with highest DP (DP>70%) and earliest rust onset (DOT0.73 pp/%(-1)) were estimated for studies with DOT70%; the latter possibly due to high fungicide efficacy when DP is low, thus leading to higher yield differences between fungicide-protected and nontreated plots. The critical-point meta-analytic models can provide general estimates of yield loss based on a composite measure of disease severity. They can also be useful for crop loss assessments and economic analysis under scenarios of varying DOT and weather favorableness for epidemic development.

Meta-analysis for evidence synthesis in plant pathology: an overview

Meta-analysis is the analysis of the results of multiple studies, which is typically performed in order to synthesize evidence from many possible sources in a formal probabilistic manner. In a simple sense, the outcome of each study becomes a single observation in the meta-analysis of all available studies. The methodology was developed originally in the social sciences by Smith, Glass, Rosenthal, Hunter, and Schmidt, based on earlier pioneering contributions in statistics by Fisher, Pearson, Yates, and Cochran, but this approach to research synthesis has now been embraced within many scientific disciplines. However, only a handful of articles have been published in plant pathology and related fields utilizing meta-analysis. After reviewing basic concepts and approaches, methods for estimating parameters and interpreting results are shown. The advantages of meta-analysis are presented in terms of prediction and risk analysis, and the high statistical power that can be achieved for detecting significant effects of treatments or significant relationships between variables. Based on power considerations, the fallacy of naïve counting of P values in a narrative review is demonstrated. Although there are many advantages to meta-analysis, results can be biased if the analysis is based on a nonrepresentative sample of study outcomes. Therefore, novel approaches for characterizing the upper bound on the bias are discussed, in order to show the robustness of meta-analysis to possible violation of assumptions.

Meta-analysis to determine the effects of plant disease management measures: review and case studies on soybean and apple

The continuing exponential increase in scientific knowledge, the growing availability of large databases containing raw or partially annotated information, and the increased need to document impacts of large-scale research and funding programs provide a great incentive for integrating and adding value to previously published (or unpublished) research through quantitative synthesis. Meta-analysis has become the standard for quantitative evidence synthesis in many disciplines, offering a broadly accepted and statistically powerful framework for estimating the magnitude, consistency, and homogeneity of the effect of interest across studies. Here, we review previous and current uses of meta-analysis in plant pathology with a focus on applications in epidemiology and disease management. About a dozen formal meta-analyses have been published in the plant pathological literature in the past decade, and several more are currently in progress. Three broad research questions have been addressed, the most common being the comparative efficacy of chemical treatments for managing disease and reducing yield loss across environments. The second most common application has been the quantification of relationships between disease intensity and yield, or between different measures of disease, across studies. Lastly, meta-analysis has been applied to assess factors affecting pathogen-biocontrol agent interactions or the effectiveness of biological control of plant disease or weeds. In recent years, fixed-effects meta-analysis has been largely replaced by random- (or mixed-) effects analysis owing to the statistical benefits associated with the latter and the wider availability of computer software to conduct these analyses. Another recent trend has been the more common use of multivariate meta-analysis or meta-regression to analyze the impacts of study-level independent variables (moderator variables) on the response of interest. The application of meta-analysis to practical problems in epidemiology and disease management is illustrated with case studies from our work on Phakopsora pachyrhizi on soybean and Erwinia amylovora on apple. We show that although meta-analyses are often used to corroborate and validate general conclusions drawn from more traditional, qualitative reviews, they can also reveal new patterns and interpretations not obvious from individual studies.

Managing Foliar Diseases of Processing Sweet Corn in New York with Strobilurin Fungicides

Processing sweet corn (Zea mays) growers in New York are more concerned about the cost effectiveness of fungicide use against foliar fungal diseases (common rust and Northern corn leaf blight) and less about whether such sprays will reduce disease intensity. To address this concern, field trials were done in 2006 and 2007 with three processing sweet corn hybrids (Jubilee, Bold, and GH 9597) that differed in susceptibility to common rust and Northern corn leaf blight, and two strobilurin fungicides (azoxystrobin and pyraclostrobin). Single strobilurin applications were applied in response to foliar disease severity thresholds of 1, 10, and 20%. Single fungicide applications did reduce foliar disease severities. Applications were most cost effective when made in response to the 1 and 10% foliar severity thresholds, and generally only in the susceptible hybrid Bold. Spraying at the 20% severity threshold did reduce final foliar disease severity but was not cost effective. Azoxystrobin and pyraclostrobin were equally effective in disease management. The results suggest that a single application of a strobilurin fungicide against common rust and Northern corn leaf blight can be cost effective for New York processing sweet corn growers when such an application is made before foliar disease severity exceeds 20%.

Reduction in Common Rust Severity Conferred by the Rp1D Gene in Sweet Corn Hybrids Infected by Mixtures of Rp1D-Virulent and Avirulent Puccinia sorghi

The Rp1D gene confers a hypersensitive, chlorotic-fleck, resistant reaction to Puccinia sorghi, the casual agent of common rust of corn. About 40% of commercial sweet corn hybrids carry the Rp1D gene. Sine 1999, Rp1D-virulent (D-virulent) isolates of P. sorghi have occurred regularly in populations of P. sorghi in North America. Observations from sweet corn hybrid nurseries and other trials indicate that the frequency of D-virulent isolates affects severity of rust on Rp1D hybrids; however, the frequency of D-virulence at which the Rp1D gene is rendered completely ineffective is not known. The objective of this study was to assess whether common rust severity is reduced by the Rp1D gene in sweet corn hybrids infected by mixtures of D-virulent and Rp1D-avirulent (avirulent) P. sorghi. Forty pairs of Rp1D-resistant and susceptible (rp1d) versions of sweet corn hybrids from six different commercial breeding programs were evaluated in 2003 and 2004 in trials inoculated with one of five different ratios of avirulent:D-virulent inocula: 100:0, 90:10, 80:20, 60:40, or 0:100. When D-virulent P. sorghi was 100% of initial inoculum, common rust was equally severe on Rp1D and rp1d versions of the same hybrid. Thus, the Rp1D gene did not confer partial or residual resistance in these trials. When initial inocula consisted of 40% or less D-virulent P. sorghi, rust was significantly less severe on Rp1D versions than on rp1d versions of the same hybrids. Relationships between rust severity on Rp1D and rp1d versions of hybrids were explained by linear regressions in all trials. Slope coefficients (i.e., rust severity on Rp1D hybrids as a proportion of that on rp1d hybrids) were related to the percentage of D-virulent P. sorghi in the initial inoculum and were 0.21, 0.29, 0.51, 0.64, and 0.93 in 2003 and 0.25, 0.50, 0.67, 0.76, and 1.0 in 2004 for trials inoculated with 0, 10, 20, 40, and 100% D-virulent P. sorghi, respectively. Thus, the Rp1D gene may convey levels of control in proportion to the frequency of virulence in mixed populations of D-virulent and avirulent P. sorghi when the frequency of virulent isolates is less than 40%.