Aflatoxin levels and Aspergillus species in maize in the Province of Isabela, Philippines

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Abstract

The province of Isabela is the top maize producer in the Philippines. The intensive cultivation and the tropical climate in the region may favour fungal growth and aflatoxin contamination in maize grains. Thus, the study aimed to determine the occurrence of aflatoxin and mycotoxigenic Aspergillus species in maize varieties in this region. Samples were obtained in six municipalities from hybrid (Bt) maize (n = 101) and open-pollinated varieties (n = 6) during the dry season (March and April) of 2019. Aflatoxin levels were quantified through enzyme-linked immunosorbent assay, and Aspergillus species were identified through cultural and molecular methods. Aflatoxin was detected in 50.5% of maize samples; 49.5% of samples were less than the limit of detection (3 μg/kg), 16.8% with 3–20 μg/kg, 10.9% with 21–50 μg/kg and 22.8% above 50 μg/kg. Samples within the acceptable level were 66.3% for food (<20 μg/kg) and 77.2% for animal feed (<50 μg/kg), while 22.8% of samples were above the acceptable level of the Philippine National Standard for raw maize grains. More than 90% of Aspergillus species detected were A. flavus. Other species identified were A. tamarii and A. terreus. Despite the dry production season in the province with low relative humidity during harvesting, inadequate post-harvest practices and the presence of A. flavus elevated the level of aflatoxin in sample grains. Additional work involving multi-year surveys is needed to confirm the results and conclusions of this study.

Characterization and pathogenicity of Fusarium species causing sugar beet root rot in Morocco

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Abstract

The sugar beet crop ranks second globally among the plant species grown mainly for sugar production. In Morocco, the area under sugar beet farming occupies approximately 57,000 ha yielding more than 3 million tons of roots. However, sugar beet root-tip rot (RTR) caused by Fusarium spp. dramatically reduces the anticipated yields, the purity of the resulting juice, and the sugar concentration. The current study aimed at identifying and characterizing the Fusarium species responsible for the root rot in sugar beet grown in the Khenifra-Beni Mellal region of Morocco. In this survey, 69 isolates of Fusarium were sampled from sugar beet roots showing typical symptoms of root rot from 2019 to 2021. After screening based on the pathogenicity test, 28 isolates were selected and identified based on morphological features and sequence analyses of the ribosomal internal transcribed spacer (ITS) region and translation elongation factor 1 α 34 (TEF-1 α). Fusarium oxysporum was the most frequently identified species, followed closely by F. solani, F. equiseti, F. nygmai, F. brachygibbosum, F. proliferatum, F. culmorum, and F. falciforme. Six weeks after inoculations under greenhouse conditions, the studied isolates caused internal vascular discoloration and tip rot of sugar beet roots, with disease incidences ranging from 37.5% to 100.0% and a disease index between 30.3% and 70.5%. Isolates belonging to F. solani were the most aggressive. Moreover, the majority of isolates significantly reduced plant growth. To our knowledge, this research article is the first report of Fusarium species inducing RTR in sugar beet in Morocco.

Improper crop rotation may enrich soil‐borne pathogens of Panax notoginseng

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Abstract

Soil-borne diseases are the main cause of yield reduction of Panax notoginseng (Sanqi), and are mainly caused by the enrichment of pathogenic fungi during continuous cropping. In the Wenshan district of Yunnan province, China, where Sanqi is widely cultivated, the rotation of Foeniculum vulgare (fennel) crops with Sanqi crops is assumed to help reduce occurrences of rot in Sanqi roots. However, in a field investigation, we found that this practice actually increased incidences of root rot in Sanqi crops. Using fennel plants obtained from the cropping system, we tested the hypothesis that fennel crops enriched communities of pathogenic fungi of Sanqi. We isolated six endophytic fungi from the roots of fennel plants and identified these based on their morphological characteristics and a sequencing analysis. The isolates were identified as Fusarium oxysporum (FV-1-R-1, FV-2-R-1), Alternaria alternata (FV-3-R-1, FV-14-R-1), Pyricularia grisea (FV-8-R-1) and Colletotrichum truncatum (FV-11-R-4). In a series of inoculation experiments, we verified the pathogenicity of these fungi to Sanqi based on Koch's postulates, and demonstrated that all isolates caused root rot in Sanqi. Our results suggest that fennel is an inappropriate crop choice for rotation with Sanqi because it may serve as an intermediate host for the pathogenic fungi that cause root rot in Sanqi, and thereby exacerbate crop diseases. Our empirical findings provide useful information for enhancing the cultivation of Sanqi and the practice of crop rotation.

The presence of the plant pathogen Fusarium graminearum as a soil inoculum enhances the rhizosphere survival of bacterial biocontrol strains aimed at the pathogen

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Abstract

The serious wheat pathogen Fusarium graminearum causes both root rot and head blight. Some classical biocontrol tests were first used to explore the biocontrol ability of 39 Pseudomonas fluorescens strains. The five most antifungal strains B4, P13, UTPf127, UTPf125 and UTPf105 were selected to screen known antifungal antibiotic genes and greenhouse experiments. The ability of bacteria to colonize wheat rhizosphere and their effect on plant growth in the presence and absence of soil F. graminearum inoculum was studied under greenhouse conditions. Overall, biocontrol bacteria populations were significantly higher in both wheat endo-and ectorhizosphere of pathogen-inoculated soil than in healthy soil. The population of all strains differently decreased with time. On day 28, endorhizosphere populations of strain B4 could be detected in inoculated but not healthy soil, while UTPf127 populations remained high in endorhizospheres at all tested times. Isolate B4 and UTPf105 showed the most substantial plant growth in pathogen-inoculated soil compared to pathogen-inoculated soil without added bacteria. UTPf127-treated plants grew better in control soil than when the pathogen was present. In contrast, UTPf125 and P13 showed little effect on plant growth. These results point to complex interactions between pathogen and biocontrol bacteria and suggest that a fungal pathogen in the soil can affect the survival of potential bacterial biological control agents. Additionally, they highlight the importance of screening and evaluating potential biocontrol bacteria against soilborne fungal pathogens by in vivo tests rather than relying on plate screenings.

Characterization of causal agents of bacterial canker on apricot plantations and risk mapping using GIS in Aras Basin (Türkiye)

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Abstract

Bacterial canker of stone fruits caused by Pseudomonas syringae pv. syringae (Pss) and Pseudomonas syringae pv. morsprunorum (Psm race-1/Psm race-2) may lead to significant yield and crop losses in apricot (Prunus armeniaca L.) cultivation areas in Türkiye. Strains pathogenic to apricot were isolated from trees with symptoms (mainly necrotized buds and dieback) of bacterial canker in orchards in Aras Basin. Pathogens were characterized using pathogenicity tests, phenotypic assays, end-point PCR and multilocus sequence analysis (MLSA). Fifteen Pseudomonas syringae strains were isolated from 205 plant samples collected from apricot orchards showing symptoms of bacterial canker. As a consequence of the diagnostic tests, all isolates were identified as P. syringae pv. syringae. In this study, Pss, Psm R1 and Psm R2 strains in stone fruits were separated into different phylogroups (Pg-2, Pg-3, sPg-1b) based on MLSA. Turkish strains obtained from stone fruits, particularly apricot, showed genetic heterogeneity, and clustered in different sub-phylogroups (sPg-2b, sPg-2c, sPg-2d). All these strains except strain K258 are also clustered in the same sub-phylogroups (sPg-2b and sPg-2d) with other strains from different countries especially Iran, Lebanon, etc. Strain K258 isolated from apricot was clustered in sPg-2c with Pss strain 642 (USA). The risk of bacterial canker disease in apricot growing areas is considered using GIS in this study. It was determined that a significant part of the Iğdır Plain, the biggest agricultural area in the Aras Basin, is at very high risk.

Determination of low‐temperature stress during the vegetative stage as a tool to predict plant yield in rice genotypes with contrasting tolerance levels

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Abstract

In this study, the first aim was to develop a rapid and non-destructive method for analysing rice genotypes' tolerance to low temperatures (LT) during the seedling stage. Using a growth parameter and a physiological parameter, a discriminant formula was developed to differentiate between tolerant and sensitive genotypes based on their LT tolerance score. The study identified several benefits of the discriminant formula, including its low classification error rate, scalability, and ability to be used in controlled and reduced environments. Additionally, a second study was conducted, which found a strong correlation between the LT tolerance score during the seedling stage and plant yield at the ripening stage in plants grown under field LT during the vegetative stage. Panicle weight was the main mediator of the effect of the LT tolerance score on plant yield, but the number of panicles per plant also played a role. Overall, the results suggest that the LT tolerance score can serve as an indirect selection factor for plants for both LT tolerance and plant yield. This is especially relevant for rice-growing regions with temperate climates and LT at the beginning of the cultivation season.

Use of genomic prediction to screen sorghum B‐lines in hybrid testcrosses

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Abstract

Use of trifluoromethanesulfonamide (TFMSA), a male gametocide, increases the opportunities to identify promising B-lines because large quantities of F1 seed can be generated prior to the laborious task of B-line sterilization. Combining TFMSA technology with genomic selection could efficiently evaluate sorghum B-lines in hybrid combination to maximize the rates of genetic gain of the crop. This study used two recombinant inbred B-line populations, consisting of 217 lines, which were testcrossed to two R-lines to produce 434 hybrids. Each population of testcross hybrids were evaluated across five environments. Population-based genomic prediction models were assessed across environments using three different cross-validation (CV) schemes, each with 70% training and 30% validation sets. The validation schemes were as follows: CV1—hybrids chosen randomly for validation; CV2—B-lines were randomly chosen, and each chosen B-line had one of the two corresponding testcross hybrids randomly chosen for the validation; and CV3—B-lines were randomly chosen, and each chosen B-line had both corresponding testcross hybrids chosen for the validation. CV1 and CV2 presented the highest prediction accuracies; nonetheless, the prediction accuracies of the CV schemes were not statistically different in many environments. We determined that combining the B-line populations could improve prediction accuracies, and the genomic prediction models were able to effectively rank the poorest 70% of hybrids even when genomic prediction accuracies themselves were low. Results indicate that combining genomic prediction models and TFMSA technology can effectively aid breeders in predicting B-line hybrid performance in early generations prior to the laborious task of generating A/B-line pairs.

Core Ideas

Genomic prediction can be used to screen sorghum B-lines for hybrid grain yield and days to mid-anthesis. Using genomic prediction and the chemical gametocide TFMSA can increase the rate of genetic gain in sorghum B-lines. Using testers to screen sorghum B-line populations is an effective method for screening with genomic prediction. Genomic prediction can effectively predict hybrid performance within and across populations of sorghum B-lines. The ability to accurately rank hybrid performance remained relatively consistent regardless of prediction accuracy.

All families of transposable elements were active in the recent wheat genome evolution and polyploidy had no impact on their activity

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Abstract

Bread wheat (Triticum aestivum L.) is a major crop and its genome is one of the largest ever assembled at reference-quality level. It is 15 Gb, hexaploid, with 85% of transposable elements (TEs). Wheat genetic diversity was mainly focused on genes and little is known about the extent of genomic variability affecting TEs, transposition rate, and the impact of polyploidy. Multiple chromosome-scale assemblies are now available for bread wheat and for its tetraploid and diploid wild relatives. In this study, we computed base pair-resolved, gene-anchored, whole genome alignments of A, B, and D lineages at different ploidy levels in order to estimate the variability that affects the TE space. We used assembled genomes of 13 T. aestivum cultivars (6x = AABBDD) and a single genome for Triticum durum (4x = AABB), Triticum dicoccoides (4x = AABB), Triticum urartu (2x = AA), and Aegilops tauschii (2x = DD). We show that 5%–34% of the TE fraction is variable, depending on the species divergence. Between 400 and 13,000 novel TE insertions per subgenome were detected. We found lineage-specific insertions for nearly all TE families in di-, tetra-, and hexaploids. No burst of transposition was observed and polyploidization did not trigger any boost of transposition. This study challenges the prevailing idea of wheat TE dynamics and is more in agreement with an equilibrium model of evolution.