Distribution and Biodiversity of Seed-Borne Pathogenic and Toxigenic Fungi of Maize in Egypt and Their Correlations with Weather Variables.

Studies of the biodiversity of plant pathogenic and toxigenic fungi are attracting great attention to improve the predictability of their epidemics and the development of their control programs. Two hundred maize grain samples were gathered from 25 maize-growing governorates in Egypt and 189 samples were processed for the isolation and identification of seed-borne fungal microbiome. Twenty-six fungal genera comprising 42 species were identified according to their morphological characteristics and ITS DNA sequence analysis. Occurrence and biodiversity indicators of these fungal species were calculated. Ustilago maydis, Alternaria alternata, Aspergillus flavus, A. niger, Penicillium spp., Cladosporium spp. and Fusarium verticillioides were the highly frequent (>90% for each), recording the highest relative abundance (˃50%). Al-Menia governorate showed the highest species diversity and richness, followed by Sohag, Al-Nobaria and New Valley governorates. Correlations of 18 fungal species with temperature, relative humidity, precipitation, wind speed, and solar radiation were analyzed using canonical correspondence analysis. Results showed that relative humidity, temperature, and wind speed, respectively, were the most impactful weather variables. However, the occurrence and distribution of these fungi were not clearly grouped into the distinctive climatic regions in which maize crops are grown. Monitoring the occurrence and distribution of the fungal pathogens of maize grains in Egypt will play an important role in predicting their outbreaks and developing appropriate future management strategies. The findings in this study may be useful to other maize-growing countries that have similar climatic conditions.

Antifungal Activities of Sulfur and Copper Nanoparticles against Cucumber Postharvest Diseases Caused by Botrytis cinerea and Sclerotinia sclerotiorum.

Nanoparticles (NPs) have attracted great interest in various fields owing to their antimicrobial activity; however, the use of NPs as fungicides on plants has not been sufficiently investigated. In this study, the antifungal activities of sulfur nanoparticles (S-NPs) and copper nanoparticles (Cu-NPs) prepared by a green method were evaluated against Botrytis cinerea and Sclerotinia sclerotiorum. The formation of NPs was confirmed by transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). The antifungal activities of NPs (5-100 µg/mL), CuSO4 (4000 µg/mL), and micro sulfur (MS) were compared to those of the recommended chemical fungicide Topsin-M 70 WP at a dose of 1000 µg/mL. They were evaluated in vitro and then in vivo at different temperatures (10 and 20 °C) on cucumber (Cucumis sativus) fruits. The total phenolic content (TPC) and total soluble solids (TSS) were determined to study the effects of various treatments on the shelf life of cucumber fruits, compared to untreated cucumber as a positive control. The diameters of S-NPs and Cu-NPs ranged from 10 to 50 nm, and 2 to 12 nm, respectively. The results revealed that S-NPs exhibited the highest antifungal activity, followed by Cu-NPs. However, CuSO4 showed the lowest antifungal activity among all treatments. The antifungal activity of the prepared NPs increased with the increase in NP concentration, while the fungal growth was less at low temperature. The cytotoxicity of the prepared NPs was evaluated against the WI-38 and Vero cell lines in order to assess their applicability and sustainability. S-NPs caused less cytotoxicity than Cu-NPs.

Biodiversity of Pathogenic and Toxigenic Seed-Borne Mycoflora of Wheat in Egypt and Their Correlations with Weather Variables.

Surveillance investigations for pathogenic and toxigenic fungi are important to refine our understanding of their epidemiology and help in predicting their outbreaks. During 2019, 198 samples of wheat grains were collected from 25 wheat-growing governorates in Egypt to detect and identify seed-borne mycoflora in vitro. Forty-four fungal species belonging to 20 genera were identified. Molecular data for these fungi were analyzed to construct a phylogenetic tree. Occurrence and biodiversity indicators were calculated. Two prevalent pathogens (average incidence > 40%) were Alternaria alternata and Cladosporium spp. Ustilago tritici was present in only seven of the 25 governorates, and less abundant than Tilletia tritici, the causal agent of stinking smut. Sinai governorate recorded the greatest species diversity, while the greatest species richness was in Qena and Sohag governorates. Canonical correspondence analysis of data for 20 fungal genera with temperature, relative humidity, precipitation, wind speed or solar radiation revealed that relative humidity was the most influential weather variable. It showed that occurrence and distribution of the 20 genera corresponded well with three out of four Egyptian climatic regions: Mediterranean, semi-arid, and arid. Knowing pathogen occurrence and distribution in Egypt is the first step to developing future disease management strategies to limit yield losses and improve food security. Despite this study being conducted on the wheat-growing areas in Egypt, our findings are useful for other wheat-growing countries that share the same climatic conditions. The correlation between a given fungus and the climatic variables can be useful in other ecosystems.

Enhancing the performance of micro-biosensors by functionally graded geometrical and material parameters.

Most recently, the whole world is struggling against the virulent pandemic COVID-19. Due to the unbounded global spread of the disease, having biosensors with high performance such as high sensitivity and accuracy is of utmost importance. In this paper, the effects of various parameters on the behaviors of micro-biosensors are investigated in order to enhance their performance. These parameters are related to the geometry and material, and they are assumed to be gradually changing in the longitudinal direction of the biosensor according to a power law. Therefore, they are called functionally graded geometrical and material parameters. Another aspect is when considering microcantilever-based biosensors, the main behavior parameter is the deflection at the free end. In the analyses, the influences of the surface stress and van der Waals intermolecular forces are taken into account. Also, the total energy of the beam, which is the combination of the van der Waals energy and the elastic strain energy, is accomplished. In addition, the equivalent force causing the deflection is also evaluated using Castigliano method for two cases. These cases account for a concentrated force at the free end and a distributed load along the biosensor, respectively. Since the governing equations account for the size dependency and the considered parameters are functions of the position, the solution is too complex to be achieved analytically, and therefore, numerical methods are applied. For uniform biosensors made of homogeneous materials, or in other words when all parameters are not varying with the position, the obtained results are compared with those in the literature, and good agreement is obtained. On the other hand, the performance, which include sensitivity and limit of detection, of functionally graded biosensors can be enhanced by proper choices of the considered parameters and the corresponding exponent of the gradation function.

Occurrence and distribution of tomato seed-borne mycoflora in Saudi Arabia and its correlation with the climatic variables.

One hundred samples of tomato seeds were collected in 2011 and 2012 from tomato-cultivated fields in Saudi Arabia and screened for their seed-borne mycoflora. A total of 30 genera and 57 species of fungi were recovered from the collected seed samples using agar plate and deep-freezing blotter methods. The two methods differed as regards the frequency of recovered seed-borne fungi. Seven fungi among those recovered from tomato seeds, which are known as plant pathogens, were tested for their pathogenicity and transmission on tomato seedlings. The recovery rate of these pathogens gradually decreased from root up to the upper stem, and did not reach to the stem apex. The distribution of tomato seed-borne fungi was also investigated throughout Saudi Arabia. In this concern, Al-Madena governorate recorded the highest incidence of fungal flora associated with tomato seeds. The impact of meteorological variables on the distribution of tomato seed-borne mycoflora was explored using the ordination technique (canonical correspondence analysis). Among all climatic factors, relative humidity was the most influential variable in this regard. Our findings may provide a valuable contribution to our understanding of future global disease change and may be used also to predict disease occurrence and fungal transfer to new uninfected areas.

Granular formulation of Fusarium oxysporum for biological control of faba bean and tomato Orobanche.

BACKGROUND: Orobanche spp. represent a serious threat to a wide range of crops. They are difficult targets for herbicides, and biological control could provide a possible solution. This work therefore aimed to formulate mycoherbicides of Fusarium with adequate shelf life and virulence against Orobanche but safe to faba bean and tomato. RESULTS: Only two isolates of Fusarium oxysporum Schlecht. (Foxy I and Foxy II) obtained from diseased Orobanche shoots were found to be pathogenic to Orobanche crenata Forsk. and Orobanche ramosa L. Conidial suspension of both isolates significantly decreased germination, attachments and tubercles of Orobanche. Microconidia and chlamydospores of both isolates were formulated as mycoherbicides encapsulated in a wheat flour-kaolin matrix (four different formulations). All formulations greatly diminished Orobanche emerged shoots, total shoot number, shoot height, attachment of emerged shoots, the germinated seeds that succeeded in emerging above the soil surface and dry weight. Meanwhile, disease incidence and disease severity of emerged shoots were enhanced. The shelf life was adequate, particularly for coarse, freshly prepared, low-temperature-stored, microconidia-rich formulations. The induced growth reduction of Orobanche-infected host plants seemed to be nullified by formulations, particularly at the highest dose. CONCLUSION: These formulations seemed to destroy Orobanche but appeared harmless to host plants. Hence, they could be efficiently used as mycoherbicides for biological control of Orobanche in faba bean and tomato.

Trichoderma harzianum: a biocontrol agent against Bipolaris oryzae.

Rice brown spot, caused by Bipolaris oryzae, can be a serious disease causing a considerable yield loss. Trichoderma harzianum is an effective biocontrol agent for a number of plant fungal diseases. Thus, this research was carried out to investigate the mechanisms of action by which T. harzianum antagonizes Bipolaris oryzae in vitro, and the efficacy of spray application of a spore suspension of T. harzianum for control of rice brown spot disease under field conditions. In vitro, the antagonistic behavior of T. harzianum resulted in the overgrowth of B. oryzae by T. harzianum, while the antifungal metabolites of T. harzianum completely prevented the linear growth of B. oryzae. Light and scanning electron microscope (SEM) observations showed no evidence that mycoparasitism contributed to the aggressive nature of the tested isolate of T. harzianum against B. oryzae. Under field conditions, spraying of a spore suspension of T. harzianum at 10(8)spore ml(-1) significantly reduced the disease severity (DS) and disease incidence (DI) on the plant leaves, and also significantly increased the grain yield, total grain carbohydrate, and protein, and led to a significant increase in the total photosynthetic pigments (chlorophyll a and b and carotenoids) in rice leaves.