First Report of Rhizopus arrhizus (syn. R. oryzae) causing Sunflower Head Rot in Arizona, USA.

Sunflower (Helianthus annuus) is an ornamental, edible-seed, and important oil source plant in the USA. In June 2023, head rot was observed in sunflowers grown in an experimental field at Yuma County Cooperative Extension, University of Arizona, AZ (32°42'35.5"N, 114°42'25.0"W). The disease incidence was of >70%. Head lesions were dark-brown and extended through the head to the bracts and stem. White to gray mycelia and black sporangia-like structures were also observed on sunflower heads. Symptomatic plants (n =10) were sampled to determine the disease causing agent. Five symptomatic tissues for each plant (0.5 to 1 cm) were submitted to surface sterilization by dipping in 75% ethanol 2min, 1% NaOCl for 2 mins and rinsing with sterile water. Once sterilized, the tissues were plated on potato dextrose agar (PDA) plates and incubated at 25±0.2 °C. After two days, hyaline mycelia were observed on PDA which turned white after 7 days. A total of 50 isolates were obtained, of which ten were randomly selected and purified by the hyphal-tip method and later used for morphological analysis. Microscopic observations revealed hyaline and aseptate hyphae, sporangiophores measuring 900 to 1.2000 µm in length and dark-brown sporangium (72 to 144 µm, mean = 90). The columella was sub-globose, and the sporangiospores ranged from 7.29 to 9.37 µm in size (mean = 7.5 µm). The morphological characteristics described above were similar for the ten isolates and were in accordance with the species R. arrhizus as described by (Gryganskyi et al. 2018). Genomic DNA was extracted from three randomly chosen isolates using The DNeasy Plant kit (Qiagen) and used for further molecular identification. The internal transcribed spacer (ITS) region was amplified using ITS1/ITS4 primers (White et al. 1990) and then Sanger sequenced. The sequences shared 100% nucleotide identity with each other (GenBank accession numbers PP747852, PP747853 and PP747854) and shared 100% identity to R. arrhizus GenBank accessions (MT316366.1, MN547407.1). One isolate, YPHC-94-A, was randomly selected for Phylogenetics and Pathogenicity analyses. Phylogenetics analysis based on sequence data of ITS showed that the isolated YPHC-94-A clustered together with R. arrhizus species (Zhang. 2023). Pathogenicity test was conducted by inoculating four sunflower varieties (American giant, Lemon queen, Solar eclipse and Mammoth) (n = 12 for each variety). Plant heads were inoculated with a disc of mycelia (0.5 cm2) and incubated for 24 h at 30 ±2 °C and 94% RH. Five uninoculated plants of each variety were used as controls. Head rot symptoms were observed within 3-5 days on inoculated plant post inoculation depending on the variety, whereas the control plants stayed asymptomatic. R. arrhizus was re-isolated from all the inoculated plants and was morphologically and molecularly identical to the field isolates, thus fulfilling Koch's postulates. R. arrhizus has already been reported in different US regions (Sanogo et al. 2010), however, to the best of our knowledge this is the first report in Arizona. Due the high disease incidence and pathogen aggressiveness found in the environmental conditions of the U.S southwest desert, we consider sunflower Head rot a potential risk for sunflower production in Arizona as well as the large population of wild sunflowers in the State.

Bacterial diversity and composition on the rinds of specific melon cultivars and hybrids from across different growing regions in the United States.

The goal of this study was to characterize the bacterial diversity on different melon varieties grown in different regions of the US, and determine the influence that region, rind netting, and variety of melon has on the composition of the melon microbiome. Assessing the bacterial diversity of the microbiome on the melon rind can identify antagonistic and protagonistic bacteria for foodborne pathogens and spoilage organisms to improve melon safety, prolong shelf-life, and/or improve overall plant health. Bacterial community composition of melons (n = 603) grown in seven locations over a four-year period were used for 16S rRNA gene amplicon sequencing and analysis to identify bacterial diversity and constituents. Statistically significant differences in alpha diversity based on the rind netting and growing region (p < 0.01) were found among the melon samples. Principal Coordinate Analysis based on the Bray-Curtis dissimilarity distance matrix found that the melon bacterial communities clustered more by region rather than melon variety (R2 value: 0.09 & R2 value: 0.02 respectively). Taxonomic profiling among the growing regions found Enterobacteriaceae, Bacillaceae, Microbacteriaceae, and Pseudomonadaceae present on the different melon rinds at an abundance of ≥ 0.1%, but no specific core microbiome was found for netted melons. However, a core of Pseudomonadaceae, Bacillaceae, and Exiguobacteraceae were found for non-netted melons. The results of this study indicate that bacterial diversity is driven more by the region that the melons were grown in compared to rind netting or melon type. Establishing the foundation for regional differences could improve melon safety, shelf-life, and quality as well as the consumers' health.

Plant-based antimicrobials inactivate Listeria monocytogenes and Salmonella enterica on melons grown in different regions of the United States.

The efficacy of plant-based antimicrobials against Salmonella Newport and Listeria monocytogenes on melon rinds was evaluated. Four cantaloupe and 3 honeydew melon varieties grown in Georgia, Arizona, Texas, North Carolina, Indiana and California were tested. Melon rinds (10 g pieces) were inoculated with 5-6 log CFU/10 g rind of S. Newport or L. monocytogenes. Samples were then immersed in 5 % olive extract or 0.5 % oregano oil antimicrobial solution and gently agitated for 2 min. Samples were stored at 4 °C and surviving populations of both bacteria were enumerated at days 0 and 3. Plant-based antimicrobials reduced S. Newport and L.monocytogenes population on all rind samples, regardless of the melon types, varieties or growing locations. Compared to the control, antimicrobial treatments caused up to 3.6 and 4.0 log reductions in populations of Salmonella and L. monocytogenes, respectively. In most cases, plant-based antimicrobial treatments reduced pathogen populations to below the detection limit (1 log CFU/g) at day 3. In general, oregano oil had better antimicrobial activity than olive extract and the antimicrobial treatments were more effective on Salmonella than on L. monocytogenes. The plant-based antimicrobial treatments exhibited better microbial reductions on honeydews than on cantaloupes. These antimicrobials could potentially be used as sanitizers for decontaminating melons.

Efficacy of Fungicides and Rotational Programs for Management of Powdery Mildew on Cantaloupe.

Powdery mildew of cucurbits, caused by Podosphaera xanthii (syn. Sphaerotheca fuliginia auct. p.p. (Schltdl.) Pollacci), is a common and often severe disease in most areas of the world. Field trials were conducted with cantaloupe to compare disease management success provided by conventional fungicides and biofungicides having different inherent efficacies and modes of action, when applied alone throughout the treatment period or as components of fungicide application programs. Additionally, the portion of total disease control provided by each component fungicide within selected rotational programs was determined. When applied alone throughout the treatment period, disease severity in 2008 and 2009 compared with nontreated plants was reduced by values of 100, 99.3, and 98.1% by wettable sulfur (Microthiol Disperss), triflumizole (Procure), and quinoxyfen (Quintec), respectively; 83.9, 76.4, and 57.4% by trifloxystrobin (Flint), pyraclostrobin (Cabrio), or azoxystrobin (Quadris), respectively; and 39.8, 31.1, 30.0, and 28.6% by thiophanate-methyl (Topsin M), potassium bicarbonate (Kaligreen), kresoxim-methyl (Sovran), and Bacillus subtilis (Serenade), respectively. Rotational application programs composed of Microthiol Disperss, Procure, and Quintec reduced powdery mildew severity on cantaloupe by 97.5 to 100% in both trials. In comparison, disease reduction of 86.0 to 100% was achieved when the first and third fungicide applications were Quintec or Procure and the second and fourth applications were Cabrio, Flint, Kaligreen, Quadris, Serenade, Sovran, or Topsin M. In field trials designed to elucidate the portion of total disease control provided by each component fungicide within a rotational program, application sequences of Procure, Streptomyces lydicus (Actinovate), Procure, and Actinovate or Procure, Kaligreen, Procure, and Kaligreen resulted in reductions in powdery mildew severity of 69.1 and 78.7%, respectively. In comparison, inclusion of only the two Procure applications brought about a mean disease reduction of 85%, whereas inclusion of only the two Actinovate or Kaligreen applications reduced the level of powdery mildew control to 17.6 and 12.9%, respectively. The usefulness of fungicides with low inherent efficacy as resistance management partners when applied with highly efficacious at-risk fungicides may be questioned; however, the importance of any fungicide as a resistance management partner should be measured by its ability to dilute the selection pressure of the at-risk fungicide and to inhibit the growth of any resistant biotypes that may arise, factors which may not be reflected by its inherent efficacy in controlling disease. Because less efficacious fungicides did not increase the overall level of disease control, encouraging growers and pest control advisors to incorporate them into powdery mildew treatment programs may be a challenge, because resistance management is not their top priority. An ongoing educational effort emphasizing the benefits of resistance management programs with respect to prolonging the effectiveness of single-site mode of action fungicides is essential.

Evaluation of Soil Solarization and Flooding As Management Tools for Fusarium Wilt of Lettuce.

Fusarium wilt of lettuce caused by Fusarium oxysporum f. sp. lactucae continues to spread and cause economic losses in Arizona lettuce fields since the initial discovery of the disease in the state in 2001. Studies were initiated to assess the potential of summer soil solarization and flooding as management tools for Fusarium wilt of lettuce in southwestern Arizona production fields. In microplot studies, lettuce plant growth in soil naturally infested with F. oxysporum f. sp. lactucae that was solarized from 2 to 8 weeks was consistently greater than growth in nonsolarized soil. Growth of lettuce in flooded soil containing the pathogen occasionally was significantly higher than in nonflooded soil; however, the effect on plant growth and health was not as consistent as that recorded for solarized soil. In four trials within a field containing F. oxysporum f. sp. lactucae, the incidence of Fusarium wilt on lettuce sown in soil after solarization was reduced from 42 to 91% compared with disease in nonsolarized plots. There was no significant benefit of a 2- over a 1-month solarization period under the conditions of these trials, where the mean soil temperature at a depth of 5 cm during a 1-month solarization period in 2005 and 2006 was 47 and 49°C, respectively. These findings suggest that soil solarization can be an effective tool for management of Fusarium wilt on lettuce, especially when used within an integrated program in conjunction with existing disease management tactics.