Aspergillus flavus infects peanuts and produces a mycotoxin called aflatoxin, a potent human carcinogen. In infected peanuts, it can also affect peanut seed quality by causing seed rot and reducing seed viability, resulting in low germination. In 2020, peanut seeds in Georgia had lower than expected germination and a high frequency of A. flavus contamination. A total of 76 Aspergillus isolates were collected from seven seed lots and their identity and in vitro reaction to QoI (quinone outside inhibitor) fungicide (azoxystrobin) were studied. The isolates were confirmed as A. flavus by morphological characteristics and a PCR (polymerase chain reaction)-based method using species-specific primers. In vitro, these isolates were tested for sensitivity to azoxystrobin. The mean EC₅₀ values ranged from 0.12 to 297.22 μg/mL, suggesting that some isolates were resistant or tolerate to this fungicide. The sequences of cytochrome b gene from these isolates were compared and a single nucleotide mutation (36.8% isolates) was found as Cyt B G143A, which was associated with the total resistance to the QoIs. Another single mutation (15.8% isolates) was also observed as Cyt B F129L, which had been documented for QoI resistance. Therefore, a new major single mutation was detected in the A. flavus natural population in this study, and it might explain the cause of the bad seed quality in 2020. The high frequency of this new single nucleotide mutation exists in the natural population of A. flavus and results in the ineffectiveness of using azoxystrobin seed treatment. New seed treatment fungicides are needed.

Turfgrass is a multibillion-dollar industry severely affected by plant pathogens including fungi, bacteria, viruses, and nematodes. Many of the diseases in turfgrass have similar signs and symptoms, making it difficult to diagnose the specific problem pathogen. Incorrect diagnosis leads to the delay of treatment and excessive use of chemicals. To effectively control these diseases, it is important to have rapid and accurate detection systems in the early stages of infection that harbor relatively low pathogen populations. There are many methods for diagnosing pathogens on turfgrass. Traditional methods include symptoms, morphology, and microscopy identification. These have been followed by nucleic acid detection and onsite detection techniques. Many of these methods allow for rapid diagnosis, some even within the field without much expertise. There are several methods that have great potential, such as high-throughput sequencing and remote sensing. Utilization of these techniques for disease diagnosis allows for faster and accurate disease diagnosis and a reduction in damage and cost of control. Understanding of each of these techniques can allow researchers to select which method is best suited for their pathogen of interest. The objective of this article is to provide an overview of the turfgrass diagnostics efforts used and highlight prospects for disease detection.

Dollar spot is one of the most destructive diseases in turfgrass. The causal agents belong to the genus Clarireedia, which are known for causing necrotic, sunken spots in turfgrass that coalesce into large damaged areas. In low tolerance settings like turfgrass, it is of vital importance to rapidly detect and identify the pathogens. There are a few methods available to identify the genus Clarireedia, but none of those are rapid enough and characterize down to the species level. This study produced a co-dominant cleaved amplified polymorphic sequences (CAPS) test that differentiates between C. jacksonii and C. monteithiana, the two species that cause dollar spot disease within the United States. The calmodulin gene (CaM) was targeted to generate Clarireedia spp. specific PCR primers. The CAPS assay was optimized and tested for specificity and sensitivity using DNA extracted from pure cultures of two Clarireedia spp. and other closely related fungal species. The results showed that the newly developed primer set could amplify both species and was highly sensitive as it detected DNA concentrations as low as 0.005 ng/µL. The assay was further validated using direct PCR to speed up the diagnosis process. This drastically reduces the time needed to identify the dollar spot pathogens. The resulting assay could be used throughout turfgrass settings for a rapid and precise identification method in the US.

Citrus tristeza virus (CTV) [genus Closterovirus; family Closteroviridae] is one of the most important, economically devastating viruses of citrus worldwide. On citrus trees grafted onto sour orang...

In recent years, citrus production has rapidly increased within the state of Georgia (USA), and there are now citrus plantings within at least 32 counties in residential, production, and nursery se...

Dollar spot is a major fungal disease affecting turfgrass worldwide and can quickly destroy turfgrass swards. An assimilating probe–based loop-mediated isothermal amplification (LAMP) assay was developed to detect Clarireedia monteithiana and C. jacksonii, the causal agents of dollar spot within the continental United States. Five LAMP primers were designed to target the calmodulin gene with the addition of a 6-carboxyl-fluorescein florescent assimilating probe, and the temperature amplification was optimized for C. jacksonii and C. monteithiana identification. The minimum amount of purified DNA needed for detection was 0.05 ng μl⁻¹. Specificity assays against host DNA and other turfgrass pathogens were negative. Successful LAMP amplification was also observed for dollar spot–infected turfgrass field samples. Further, a DNA extraction technique via rapid heat-chill cycles and visualization of LAMP results via a florescent flashlight was developed and adapted for fast, simple, and reliable detection in 1.25 h. This assimilating probe–based LAMP assay has proved successful as a rapid, sensitive, and specific method for the detection of C. monteithiana and C. jacksonii in pure cultures and from symptomatic turfgrass leaves blades. The assay represents a promising technology to be used in the field for on-site, point-of-care pathogen detection.