Graduate students receive grants from Northeast SARE

UNIVERSITY PARK, Pa. – The Northeast Sustainable Agriculture Research & Education (SARE) program selected proposals of four plant pathology graduate students for the 2021 Graduate Student Grant Awards. SARE offers competitive grants to projects that explore and address key issues affecting the sustainability and future economic viability of agriculture.

Jeremy Held
Identification of a potential nonhost fire blight resistance gene

Fire blight, caused by the bacterium Erwinia amylovora, is a costly disease to apple and pear growers in the Northeast U.S. While management is achieved via antibiotics, genetic resistance represents a more sustainable strategy. The E. amylovora secreted protein HrpN, an essential virulence factor, triggers an unusually strong defense response in tobacco (Nicotiana tabacum) that suggests a resistance (R) gene-mediated recognition pathway. This project seeks to uncover the genetic basis of HrpN recognition in tobacco for potential transfer to apple or pear to confer HrpN recognition and fire blight resistance. A preliminary survey of tobacco germplasm identified accessions that are unresponsive to HrpN, suggesting a mutation in one or more genes responsible for HrpN recognition. To elucidate the heritability of this phenotype, three accessions unresponsive to HrpN will be crossed with a HrpN-responsive accession to generate segregating F2 populations. After phenotyping, a bulked segregant analysis will be performed on HrpN-responsive and HrpN-unresponsive pools of individuals to detect genetic variations strongly associated with the trait. This research will produce candidate resistance genes that will be evaluated through additional lab and field studies beyond the termination of the grant. Identification of genes involved in HrpN recognition would advance the fire blight field, as few genetic sources of fire blight resistance have been characterized. Communication of results to regional and international plant pathology researchers will be achieved through conference attendance and journal publications. Local tree fruit producers will also be engaged through an on-farm outreach event at the end of the project period.

Elisa Lauritzen
Adapting Anaerobic Soil Disinfestation (ASD) as a Pre-Plant Non-Chemical Soilborne Disease Management Tactic for Use in High Tunnel Tomato Systems 

Fresh-market tomatoes are increasingly being grown in high tunnels to extend the growing season, meet demand for local food, and to avoid disease due to extreme precipitation events. Because tomatoes are a high value crop, high tunnel growers have forgone crop rotations in favor of continuous cropping cycles. Such intensification leads to increased soilborne disease pressure which can impact yields. Soilborne disease identification is difficult because of the below-ground nature of the pathogens and symptoms that can be mistaken for other factors. If yield losses are attributed to soilborne disease, available chemical and non-chemical treatments are often not used due to expense, health or environmental concerns, and availability. Without a clear understanding about what is causing declines, growers will use grafted tomatoes or move to soilless systems, increasing production costs. Anaerobic soil disinfection (ASD) has been demonstrated as an effective pre-plant non-chemical treatment for control of soilborne diseases in many cropping systems including tomato. However, there is little information regarding the efficacy of ASD in Northeastern high tunnels systems. ASD combines the incorporation of organic amendments, flooding, and soil sterilization into a single tactic and elicits microbial changes that are antagonistic to soilborne pathogens. These changes are influenced by the organic amendment addition, soil temperatures, and treatment duration. This project seeks to identify soilborne pathogens in high tunnels, evaluate ASD using local carbon sources to manage soilborne pathogens, and determine the reapplication frequency that the tactic should be reapplied. Soilborne disease management recommendations will be generated through this work.

Rachel Richardson
Identification of Non-Pseudomonas Blotch Pathogens Using High-Throughput Isolation

Bacterial blotch refers to a group of diseases characterized by the formation of spots and discoloration on the mushroom cap. Blotch diseases are common threats in mushroom production and were once thought to have been caused by a few Pseudomonas species. Several non-Pseudomonads, including Mycetocola spp., Burkholderia cepacia, and Ewingella americana, have been identified as causal agents of bacterial blotch and found in different combinations with other species on the surface of mushroom caps. The complete diversity of pathogens, both Pseudomonas and non-Pseudomonas, causing blotch on white button mushroom caps is still unknown. One barrier to discovering the complete diversity of blotch diseases is the labor-intensive nature of pathogen isolation and identification. Using traditional low-throughput schemes, bacteria are isolated on non- or semi-selective media followed by multiple rounds of purification and storage of individual isolates prior to intensive pathogenicity testing. This results in a high demand for supplies, hands-on effort, time, and space to conduct the study. 

In this study, a high-throughput bacterial isolation system and traditional isolation scheme will be used to recover pathogenic bacteria from symptomatic mushrooms. The Prospector System ™ (manufactured by General Automation Laboratory Technologies (GALT)) will be used for high-throughput isolation, cultivation, and screening of bacteria from symptomatic mushrooms in Pennsylvania. High-throughput isolation and standard isolation, followed by pathogenicity tests, will be used to build a collection of blotch pathogens. 16S rDNA sequence analysis will determine the preliminary identification of the isolates, additional methods will be used to confirm the 16S rDNA results.

Ryan Spelman
Determining the effect of cover cropping legacy on mycotoxin accumulation and fusarium disease in maize

Fusarium (caused by Fusarium verticillioides) and Gibberella (caused by Fusarium graminearum) ear and stalk rot are economically and toxicologically important diseases of maize in the Northeast causing ear rot, stalk rot and seedling blight. While Fusarium infection can reduce maize yield, the mycotoxins produced by these pathogens are of greatest concern and pose a threat to human and animal health upon ingestion. Management options are limited, and many farmers rely on genetic resistance through the use of transgenic Bt maize, which reduces insect damage and wounding, where Fusarium infection can occur. This management option is however inaccessible to organic operations, and producers and increasing evidence of pest resistance to Bt-maize is reducing its efficacy in conventional operations as well. Therefore, new management strategies must be developed which are sustainable, affordable, and can be implemented by organic operations producers, as well as in conventional production systems. One agronomic practice that has been identified to influence F. verticillioides disease severity is cover cropping. Cover crops are known to modify nutrient cycling and biological activity in the soil. These soil modifications are known to influence weed growth, insect pest pressure, and below ground pathogens, however there is minimal knowledge regarding how these systems influence above ground fungal pathogens. The purpose of this research is to identify the effect of various cover crop species legacies on stalk and ear rot severity and mycotoxin contamination by F. graminearum and F. verticillioides infection.