Progress 07/01/20 to 10/27/22
Outputs
Target Audience:Target audiences reached through our work this reporting year include both conventional and organic growers of multiple scales. I also worked closely with extension faculty, the project mentor (an extension pathologist), farm advisors and growers for outreach regarding project findings and outcomes. Additionally, undergraduate interns and research assistants were both directly involved with this project or closely related projects. Academic audiences also benefited from an increased understanding of interactions between southern blight, the environment, and management questions. Efforts: Results were presented at two potato and one tomato commodity board meetings. I also presented results at a Swett Lab Tomato Disease Management Field Day at Armstrong (July 13, 2021; attended by around 30 participants). I also published a Southern blight newsletter update for CA processing tomato producers and a UC ANR extension article on our work (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=42977). I mentored three interns, two of which received three course credits, and one stayed for multiple quarters, earning six credits. Interns assisted by examining climate data related to southern blight development and by assisting with lab assays to better understand the temperature response of sclerotia to temperature. I developed syllabi for these students and helped them to take on related projects while also instructing on experimental design, data analyses, developing scientific presentations, reading scientific papers, and writing reports. Mentoring was conducted in person while COVID restrictions permitted and over Zoom when they did not. I mentored 6 undergraduate assistants who helped with research lab and field activities as part of their positions. Interns and assistants met weekly for southern blight team meetings to trouble shoot research questions and to discuss relevant readings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Project and professional development was extensive and continuous. This included monthly one-on-one research meetings during the academic year, which were typically 2 hrs or longer. During these meetings, I discussed progress on past goals with the project mentor, Cassandra Swett, and discussed project updates and timelines, and set new monthly goals and objectives. While working from home during university COVID-19 closures, these meetings continued over Zoom. Additionally, we met quarterly to discuss professional mentoring topics including preparing statements for academic positions and curriculum vitae development. We also met every 6 months to discuss self-evaluations and project progress. I presented for lab meetings each quarter, where I received feedback from the lab, and as a lab we organized journal clubs and writing workshops to enhance lab members' scientific knowledge and writing abilities. I also worked collaboratively with Dr. Neil McRoberts for input on model development questions, and I worked closely with several farm advisors including Amber Vinchesi-Vahl, Brenna Aegerter, and Jaspreet Sidhu on project implementation. I regularly talked to growers involved with the potato and tomato commodity boards for project development and gained experience in extension. This year, I wrote information for a southern blight webpage, presented a potato and tomato commodity board meeting, co-authored a UC ANR southern blight blog post, and presented at a field day for UC ANR farm advisors. Other mentoring activities included writing grants together (leveraging results from NIFA work), preparing interview materials for my current position, and preparing conference posters and presentations on results from her NIFA fellowship (Plant Health Online meetings 2020 and 2021). I was able to develop as a mentor in the past year. During my time in the Swett Lab, I mentored two interns, for three quarters. To advise the mentors, I developed a syllabus and had regular, weekly meetings to discuss project progress. I also provided extensive direction on project and presentation development (for lab meeting), data organization, and provided two rounds of feedback on the students' final reports. I directly mentored a total of six undergraduate research assistants. Five of the six undergraduates stayed in the lab for multiple quarters, and they have all grown in their skill sets and understanding of the experimental process over time. Additionally, I provided project support to other lab members including graduate students, technicians, and junior specialists with input during lab meeting and practice presentations and by assisting with planting, harvests, and data collection for projects in 2020 and 2021. Despite the remote status of our department, I was able to participate in several opportunities to share my research and develop professionally. I presented results of our first NIFA-funded field season during the virtual 2020 UC Davis Department of Plant Pathology Retreat. I also worked to develop my leadership skills while a postdoc at UC Davis. This included helping with seminar planning in the winter of 2021 and coordinating departmental seminar with one other postdoc and Dr. Cassandra Swett for the spring of 2021. Additionally, I worked with two other postdoctoral researchers to coordinate a postdoctoral researcher group and biweekly meeting and question and answer session. We brought in outside speakers, such as recent faculty hires and industry researchers, to discuss their experiences and aid in professional development. How have the results been disseminated to communities of interest?Results were presented at two potato and one tomato commodity board meetings. I also presented results at a Swett Lab Tomato Disease Management Field Day at Armstrong (July 13, 2021; attended by around 30 participants). I also published a Southern blight newsletter update for CA processing tomato producers and a UC ANR extension article on our work (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=42977). This newsletter was email to growers throughout the central valley. Additionally, the project mentor and I intend will publish the results of these findings in the UC vegetable research and information center, so they are available to growers. Results have also been presented for academic communities including two interactive poster presentations for American Phytopathological Society and a departmental retreat. Manuscripts are in progress. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1-Towards this objective I conducted growth assays of sclerotia at varied temperatures from multiple crops &locations throughout the Central Valley. These propagules are the key driver of southern blight, caused by Athelia rolfsii. Isolates were collected from various crops including potato, tomato, sunflower, &sweet potato. Isolates were evaluated at 10 °C, 15°C, room temperature, 35 °C, and 40 °C. Assays of 10 isolates have been completed, &all isolates have been assayed in two experimental replicates. We determined that germination is favored above 10 °C &below 37 °C and germination occurs most quickly around 30 °C. Several isolates were able to germinate at high temperatures, but germination was not 100%. After two weeks at 40 °C, sclerotia also lost viability &were no longer able to germinate at a rate of 100%. Differential germination rates at high temperatures indicated that we will need to use an average temperature response for the lab-based model. Additionally, we validated the temperature response of isolates with field soil using a methanol method which prompts the germination of A. rolfsii sclerotia &prevents the germination of other fungi. For validation, soils was collected from a field with known southern blight at a sampling depth of 3" (the depth at which A. rolfsii sclerotia are known to germinate). In this assay, sclerotia did not germinate at 12 °C, but they did germinate at room temperature. Using field soil, no sclerotia germinated at 40°C. The work completed on this objective has led to an important change in knowledge regarding the specific conditions that are favorable for the germination of A. rolfsii sclerotia. This knowledge may lead to a change in action regarding management &will inform our lab-based model. We also learned that model development will need to be based on an average response of multiple isolates. This fall, we will work to develop the lab based model &compare the results with our field-based findings. We have also collected additional field soil samples this summer, &we will use this soil to further validate the model. Objective 2- I collected information on disease progression in addition to temperature &moisture in two potato fields in 2020 & 2021 in plots nested within an integrated management trial in San Joaquin County &Kern County. Potato tubers were evaluated for disease prior to desiccation (when herbicide is applied to the field), just before rewetting (when moisture is applied to the field before harvest), &at harvest, along with yields. We found a 2.5-fold increase in disease that corresponded in accumulated with degree days between our pre-desiccation &harvest evaluation, indicating a key window was identified for southern blight management. In 2020, 2tomato fields were, similarly monitored for southern blight development in a grower field in Yolo County &a field at Shafter Ag. Research Facility. However, in 2020, we did not have disease pressure in the field located in Yolo County, &the research site in Kern experienced a canopy collapse due to a viral disease. This confounded southern blight disease assessments. In 2021, we scouted for disease and monitored temperature & moisture conditions in two additional fields, 1in Sutter & 1in Yolo counties. This year, we were able to collect data in the 2fields on temperature, moisture, &disease incidence. In addition to data collection for model development, in our potato trials in 2020 &2021, we had separate, replicated plots that we used to collect data for model validation. These plots were monitored at the same time as our model development plots. These data will be used to test the accuracy of the model developed using the model generation plots. We now have a better understanding of the primary risk windows for southern blight in annual crops. The risk window corresponds with end of season practices such as desiccation &rewetting. This presents valuable &new information on treatment timings to control for southern blight.This fall &winter, I will work in collaboration with Dr. Neil McRoberts to complete model development &we will examine the accuracy of the model using validation data collected during the previous field season. Objective 3:Based on observations in the lab and field &our understanding of A. rolfsii biology, we determined that a key window for southern blight development in potato is near the end of season, at rewetting. At rewetting, the ground has warmed due to a lack of canopy from desiccation &additional moisture is added to the field. In 2020, we applied the fungicides Elatus (9.5 oz per acre), Quadris (14 fl oz per acre), &Miravis (11.4 fl oz per acre), &ammonium bicarbonate (17lbs per acre) at rewetting. Both Quadris &the low rate of ammonium bicarbonate applied at the end of the season reduced southern blight compared to the untreated control. However, yields were not different between treated &untreated plots. In 2021, we trialed ammonium bicarbonate at a low rate (25 lbs), ammonium bicarbonate at a higher rate (100 lbs) sodium bicarbonate (25 lbs), Quadris at desiccation (14 fl oz), Pyrazaflumid at rewetting (4.5 fl oz), Quadris at rewetting (14 fl oz), and Quadris (14 flz oz) at desiccation with ammonium bicarbonate at rewetting (25 lbs). Interestingly, all chemicals reduced the incidence of all diseased tubers at harvest. In 2021, all treatments yielded higher than the control treatment &several appear to be significant based on SE (analysis pending): Quadris at desiccation with ammonium bicarbonate at rewetting (86.26 CWT/ac difference); sodium bicarbonate at a low rate (115.55 CWT/ac difference); ammonium bicarbonate at a higher rate (150.02 CWT/ac); &Quadris at rewetting (135.19 CWT/ac difference). To better understand the impact of crop rotation on southern blight risk, we collected soil at the beginning and end of the season from 15 crops in 2020 &2021: brassica &cucurbit seed production fields, tomato, sunflower, corn, onion, potato, rice, fallow fields, &beans. Soil was collected from the top 3inches (the depth from which sclerotia germinate) and assayed with methanol. The number of germinated sclerotia were counted in each methanol tray. All soil from 2020 has been assayed, &soil from 2021 is currently be processed. We have found that increased in sclerotia number are greater in some crops than others. For example, sclerotia numbers increased by 11 fold after rotations with onion but decreased after rotations with tomato. While many crops are susceptible to southern blight, infections on certain crops may not cause as much inoculum to occur in the soil. Additional data are needed to evaluate how consistent these trends are. This objective has already resulted in a more targeted understanding of when to best manage southern blight, particularly in potato. Effective chemical applications during the desiccation &rewetting period in potato will allow growers to reduce yield losses from southern blight. We are generating helpful data on effective crop rotations to reduce inoculum in the soil from southern blight. We will work to develop an online risk tool that will allow growers to understand the field-level risk of southern blight on their operation. Additional resources, including crop rotation findings will also be made available online for growers to access. After harvest soil samples were collected this fall &will be processed this fall &winter. Multiple years of data on the impact of crop rotation on sclerotia will provide a robust data set to better understand options for growers to reduce A. rolfsi inoculum.
Publications
|
Progress 07/01/21 to 01/03/22
Outputs
Target Audience: \\\ Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Project and professional development was extensive and continuous. This included monthly one-on-one research meetings during the academic year, which were typically 2 hrs or longer. During these meetings, I discussed progress on past goals with the project mentor, Cassandra Swett, and discussed project updates and timelines, and set new monthly goals and objectives. While working from home during university COVID-19 closures, these meetings continued over Zoom. Additionally, we met quarterly to discuss professional mentoring topics including preparing statements for academic positions and curriculum vitae development. We also met every 6 months to discuss self-evaluations and project progress. I presented for lab meetings each quarter, where I received feedback from the lab, and as a lab we organized journal clubs and writing workshops to enhance lab members' scientific knowledge and writing abilities. I also worked collaboratively with Dr. Neil McRoberts for input on model development questions, and I worked closely with several farm advisors including Amber Vinchesi-Vahl, Brenna Aegerter, and Jaspreet Sidhu on project implementation. I regularly talked to growers involved with the potato and tomato commodity boards for project development and gained experience in extension. This year, I wrote information for a southern blight webpage, presented a potato and tomato commodity board meeting, co-authored a UC ANR southern blight blog post, and presented at a field day for UC ANR farm advisors. Other mentoring activities included writing grants together (leveraging results from NIFA work), preparing interview materials for my current position, and preparing conference posters and presentations on results from her NIFA fellowship (Plant Health Online meetings 2020 and 2021). I was able to develop as a mentor in the past year. During my time in the Swett Lab, I mentored two interns, for three quarters. To advise the mentors, I developed a syllabus and had regular, weekly meetings to discuss project progress. I also provided extensive direction on project and presentation development (for lab meeting), data organization, and provided two rounds of feedback on the students' final reports. I directly mentored a total of six undergraduate research assistants. Five of the six undergraduates stayed in the lab for multiple quarters, and they have all grown in their skill sets and understanding of the experimental process over time. Additionally, I provided project support to other lab members including graduate students, technicians, and junior specialists with input during lab meeting and practice presentations and by assisting with planting, harvests, and data collection for projects in 2020 and 2021. Despite the remote status of our department, I was able to participate in several opportunities to share my research and develop professionally. I presented results of our first NIFA-funded field season during the virtual 2020 UC Davis Department of Plant Pathology Retreat. I also worked to develop my leadership skills while a postdoc at UC Davis. This included helping with seminar planning in the winter of 2021 and coordinating departmental seminar with one other postdoc and Dr. Cassandra Swett for the spring of 2021. Additionally, I worked with two other postdoctoral researchers to coordinate a postdoctoral researcher group and biweekly meeting and question and answer session. We brought in outside speakers, such as recent faculty hires and industry researchers, to discuss their experiences and aid in professional development. How have the results been disseminated to communities of interest? Results were presented at two potato and one tomato commodity board meetings. I also presented results at a Swett Lab Tomato Disease Management Field Day at Armstrong (July 13, 2021; attended by around 30 participants). I also published a Southern blight newsletter update for CA processing tomato producers and a UC ANR extension article on our work(https: ? What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1- Towards this objective I conducted growth assays of sclerotia at varied temperatures from multiple crops & locations throughout the Central Valley. These propagules are the key driver of southern blight, caused by Athelia rolfsii. Isolates were collected from various crops including potato, tomato, sunflower, & sweet potato. Isolates were evaluated at 10°C, 15°C, room temperature, 35 °C, and 40 °C. Assays of 10 isolates have been completed, & all isolates have been assayed in two experimental replicates. We determined that germination is favored above 10 °C & below 37 °C and germination occurs most quickly around 30 °C. Several isolates were able to germinate at high temperatures, but germination was not 100%.After two weeks at 40 °C, sclerotia also lost viability & were no longer able to germinate at a rate of 100%. Differential germination rates at high temperatures indicated that we will need to use an average temperature response for the lab-based model. Additionally, we validated the temperature response of isolates with field soil using a methanol method which prompts the germination of A. rolfsii sclerotia & prevents the germination of other fungi. For validation, soils was collected from a field with known southern blight at a sampling depth of 3" (the depth at which A. rolfsii sclerotia are known to germinate). In this assay, sclerotia did not germinate at 12 °C, but they did germinate at room temperature. Using field soil, no sclerotia germinated at 40°c. The work completed on this objective has led to an important change in knowledge regarding the specific conditions that are favorable for the germination of A. rolfsii sclerotia. This knowledge may lead to a change in action regarding management & will inform our lab-based model. We also learned that model development will need to be based on an average response of multiple isolates. This fall, we will work to develop the lab based model & compare the results with our field-based findings. We have also collected additional field soil samples this summer, & we will use this soil to further validate the model. Objective 2- I collected information on disease progression in addition to temperature & moisture in two potato fields in 2020 & 2021 in plots nested within an integrated management trial in San Joaquin County & Kern County. Potato tubers were evaluated for disease prior to desiccation (when herbicide is applied to the field), just before rewetting (when moisture is applied to the field before harvest), & at harvest, along with yields. We found a 2.5-fold increase in disease that corresponded in accumulated with degree days between our pre-desiccation & harvest evaluation, indicating a key window was identified for southern blight management. In 2020, 2 tomato fields were, similarly monitored for southern blight development in a grower field in Yolo County & a field at Shafter Ag. Research Facility. However, in 2020, we did not have disease pressure in the field located in Yolo County, & the research site in Kern experienced a canopy collapse due to a viral disease. This confounded southern blight disease assessments. In 2021, we scouted for disease and monitored temperature & moisture conditions in two additional fields, 1 in Sutter & 1 in Yolo counties. This year, we were able to collect data in the 2 fields on temperature, moisture, & disease incidence. In addition to data collection for model development, in our potato trials in 2020 & 2021, we had separate, replicated plots that we used to collect data for model validation. These plots were monitored at the same time as our model development plots. These data will be used to test the accuracy of the model developed using the model generation plots.We now have a better understanding of the primary risk windows for southern blight in annual crops. The risk window corresponds with end of season practices such as desiccation & rewetting. This presents valuable & new information on treatment timings to control for southern blight. This fall & winter, I will work in collaboration with Dr. Neil McRoberts to complete model development & we will examine the accuracy of the model using validation data collected during the previous field season. Objective 3: Based on observations in the lab and field & our understanding of A. rolfsii biology, we determined that a key window for southern blight development in potato is near the end of season, at rewetting. At rewetting, the ground has warmed due to a lack of canopy from desiccation & additional moisture is added to the field. In 2020, we applied the fungicides Elatus (9.5 oz per acre), Quadris (14 fl oz per acre), & Miravis (11.4 fl oz per acre), & ammonium bicarbonate (17Ibs per acre) at rewetting. Both Quadris & the low rate of ammonium bicarbonate applied at the end of the season reduced southern blight compared to the untreated control. However, yields were not different between treated & untreated plots. In 2021, we trialed ammonium bicarbonate at a low rate (25 lbs), ammonium bicarbonate at a higher rate (100 lbs) sodium bicarbonate (25 lbs), Quadris at desiccation (14 fl oz), Pyrazaflumid at rewetting (4.5 fl oz), Quadris at rewetting (14 fl oz), and Quadris (14 flz oz) at desiccation with ammonium bicarbonate at rewetting (25 lbs). Interestingly, all chemicals reduced the incidence of all diseased tubers at harvest. In 2021, all treatments yielded higher than the control treatment & several appear to be significant based on SE (analysis pending): Quadris at desiccation with ammonium bicarbonate at rewetting (86.26 CWT/ac difference); sodium bicarbonate at a low rate (115.55 CWT/ac difference); ammonium bicarbonate at a higher rate (150.02 CWT/ac); & Quadris at rewetting (135.19 CWT/ac difference). To better understand the impact of crop rotation on southern blight risk, we collected soil at the beginning and end of the season from 15 crops in 2020 & 2021: brassica & cucurbit seed production fields, tomato, sunflower, corn, onion, potato, rice, fallow fields, & beans. Soil was collected from the top 3 inches (the depth from which sclerotia germinate) and assayed with methanol. The number of germinated sclerotia were counted in each methanol tray. All soil from 2020 has been assayed, & soil from 2021 is currently be processed. We have found that increased in sclerotia number are greater in some crops than others. For example, sclerotia numbers increased by 11 fold after rotations with onion but decreased after rotations with tomato. While many crops are susceptible to southern blight, infections on certain crops may not cause as much inoculum to occur in the soil. Additional data are needed to evaluate how consistent these trends are. ?This objective has already resulted in a more targeted understanding of when to best manage southern blight, particularly in potato. Effective chemical applications during the desiccation & rewetting period in potato will allow growers to reduce yield losses from southern blight. We are generating helpful data on effective crop rotations to reduce inoculum in the soil from southern blight. We will work to develop an online risk tool that will allow growers to understand the field-level risk of southern blight on their operation. Additional resources, including crop rotation findings will also be made available online for growers to access. After harvest soil samples were collected this fall & will be processed this fall & winter. Multiple years of data on the impact of crop rotation on sclerotia will provide a robust data set to better understand options for growers to reduce A. rolfsi inoculum.
Publications
|
Progress 07/01/20 to 06/30/21
Outputs
Target Audience:Target audiences reached through our work this reporting year include both conventional and organic growers of multiple scales. I also worked closely with extension faculty, the project mentor (an extension pathologist), farm advisors and growers for outreach regarding project findings and outcomes. Additionally, undergraduate interns and research assistants were both directly involved with this project or closely related projects. Academic audiences also benefited from an increased understanding of interactions between southern blight, the environment, and management questions. Efforts: Results were presented at two potato and one tomato commodity board meetings. I also presented results at a Swett Lab Tomato Disease Management Field Day at Armstrong (July 13, 2021; attended by around 30 participants). I also published a Southern blight newsletter update for CA processing tomato producers and a UC ANR extension article on our work (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=42977). I mentored three interns, two of which received three course credits, and one stayed for multiple quarters, earning six credits. Interns assisted by examining climate data related to southern blight development and by assisting with lab assays to better understand the temperature response of sclerotia to temperature. I developed syllabi for these students and helped them to take on related projects while also instructing on experimental design, data analyses, developing scientific presentations, reading scientific papers, and writing reports. Mentoring was conducted in person while COVID restrictions permitted and over Zoom when they did not. I mentored 6 undergraduate assistants who helped with research lab and field activities as part of their positions. Interns and assistants met weekly for southern blight team meetings to trouble shoot research questions and to discuss relevant readings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Project and professional development was extensive and continuous. This included monthly one-on-one research meetings during the academic year, which were typically 2 hrs or longer. During these meetings, I discussed progress on past goals with the project mentor, Cassandra Swett, and discussed project updates and timelines, and set new monthly goals and objectives. While working from home during university COVID-19 closures, these meetings continued over Zoom. Additionally, we met quarterly to discuss professional mentoring topics including preparing statements for academic positions and curriculum vitae development. We also met every 6 months to discuss self-evaluations and project progress. I presented for lab meetings each quarter, where I received feedback from the lab, and as a lab we organized journal clubs and writing workshops to enhance lab members' scientific knowledge and writing abilities. I also worked collaboratively with Dr. Neil McRoberts for input on model development questions, and I worked closely with several farm advisors including Amber Vinchesi-Vahl, Brenna Aegerter, and Jaspreet Sidhu on project implementation. I regularly talked to growers involved with the potato and tomato commodity boards for project development and gained experience in extension. This year, I wrote information for a southern blight webpage, presented a potato and tomato commodity board meeting, co-authored a UC ANR southern blight blog post, and presented at a field day for UC ANR farm advisors. Other mentoring activities included writing grants together (leveraging results from NIFA work), preparing interview materials for my current position, and preparing conference posters and presentations on results from her NIFA fellowship (Plant Health Online meetings 2020 and 2021). I was able to develop as a mentor in the past year. During my time in the Swett Lab, I mentored two interns, for three quarters. To advise the mentors, I developed a syllabus and had regular, weekly meetings to discuss project progress. I also provided extensive direction on project and presentation development (for lab meeting), data organization, and provided two rounds of feedback on the students' final reports. I directly mentored a total of six undergraduate research assistants. Five of the six undergraduates stayed in the lab for multiple quarters, and they have all grown in their skill sets and understanding of the experimental process over time. Additionally, I provided project support to other lab members including graduate students, technicians, and junior specialists with input during lab meeting and practice presentations and by assisting with planting, harvests, and data collection for projects in 2020 and 2021. Despite the remote status of our department, I was able to participate in several opportunities to share my research and develop professionally. I presented results of our first NIFA-funded field season during the virtual 2020 UC Davis Department of Plant Pathology Retreat. I also worked to develop my leadership skills while a postdoc at UC Davis. This included helping with seminar planning in the winter of 2021 and coordinating departmental seminar with one other postdoc and Dr. Cassandra Swett for the spring of 2021. Additionally, I worked with two other postdoctoral researchers to coordinate a postdoctoral researcher group and biweekly meeting and question and answer session. We brought in outside speakers, such as recent faculty hires and industry researchers, to discuss their experiences and aid in professional development. How have the results been disseminated to communities of interest?Results were presented at two potato and one tomato commodity board meetings. I also presented results at a Swett Lab Tomato Disease Management Field Day at Armstrong (July 13, 2021; attended by around 30 participants). I also published a Southern blight newsletter update for CA processing tomato producers and a UC ANR extension article on our work (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=42977). This newsletter was email to growers throughout the central valley. Additionally, the project mentor and I intend will publish the results of these findings in the UC vegetable research and information center, so they are available to growers. Results have also been presented for academic communities including two interactive poster presentations for American Phytopathological Society and a departmental retreat. Manuscripts are in progress. What do you plan to do during the next reporting period to accomplish the goals?This fall, we will work to develop the lab-based model with the data we have generate, and we compare the results with our field-based findings. We have also collected additional field soil samples this summer, and we will use this soil to further validate the lab-based sclerotia germination model. Now that data are collected for both field based model development and initial validations, it is important to analyze these data. This fall and winter, I will work in collaboration with Dr. Neil McRoberts to complete model development and we will examine the accuracy of the model using validation data collected during the previous field season. Over the next year, we will work to develop a web platform and/or mobile app that can be used by growers as a tool for management decisions. After the model is validated with data collected this summer, we will work to develop an online platform that will allow growers to understand the field-level risk of southern blight on their operation. Additional resources, including crop rotation findings and chemical trial results will also be made available online for growers to access. After harvest soil samples were collected this fall and will be processed this fall and winter. Multiple years of data collected on the impact of crop rotation on sclerotia density will provide a robust data set to better understand options for growers to reduce the A. rolfsii inoculum in their soils.
Impacts
What was accomplished under these goals?
Objective 1- Determine growth thresholds for A. rolfsii in a laboratory setting:Towards this objective I conducted growth assays of sclerotia at varied temperatures from multiple crops &locations throughout the Central Valley.These propagules are the key driver of southern blight,caused by Athelia rolfsii. Isolates were collected from various crops including potato,tomato,sunflower, &sweet potato.Isolates were evaluated at 10 °C, 15°C, room temperature, 35 °C, & 40 °C.Assays of 10 isolates have been completed, & all isolates have been assayed in 2 experimental replicates.We determined that germination is favored above 10 °C & below 37 °C &germination occurs most quickly around 30 °C. Several isolates were able to germinate at high temperatures,but germination was not 100%.After 2 weeks at 40 °C, sclerotia also lost viability &were no longer able to germinate at a rate of 100%.Differential germination rates at high temperatures indicated that we will need to use an average temp. response for the lab-based model.Additionally,we validated the temperature response of isolates with field soil using a methanol method which prompts the germination of A. rolfsii sclerotia &prevents the germination of other fungi.For validation, soils was collected from a field with known southern blight at a sampling depth of 3" (the depth at which A. rolfsii sclerotia are known to germinate).In this assay, sclerotia did not germinate at 12 °C, but they did germinate at room temperature.Using field soil, no sclerotia germinated at 40°C.The work completed on this objective has led to an important change in knowledge regarding the specific conditions that are favorable for the germination of A. rolfsii sclerotia.This knowledge may lead to a change in action regarding management &will inform our lab-based model.We also learned that model development will need to be based on an average response of multiple isolates.This fall, we will work to develop the lab based model &compare the results with our field-based findings.We have also collected additional field soil samples this summer, &we will use this soil to further validate the model. Objective 2- Develop a model to predict the risk for southern blight in tomato &potato:I collected information on disease progression in addition to temperature &moisture in two potato fields in 2020 &2021 in plots nested within an integrated management trial in San Joaquin County &Kern County. Potato tubers were evaluated for disease prior to desiccation (when herbicide is applied to the field),just before rewetting (when moisture is applied to the field before harvest), &at harvest, along with yields.We found a 2.5-fold increase in disease that corresponded in accumulated with degree days between our pre-desiccation &harvest evaluation, indicating a key window was identified for southern blight management.In 2020,2 tomato fields were, similarly monitored for southern blight development in a grower field in Yolo County &a field at Shafter Ag. Research Facility.However,in 2020,we did not have disease pressure in the field located in Yolo County & the research site in Kern experienced a canopy collapse due to a viral disease.This confounded southern blight disease assessments.In 2021, we scouted for disease &monitored temperature & moisture conditions in two additional fields,1 in Sutter &1 in Yolo counties.This year, we were able to collect data in the 2 fields on temperature,moisture, &disease incidence.In addition to data collection for model development, in our potato trials in 2020 &2021, we had separate, replicated plots that we used to collect data for model validation.These plots were monitored at the same time as our model development plots.These data will be used to test the accuracy of the model developed using the model generation plots.We now have a better understanding of the primary risk windows for southern blight in annual crops.The risk window corresponds with end of season practices such as desiccation & rewetting.This presents valuable & new information on treatment timings to control for southern blight.This fall &winter,I will work in collaboration with Dr. Neil McRoberts to complete model development &we will examine the accuracy of the model using validation data collected during the previous field season. Objective 3:Implement the model for integrated management of southern blight in annual rotations: Based on observations in the lab &field & our understanding of A. rolfsii biology,we determined that a key window for southern blight development in potato is near the end of season,at rewetting.At rewetting, the ground has warmed due to a lack of canopy from desiccation &additional moisture is added to the field. In 2020, we applied the fungicides Elatus (9.5 oz per acre), Quadris (14 fl oz per acre), & Miravis (11.4 fl oz per acre)&ammonium bicarbonate (17lbs per acre) at rewetting. Both Quadris &the low rate of ammonium bicarbonate applied at the end of the season reduced southern blight compared to the untreated control.However,yields were not different between treated &untreated plots.In 2021 we trialed ammonium bicarbonate at a low rate (25 lbs),ammonium bicarbonate at a higher rate (100 lbs) sodium bicarbonate (25 lbs), Quadris at desiccation (14 fl oz), Pyrazaflumid at rewetting (4.5 fl oz), Quadris at rewetting (14 fl oz), & Quadris (14 flz oz) at desiccation with ammonium bicarbonate at rewetting (25 lbs). Interestingly,all chemicals reduced the incidence of all diseased tubers at harvest. In 2021,all treatments yielded higher than the control treatment &several appear to be significant based on SE (analysis pending):Quadris at desiccation with ammonium bicarbonate at rewetting (86.26 CWT/ac difference); sodium bicarbonate at a low rate(115.55 CWT/ac difference) ammonium bicarbonate at a higher rate (150.02 CWT/ac); &Quadris at rewetting (135.19 CWT/ac difference).To better understand the impact of crop rotation on southern blight risk, we collected soil at the beginning &end of the season from 15 crops in 2020 &2021:brassica & cucurbit seed production fields, tomato,sunflower,corn,onion,potato rice,fallow fields &beans.Soil was collected from the top three inches (the depth from which sclerotia germinate) &assayed with methanol.The number of germinated sclerotia were counted in each methanol tray. All soil from 2020 has been assayed, &soil from 2021 is currently be processed.We have found that increased in sclerotia number are greater in some crops than others.For example,sclerotia numbers increased by 11 fold after rotations with onion but decreased after rotations with tomato.While many crops are susceptible to southern blight,infections on certain crops may not cause as much inoculum to occur in the soil. Additional data are needed to evaluate how consistent these trends are.This objective has already resulted in a more targeted understanding of when to best manage southern blight,particularly in potato. Effective chemical applications during the desiccation &rewetting period in potato will allow growers to reduce yield losses from southern blight.We are generating helpful data on effective crop rotations to reduce inoculum in the soil from southern blight.We will work to develop an online risk tool that will allow growers to understand the field-level risk of southern blight on their operation.Additional resources, including crop rotation findings will also be made available online for growers to access.After harvest soil samples were collected this fall &will be processed this fall &winter.Multiple years of data on the impact of crop rotation on sclerotia will provide a robust data set to better understand options for growers to reduce A. rolfsi inoculum.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
McCaghey, M., Helpio, E.L., McRoberts, N., Sidhu, J., Aegerter, B.J. and Swett, C.L., 2020. Understanding the ecobiology of Sclerotium rolfsii, as a tuber rot of potatoes, to develop disease forecasting tools for chemical management. Plant Health 2020 Online.
- Type:
Conference Papers and Presentations
Status:
Awaiting Publication
Year Published:
2021
Citation:
McCaghey, M., McRoberts, N., Aegerter, B., Sidhu, J., Helpio, E., and Swett, C., 2021.
Identifying target control periods to optimize southern blight management in California specialty potato production
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