DEVELOPING DOWNY MILDEW RESISTANT IMPATIENS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1017868
• Project Start Date: Oct 5, 2018
• Project End Date: Sep 30, 2021
• Program Code: [(N/A)]- (N/A)

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
Horticulture

Non Technical Summary
Impatiens walleriana, the busy Lizzy or garden impatiens, was the most popular annual plant for home gardens and landscaping prior to 2011. In New York, this plant had more than $10 million in sales in 2009. However, Impatiens Downy Mildew (IDM) appeared and changed this. This devastating disease was introduced to the United States via a hurricane from Africa; its prolific spores then spread up the east coast on prevailing winds, and eventually infected the entire country. By 2011, the infection had spread and been reported across the nation. By 2014 the value of impatiens in New York had dwindled to only $1 million.The impatiens plant has the ability to grow and flower in full sun or in shade. It has diverse flower colors including red, pink, rose, white, orange, and purple. By losing this diverse and popular plant due to the new disease, the economy of the United States was dramatically affected. Greenhouse growers and wholesale and retail nurseries were damaged commercially.The financial impact of this new disease, the Impatiens Downy Mildew, has had on the greenhouse industry has confirmed the need to conduct a breeding program for the development of impatiens hybrids that are resistant to the disease. To meet this need, Cornell University has begun a research project to identify impatiens species that are resistant to Impatiens Downy Mildew. Just recently, there were 2 impatiens plants that were produced from this endeavor that are resistant to the new disease. These 2 plants will be cross pollinated and self-pollinated with each other to produce intraspecific hybrids. The new plants will be grown outside in field conditions and exposed to Impatiens Downy Mildew. Plants that survive the attack will be used for further breeding and will again be self-pollinated and cross-pollinated to generate seeds. New plants that arise from this hybridization will be grown in the greenhouse and field-planted during the summer. Field plants from this second generation will be evaluated to see if they are resistant to the disease. Eventually, homozygous lines will be cross pollinated to generate F1 hybrids. The F1 hybrids will also be field tested for resistance to the Impatiens Downy Mildew. If successful, new, resistant cultivars of Impatiens will introduced to the American green industry for commercial introduction. Eventually, these seed-propagated plants will be available to the home gardener and professional landscaper and greenhouse grower.

Animal Health Component

50%

Research Effort Categories

Basic

(N/A)

Applied

50%

Developmental

50%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
201	2123	1081	40%
202	2123	1081	40%
216	2123	1081	20%

Knowledge Area
216 - Integrated Pest Management Systems; 202 - Plant Genetic Resources; 201 - Plant Genome, Genetics, and Genetic Mechanisms;

Subject Of Investigation
2123 - Bedding/garden plants;

Field Of Science
1081 - Breeding;

Keywords

plant breeding

plant propagation

plant tissue culture

disease resistance

plant micropropagation

disease tolerance

garden flowers

Goals / Objectives
Prior to 2011, Impatiens walleriana was one of the most popular annual flowers for gardens and landscaping. Their ability to grow and flower in full shade or sun, as well as the presence of a wide range of color forms, led to a large following among consumers, greenhouse growers, and garden centers, and formed a significant part of the economy for greenhouse growers. However, Impatiens Downy Mildew (IDM) appeared and changed this. By 2011, the infection had spread and been reported across the nation. While New York State had reported over $10 million in sales of common impatiens in 2009, by 2014 this had dwindled to only $1 million. This virulent new race of IDM has decimated impatiens plants across the country. Impatiens is a key crop for greenhouse growers and nurseries, and a fixture in landscapes and home gardens, but susceptibility appears to be near-universal. There is a critical need for breeding research with Impatiens to develop resistance to IDM. In 2015, we successfully confirmed that an Impatiens walleriana can be hybridized with other resistant species of Impatiens to develop impatiens plants that are resistant to IDM. The next step in this important research is to continue this breeding research and develop seed-propagated lines of Impatiens that are resistant to IDM. The new plant products that will be generated from this research will have great potential for the ornamental horticulture industry. By developing new resistant varieties and releasing them to the American market, they will be able to fill the void left by current impatiens cultivars.Objectives.1. To take two existing lines of Impatiens walleriana plants that have been developed at Cornell University, and that are resistant to Impatiens Downy Mildew, and successfully hybridize them into seed-propagated lines of plants that are attractive and resistant to the disease.2. To assess the success of the breeding process for the development of new flower colors and plant forms, as well as the resistance of seed-propagated plants to Impatiens Downy Mildew.3. To present information on downy mildew resistant varieties to gardeners, growers, extension personnel, and representatives from the horticulture industry. And, to evaluate the popularity and consumer appeal of the new hybrids with these stakeholders.

Project Methods
In 2015, we successfully produced two interspecific hybrids of Impatiens that are resistant to attack from downy mildew and that look and grow like I. walleriana. Remembering that the ultimate goal of this project is to produce seed-propagated lines of Impatiens that are IDM-resistant, the next step is to demonstrate that this resistance is genetically transferred. These plants will be self-pollinated and cross-pollinated to allow segregation to occur.This is accomplished by self- and cross-pollinating these 2 plants to allow segregation to occur. During preliminary research in 2016, we produced the first batch of hybrids from the self-pollinations; the resulting plants were very diverse and have a range of flower colors from red, rose, pink, purple, orange, and white. These plants were vegetatively-propagated and half of each line were moved to Long Island for field testing during the summer of 2017. There were 3 replications per clone and approximately 100 difference accessions that were evaluated. Thirteen I. walleriana hybrids displayed strong IDM-resistance, showing no symptoms despite the presence of the IDM disease. This demonstrated that resistance to IDM is genetically transferred. The hybrid Impatiens plants that remain in Ithaca will continue to be self-pollinated to produce the next generation of plants. The two lines of original IDM-resistant Impatiens plants will also continue to be self-pollinated. Each new generation of plants that will be generated, will be vegetatively-propagated and evaluated for their resistance to IDM. Successfully resistant plants will be used for further breeding. By using these downy mildew resistant I. walleriana hybrids as parents, it is possible to search for particularly resistant progeny in the segregating F2 population. After finding multiple notably resistant progeny, it will then be possible to begin to introgress more resistance or new traits into the plants and to develop seed-propagated lines that would be commercially desirable. In all research that follows, new hybrid plants will be confirmed to be resistant to Impatiens Downy Mildew by comparing hybrid plants to I. walleriana, the susceptible control, and I. hawkeri and Impatiens 'Bounce' as resistant controls. Data will be collected on their resistance to IDM similar to what was conducted for the first 2 resistant lines. Two ranking systems from 0 to 5 have been established to evaluate field plants. These ranking systems evaluate the appearance of the plants and the degree to which they are attacked by IDM. A new plant that is not popular with the consumer is of little value. Therefore, consumer appeal of the new hybrids will be evaluated through meetings with growers and representatives from the floriculture industry, and an Advisory Board of New York greenhouse growers. Finally, information on resistant Impatiens species will be prepared and presented to gardeners, growers, extension personnel, and representatives from industry through popular press outlets (newspapers, growers' magazines, extension bulletins, etc.), presentations, publications, and websites. In addition, peer-reviewed journal articles will be used to present the more detailed data. This will be supplemented with presentations and posters at professional and non-professional conferences.

Progress 10/05/18 to 09/30/21

Outputs
Target Audience:Our stakeholders in New York are the target audience, especially the greenhouse growers and nursery outlets that sell impatiens plants, the Long Island Flower Growers' Association (LIFGA), the New York Farm Bureau and especially the Long Island Farm Bureau, Long Island Nursery & Landscape Association (LINLA), the Nassau Suffolk Landscape Growers Association (NSLGA), and all consumers of garden and greenhouse plants. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided training to undergraduate and graduate students and technical staff, as well as the principal investigator. Student interns from other universities and students from Cornell University have worked on this project and have gained valuable training and experience with a new, innovative technology. How have the results been disseminated to communities of interest?Results have been disseminated by presentations at scientific meetings, seminars, educational programs, classroom presentations, and extension/outreach activities. The horticultural industry in the state of New York and its stakeholders have been informed at twilight meetings, open houses, and field days, mostly through their association with Cornell University's Long Island Horticultural Research & Extension Center. They became aware of the research through these activities and were able to comment on the research. Specific to this project, members of the Long Island Flower Growers Association and the Greenhouse Program Working Team (GHPWT) were involved. They were asked to participate in the design and evaluation of the research. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Back in 2015, we successfully produced two interspecific hybrids of Impatiens that are resistant to attack from downy mildew and that look and grow like I. walleriana. These two plants were the beginning of the production of an entire series of plant that are resistant to Impatiens Downy Mildew (IDM). The two original resistant plants were self-pollinated and cross-pollinated to allow segregation to occur. These crosses produced hybrid impatiens plants. The resulting plants were very diverse and have a range of flower colors from red, rose, pink, purple, coral, and orange. These plants were vegetatively propagated and field tested during the summers. Some of the hybrid plants were resistant to Impatiens Downy Mildew and others were not. These results confirmed that resistance to IDM is genetically transferred. Thirteen of the hybrid impatiens displayed strong IDM-resistance, showing no symptoms despite the presence of the IDM disease. The hybrid Impatiens plants continued to be self-pollinated to produce the next generation of plants. Each summer, the new generation of plants were vegetatively propagated and evaluated for their resistance to IDM. Successfully resistant plants were identified at the ends of the summers and susceptible plants were discarded. Resistant plants were used for further breeding. By using these downy mildew resistant I. walleriana hybrids as parents, it was possible to search for resistant progeny in the segregating F2 population. After finding multiple notably resistant progeny, it was then possible to introgress more resistance or new traits into the plants and to develop seed-propagated lines that will be commercially desirable. In all of this research, new hybrid plants were confirmed to be resistant to Impatiens Downy Mildew by comparing hybrid plants to I. walleriana, the susceptible control, and I. hawkeri and Impatiens 'Bounce', the resistant controls. Data were collected on their resistance to IDM by using two ranking systems from 0 to 5. These ranking systems evaluated the appearance of the plants and the degree to which they are attacked by IDM. The outcomes from this project will be the introduction of new, seed-propagated varieties of Impatiens plants that are resistant to Impatiens Downy Mildew (IDM). These new varieties will have multiple colored flowers including red, rose, pink, orange, and purple. They will be able to replace the old impatiens plant that used to be the most popular garden and bedding plant, and renew the strong economic growth of this plant species. The introduction of these new plants will be popular with consumers of plants, and they will be an economic boost to the greenhouses and nurseries that grow annual plants. In addition, plant propagators and seed producers will benefit economically from the new products that are available.

Publications

• Type: Other Status: Published Year Published: 2021 Citation: Stephen, Conor and M.P. Bridgen. 2021. Micropropagation of hemp. Inside Grower. November. pp 18-19.
• Type: Other Status: Published Year Published: 2021 Citation: Bridgen, M.P. 2021. Breeding a More Disease-Resistant Impatiens. Greenhouse Grower. June pp. 24-25.
• Type: Other Status: Published Year Published: 2021 Citation: Bridgen, M.P. 2021. 2021 Grants Announced by the Friends of Long Island Horticulture. Suffolk Country Agricultural News. Vol. 106(5).
• Type: Other Status: Published Year Published: 2021 Citation: Bridgen, M.P. 2021. Changes in Farm Manager at Cornells LIHREC. Suffolk Country Agricultural News. Vol. 105(3).
• Type: Other Status: Published Year Published: 2020 Citation: Bridgen, M.P. 2020. Greenhouse Campaign Begins. Suffolk Country Agricultural News. Vol. 104(12):

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:Floriculture and greenhouse industries Ornamental plant industries Members of the Green Industries Members of the Cornell Gardeners and other homeowners Long Island Flower Growers Association (LIFGA) Long Island Nursery and Landscape Association (LINLA) Nassau Suffolk Landscape Growers Association (NSLGA) New York State Flower Industries (NYSFI) Long Island Arborists Association (LIAA) Changes/Problems:The world pandemic in 2020 slowed down progress on this project, but some good data were collected. Due to COVID-19 restrictions, we needed to hire less summer workers and less research was accomplished. This should improve in 2021. What opportunities for training and professional development has the project provided?This project has provided training to undergraduate and graduate students and technical staff, as well as the principal investigator. Student interns from other universities and students from Cornell University have worked on this project and have gained valuable training and experience with a new, innovative technology. A laboratory technician was hired to work on this project. She had no tissue culture experience and training in plant breeding or plant tissue culture. However, she quickly learned procedures in plant tissue culture and plant breeding. How have the results been disseminated to communities of interest?This is only the second year of this project and there was nothing to report here. What do you plan to do during the next reporting period to accomplish the goals?In addition to the self-pollinations, cross pollinations will be made between the plants that were developed in 2019. Since certain genetic traits are transferred from the seed parents (mother plants) and others are transferred from the pollen parents (father plants), reciprocal crosses will be made. Seeds will be collected from these plants and properly labeled to track the lineage, and plants will be grown from these seeds. Once seeds are collected and dried, they will be planted, germinated, and grown in 2 ½ inch pots in preparation for field planting. As seeds are removed from their envelope and planted, accession numbers will be assigned to each seed (future plant) and clear identification of the parentage for each accession number will be documented. The germination rate and viability will be determined for all crosses. This will determine if there is a problem with developing a seed-propagated line from these crosses. Preliminary studies in 2018 did not show any problems with these crosses, but larger numbers of hybrids will show a clearer picture to determine if there would be a problem. Seedlings will be grown for 4 to 6 weeks in 2 ½ inch plastic pots in the Cornell greenhouses in preparation for the next stage of research. During their growth, they will be fertilized on a weekly basis, inspected for insect infestations and treated accordingly, and pinched if necessary.

Impacts
What was accomplished under these goals? Impatiens walleriana, the common Impatiens, is a very popular ornamental bedding plant that is shade tolerant and available in a wide variety of bright flower colors and forms. The popularity of Impatiens makes them extremely important to the floriculture industry. Unfortunately, I. walleriana is very susceptible to a relatively new fungal disease called Impatiens Downy Mildew (IDM). This disease defoliates and kills entire plantings of Impatiens very quickly. In 2010, there were $151 million in sales of Impatiens in the United States. By 2011, IDM had spread across the nation and worldwide, and by 2012, sales were only a fraction of their previous value. The nationwide emergence of IDM caused losses in production that proved devastating to the bedding plant industry. In the past two years, there have been some cultivars of IDM-resistant Impatiens that have been introduced to the American market by commercial seed companies. However, there remains an imperative need to fill the market niche left by I. walleriana. Here at Cornell University, we are using traditional plant breeding procedures as a way to produce Impatiens that are resistant to IDM. Our strategy is to integrate resistance into the common impatiens by hybridizing with other native Impatiens species that are resistant to the disease. This procedure allows us to widen genetic diversity and increase the options for resistance. When we began this research, the first step was to collect a diverse population of Impatiens species from around the world. These plants were screened for durable resistance to IDM under controlled environmental conditions. From these studies, resistant species were identified for the breeding program. After identifying IDM-resistant species of Impatiens, the next step was to hybridize these resistant species with common impatiens to introgress resistance. Tissue culture, a process of growing plants on a nutrient medium under aseptic and controlled environmental conditions, was vital for this plant improvement activity. Because Impatiens plants have explosive seed pods, it is difficult to collect seeds from mature seed pods. To avoid this problem, the tissue culture technique called embryo rescue is being used. During this process, immature ovaries (seeds) from hybridized plants are removed from the mother plants approximately 13 days after pollination and placed in tissue culture until germination. After the seeds germinate and produce their cotyledonal leaves, they are removed from tissue culture, transplanted onto a greenhouse medium, and placed under intermittent mist system to acclimate and grow. These novel plants are grown in the greenhouses and asexually propagated to produce clones of each plant. When early summer arrives, they are planted outside in the field trials at Cornell University's Long Island campus where they are subjected to natural IDM. Planted among the new hybrid plants are commercial cultivars of Impatiens that are known to be susceptible to IDM; these are the control plants. At the end of the summer, resistant plants are identified and used for further breeding. In 2015, the first two interspecific hybrids of Impatiens that are resistant to attack from IDM were identified. These two noteworthy plants were cross pollinated and self pollinated to produce offspring. From these crosses, plants with a wide variety of flower colors and growth habits were produced. These offspring were also field tested for resistance to IDM and eventually a large number of attractive, resistant plants were produced. In order for these plants to be introduced to the commercial market, they would need to be vegetatively propagated. This kind of propagation adds an additional layer of complexity and expense to the greenhouse grower. Therefore, after discussing this situation with several New York greenhouse growers, the decision was made to continue with our breeding program with the ultimate goal to produce IDM-resistant Impatiens that are seed propagated. There have been several landmark discoveries during this breeding project. We have confirmed that IDM-resistance is genetically inherited with impatiens. We have shown that the popular Impatiens walleriana is compatible for cross-fertilization with other Impatiens species that are resistant to IDM and that the ornamental qualities of the common impatiens can be combined with the disease resistance of the wild relatives to produce improved plants. This past summer of 2020, we had some very exciting results from the field trials. Our research demonstrated that there is polygenic inheritance to IDM resistance with our Impatiens hybrids. This kind of inheritance indicates that two or more nonallelic genes are involved collectively in determining inherited resistance to IDM. This means is that resistance to IDM will possibly be greater than those resistant hybrids that are currently available. Currently, with the help of undergraduate and graduate students, our breeding of Impatiens continues. We plan to use the success of the past 6 years to continue breeding for new and more diverse forms of Impatiens that are both resistant to IDM and seed propagated.

Publications

• Type: Journal Articles Status: Published Year Published: 2019 Citation: Sax, Miles Schwartz., Nina Bassuk, Mark Bridgen. 2019. Tissue Culture Clonal Propagation of Hybrid White Oak Cultivars for The Urban Environment. HortScience 54(12): 22142223.
• Type: Other Status: Published Year Published: 2020 Citation: Bridgen, M.P. 2020. $110,000 Endowment Established at Cornells Long Island Horticultural Research and Extension Center. Suffolk Country Agricultural News. Vol. 104(6):17.
• Type: Other Status: Published Year Published: 2020 Citation: Bridgen, M.P. 2020. Join your Friends in Agriculture for Dinner. Suffolk Country Agricultural News. Vol. 104(2):20.
• Type: Other Status: Published Year Published: 2019 Citation: Bridgen, M.P. 2019. Gardens of London and the Chelsea Flower Show  May 17-23, 2020. Suffolk Country Agricultural News. Vol. 103(12):8.
• Type: Other Status: Published Year Published: 2019 Citation: Bridgen, M.P. 2019. Ray Bell Establishes a $100,000 Endowment at Cornell Universitys LIHREC. Suffolk Country Agricultural News. Vol. 103(11):3.

Progress 10/05/18 to 09/30/19

Outputs
Target Audience:The target audience is our stakeholders in New York, especially the greenhouse growers and nursery outlets that sell impatiens plants, the Long Island Flower Growers' Association (LIFGA), the New York Farm Bureau and especially the Long Island Farm Bureau, Long Island Nursery & Landscape Association (LINLA), the Nassau Suffolk Landscape Growers Association (NSLGA), and all consumers of garden and greenhouse plants. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A laboratory technician was hired to work on this project. Her name is Agnieszka Ulinski; shehad no tissue culture experience and training in plant breeding or plant tissue culture. However, she quickly learned procedures in plant tissue culture and plant breeding. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals?In addition to the self-pollinations, cross pollinations will be made between the 2 IDM-resistant plants: #222 and #219. Care will be taken to ensure reciprocal crosses are made in order to have #222 as both a seed parent and as a pollen parent, and #219 as both a seed parent and as a pollen parent. Since certain genetic traits are transferred from the seed parents (mother plants) and others are transferred from the pollen parents (father plants), reciprocal crosses will be made. Seeds will be collected from these plants and properly labeled to track the lineage, and plants will be grown from these seeds. Once seeds are collected and dried, they will be planted, germinated, and grown in 2 ½ inch pots in preparation for field planting. As seeds are removed from their envelope and planted, accession numbers will be assigned to each seed (future plant) and clear identification of the parentage for each accession number will be documented. The germination rate and viability will be determined for all crosses. This will determine if there is a problem with developing a seed-propagated line from these crosses. Preliminary studies in 2017 did not show any problems with these crosses, but larger numbers of hybrids will show a clearer picture to determine if there would be a problem. Seedlings will be grown for 4 to 6 weeks in 2 ½ inch plastic pots in the Cornell greenhouses in preparation for the next stage of research. During their growth, they will be fertilized on a weekly basis, inspected for insect infestations and treated accordingly, and pinched if necessary.

Impacts
What was accomplished under these goals? Back in 2015, we successfully produced two unique, interspecific hybrids of Impatiens plants that are resistant to attack from downy mildew and that look and grow like I. walleriana. Remembering that the ultimate goal of this project is to produce seed-propagated lines of Impatiens that are IDM-resistant, the first objective was to self-pollinate and cross-pollinate these 2 plants to produce hybrid seeds. By self- and cross-pollinating these 2 heterozygous plants, seeds will be produced that will visibly show what kind of segregation is occurring in the offspring. The primary observations from this process will be resistance to IDM and flower color. We conducted preliminary studies with this in 2016 and the offspring had flower colors of red, rose, pink, purple, orange, and white. Field trials during the summer of 2017 demonstrated that the trait for resistance to IDM is genetically transferred and stable. By using these downy mildew-resistant I. walleriana hybrids as parents, it is possible to search for resistant progeny in the segregating population. After finding multiple, notably resistant progeny, later it will be possible to begin to introgress more resistance or new traits into the plants and to develop seed-propagated lines that would be commercially desirable. Therefore, the first Performance Target was to produce seeds from our 2 IDM-resistant parent plants by self-pollinating and cross-pollinating them. Each of the two IDM-resistant plants were asexually propagated by stem cuttings to produce sufficient numbers of mother plants to pollinate. With sufficient numbers of plants, we were able to self-pollinate both of the key, mother plants. Seeds were collected from these plants and properly labeled to track the lineage, and plants were grown from these seeds.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Nor Hisham Shah, N.K.A. and M. Bridgen. 2018. Inducing mutations in vitro of the Chaste Tree, Vitex agnus-castus, with the herbicide, Oryzalin (Surflan). Combined Proceedings International Plant Propagator's Society. Vol. 68.
• Type: Journal Articles Status: Published Year Published: 2019 Citation: Aros, D., M. Suazo, C. Rivas, P. Zapata, C. �beda, and M. Bridgen. 2019. Characterization of new hybrids of Alstroemeria originated from A. caryophylleae scented lines. Euphytica 215:93.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2019 Citation: Schwartz Sax, M., N. Bassuk, M.P. Bridgen, and K. Nixon. 2019. Tissue Culture Clonal Propagation of Hybrid White Oak Cultivars for The Urban Environment. HortScience.
• Type: Book Chapters Status: Published Year Published: 2018 Citation: Bridgen, M.P. 2018. Plant Tissue Culture Techniques for Breeding. In: Johan Van Huylenbroeck, (Ed). Handbook of Plant Breeding: Ornamental Crops. Springer Publishers. Vol 11: 127-144.
• Type: Book Chapters Status: Published Year Published: 2018 Citation: Bridgen, M.P. 2018. Breeding Alstroemeria. In: Johan Van Huylenbroeck, (Ed). Handbook of Plant Breeding: Ornamental Crops. Springer Publishers. Vol 11: 231-236.