Breeding a more disease-resistant impatiens

In 2010, there were $151 million in sales of impatiens in the U.S. 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 North 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 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. ? Identifying Ideal SpeciesWhen 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 an 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.