Soil temperatures 4 inches below the surface have reached or reliably exceeded 65 degrees, signaling freedom from cold temperature damage for warm-season crops. Corn planting and pepper and tomato transplanting are likely in full swing.

Planting season brings with it the anticipation of bountiful and attractive fruits and vegetables. For many home gardeners, the “perfect tomato” represents a successful gardening season.

Unfortunately, many tomatoes, which appear to be ripening toward the prized outcome, develop dark, sunken pits at the blossom end of the fruit not long after flowering. Called blossom-end rot (BER), this physiological disorder is prevalent in fruit and vegetable crops, including tomatoes, and can cause severe economic losses.

A $475,000 grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture is supporting University of Georgia researchers who are examining genetic and physiological factors which may contribute to the development of BER. Identification of causal mechanisms would lead to better prevention and mitigation practices to limit or eliminate the disorder.

Assistant research scientist Savithri Nambeesan, who specializes in ripening and postharvest physiology in the UGA Department of Horticulture at the College of Agricultural and Environmental Sciences, will lead the study to compare the genetic traits of tomato lines that are susceptible and resistant to BER. Researchers will use genetic mapping to identify the regions in the tomato genome that cause or lead to BER. The project will also examine developmental and molecular processes contributing to the disorder.

“If we can find the factors that lead to BER, we can use that information to tailor management practices to minimize the disorder,” said Nambeesan, who is working on the project with horticulture professor and plant geneticist Esther van der Knaap, who has done extensive work on tracing tomato genomes.

Nambeesan said the disorder is influenced by genetic, developmental and environmental factors, so the study will combine molecular and developmental approaches to understand potential causes.

“Currently, the underlying cause of BER is thought to be due to calcium deficiency, but current field management strategies to correct that via irrigation and calcium fertigation have met with limited success. Generating more basic information on this disorder will help with breeding cultivars that are BER-resistant or provide more tailored management strategies to minimize this disorder,” she said. “We will determine if BER can occur in fruits that grow relatively fast during their development and therefore have a higher demand for calcium. Fruit receive their calcium through vascular tissues such as xylem, and therefore investigating how the xylem develops during fruit development may be critical in understanding calcium translocation into the fruit.”

Because BER is related to several interacting factors, an integrated approach will be required to find the underlying cause of BER in tomatoes. Because greater genetic and genomic resources are available with tomatoes, they are the best model system for research. Improved understanding of factors affecting tomatoes will lead to knowledge applicable to other crops that are also subject to BER losses including pepper, watermelon, squash and eggplant.

“If we can tackle the problem using two approaches in molecular physiology — how fruit growth rates and xylem development tie into subcellular calcium localization — we can find the causative factors for it and we can address it more effectively,” she said. “We also are taking a two-pronged genetic approach, identifying certain loci that are involved in blossom end rot and finding genes in the genome to develop lines that are resistant.”

The U.S. tomato crop was valued at more than $1.6 billion in 2019. In severe cases, BER can cause crop losses of up to 50% of the total yield in affected fields. Solutions that limit damage from BER could provide significant economic benefits for commercial growers.

For home gardeners, the development of resistant varieties represents the best hope for limiting losses to BER. Until improved germplasm is available, prevention may be the best approach. Limiting BER begins with maintaining proper soil pH and nutrient availability. Corrections of soil test calcium are best made before planting. Other nutrients, particularly nitrogen and potassium, will compete with calcium for plant uptake. Excessive fertilization with nitrogen or potassium should be avoided. Moisture stress caused by either insufficient or excessive water may also contribute to BER. Tomatoes and other crops susceptible to BER should be planted in sites where soil drainage is sufficient to prevent water-logging. Irrigation must be managed to prevent stress from dry conditions.

Blossom-end rot has been a frustratingly difficult disorder to understand and manage. New research may hold the key to coordinated solutions.

Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at roger.gates@uga.edu.

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