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Crop Breeding for Trait Enhancement and Disease Resistance

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ARS advances multiple crop industries by developing new crop varieties with disease resistance and other trait enhancements and providing new tools and approaches that will support future breeding efforts. In addition to supporting major commodities, ARS breeding programs advance specialty crops, which alone have a U.S. farm gate value of $87.7 billion. The following accomplishments are examples of ARS advances in crop breeding for disease resistance and trait enhancement in FY 2019. Hyperlinked accomplishment titles point to active parent research projects.

New tomato flavor gene discovered. Tomatoes are the most valuable fruit crop globally and are among the most widely consumed fruit or vegetable in the United States at 70 pounds per capita annually. Tomatoes are also an important source of the antioxidant lycopene, which gives tomatoes their red color, and beta-carotene, which our bodies convert to vitamin A. However, many consumers complain that store-bought tomatoes lack flavor. ARS researchers in Ithaca, New York, identified a rare version of the TomLoxC gene that is prevalent in the wild ancestors of tomato but is absent from most cultivated lines, including the genome of Heinz 1706, the reference tomato genome sequence. TomLoxC contributes to tomato flavor by catalyzing the synthesis of aromatic compounds that taste panels show consumers really like. TomLoxC, while still rare, is seeing a resurgence in modern tomato varieties in parallel with a renewed interest in flavor by breeders attempting to address consumer demands.

World’s first red leaf spinach. Spinach has always been known as a green leafy vegetable. Although there are currently some red spinach cultivars on the market, the red color is limited to the veins of the leaves. ARS researchers in Salinas, California, developed ‘USDA Red’, the world’s first spinach variety with red color on the surface of the leaves. ‘USDA Red’ had 65 percent higher betacyanin content and 53 percent higher antioxidant capacity than red-veined spinach cultivars on average in field trials conducted between 2015 and 2018. The betacyanin adds another punch to a plant already loaded with phytonutrients, making spinach a true “super food.” The red spinach may bring some excitement to the spinach market and attract consumers to the colorful new product, helping increase the consumption of spinach and aid in the fight against obesity.

A new table grape. ARS researchers in Parlier, California, have released a new early season table grape named ‘Solbrio’ that has both exceptional eating quality and reduced needs for cultural input from growers. Consumers have shown a strong interest in the new variety because of its large berry size, crisp and crunchy flesh, and fully colored berries. Many of the standard—and expensive—cultural practices used to enhance characteristics of current table grape varieties were evaluated on the new variety, but none of the treatments produced a significant change on berry quality or yield. Hence, growers are very pleased with the new variety that is both easy and inexpensive to grow.

ARS supports U.S.-Pakistan Wheat Productivity Enhancement Program. In FY 2019, ARS received additional funding to support the U.S.-Pakistan Wheat Productivity Enhancement Program (WPEP). Initiated in 2011, WPEP has developed and released 35 high-yielding, disease-resistant wheat varieties to the farmers in Pakistan. Partners in Pakistan also monitor wheat fields for stem rust annually. Due to these early and aggressive efforts, the eastern spread of the deadly Ug99 strain of stem rust was halted before it could reach the massive wheat growing areas of India and China.

New seedling screening method for Phomopsis seed decay in soybean. Seed decay in soybeans caused by Phomopsis fungi can cause both yield and seed quality losses under some harvest conditions. Qualitative measurements of the disease can be extremely time consuming and expensive. In addition, Phomopsis seed decay is a seedborne disease and researchers must wait until after harvest to evaluate symptoms on the seed. A seedling inoculation and evaluation method to rapidly screen soybean for resistance to Phomopsis in the seedling stage has been developed by ARS researchers in Stoneville, Mississippi. Results from this innovative cut-seedling inoculation method were comparable to those obtained from tests conducted with mature seeds. This research can facilitate the identification of resistance to Phomopsis seed decay without having to wait for an entire growing season to conduct the seed assay. Also, this approach could provide a more uniform distribution of the pathogen on soybean seeds tested, thus reducing the chance of escapes, especially when the environmental conditions are not conducive to disease development. The method has been adopted by public soybean breeders at other laboratories in the United States and in China.

More efficient method for analyzing genetic data for tree breeding. Tree breeding requires long periods of plant growth and significant expenses of land and personnel. Genotyping trees at the seedling stage can increase the efficiency and reduce the costs of tree breeding by identifying the best parents for breeding crosses and the best resulting progeny. ARS researchers in Miami, Florida, and cooperators from Florida International University, University of Florida, and Department of Agriculture and Fisheries in Queensland, Australia, developed a more efficient method of analyzing DNA genotype data for mango and avocado germplasm and hybrids. This method can distinguish specific cultivars of interest from all other cultivars and identify self-pollinated individuals and the possible paternal parents of particular trees. Identifying self-pollinated individuals is particularly important because it can help uncover deleterious traits to eliminate from breeding stocks. With this method, breeders can determine the genetic content of breeding stock early at the seedling stage to optimize breeding efficiency and accelerate genetic gain.