Over 50% of the Concord vineyards in central Washington State suffer from iron (Fe) chlorosis. Once a vineyard region displays chlorotic symptoms, the area remains affected year after year, leading to diminished fruit yield and quality. Chlorotic symptoms initially appear around bloom and eventually lead to leaf necrosis. Concord chlorosis resembles typical Fe deficiency, common in calcareous high pH soils of vineyards and orchards worldwide

            While iron is abundant in soils, its bioavailability is highly pH dependent, with minimum solubility near neutral to alkaline pH. At higher pH, it is poorly to non-soluble and unavailable for plant uptake. Plants and microorganisms employ various strategies to convert Fe into a soluble form for uptake. Microorganisms produce organic acids and siderophores to combat Fe deficiency. Siderophores are low molecular weight organic ligands with an extremely high affinity for Fe³⁺ .  These microbial siderophores may enhance or decrease Fe availability for the plant depending on the type and quantity excreted.  Microorganisms also provide a host of other plant-growth promoting phytochemicals in the rhizosphere.

            This study will compare the capacity for the rhizosphere microbial isolates associated with chlorotic and healthy Concord grape vines in central Washington to secrete organic acids, siderophores, and perform plant-growth promotion activities. We intend to identify rooting-zone microbial communities that may be beneficial to grape Fe nutrition and vine growth characteristics. In the long-term, we hope to provide a more sustainable and cost effective alternative to the application of synthetic Fe chelates. Given that Washington is the nation’s top producer of Concord juice grapes, with a production value of over $60 million, it is critical to the industry’s economic viability to remedy this condition.