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Chloride Effects on Water Potentials and Yield of Winter Wheat Infected with Take-all Root Rot¹

Severity of take-all root rot (caused by Gaeumannomyces graminis var. tritici) of winter wheat (Triticum aestivum L.) has been decreased in the Willamette Valley of western Oregon by applying Cl containing fertilizers. Apparent increases in leaf turgor of field grown wheat following spring topdressing with NH₄Cl fertilizer suggested that Cl salts affect plant water potential components. Since the growth rate of G. graminis tritici declines with declining water potential, changes in plant water potential could influence the rate of host colonization by the pathogen. Leaf water (), osmotic (), and turgor (P) potentials of winter wheat grown in replicated field trials on an Argiaquic Xeric Argialboll, an Aquultic Argixeroll, and a Pachic Ultic Argixeroll fertilized in March with 135 to 140 kg N/ha as (NH₄)₂SO₄ or NH₄Cl were measured in May and June to ascertain whether application of Cl salts influences water potential components in wheat. Fresh plant weight at milky ripe stage, grain yield, and grain kernel weight were measured to evaluate treatment effects on yield of wheat infected with take-all root rot.

Applying 342 and 355 kg Cl/ha as NH₄Cl reduced in ‘Yamhill’ and ‘Stephens’ winter wheat leaves measured in May by 4 and 2 bars, respectively. Chloride treatment effects on ‘ generally persisted through June. The slope of the regression of ‘ on percent Cl in leaf tissue at one site was the same as that predicted by the van't Hoff equation indicating that increased symplasm Cl concentration probably accounted for the measured change in ‘. Leaf water and turgor potentials tended to be lower and higher, respectively, when these parameters were influenced by Cl treatment.

Use of NH₄Cl fertilizer increased grain yields from 770 to 2,150 kg/ha (11 to 40%) over those obtained with (NH₄)₂,SO₄. Fresh weight yield and kernel weight were also increased with NH₄Cl fertilization. Application of (NH₄)₂SO₄ plus KCl or NaCl(lO1, kg Cl/ha) at one site increased grain yield and kernel weights over those obtained with (NH₄)₂SO₄ alone.

Results of this study suggest that the susceptibility of winter wheat plants to G. graminis tritici colonization may be reduced by lowering the chemical potential of water in the plant. Because the osmotic potential in wheat plants changes readily with Cl application, fertilization with Cl salts provides an opportunity to actively manage plant water potential components for the express purpose of take-all root rot suppression.

Key Words: Triticum aestivum L. vars • Yamhill and Stephens • Gaeumannomyces graminis var. tritici • Take-all root rot • Leaf water potential • Turgor potential • Osmotic potential • Osmoregulation

² Assistant professor, graduate research assistant, professor, and graduate research assistant, respectively.

Received for publication November 21, 1980.

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