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United States Department of Agriculture

Agricultural Research Service

Title: Chemical and Cultural Approaches to Enhance Host Resistance to Fire Blight: Growth Regulators

Authors
item Miller, Stephen
item Yoder, K. - VIRGINIA TECH

Submitted to: Fire Blight - History, Biology and Control Management
Publication Type: Book / Chapter
Publication Acceptance Date: November 20, 2006
Publication Date: N/A

Interpretive Summary: Fire blight is a very destructive and common disease in apple and pear trees. The disease is caused by a bacterium that attacks blossoms and young vigorous shoots several weeks after bloom. Recent research has demonstrated a very positive effect of the plant growth regulator, prohexadione-calcium on suppressing the shoot blight stage of fire blight. This paper discusses this and other growth regulators and provides references as to the mode of action for prohexadione-calcium in the control of fire blight. This information provides a valuable reference source for students, growers and researchers in the study of fire blight.

Technical Abstract: Fire blight caused by the bacterium Erwinia amylovora [(Burrill) Winslow et al.] is one of the most destructive diseases in apple. Infection is initiated in the spring on flowers and with a second stage in late spring and summer termed shoot blight. Vigorous succulent growth favors fire blight infection. Suppressing shoot growth would appear to be one method of reducing the incidence of fire blight in apple. This paper reviews and discusses the use of plant growth regulators to suppress shoot growth and reduce the incidence and severity of fire blight in apple. Early studies with indoleacetic acid and daminozide produced marginal results. In the mid-1990s a new growth regulator, prohexadione-calcium (P-Ca), a gibberellin biosynthesis inhibitor, was evaluated for growth control and suppression of the shoot blight stage of fire blight. Studies between 1994 and 2000 demonstrated that P-Ca applied at 250 mg.L-1 soon after bloom was very effective in reducing the incidence and severity of shoot blight. P-Ca was registered for use to suppress the shoot blight stage of fire blight in the United States in 2000 and in Europe beginning in 2001. More recent studies indicate that P-Ca may have some activity against the blossom blight stage of fire blight. Studies have demonstrated the ability of P-Ca to trigger defense reactions against E. amylovora in both apple and pear through qualitative and quantitative changes in the spectrum of flavonoids and other phenylpropanoids. It is suggested that P-Ca acts as both a growth retardant and a phytoalexin when applied to apple.

Last Modified: 10/26/2014
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