Factors affecting the timing of abscission of peach and nectarine leaves infected with Xanthomonas arboricola pv. pruni
S. BARDSLEY (1), H. Ngugi (1), M. d. Jimenez-Gasco (1). (1) The Pennsylvania State University, University Park, PA, U.S.A.
Bacterial spot (caused by <i>Xanthomonas arboricola</i> pv. <i>pruni</i> [<i>Xap</i>]) is the most important bacterial disease of stone fruit in the eastern U.S. where yield limiting symptoms on fruit regularly reduce crop values in Pennsylvania. One often over-looked symptom, premature defoliation, ultimately reduces fruit quality and overall tree vigor. The objective of this study was to gain basic knowledge of the factors affecting premature defoliation as they relate to the current management strategies in PA. Data on bacterial spot severity and the time of leaf abscission were obtained on a 7 day interval in replicated field plots of four cultivars subjected to different bactericide programs in 2009. Survival analysis using the Kaplan – Meier and the accelerated failure time (AFT) models of time to leaf abscission was conducted in order to assess the effects of bactericide treatment, cultivar, leaf age, and initial disease onset on the survival of leaves infected by <i>Xap</i>. Of the leaves assessed for disease severity, 48% of them abscised before the end of the study. The mean time to leave abscission ranged from 41.8 to 56.3 days and was significantly (P < 0.0001) affected by cultivar, initial disease onset, and leaf age but not by bactericide treatment. The AFT model indicated that every additional 1% initial disease severity decreased the time to leaf abscission by 10.7%. These results indicate that strategies for bacterial spot management should focus on reducing initial disease.
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