Survival analysis of time to abscission of blueberry leaves affected by septoria leaf spot.

ABSTRACT In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (>/=5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were approximately 2 weeks shorter for the older leaf group and approximately 3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).

[1]  Frank E. Harrell,et al.  Regression Modeling Strategies: With Applications to Linear Models, Logistic Regression, and Survival Analysis , 2001 .

[2]  P. Allison.  Survival analysis using the SAS system : a practical guide , 1995 .

[3]  J. Effrey,et al.  Early and mid-fall defoliation reduces flower bud number and yield of southern highbush blueberry. , 2003 .

[4]  W. Vermerris,et al.  Time to flowering in brown midrib mutants of maize: an alternative approach to the analysis of developmental traits , 1999, Heredity.

[5]  R. D. Berger,et al.  The effects of rust and anthracnose on the photosynthetic competence of diseased bean leaves. , 2001, Phytopathology.

[6]  H. Scherm,et al.  Applications of survival analysis in botanical epidemiology. , 2004, Phytopathology.

[7]  R. Darnell.  PHOTOPERIOD, CARBON PARTITIONING, AND REPRODUCTIVE DEVELOPMENT IN RABBITEYE BLUEBERRY , 1991 .

[8]  J. Gardner,et al.  Seasonal development of septoria leaf blight in young Eucalyptus nitens plantations in New Zealand , 2002 .

[9]  J. Verreet,et al.  Regional Monitoring for Disease Prediction and Optimization of Plant Protection Measuares: The IPM Wheat Model. , 2000, Plant disease.

[10]  H. Scherm,et al.  Photosynthesis of Blueberry Leaves as Affected by Septoria Leaf Spot and Abiotic Leaf Damage. , 2004, Plant disease.

[11]  H. Scherm,et al.  Blueberry Production in Georgia , 2003 .

[12]  Bertrand D. Tanner,et al.  Automated weather stations , 1990 .

[13]  P. Lyrene.  Early defoliation reduces flower bud counts on rabbiteye blueberry , 1992 .

[14]  M. E. Austin.  Rabbiteye Blueberries: Development, Production, and Marketing , 1994 .

[15]  J. Williamson,et al.  Early and Mid-fall Defoliation Reduces Flower Bud Number and Yield of Southern Highbush Blueberry , 2002 .

[16]  Investigating leaf lifespans with interval-censored failure time analysis , 2003 .

[17]  Gary G. Koch,et al.  Categorical Data Analysis Using The SAS1 System , 1995 .

[18]  A. Sztejnberg.  Etiology and control of cherry leaf spot disease in Israel caused by Cercospora circumscissa , 1986 .

[19]  J. Lawless.  Statistical Models and Methods for Lifetime Data , 2002 .

[20]  A. Westra,et al.  Effect of interaction of inoculum dose, cultivar, and geographic location on the development of foliar symptoms of bacterial ring hot of potato , 1994 .

[21]  D. Peart,et al.  Dealing with death data: individual hazards, mortality and bias , 2003 .

[22]  Chung-li Chen,et al.  Partial vacuum storage improves the longevity of primed sh-2 sweet corn seeds , 2003 .

[23]  P. Paul,et al.  Relationships Between Angular Leaf Spot, Healthy Leaf Area, Effective Leaf Area and Yield of Phaseolus vulgaris , 2003, European Journal of Plant Pathology.

[24]  William D. Ritts,et al.  SPREAD OF AN INVASIVE PATHOGEN OVER A VARIABLE LANDSCAPE: A NONNATIVE ROOT ROT ON PORT ORFORD CEDAR , 2002 .

[25]  J. Williamson,et al.  A leaf bud development scale for rabbiteye blueberry (Vaccinium ashei reade) , 1998 .

[26]  D. Rosenberger,et al.  Effects of Management Practices and Fungicides on Sooty Blotch and Flyspeck Diseases and Productivity of 'Liberty' Apples , 1996 .

[27]  D. Layne,et al.  Physiological responses of Prunus cerasus to whole-plant source manipulation. Leaf gas exchange, chlorophyll fluorescence, water relations and carbohydrate concentrations. , 1993 .

[28]  L. Madden,et al.  Differential pathogenicity of corn stunting mollicutes to leafhopper vectors in Dalbulus and Baldulus species. , 1983 .

[29]  Felipe Arauz,et al.  Epidemiology and Control of Citrus Greasy Spot on Valencia Orange in the Humid Tropics of Costa Rica. , 1997, Plant disease.

[30]  Eric R. Ziegel,et al.  Survival analysis using the SAS system , 1995 .

[31]  W. Cline.  BLUEBERRY BUD SET AND YIELD FOLLOWING THE USE OF FUNGICIDES FOR LEAF SPOT CONTROL IN NORTH CAROLINA , 2002 .

[32]  T. Gottwald,et al.  Factors Affecting the Spread of Plum pox virus Strain M in Peach Orchards Subjected to Roguing in France. , 2004, Phytopathology.