Peach Rusty Spot Epidemics: Temporal Analysis and Relationship to Fruit Growth

Abstract

Incidence and severity of peach rusty spot were monitored throughout the growing seasons of 1999 to 2001. Graphical and statistical analysis revealed that disease increased from the shuckoff stage of fruit development until 60 days after full bloom; epidemics typically lasted from 17 to 30 days. An analysis of fruit growth indicated that the early-season epidemic coincided with the first stage of stone fruit development, physiologically characterized as the period of cell division. During this period, as fruit growth slowed and approached initiation of pit-hardening, the rate of disease increase slowed. Since fruit infection was greatest during the period of fruit growth, disease progression was modeled as a function of plant growth instead of time. Temporal analysis revealed that the logistic function was appropriate for describing both growth processes, and a synchronous logistic/logistic composite disease progression/fruit growth model was fit to all data sets. No change in disease levels occurred during midseason, which coincided with the second stage of fruit development, a period of slow growth. Subsequently, disease incidence and severity significantly declined on average by 26% and 1.3 lesions per fruit, respectively, during the 20 to 30 days prior to harvest. This decline phase coincided with the third stage of fruit growth, the period of cell enlargement and coloration. These disease reductions may be related to physical changes in fruit size and pigmentation, as opposed to resistance development, causing younger, less established lesions to become undetectable.

Using UV-C radiation and image analysis for fungus control in tomato plants

“…Traditionally, assessment of plant disease severity relies on visual inspection of plant tissue by trained raters [36][37][38][39][40]53], who categorize disease severity according to a discrete scale [31]. Disease symptoms often result from physiological changes that may alter the spectral pattern of the plant [54].…”

“…The growth of the lesion caused by the disease was measured calculating the growth rate of the lesion area through 10 days. The area of the lesion was determined classically [36][37][38][39][40] measuring the diameter of lesion with a caliper and assuming a circle-shaped lesion.…”

Peach Rusty Spot Is Caused by the Apple Powdery Mildew Fungus, Podosphaera leucotricha

“…The disease was first described in Idaho in 1941 (1) and then from other parts of the United States (7,8,26) and other countries (9,10). Fungicide treattnents were effective in disease management (12,21) in spite of iticonclusive information on the etiology of the disease. The apple powdery mildew fungus {Podosphaera leucotricha (Ellis & Everh.)…”

“…E.S. Salmon) was generally thought to be responsible for the symptoms (8,12,13,19,21,26,27) but additional, unidentified causal agents were also suspected to play a role in this disease (12,13,31). P. leucotricha was considered to be the rusty spot pathogen because the disease occurred mainly on peach trees planted close to apple orchards infected by P. leucotricha (8,26,27) and powdery mildew tnyceliutn was sometimes found on symptomatic peach fruit (7,26).…”

Evaluation of hydrophobic and hydrophilic kaolin particle films for peach crop, arthropod and disease management

“…Assessment of peach rusty spot, caused by the apple powdery mildew pathogen P leucotricha , was performed in the EC orchard at harvest on 11 August 97; all fruit were harvested and evaluated. In the LG orchard, assessments were conducted at initiation of pit‐hardening on 1 June 98, 8 June 99 and 7 June 00, which coincided with the end of the progressive phase of the epidemics 24. In 1998, a total of 25 fruit was arbitrarily picked from throughout the canopy of each tree, while in 1999 and 2000, a total of 40 fruit was similarly harvested.…”