Historical 1929 and 1930 phony peach disease (caused by Xylella fastidiosa) incidence data and relationships to physical variables and climatological data

Authors: BRANNEN, PHILLIP - University Of Georgia; Bock, Clive

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 11/29/2022
Publication Date: 12/12/2022
Citation: Brannen, P.M., Bock, C.H. 2022. Historical 1929 and 1930 phony peach disease (caused by Xylella fastidiosa) incidence data and relationships to physical variables and climatological data. Acta Horticulturae. Vol 1352:479-486.

Interpretive Summary: Phony peach disease (PPD) is caused by the bacterium Xylella fastidiosa subspecies multiplex (Xfm). The disease has caused yield loss in peach in Georgia (USA) since the first report of the disease in 1885. PPD spread to several peach production states in the southeastern USA. A federally-sponsored government eradication program was initiated in 1929, resulting in over a million PPD trees being destroyed by 1933. We analyzed latitude, elevation and long-term climatological data in relation to PPD incidence for 1929 and 1930. Results indicated that decreasing temperature, whether associated with latitude or elevation, was negatively associated with disease incidence. The results are useful to predict where PPD remains a threat in the USA, and where it will likely spread if introduced elsewhere. Other factors including vector species and abundance of alternative hosts could play a role in regional disease spread, so in addition to potential climatological effects, future research may further elucidate the mysteries associated with the PPD epidemic of ~100 years ago in the southeastern USA.

Technical Abstract: Phony peach disease (PPD), caused by Xylella fastidiosa subspecies multiplex (Xfm), has been a constant threat to peach (Prunus persica) production in Georgia (USA) since its first report in 1885. Subsequently, PPD spread to several peach production states in the southeastern USA. Arguably, the height of the epidemic in Georgia occurred in 1929, as a federally-sponsored government eradication program was initiated, resulting in over a million trees being destroyed by 1933. Fortuitously, records were preserved of PPD incidence by county in 1929 and 1930, allowing for accurate mapping of the incidence across the state at that time. While the relationship between environmental parameters and incidence of Pierce’s disease and almond leaf scorch have been studied, indicating that cold winter temperatures negatively impact disease establishment, environmental effects have not been explored for PPD. Relating climatological data to PPD incidence for 1929 and 1930, valuable insights can be determined with implications for modern epidemics. Latitude and elevation of each county geographic center was used for location, and long-term climatological data (30 y) was obtained for the period 1961 to 1990. Weather variables included total rain, min temp, mean temp, and max temp. Linear regression, stepwise multiple regression, and a principal component analyses were conducted. A synopsis of the results indicated that decreasing temperature, whether associated with latitude or elevation, was negatively associated with disease incidence. The results are useful in predicting where PPD remains a threat in the USA, and where it will likely spread if introduced to other international peach production regions. Other factors including vector species and abundance or alternative hosts could also play a role in regional disease spread, so in addition to potential climatological effects, future research may further elucidate the mysteries associated with the PPD epidemic of ~100 years ago in the southeastern USA.