Sweet orange fruit susceptibility to infections of Phyllosticta citricarpa and validation of CRI-PhytRisk system for citrus black spot under Brazilian conditions

Abstract

Citrus black spot (CBS) caused by Phyllosticta citricarpa is the main fungal disease in important citrus growing areas, such as Brazil and South Africa. The fruit susceptibility period to infection by Phyllosticta citricarpa has been reported as variable in different areas of the Southern Hemisphere; however, there is no a consensus on this subject. A field trial "Susceptibility of sweet orange fruit to infection by Phyllosticta citricarpa" (FAPESP 2018/14514-0 item 3.2) has been conducted under Brazilian conditions, and a similar experiment need to be performed in South Africa in order to compare the data from both countries. The experiment will be conducted in South Africa by Regis Fialho in partnership with the team of Citrus Research International (CRI) and the Department of Plant Pathology, Stellenbosch University, supervised by Dr. Paul Fourie and Dr. Providence Moyo. In addition, this project aims to help researchers at CRI improve and validate a CBS system called CRI-PhytRisk. This system was developed by CRI for indicate when the weather is perfect for spraying orchards and when conditions are favorable for CBS infection under South Africa conditions. Thus, the project will be focused on the conduction of the field trials and also on the validation of the mathematical model used in CRI-PhytRisk in order to understand the different variables that affect the CBS cycle in both countries. Researchers from South Africa are specialists in epidemiological modeling in the CBS pathosystem, and they have studied the interaction between the disease and the climate for several decades, since the first report there was in 1929. In Brazil, the CBS was detected in 1990' and the management of the disease was based on the SA recommendations. However, recent studies conducted under Brazilian conditions have demonstrated that some differences on weather can determine the strategy to be used for CBS control. It is expected that the results obtained in our studies could help citrus growers to control CBS only at the critical periods, in which the climatic conditions are favorable for greater inoculum production and the fruit are susceptible to the pathogen infections. (AU)