Influence of temperature and wetness periods in Phyllosticta citricarpa ascospores and pycnidiospores germination

• Grant number: 22/15086-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2023
• End date: July 31, 2023
• Field of knowledge: Agronomical Sciences - Agronomy - Plant Health
• Principal Investigator: Lilian Amorim
• Grantee: Lorraine Binatti Durães
• Host Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

Phyllosticta citricarpa, the causal agent of citrus black spot (CBS), produces two types of spores: ascospores and pycnidiospores. Pycnidiospores are responsible for the secondary cycles of the disease, while ascospores are responsible for both primary and secondary cycles. There are few studies on the environmental conditions favorable to ascospores germination due to the difficulty to produce ascospores in vitro. Recently, protocols for the production of ascospores and the verification of mating types were published, and both were validated in Brazilian isolates by our research group. Production of both inoculum types in high quantity will allow to assess environmental factors that affect their germination,which could be the basis for a black spot forecast system. This study aims to assess the effect of different temperatures and wetness periods over P. citricarpa ascospores and pycnidiospores. A completely randomized factorial experimental design with two factors, will be used. Each factor will have three levels: temperatures of 15ºC, 25ºC and 35ºC, and wetness periods of 12, 24 and 48 hours.Each treatment will have four replicates (four Petri dishes). Eight P. citricarpa isolates from four São Paulo state regions (north, south, center and southwestern) will be used.These isolates (two per region) are preserved in ESALQ at 5ºC using the sterilized filter paper method and have already had their mating type identified by duplex PCR. Pycnidiospores suspension will be obtained from 23-day-old colonies growing PDA culture media at 25ºC and 12 light hours photoperiod. To obtain ascospores, 14-day-colonies of compatible mating type isolates will be crossed by using the suspension method. Spores concentration will be standardized to 104 spores/mL. The percentage of germination will be calculated by counting 100 spores from each aliquot.