Temporal patterns of citrus greasy spot‐induced defoliation of sweet orange cultivars in Brazil

Abstract

Recôncavo Baiano is an area favourable for the occurrence of citrus greasy spot (CGS) (Mycosphaerella citri), but there has been no study of this pathosystem in Brazil. This work aimed to characterise the temporal patterns of CGS-induced defoliation in sweet orange cultivars 'Bahia' (Washington Navel) and 'Pêra'. Temperature, rainfall and relative humidity were recorded, as well as weekly defoliation (fallen leaves/canopy m 2 or m 3 ). Considering the mean of fallen leaves per canopy m 2 , and mean canopy area, the total annual defoliation was estimated to be around 32 000 leaves per plant for 'Bahia' and 18 500 for 'Pêra' sweet orange. Spectral density analysis showed that defoliation has a 5-week-long main cycle for both cultivars. The proportion of symptomatic fallen leaves was never below 0.97. The monthly number of fallen leaves per canopy area was positively correlated with the mean CGS incidence on leaves. Defoliation was significant, resulting in a low leaf density throughout the year. Many defoliation cycles and the very high proportion of symptomatic fallen leaves assure a constant inoculum supply. Based on these results, CGS cannot be considered a minor disease, at least in Recôncavo Baiano.

Spatiotemporal dynamics and modelling support the case for area‐wide management of citrus greasy spot in a Brazilian smallholder farming region

“…Citrus greasy spot (CGS), caused by Zasmidium citri , is considered an important fungal disease in areas of high relative air humidity and temperature (Whiteside, ; Timmer and Gottwald, ; Mondal and Timmer, ; Silva et al , ), such as the Caribbean Basin and Florida in the USA. The main symptoms are irregular leaf spots resembling a brownish‐black grease, surrounded by a greenish‐yellow halo that is more conspicuous in the initial stages of the disease (Hidalgo et al , ).…”

“…A regional survey in Bahia showed that the disease occurs at high prevalence (100% of the sampled groves) meaning CGS is endemic, as it is regularly found and very common in the area (Silva et al , ). Moreover, CGS has been shown to exert a severe defoliating effect on cultivated citrus in Bahia, with one study estimating that 500 leaves are lost due to the disease per year from each infected Pêra sweet orange plant (Silva et al , ). However, surprisingly, our discussions with citrus growers in Bahia reveal they do not perceive CGS to be a yield‐limiting factor, and recent reports indicate that less than 4% of growers try to manage the disease (Rodrigues, ).…”

“…A regional survey in Bahia showed that the disease occurs at high prevalence (100% of the sampled groves) meaning CGS is endemic, as it is regularly found and very common in the area (Silva et al, 2009). Moreover, CGS has been shown to exert a severe defoliating effect on cultivated citrus in Bahia, with one study estimating that 500 leaves are lost due to the disease per year from each infected Pêra sweet orange plant (Silva et al, 2015).…”

Spatiotemporal dynamics and modelling support the case for area-wide management of citrus greasy spot in a Brazilian smallholder farming region

“…Northeastern Brazil (Bahia), however, the weather conditions are conducive for inoculum 84 production in all seasons. The relative humidity is always higher than 70% and rain events 85 occur throughout the year (Silva et al, 2015). 86…”

Principales enfermedades de los cítricos

“…Dentro de las enfermedades criptogámicas de mayor importancia en los cítricos, se encuentran: Phytophthora spp., Mycosphaerella citri y Lasiodiploida theobromae (Zhao et al, 2015;García-Martín et al, 2018). De manera general, estos patógenos provocan lesiones y pudrición del tallo (Yan et al, 2017), manchas necróticas en hojas (Silva et al, 2015), defoliación del árbol (Picos-Muñoz et al, 2015), pudrición de frutos y raíces, disminuyen el vigor y la producción del árbol (Showler, 2017) y por último la muerte .…”