Régis de Oliveira Fialho

Citrus black spot (CBS), caused by Phyllosticta citricarpa, is an important fungal disease of citrus. Higher CBS severity has been associated with P. citricarpa infections at the young and green stages of fruit. The length of the fruit susceptibility period may be influenced by the amount of inoculum and the climate of the citrus growing region. This study was conducted in orchards across two South African provinces to assess the intensity of CBS under two conditions: (i) unsprayed fruit of Valencia sweet orange, Nova, and Empress mandarins inoculated with P. citricarpa at 10¹, 10³, and 10⁵ pycnidiospores/mL at various intervals after fruit set, from October (petal fall stage) to March (for mandarins) or June (for sweet orange), and (ii) non‐inoculated Valencia fruit from orchards subjected to spray programs ranging from one to nine applications between October and June. Higher CBS intensity was observed in Valencia fruit inoculated between November and January, with an average disease severity index (DSI) of 0.94, compared to a significantly lower (0.07) for fruit inoculated from February to June. Inoculations in November or December for Nova mandarins and in December for Empress with 10⁵ pycnidiospores/mL resulted in higher CBS intensity compared to those with lower pycnidiospore concentrations. The absence of fungicide applications from October to December during the 2017–2018 season led to increased CBS intensity, with a DSI of ~0.47, a value which was not significantly different from that of non‐treated control (NTC) trees. Leaving sweet orange trees unprotected from January onwards did not significantly increase the CBS intensity. These results confirm that citrus growers should focus on protecting citrus fruit, against P. citricarpa infection, in their dark green and young stages (c.15–30 mm diameter) to control CBS.

Monitoring of Phyllosticta citricarpa (causal agent of citrus black spot [CBS]) inoculum in orchards has previously been performed using volumetric spore traps. However, volumetric traps are nonspecific, and only capture ascospores (not pycnidiospores) of different Phyllosticta species. This research aimed to monitor and quantify the DNA of P . citricarpa using young citrus plants as a spore trap combined with quantitative PCR (qPCR), as well as quantify the number of ascospores and pycnidiospores, and to correlate results with weather variables. Citrus nursery plants were placed as traps under and outside tree canopies during fruit developmental stages (from October to July) in two seasons in commercial ‘Valencia’ sweet orange orchards. DNA was extracted from trap leaves to quantify P . citricarpa inoculum by qPCR of the ribosomal internal transcribed spacer 1 (ITS1 rRNA) region of P . citricarpa (Pc‐ITS). Correlations of Pc‐ITS to rainy days, leaf wetness and temperature were performed. Overall, the highest numbers of 400 Pc‐ITS/cm ² of leaf tissue, which represented up to 12 ascospores or pycnidiospores per cm ² , were detected on leaves sampled from October to March, regardless of the trap position, season and orchard. Trap plants placed under canopies had up to 20‐fold more Pc‐ITS than those placed outside. Rainy days and leaf wetness were the variables most positively correlated with Pc‐ITS. Both results in the fluctuation of P . citricarpa inoculum in orchards and the most favourable weather variables associated with inoculum production contribute to better understanding of the critical periods for CBS management in citrus‐growing areas.

Citrus black spot (CBS) symptom expression on sweet oranges has been reported to be affected by the fruit developmental stage and inoculum concentration in greenhouse conditions. However, there is little information concerning the period in which the fruit is susceptible in commercial orchards. This study assessed the influence of fruit age and inoculum concentration of Phyllosticta citricarpa on CBS intensity and fruit drop in the field. Two field trials were conducted in commercial ‘Valencia’ orchards in São Paulo state, Brazil. Fruit were inoculated from October (petal fall stage) to July (c.6.5 cm diameter), with 10 ¹ , 10 ³ and 10 ⁵ pycnidiospores/ml. CBS symptoms and fruit drop were observed in higher levels for fruit inoculated from October to February than from March to July. In both trials, when fruit were inoculated 10 times from October to July or single‐inoculated in November or December, high CBS severities of 11%–22% were observed and the proportion of fruit remaining on the tree was 48%–77%; in contrast, noninoculated fruit had severity below 1.1% and 90% remained on the tree. Inoculations in November or December of green fruit with 1.5–3.0 cm diameter using 10 ⁵ pycnidiospores/ml were associated with higher CBS intensity and fruit drop and shorter incubation period than inoculations with lower concentrations. This work provides a better understanding of fruit stages and P . citricarpa inoculum concentrations most related to symptom expression and losses under natural conditions and may be helpful for improvement of CBS management in the São Paulo citrus belt.

Citrus black spot (CBS) is caused by Phyllosticta citricarpa, which is classified as a quarantine organism in certain countries whose concerns are that CBS-infected fruit may be a pathway for introduction of the pathogen. This study evaluated the reproductive capability and viability of P. citricarpa under simulated conditions in which the whole fruit, peel segments, or citrus pulp with CBS lesions were discarded. Naturally infected ‘Midknight’ Valencia orange and ‘Eureka’ lemon fruit, either treated using standard postharvest sanitation, fungicide, and wax coating treatments or untreated, were placed into cold storage for 5 weeks (oranges at 4 °C and lemons at 7 °C). Thereafter, treated and untreated fruit were incubated for a further 2 weeks at conditions conducive for CBS symptom expression and formation of pycnidia. The ability of pycnidia to secrete viable pycnidiospores after whole fruit and peel segments or peel pieces from citrus pulp were exposed to sunlight at warm temperatures (±28 °C) and ±75% relative humidity levels was then investigated. The combination of postharvest treatments and cold storage effectively controlled CBS latent infections (>83.6% control) and pycnidium formation (P. citricarpa.

This study aimed to evaluate the fungitoxic (antifungal) effect of seven essential oils on Plasmopara viticola, the causal agent of grapevine downy mildew. The cinnamon, eucalyptus globulus, marjoram, melaleuca, peppermint, oregano and white thyme essential oils were compared with the mancozeb + metalaxyl-M fungicide. Three experiments were conducted to evaluate the effect of essential oils on spore germination. The first experiment evaluated the effect of direct contact of essential oils on the pathogen; the second evaluated the effect of volatile compounds on the pathogen and the third assessed the behavior of essential oils, when applied to vine leaves in field conditions, on the pathogen. All essential oils inhibited the spores’ germination, but in varying degrees, in addition, presenting fungistatic activity. All the essential oils showed chemical instability when the incubation time or the interval between products application where increased, all oils decrease antifungal activity percentage. Noteworthy, the cinnamon and the eucalyptus globulus essential oils were the most fungitoxic (antifungal) on P. viticola.

O conhecimento sobre os efeitos indesejáveis do uso de fungicidas convencionais, associado à preocupação de órgãos reguladores e consumidores quanto à qualidade dos alimentos, tem estimulado a busca por novas alternativas para o controle de doenças de plantas. O objetivo deste trabalho foi avaliar, em laboratório e em campo, a atividade antifúngica de 16 óleos essenciais sobre Phakopsora euvitis , agente causal da ferrugem da videira. Foram utilizados os óleos essenciais de orégano, menta piperita, pimenta preta, nim, eucalipto globulus , citronela, canela, manjerona, alecrim, manjericão, camomila azul, cânfora branca, cravo, gengibre, tomilho branco e melaleuca. No laboratório foram realizados dois experimentos: no primeiro, foi avaliada a germinação de esporos, em meio ágar-água acrescido do óleo essencial, nas concentrações de 0,0, 0,1, 0,5, 1, 2 e 4% (v/v), e sobre este foi depositada a suspensão de esporos. No segundo experimento, aplicaram-se os óleos essenciais em folhas destacadas de videira, seguindo-se a inoculação dos esporos de P. euvitis , avaliando-se a germinação dos esporos. A partir dos dados obtidos foram calculadas as percentagens de inibições da germinação de esporos e a dose letal (DL₉₀). Em plantas de videira no campo foi realizada uma aplicação dos óleos essenciais, na concentração de 1%, e avaliada a severidade da ferrugem, após 15 e 30 dias. As DL₉₀ dos óleos essenciais variaram entre 0,39% (nim) e 3,9% (orégano). Os óleos essenciais mais eficientes sobre P. euvitis , em condições in vitro , foram os de camomila azul, citronela, eucalipto globulus , gengibre, nim e tomilho branco. Na aplicação realizada em campo todos os óleos essenciais reduziram significativamente a severidade da ferrugem, destacando-se os óleos essenciais de canela, citronela, nim e tomilho branco. Aspectos relacionados à fitotoxicidade necessitam ser elucidados. Os óleos essenciais avaliados apresentam potencial para serem utilizados no manejo da ferrugem da videira, contudo estudos complementares fazem-se necessários.

O presente trabalho teve como objetivo avaliar a atividade antifúngica in vitro de dez óleos essenciais sobre o crescimento micelial e a germinação de esporos de Sphaceloma ampelinum, agente causal da antracnose da videira. Foram utilizados os óleos essenciais de uva (Vitis vinifera), tangerina (Citrus reticulata), laranja doce (Citrus aurantium), citronela (Cymbopogon winterianus), canela (Cinnamomum zeylanicum), eucalipto (Eucalyptus staigeriana), anis estrelado (Illicium verun), alecrim (Rosmarinus officinalis), cravo (Eugenia caryophyllus) e tomilho branco (Thymus vulgaris) nas concentrações de 0,3 e 1% em relação ao volume total, os quais foram incorporados em meio de cultura ou suspensão de esporos. Determinaram-se as percentagens de inibições do crescimento micelial e da germinação de esporos. Constatou-se que os óleos essenciais de canela, tomilho branco e cravo proporcionaram os melhores efeitos de inibição sobre o crescimento micelial e a germinação de esporos de S. ampelinum e merecem mais estudos, para comprovação de sua eficiência em condições de campo.