Xylella fastidiosa subsp. pauca is genetically diverse and has many vector species. However, there is limited information on vector specificity and efficiency for different sequence types (STs) within the pathogen subspecies. Both STs of X. fastidiosa and vectors differ in their associations with plants; therefore, assessment of vector competence should include the standardized vector acquisition ability of bacteria from artificial diets. This work aimed to adapt and validate an in vitro acquisition system for strains of X. fastidiosa that cause citrus variegated chlorosis, and to compare the transmission efficiency of STs of subsp. pauca by different species of sharpshooter vector. First, acquisition and transmission of ST13 by Bucephalogonia xanthophis and Macugonalia leucomelas was tested using an artificial diet with bacteria grown on minimum defined medium (X. fastidiosa medium) with or without 1% galacturonic acid (GA). Subsequently, four sharpshooter species (B. xanthophis, M. leucomelas, M. cavifrons, and Sibovia sagata) were compared as vectors of ST13 acquired from artificial diets, and four STs of subsp. pauca (11, 13, 65, and 70) were tested for acquisition and transmission by M. leucomelas. The artificial system allowed efficient acquisition and transmission of ST13 to plants, with no differences between the media tested. ST13 was transmitted more efficiently by B. xanthophis and M. leucomelas when compared with M. cavifrons and S. sagata. Different STs influenced acquisition and transmission rates by M. leucomelas. The differences in vector competence, despite the standardized acquisition system, suggest that ST–vector foregut or vector–plant interactions may influence bacterial acquisition, retention and inoculation by the insect.

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Plum leaf scald (PLS) was detected in P. salicina trees in Brazil in the 70s (Frenck; Kitajima 1978); ◼ PLS is the most destructive disease affecting plum trees in Brazil; ◼ Symptoms: leaf marginal chlorosis, leaf necrosis, branch dieback, reduced size fruits, and sometimes premature plant death (Hickel et al. 2001); ◼ Despite the importance of PLS, the vector species responsible for bacterial spread in plums remain unknown; ◼ Purpose of the study => to determine the X. fastidiosa transmission ability of three sharpshooter species commonly found in plum orchards in Brazil.

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Poplar (Populus deltoides) is a forest species that has several phytosanitary problems, such as leaf spots, rusts and root rots. Since 2010, the death of poplar trees has been observed in commercial plantations in the state of Paraná, Brazil, caused by the fungus Rosellinia bunodes. Due to the lack of information about this pathosystem, the aim of this work was to carry out the physiological characterization of R. bunodes isolates collected from P. deltoides and the symptomatological characterization of Rosellinia root rot in the same host. Experiments were conducted at Embrapa Florestas, located in Colombo (PR), Brazil. The mycelial growth of nine R. bunodes isolates was evaluated in four culture media (potato-dextrose-agar, V8-agar, carrot-agar and water-agar) and seven different incubation temperatures (8, 12, 16, 20 24, 28 and 32 °C). The symptomatological characterization of Rosellinia root rot was performed on six-month-old poplar seedlings. The most favorable conditions for mycelial growth of R. bunodes were observed in potato dextrose agar (PDA) at 24 °C. The symptoms and signs of the disease internally in the stem showed up at 7 days after inoculation (DAI); however, chlorosis and wilting were observed only at 14 DAI. Sexual and asexual reproductive structures of R. bunodes were not observed on inoculated plants.

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This study aimed to evaluate the effect of temperature and wetness period (WP) on urediniospore germination of Tranzschelia discolor and the influence of temperature in the latent period and the number of pustules/cm2 produced by isolates obtained from São Paulo (SP), Paraná (PR) and Santa Catarina (SC) states in Brazil. Spore germination was assessed under six temperatures (10–35°C) in combination with six WPs (3–48 hr). The latent period and the number of pustules were assessed in detached plum leaves inoculated with T. discolor at temperatures from 10 to 35ºC. In addition, the number of pustules produced by the three isolates was compared for 15 days at 23°C. The optimum temperatures for urediniospore germination estimated were 24.2, 24.4 and 24.3°C for isolates from PR, SC and SP, respectively, in the WP of 48 hr. The shortest latent periods estimated for PR, SC and SP isolates observed were 10.3, 8.9 and 10.6 days, at the optimal temperature of 21.9, 22.1 and 22.4°C, respectively. The greatest number of pustules/cm2 was 39.8, 158.5 and 63.1, for PR, SC and SP isolates, at the optimal temperature of 22.2, 22.2 and 22.7°C, respectively. Differences between isolates were observed for the latent period, which was shorter in leaves inoculated with the SC isolate. In addition, the number of pustules was greater in leaves inoculated with the SC isolate as compared to the latent periods and the number of pustules on leaves inoculated with the isolates from the other states. The highest rust progress rates were observed for isolates from the states of Santa Catarina and São Paulo. This information serves as a background study to better understand how plum leaf rust epidemics occur in the field under different environmental conditions, thus aiding in both the prevention of possible epidemics and the conception of more efficient control strategies.