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.
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.
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.
Brown rot is the main disease of stone fruits in Brazil, but the susceptibility of peaches to brown rot at different stages of development in the field has not been studied under subtropical conditions. This information is relevant to guide the management of the disease. The objective of this research was to determine the influence of inoculating peaches with Monilinia fructicola at different stages of development on the infection and progress of brown rot at postharvest. Two experiments were carried out: one ex vivo with two cultivars and the other in the field for two seasons. Peaches were inoculated at different sizes for both experiments. In the field, peaches were bagged to avoid natural infection, and M. fructicola inoculum was monitored. The ex vivo incidence of the disease was lower at pit hardening than at other fruit stages for both cultivars. The incidence of brown rot for peaches attached to the trees increased with fruit ripening. Conversely, the time for symptom expression was reduced according to peach diameter. Peaches inoculated with a diameter smaller than 2 cm showed a lower incidence of brown rot and longer periods for disease expression than fruit inoculated near harvest. In conclusion, in areas with high inoculum in the orchard, a common condition in the subtropics, the grower must prevent infection at all stages of fruit development, thus avoiding losses during marketing.
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