In São Paulo State, besides the occurrence of Candidatus Liberibacter americanus and Ca. L. asiaticus, a 16Sr IX group phytoplasma was associated with HLB symptoms, indistinguishable from those caused by liberibacters. This phytoplasma is called HLB phytoplasma and was found widespread in citrus orchards, although at low incidence. The same phytoplasma was found in Sunn Hemp (Crotalaria juncea) in 2008 and witches’-broom was commonly found associated with 16Sr group IX detection. The aim of this work was to assess the phytoplasma diversity in Sunn Hemp with emphasis at the detection of group 16Sr IX phytoplasma and to establish an association between the occurrence of HLB phytoplasma and symptoms. Sunn Hemp samples were harvested close to the blooming period. Plants were selected in the field when showing symptoms common to phytoplasma infection. We employed universal primers do amplify phytoplasmas in general and group specific primers for 16Sr group IX. PCR products were sequenced to allow grouping of phytoplasmas. We identified five phytoplasmas groups in 48 out of 99 Sunn Hemp plants, belonging to phytoplasma groups 16Sr I, III, VII, IX and XV. The most abundant phytoplasma was the group 16Sr IX, present in 70% of the samples, found in central and north São Paulo State. The occurrence of HLB phytoplasma in Sunn Hemp samples, showing 100% of similarity to the citrus phytoplasma, was highly related to virescence and the second most conspicuous symptom for this infection was witches’-broom.
The assessment of bacterialiferous Asian citrus psyllid (ACP) frequency is important in epidemiological and management studies because it can be related with the abundance of inoculum sources and with putative new HLB infections. For that, ACP can be collected directly or on yellow sticky traps (YST) commonly used by Brazilian growers to monitor psyllid population. The YST are usually left in the field for 2 weeks after which time YST are visually evaluated for the ACP presence, and if present, the psyllids are removed from the YST and tested by real-time PCR (qPCR) for liberibacter presence. Previous studies in Florida showed that the incidence of Las-positive ACP declined with increasing time on the YST (Irey et al., 2011). Thus, the objective of this work was to determine if time ACP is keep on YST affects qPCR results for Las and if it was related to weather conditions during winter and summer of Araraquara-SP (Brazil). ACP adults from nymphs reared on Las infected trees were placed on YST (BUG-Agentes Biológicos) in the field and 20 samples with 3 individuals were tested after 0, 1, 3, 9, 12 and 15 days. The results were compared with samples directly collected without trap glue. Experiments were done in June, July and August (winter) and in January, February and March (summer). In contrast with previous report in Florida, no difference on the incidence of Las-positive ACP samples was observed up to 15 days on the YST in both seasons.
Widespread contamination of surface water with nitrate-nitrogen (NO3-N) has led to increasing regulatory pressure to minimize NO3-N release from agricultural operations. We evaluated the use of wood chip denitrification bioreactors to remove NO3-N from tile drain effluent on two vegetable farms in Monterey County. Across several years of operation, denitrification in the bioreactors reduced NO3-N concentration by an average of 8 to 10 milligrams per liter (mg L-1) per day during the summer and approximately 5 mg L-1 per day in winter. However, due to the high NO3-N concentration in the tile drainage (60 to 190 mg L-1), water discharged from the bioreactors still contained NO3-N far above the regulatory target of < 10 mg L-1. Carbon enrichment (applying soluble carbon to stimulate denitrifying bacteria) using methanol as the carbon source substantially increased denitrification, both in laboratory experiments and in the on-farm bioreactors. Using a carbon enrichment system in which methanol was proportionally injected based on tile drainage NO3-N concentration allowed nearly complete NO3-N removal with minimal adverse environmental effects.
The assessment of bacterialiferous Asian citrus psyllid (ACP) frequency is important for (i) studies of bacteria acquisition and inoculation by ACP, (ii) disease detection in disease free areas but with ACP presence, (iii) efficiency evaluation of inoculum reduction strategies, (iv) evaluation of frequency of Candidatus Liberibacter asiaticus (Las)-positive ACP and the abundance of inoculum sources or putative new HLB infections relationships. Depending on the conditions and time of storage of collected psyllids, Las DNA in ACP could degrade and Las-false negative results might occur. Thus, this study was conducted to evaluate the detection of Las in ACP adults submitted to different storage methods and time of storage by real-time PCR (qPCR). Two 2x3x7 factorial experiments were conducted. Factors were ‘Ethanol’ (with or without 70% ethanol), ‘Temperature’ (-20°C, 4°C and 26°C) and ‘Time’ (0, 3, 7, 14, 21, 28 and 35 days). For each treatment, 20 samples with 3 ACP adults from nymphs reared on Las infected trees were tested for Las presence by qPCR. No significant differences in percentages of psyllids samples positive for Las were observed among the storage methods up to 35 days, except a slight trend of decline in Las detection in samples storage without ethanol at 26°C after 14 days of storage.
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