Soilborne disease complexes are an emerging constraint in protected culture tomato production systems in the Midwestern United States. Diseases in these complexes include Verticillium wilt (Verticillium dahliae), black dot root rot (Colletotrichum coccodes), corky root rot (Pyrenochaeta lycopersici), and root knot (Meloidogyne spp.). Anaerobic soil disinfestation (ASD) may be a viable, environmentally benign strategy for managing these complexes. Soils from two farms in Ohio were used to determine the impacts of ASD, using wheat bran, molasses, or ethanol as carbon sources, on soilborne diseases and soil bacterial communities. ASD with wheat bran or ethanol amendments led to significantly reduced tomato root rot severity, while nematode galling damage was significantly reduced following ASD with any carbon source compared with nontreated controls. When ethanol was used as a carbon source in ASD, the colonization of tomato roots by P. lycopersici and C. coccodes was observed less frequently than in control roots. A high throughput sequencing approach was used to characterize soil bacterial communities following ASD. Carbon source and soil origin influenced the composition of bacterial communities in soils treated with ASD. Bacterial community diversity decreased following ASD with wheat bran in all soils tested and following ASD with ethanol in soils from one farm. The abundance of bacteria in the phylum Firmicutes generally increased significantly following ASD, while the abundance of those in the phyla Acidobacteria, Actinobacteria, Chloroflexi, and Plantomycetes generally decreased following ASD. These findings provide insight into the impacts of ASD on microbial communities and soilborne diseases and will be used to optimize ASD as a tool for Midwestern vegetable growers.
Quinoa (Chenopodium quinoa) is an important export of the Andean region, and its key disease is quinoa downy mildew, caused by Peronospora variabilis. P. variabilis oospores can be seedborne and rapid methods to detect seedborne P. variabilis have not been developed. In this research, a polymerase chain reaction (PCR)-based detection method was developed to detect seedborne P. variabilis and a sequencing-based method was used to validate the PCR-based method. P. variabilis was detected in 31 of 33 quinoa seed lots using the PCR-based method and in 32 of 33 quinoa seed lots using the sequencing-based method. Thirty-one of the quinoa seed lots tested in this study were sold for human consumption, with seed originating from six different countries. Internal transcribed spacer (ITS) and cytochrome c oxidase subunit 2 (COX2) phylogenies were examined to determine whether geographical differences occurred in P. variabilis populations originating from Ecuador, Bolivia, and the United States. No geographical differences were observed in the ITS-derived phylogeny but the COX2 phylogeny indicated that geographical differences existed between U.S. and South American samples. Both ITS and COX2 phylogenies supported the existence of a Peronospora sp., distinct from P. variabilis, that causes systemic-like downy mildew symptoms on quinoa in Ecuador. The results of these studies allow for a better understanding of P. variabilis populations in South America and identified a new causal agent for quinoa downy mildew. The PCR-based seed detection method allows for the development of P. variabilis-free quinoa seed, which may prove important for management of quinoa downy mildew.
A participatory approach was used to improve smallholder tomato farmers’ understanding of and access to soil health monitoring in the Morogoro Region of Tanzania. Baseline soil characteristics were gathered from 50 tomato fields in the region, local soil knowledge was elicited from farmers and used to develop a soil health card to qualitatively assess soil health, and farmers (n = 32) were trained on the use of a low-cost soil test kit to quantitatively assess soil health. Farmers most often described local indicators of soil health in terms of soil texture and tilth, soil color, soil water relations, and soil fertility. Following use of the soil test kit, farmers indicated increased awareness of soil testing services (Wilcoxon signed rank Z = –3.0, P = 0.001), more agreed they had access to soil testing services (Z = –2.7, P = 0.004), and more agreed that soil management recommendations were easy to understand (Z = –3.4, P < 0.0001) compared with pre-exposure results. Farmers continued to use the soil health test kit and soil health card based on a follow-up survey administered 1 year after project completion. Participatory soil health monitoring projects can improve farmers’ ability to monitor and manage soil health, potentially impacting sustained soil and plant health.
Little is known about the abiotic factors contributing to the preharvest persistence of Salmonella in tomato tissues. Therefore, we investigated the effects of specific environmental conditions and contamination methods on the persistence and dissemination of Salmonella enterica subsp. enterica serotype Typhimurium (JSG626) in tomato plants. When plants were sprayed on the leaves with a JSG626-contaminated solution, JSG626 persistence in the phyllosphere (bacteria located on the surface of the inoculated foliage and stem tissues) was lower at higher temperatures (30°C day/25°C night) than at lower temperatures (20°C day/15°C night). However, wounding cotyledons with contaminated tools improved JSG626 persistence and the internalization rate (2.27%) in planta compared to spray inoculation (0.004%). The systemic dissemination of JSG626 to other tissues increased when contaminated plants were grown under low relative humidity (Ͻ40%); however, JSG626 was only detected in the root systems at later sampling times (between 21 and 98 days postinoculation [dpi]). Further, after tomato scions were grafted onto rootstocks using contaminated cutting tools, dissemination of JSG626 was preferentially basipetal and occasionally acropetal in the plants, with higher persistence rates and loads of JSG626 in root systems compared to foliar tissues. JSG626 was detected in the grafting point and root systems up to 242 dpi; however, none of the fruits harvested from contaminated plants between 90 and 137 dpi were positive for JSG626. This study demonstrates that environmental temperature and relative humidity could be good indicators for estimating the persistence of Salmonella enterica in tomato plants. Further, root systems may represent a risk for long-term persistence of Salmonella enterica in tomato plants. IMPORTANCE Tomatoes are one of the most widely produced vegetables around the world; however, fresh tomatoes have been connected to multiple wide-scale salmonellosis outbreaks over the past decades. Salmonella is commonly found in the environment and can persist in hostile conditions for several weeks before being internalized into plant tissues, where it is protected from conventional sanitation methods. In addition to biotic factors (host, inoculum size, and phytobiome), abiotic factors (environmental conditions) may affect the persistence of Salmonella in crop production. This study demonstrates that specific environmental conditions, the inoculation method, and the inoculum density affect the persistence and dissemination of JSG626 in tomato plant tissues. Our findings enhance the understanding of interactions between Salmonella enterica and fresh produce and may lead to the development of novel management practices on farms.
Tomato production in Ohio protected culture systems is hindered by a soilborne disease complex consisting of corky root rot (Pyrenochaeta lycopersici), black dot root rot (Colletotrichum coccodes), Verticillium wilt (Verticillium dahliae), and root-knot (Meloidogyne hapla and M. incognita). In a survey of 71 high tunnels, C. coccodes was detected in 90% of high tunnels, while P. lycopersici (46%), V. dahliae (48%) and Meloidogyne spp. (45%) were found in nearly half of high tunnels. Anaerobic soil disinfestation (ASD) with wheat bran (20.2 Mg/ha) plus molasses (10.1 Mg/ha) and grafting onto ‘Maxifort’ or ‘Estamino’ rootstocks were evaluated in high tunnels on five farms. In post-ASD bioassays using trial soils, root and taproot rot severity were significantly reduced following ASD, and root-knot galling was also reduced by ASD. Soilborne pathogenic fungi were isolated less frequently from bioassay plants grown in ASD-treated soils than control soils. Similar results were observed in tomato plants grown in high tunnels. Root rot was significantly reduced by ASD in nearly all trials. Corky root rot severity was highest in non-grafted plants grown in non-treated soils, while the lowest levels of corky root rot were observed in Maxifort-grafted plants. Black dot root rot severity was higher or equivalent in grafted plants compared to non-grafted plants. Root-knot severity was lower in plants grown in ASD-treated soils in high tunnels compared to plants grown in control soils, but grafting did not significantly decrease root-knot severity. However, soil treatment did not significantly impact yield, and grafting led to inconsistent impacts on yield.
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