Early detection of onion neck rot disease in Manitoba

Neck rot caused by the fungus Botrytis allii Munn. is one of the most devastating diseases of onions (Allium cepa L.) resulting in significant yield losses. This disease is latent in nature developing symptomless onion plants in the field with bulbs typically showing symptoms 1-2 months after harvest in the storage. Molecular studies were conducted to detect latent infections of Botrytis neck rot in the onion fields of Manitoba, Canada. Plant samples of onion cultivars Redwing and Pocono were collected every 10 days throughout the growing season starting from planting until bulb harvesting during 2018, 2019, and 2020 from a research farm in Brandon, Manitoba, and plant samples of cultivar Redwing were collected during 2019 and 2020 from a commercial vegetable farm in Portage La Prairie, Manitoba. The amplified DNA fragment of onion leaves and neck region of collected samples were subjected to polymerase chain reaction (PCR) using Botrytis specific primer pair BA2f/BA1r. Botrytis allii was detected on onion samples collected from the commercial farm as early as the end of June 2019 and 2020 when plants were at the 5-7 leaf stage. The majority of onion samples collected from the research farm also started testing positive for the pathogen from June (2019, 2020) and July (2018) onwards. This knowledge about the timing of infection in the field will be useful in helping farmers to develop and evaluate management strategies in the field, and also predict the storability and availability of quality bulbs for sale.

Transcriptional analysis of sweet corn hybrids in response to crowding stress

Crop tolerance to crowding stress, specifically plant population density, is an important target to improve productivity in processing sweet corn. Due to limited knowledge of biological mechanisms involved in crowding stress in sweet corn, a study was conducted to 1) investigate phenotypic and transcriptional response of sweet corn hybrids under different plant densties, 2) compare the crowding stress response mechanisms between hybrids and 3) identify candidate biological mechanisms involved in crowding stress response. Yield per hectare of a tolerant hybrid (DMC21-84) increased with plant density. Yield per hectare of a sensitive hybrid (GSS2259P) declined with plant density. Transcriptional analysis found 694, 537, 359 and 483 crowding stress differentially expressed genes (DEGs) for GSS2259P at the Fruit Farm and Vegetable Farm and for DMC21-84 at the Fruit Farm and Vegetable Farm, respectively. Strong transcriptional change due to hybrid was observed. Functional analyses of DEGs involved in crowding stress also revealed that protein folding and photosynthetic processes were common response mechanisms for both hybrids. However, DEGs related to starch biosynthetic, carbohydrate metabolism, and ABA related processes were significant only for DMC21-84, suggesting the genes have closer relationship to plant productivity under stress than other processes. These results collectively provide initial insight into potential crowding stress response mechanisms in sweet corn.

Phytoavailablility and fractionation of cadmium and lead in vegetable farm soils in Ilorin, north-central, Nigeria

No Abstract.

The first report of Meloidogyne enterolobii on Thai basil in Florida, United States

Thai basil (Ocimum basilicum var. thyrsiflora) is an important ethnic aromatic herb native to Southeast Asia. According to the Vegetable Production Handbook of Florida 2020-2021, Asian vegetables are currently grown on more than 4,000 ha in Florida, and Thai basil is one of the most commonly grown among these. Meloidogyne spp. cause severe damage to different basil cultivars (Brito et al. 2007). During May-July 2020, plant stunting and galled root symptoms were observed on Thai basil plants sampled from a commercial Asian vegetable farm in Wimauma, Florida (27°44.951' N; 82°16.271’ E); 1,972 root-knot nematode second-stage juveniles (J2s) were extracted from 200 cm3 soil. A pathogenicity test was performed in September 2020 at the University of Florida Gulf Coast Research and Education Center, Wimauma, Florida. Ten of 20, three-week-old nematode-free Thai basil plants were inoculated with 5,000 eggs of field nematode cultures. Two months after inoculation (temperature = 22.8 ± 3.8 °C, relative humidity = 85.6 ± 14.0 %), average gall index (Bridge and Page 1980) = 5.4 ± 1.1 were only observed in inoculated plants, and 69,276 ± 18,904 eggs were extracted from roots using the NaClO method (Hussey and Barker 1973); 5 ± 7 J2s / 200 cc soil were recovered by the modified Baermann funnel technique (Forge and Kimpinski 2007). Nematode reproduction factor (RF) = 13.86 ± 3.78 (Nicol et al. 2010). Morphological measurements (mean, standard deviation and range) of J2s (n=20) included body length = 394.0 ± 22.3 (362.8 - 437.9) µm, body width = 15.7 ± 1.2 (13.6 - 18.3) µm, and stylet length = 12.8 ± 1.1 (10.4-14.5) µm. The perineal pattern of matured female (n=5) was oval-shaped with coarse and smooth striate; the dorsal arch was high and round; no lateral line presented. Morphological characteristics of females and J2s were consistent with those described for M. enterolobii (Yang and Eisenback 1983). DNA was extracted from a single female picked from infected Thai basil root using NaOH digestion method (Hübschen et al. 2004). The D2-D3 expansion segment of 28S rDNA and the COXII region on mitochondrial DNA were amplified by PCR using the primers 28S391a/28S501 and C2F3/1108 (Ye et al. 2020); the species was also confirmed with species-specific primers Me-F/Me-R (Ye et al. 2020). PCR products were sequenced by the Genomic Sciences Laboratory (North Carolina State University, Raleigh, NC, USA) and the results were recorded in the NCBI with GeneBank Accession Nos. MW488150 and MW507374. The sequences showed 100% identity with M. enterolobii in D2/D3 (KP901079, KP411230) and COXII (MN809527, KX214350). M. enterolobii (M. mayaguensis) has been reported on sweet basil in Florida (Brito et al. 2008). To our knowledge, this is the first detection of M. enterolobii on Thai basil in Hillsborough County, Florida. It is not clear to what extent M. enterolobii reduces the yield of Thai basil, but the RF value obtained in the pathogenicity test indicates the crop is certainly a very good host. Limited information is available on the distribution of M. enterolobii in Florida and the US. M. enterolobii is known to break down the root-knot resistance of crops including soybean, sweet potatoes, and tomatoes (Philbrick et al. 2020). This nematode is considered one of the major emerging threats to agriculture in the southeastern US. A multistate research and outreach program (FINDMe program) was initiated in 2019 to study the distribution and management of this nematode in the southeastern US.

Linking smallholder producers to high-value markets through vegetable producer cooperatives in Cambodia

Modern retail markets have grown in Cambodia, but vegetable growers are unlikely to gain benefits from these high value markets (HVMs). Producer cooperatives (PCs) could play a critical role in linking smallholder farmers to HVMs. The purpose of this paper is: (1) to examine the role of PCs in linking vegetable producers to HVMs; and (2) analyse the factors affecting successful participation in HVMs. This study applied a mixed methods approach to PCs selling the members’ vegetables to HVMs (PC-HVMs), and PCs selling members’ vegetables to traditional markets (TMs) only (PC-TMs). Both groups of PCs provided services to their members (e.g. input, financial, extension services). However, the content and quality of these services were different. PC-TMs emphasised only on support linked to production, while PC-HVMs focused on both production and marketing support. This study indicated that vegetable farming experience, total vegetable produce, and average vegetable prices had a statistically significant influence on producers’ participation in HVMs. However, vegetable farm size showed a negatively significant effect on participation in HVMs. As one of the very few empirical studies on PCs in Cambodia the research provides valuable context for further studies. It has developed and tested a framework for analysing the factors affecting successful participation in HVMs and provides an explanation of why some PCs can successfully participate in HVMs.

Persistence of Human Pathogens in Manure-Amended Australian Soils Used for Production of Leafy Vegetables

Incorporation of manures into soil can add nutrients, improve soil structure and enhance biodiversity, thereby improving the sustainability of vegetable production systems. Unfortunately, manures can also potentially contain human enteric pathogens. To reduce the risk of contamination, Australian guidelines recommend a withholding period of 90 days between manure application and harvest for high-risk products such as leafy salad greens. Our study examined the appropriateness of these guidelines under conditions replicating those on a commercial vegetable farm. Cow manure and poultry litter with/without addition of non-pathogenic strains of Escherichia coli (E. coli), Listeriainnocua and Salmonella sv. sofia were added to sandy and clay loam soils typical of those used to grow vegetables. Bacterial populations were monitored in the soil and on crops of cos lettuce during spring (A), summer (B) and autumn (C) trials, with testing conducted by a commercial laboratory. Significant declines in E. coli occurred within 6 to 16 days in all trials. Modelling indicated that E. coli populations would be at or close to the limit of detection within 50 days for all of the combinations tested. A 2–3 log die-off of Salmonella spp. occurred within three weeks. However, occasional detections continued throughout trial A. As a result, the probability of detection after 50 days fell from 1.0 to 0.1 and 0.02 in trials B and C, respectively, but remained at 0.44 in trial A. Listeria spp. was the most persistent in soil but was not detected on lettuce at commercial maturity. While this study was limited in scope, the results suggest that a 90 day withholding period between application of manure and harvest significantly reduces risk from enteric pathogens under Australian field conditions.

Antimicrobial resistance profile of Salmonella present in organic farming in Selangor, Malaysia

Presence of Salmonella in organic farming may lead to contamination in fresh produce. This study was designed to detect Salmonella contamination in organic vegetable farm situated in Serdang and to evaluate the antibiotic susceptibility profiles of the isolates. A total of 460 samples of brinjal, cucumber, ladies’ fingers and soil were collected and examined for the presence of Salmonella. The obtained isolates were identified and confirmed by biochemical characterization and serotyping. Antibiotic sensitivity profiles of the isolates were determined by using agar disk diffusion method. Salmonella spp. was detected in brinjal (1.7%, n=2), cucumber (1.7%, n=2), ladies’ fingers (2.5%, n=3) and soil (5.0%, n=5) samples. The prevalent serovars were Salmonella enterica ser. Senftenberg, S. enterica ser. Weltevreden and S. enterica ser. Corvallis. All strains were resistance to penicillin and vancomycin, with multiple antibiotic resistance (MAR) index between 0.21 and 0.36, demonstrated here as multi-drug resistant (MDR) Salmonella. The result highlighted that organic vegetables constituted potential sources of Salmonella, informing continuous monitoring and tightened surveillance are necessary to ensure food safety.