Inoculum Thresholds of Soilborne Pathogens: Overview

Kuan, T.-L.

doi:10.1094/phyto-78-867

Cited by 14 publications

(8 citation statements)

References 2 publications

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“…() on successful isolation of pathogenic bacteria from both discoloured and visually clean seed. Due to the potential for seed infection, Kuan () recommends that inoculum threshold levels should be established by determining the correlation between seed infection levels based on seed testing and disease ratings in field plantings. Inoculum thresholds of seedborne pathogens are the levels of infection on, or in seed that will significantly affect seed development and result in economic loss.…”

Section: Discussionmentioning

confidence: 99%

“…The use of clean seeds (Kuan, ) or treatment of seeds before sowing to protect against diseases and to enhance crop development, are commonly practised measures in crop protection (Cottyn, ). Most seedborne pathogens are located on or under the seed hull and do not infect the embryo; they are thus relatively easily controlled by physical, chemical, or biological seed treatments (Cottyn et al ., ).…”

Section: Discussionmentioning

confidence: 99%

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Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

Adorada¹,

Stodart

Pangga

et al. 2014

Plant Pathology

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The economic impact of seedborne bacterial diseases on rice production provides a major motivation for research on seed health. This paper reports on the endophytic growth of a rifampicin-marked strain of the seedborne rice pathogen Pseudomonas fuscovaginae. The bacterium was found in most tested seeds indicating that, even without visible discolouration, seed transmission is possible. Crushed discoloured seeds contained more bacterial cells than did non-crushed discoloured seeds. These bacteria were released during seed soaking, contaminating clean seed and lowering seed germination. Cells of a rifampicin-resistant strain of P. fuscovaginae, which had been inoculated onto rice seeds, were subsequently recovered from different growth stages and from different rice tissues, thereby indicating endophytic colonization. These results have implications for seedling establishment, as symptomless seeds do not assure disease-free seeds, and the presence of seedborne bacteria results in poor germination and poor seedling establishment. Elimination of seedborne bacteria by soaking in sodium hypochlorite can increase seed germination. This could be used in developing control strategies, and, if practised regularly, reduce entry of seedborne disease-causing organisms into crops, resulting in lower disease pressure.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

Adorada¹,

Stodart

Pangga

et al. 2014

Plant Pathology

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“…Empirically determined seed inoculum thresholds have been successfully used to manage plant diseases (5,8,25); however, thresholds have not been determined for many vegetable bacterial diseases, including BFB, To establish a seed inoculum threshold, correlation analyses should be made between levels of seed infestation and disease incidence in the field or greenhouse (16). Empirically determined seed inoculum thresholds have been successfully used to manage plant diseases (5,8,25); however, thresholds have not been determined for many vegetable bacterial diseases, including BFB, To establish a seed inoculum threshold, correlation analyses should be made between levels of seed infestation and disease incidence in the field or greenhouse (16).…”

Section: Discussionmentioning

confidence: 99%

“…Because an effective seed health assay must display a pathogen detection threshold that is lower than the seed inoculum threshold for a given disease (16,25), and the BFB inoculum threshold had not been previously determined, we also sought to determine this parameter for A. citrulli under greetihouse conditions. Because an effective seed health assay must display a pathogen detection threshold that is lower than the seed inoculum threshold for a given disease (16,25), and the BFB inoculum threshold had not been previously determined, we also sought to determine this parameter for A. citrulli under greetihouse conditions.…”

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confidence: 99%

Acidovorax citrulli Seed Inoculum Load Affects Seedling Transmission and Spread of Bacterial Fruit Blotch of Watermelon Under Greenhouse Conditions

et al. 2012

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Dutta. B., Scherm, H,, Gitaitis, R. D., and Waleott, R, R, 2012, Acidovorax citrulli seed inoculum load affects seedling transmission and spread of bacterial fruit blotch of watermelon under greenhouse conditions. Plant Dis, 96:705-711, Infested seed are typically the primary source of inoculum for bacterial fruit blotch (BFB) of cucurbits. An inoculum threshold of 1 infested seed per 10,000 seeds is widely used in seed health testing for Acidovorax citrulli. However, the influence of seed inoculum load on BFB seedling transmission has not been elucidated. In this study, watermelon seedlots (128 seeds/lot) containing one seed inoculated with A. citrulli at levels ranging from 1 x 10' to 1 x 10' CFU were used to investigate the effect of seed inoculum load on seedling transmission and spatiotemporal spread of BFB under greenhouse conditions. The relationship between A. citrulli seed inoculum load and frequency of BFB seedling transmission followed a sigmoidal pattern (R-= 0.986, P = 0.0047). In all, 100 and 96.6% of seedlots containing one seed with 1 X 10' and 1 x 10^ CFU of A. citrulli, respectively, transmitted the pathogen to seedlings; in contrast, the proportion of seedlots that yielded BFB-infectcd seedlings was lower for lots with one seed infested with 1 X 10' (46,6%) and 1 x 10' (16,7%) CFU of A. citrulli. The relationship between A. citrulli seed inoculum load and frequency of pathogen detection in seedlots using immunomagnetic separation combined with a real-time polymerase chain reaction assay also followed a sigmoidal pattern (R^-= 0.997, P = 0.0034). Vvfhereas 100% of samples from seedlots (10,000 seeds/lot) with one seed containing >1 X 10-' ' CFU tested positive for A. citrulli. 75% of samples from lots with one seed containing 1x10' CFU tested positive for the pathogen, and only 16.7% of samples with one seed containing 10 CFU tested positive. Because disease transmission was observed for lots with just one seed containing 10 A. citrulli CFU, zero tolerance for seedbome A. citrulli is recommended for effective BFB management. The seedling transmission experiments also revealed that temporal spread of BFB in 128-cell seedling trays increased linearly with A. citrulli inoculum load (r-= 0,976, P = 0,0037), Additionally, the frequency of spatial spread of BFB from an inoculated seedling in the center of a planting tray to adjacent healthy seedlings over one-, two-, or three-cell distances was greater for lots with one seed infested with at least 1 x 10^ CFU than for lots with one seed infested at lower inoculum loads (1 x 10' and 1 X lO^CFU/seed),

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“…Most TLVs are propagated by seed (Grubben and Denton, 2004). However, seed is the most important vehicle for transmitting plant pathogens globally (Kuan, 1988). Plant pathogens are reported to have close associations with seed, as they can survive in, on or with seed, hence can be preserved in seed lots (Copeland and McDonald, 2001), at times in latent stage, are temperature dependent (Ngadze and Icishahayo, 2014), and manifest themselves and become problematic only when environmental conditions become conducive for their growth and reproduction (Copeland and McDonald, 2001).…”

Section: Introductionmentioning

confidence: 99%

Seed health tests of traditional leafy vegetables and pathogenicity in plants

Dube¹,

Struik²,

Ngadze³

2018

Afr. J. Agric. Res.

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Traditional leafy vegetables play a significant role in the daily diets of many people in Zimbabwe. They are produced by smallholder farmers with limited knowledge on the agronomic value of high-quality seed, on seed storage, and on plant-and seed-borne pathogens. The quality of the seed is rarely tested for seed-borne pathogens posing risks of pathogen build-up. This study was conducted in order to determine the seed-borne pathogens associated with traditional leafy vegetable seeds. Seeds were collected from five different farmers in three provinces of Zimbabwe and tested for the presence of pathogens in the plant pathology laboratory of the University of Zimbabwe. A total of 154 fungal and 233 bacterial infections were recorded on 450 seeds for each type of pathogen. Significantly high percentages of the isolates (Xanthomonas campestris, Curvularia spp., Alternaria alternata, Fusarium oxysporum and Pseudomonas syringae) were obtained from the three different species of traditional leafy vegetables (Amaranthus hybridus, Bidens pilosa and Cleome gynandra). F. oxysporum, A. alternata, X. campestris and Bacillus spp. isolates were pathogenic to traditional leafy vegetable plant species as confirmed by pathogenicity tests, hence may have significant effects on traditional leafy vegetables production. The results indicate that seed sourced from farmers 1, 2, 3 and 4 resulted in seed-borne pathogens on both the seed and plants, clearly showing that seed quality was poor. Although most pathogens observed have a broad host spectrum, pathogenicity and virulence tests confirmed that some pathogens were likely to be closely associated with these traditional leafy vegetable seed species.Key words: Seed-borne pathogens, disease occurrence, pathogenicity, bacteria, fungi, seed quality. INTRODUCTIONTraditional leafy vegetables (TLVs) of Africa refer to plant species, which originated on the continent and have a long history of cultivation, domestication and use in African conditions (Ambrose-Oji, 2009). Amaranthus spp. combine both social and socio-economic importance in Kenya and Tanzania as a multi-purpose vegetable with environmental adaptability, nutritional, medicinal and income generation properties (Weinberger and Msuya, 2004;Abukutsa-Onyango, 2007), and have gained popularity also in Zimbabwe. Mukwereza (2002) Across Africa, TLVs are produced and marketed by smallholder farmers (Ngugi et al., 2007) with limited access to advanced agro-technology including limited knowledge of the agronomic value of high-quality seed (Biemond et al., 2012), lack of information on seed storage (Cernansky, 2015), on appropriate use of chemicals like pesticides and fertilizers (Schippers, 2000), plants and seed-borne pathogens. These smallholder farmers obtain most of their seeds from their neighbours or informal seed markets (Ngwerume and Mvere, 2003;Adebooye et al., 2005;Guei et al., 2011).This seed is most likely to be of poor quality. Seed is rarely tested for germination and seed-borne pathogens, increasing risks of seed degeneratio...

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Inoculum Thresholds of Soilborne Pathogens: Overview

Cited by 14 publications

References 2 publications

Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

Implications of bacterial contaminated seed lots and endophytic colonization by Pseudomonas fuscovaginae on rice establishment

Acidovorax citrulli Seed Inoculum Load Affects Seedling Transmission and Spread of Bacterial Fruit Blotch of Watermelon Under Greenhouse Conditions

Seed health tests of traditional leafy vegetables and pathogenicity in plants

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