Interactions of Seedborne Bacterial Pathogens with Host and Non-Host Plants in Relation to Seed Infestation and Seedling Transmission

Abstract

The ability of seed-borne bacterial pathogens (Acidovorax citrulli, Clavibacter michiganensis subsp. michiganensis, Pseudomonas syringae pv. tomato, Xanthomonas euvesicatoria, and Pseudomonas syringae pv. glycinea) to infest seeds of host and non-host plants (watermelon, tomato, pepper, and soybean) and subsequent pathogen transmission to seedlings was investigated. A non-pathogenic, pigmented strain of Serratia marcescens was also included to assess a null-interacting situation with the same plant species. Flowers of host and non-host plants were inoculated with 1×106 colony forming units (CFUs)/flower for each bacterial species and allowed to develop into fruits or umbels (in case of onion). Seeds harvested from each host/non-host bacterial species combination were assayed for respective bacteria by plating on semi-selective media. Additionally, seedlots for each host/non-host bacterial species combination were also assayed for pathogen transmission by seedling grow-out (SGO) assays under greenhouse conditions. The mean percentage of seedlots infested with compatible and incompatible pathogens was 31.7 and 30.9% (by plating), respectively and they were not significantly different (P = 0.67). The percentage of seedlots infested with null-interacting bacterial species was 16.8% (by plating) and it was significantly lower than the infested lots generated with compatible and incompatible bacterial pathogens (P = 0.03). None of the seedlots with incompatible/null-interacting bacteria developed symptoms on seedlings; however, when seedlings were assayed for epiphytic bacterial presence, 19.5 and 9.4% of the lots were positive, respectively. These results indicate that the seeds of non-host plants can become infested with incompatible and null-interacting bacterial species through flower colonization and they can be transmitted via epiphytic colonization of seedlings. In addition, it was also observed that flowers and seeds of non-host plants can be colonized by compatible/incompatible/null-interacting bacteria to higher populations; however, the level of colonization differed significantly depending on the type of bacterial species used.

The Role of Nonhost Cereal Seeds in the Epidemiology of Cowpea Bacterial Blight (Xanthomonas axonopodis pv. vignicola (Burkholder) Dye)

“…The finding in the current study that Xanthomonas axonopodis pv. vignicola was able to colonize the seeds of some nonhost crops, and to be transmitted systemically from floral systems of millet and sorghum to the developing seedling is in agreement with previous reports by Darasse et al, 1 Dutta et al 4 and Darsonval et al, 26 Similar observations were also reported by Dutta et al 4 However, this study also demonstrated that sorghum and millet plants arising from contaminated seeds were unable to serve as reservoirs of the pathogen, and to subsequently cross-contaminate cowpea plants with the pathogen when the crops were grown together.…”

Monitoring the occurrence of tomato bacterial spot and range of the causal agent Xanthomonas perforans in Iran

“…Seedborne bacterial pathogens act as primary inoculum source for many important vegetable diseases and despite prophylactic measures adopted, epidemics due to seedborne inoculum continue to occur (Dutta et al ., ). The clustered or aggregated dispersal pattern of diseased tomato fields in Iranian provinces, best described by beta binomial probability distribution (Fig.…”

Differences in stability of seed-associated microbial assemblages in response to invasion by phytopathogenic microorganisms

“…Owing to the importance of seed transmission in emergence of diseases in new planting areas, the processes involved in the transmission of microorganisms from plant to seed have been mainly documented for phytopathogenic agents. The molecular determinants involved in successful transmission of microorganisms from plant to seed have been notably studied in bacteria related to the Xanthomonas genus ( Darsonval et al, 2008 ; Darsonval et al, 2009 ; Darrasse et al, 2010 ; Dutta et al, 2014 ) and fungi that belonged to Alternaria brassicicola ( Pochon et al, 2012 ; Pochon et al, 2013 ). Key molecular determinants like the bacterial Type III Secretion System ( Darsonval et al, 2008 ), bacterial adhesins ( Darsonval et al, 2009 ), fungal class III histidine-kinase or dehydrin like proteins ( Pochon et al, 2013 ) have been shown to be involved in seed transmission.…”