Colonization of siliques and seeds of rapid cycling Brassica oleracea plants by Xanthomonas campestris pv. campestris after spray-inoculation of flower clusters

Abstract

Colonization of siliques and seeds of rapid cycling Brassica oleracea plants by Xanthomonas campestris pv. campestris after spray-inoculation of flower clusters Abstract Glasshouse experiments were conducted to study the colonization of seedpods (siliques) and seeds of rapid cycling Brassica oleracea plants after spraying inoculum on clusters of recently opened flowers with Xanthomonas campestris pv. campestris (Xcc) at densities of 10 7 -10 8 cfu ml −1 . A green fluorescent protein (GFP) tagged Xcc strain was used to allow visualization of the bacteria by epifluorescence stereo microscopy (ESM) and confocal laser scanning microscopy (CLSM). The GFP-tagged strain showed reduced virulence compared to the untagged parental strain, but was still able to cause black rot symptoms. Two to three days after sprayinoculation, sepals, stamen and petals were colonized by Xcc, as observed by ESM. In green siliques a GFP-signal was observed on valves, septa and seeds, despite the fact that a high percentage of Xcc cells had lost their ability to express GFP as found by dilution-plating. Densities of Xcc in infected silique tissues were up to 10 9 cfu g −1 . A fluorescent signal using ESM was found in seeds harvested from symptomatic siliques after incubation of seeds on blotting paper wetted with broth to enhance the multiplication of Xcc. Xcc was found in association with the seed coat and in a single seed, also in the endosperm and embryo, indicating deep-seated seed infection. The estimated incidence of contaminated seeds in both years was ca. 7%. The estimated incidence of deep-seated infections, still detectable after warm water treatment of seeds, was also high (2-3.8%). It is concluded that spray-inoculation of flower clusters with Xcc can result in the infection of sepals and reproductive organs, and in deep-seated seed infections.

Mechanistic insights into host adaptation, virulence and epidemiology of the phytopathogenXanthomonas

“…Symptoms were apparent in plants that were inoculated in all developmental stages but seed colonisation was only seen when plants were inoculated during flowering time (van der Wolf, van der Zouwen and van der Heijden 2013). In a further study using GFP-labelled X. campestris, the group demonstrated that the bacteria can successfully colonise and cause symptoms in siliques and subsequently colonise both the outer seed coat and the endosperm and embryo (van der Wolf et al 2019). This data lead to the hypothesis that infected reproductive tissues later develop into infected endosperms and embryos.…”

“…vitians (Xcv) (Barak, Koike and Gilbertson 2002) while Xcc, X. euvesicatoria and X. citri pv. fuscans (Xcf) were reported to colonise the inner seeds of cauliflower, tomato and bean, respectively (Sharma and Agrawal 2014;Darrasse et al 2018;van der Wolf et al 2019). Plant to seed transmission has long been speculated to originate from infected reproductive organs.…”

“…Van der Wolf and colleagues showed that X. campestris can be transmitted to cabbage flowers though flies and bumble bees and demonstrated that flower infection can be carried on to the seeds (van der Wolf and van der Zouwen 2010 ; van der Wolf et al . 2019 ). The prevalence of such transmission in the field is still unknown and should be subjected to further study.…”

Biosensors Used for Epifluorescence and Confocal Laser Scanning Microscopies to Study Dickeya and Pectobacterium Virulence and Biocontrol

“…Of course, these fluorescent tools were also successfully applied for studies concerning phytopathogens, such as P. syringae [ 87 , 88 ], Xanthomonas campestris [ 89 , 90 , 91 ], Ralstonia solanacearum [ 92 , 93 , 94 ], and Clavibacter michiganensis [ 95 , 96 ]. Nevertheless, to our knowledge, it has only been since 2010 that FPs have been used to label SRP, leading to significant progress in the knowledge of their interactions with the host plant ( Table 1 ).…”

The Change of Bacterial Spectrum after Storage of X. campestris pv. campestris Inoculated Cabbage Heads (Brassica oleracea var. capitata L.)

“…Many studies focused on the survival of Xcc in plant debris, in the field or on seeds [7][8][9][10][11][12][13][25][26][27]. The black rot disease quickly develops in warm, humid conditions and can spread rapidly by rain dispersal and irrigation [28].…”