Interaction Between Nitrogen-Fertilized Peach Trees and Expression ofsyrB, a Gene Involved in Syringomycin Production inPseudomonas syringaepv.syringae

Abstract

The in vitro expression of the syrB gene that controls the synthesis of syringomycin, a non-host-specific phytotoxin produced by Pseudomonas syringae pv. syringae van Hall, was studied using aqueous extracts derived from bark tissues collected from nitrogen-fertilized and nonfertilized peach trees. Expression of the syrB gene was quantified as beta- galactosidase activity expressed by P. syringae pv. syringae B3AR-132 containing a syrB::lacZ fusion. Gene expression was significantly less in three of four paired comparisons using extracts derived from fertilized versus nonfertilized trees; however, canker lengths were significantly different in only one of four comparisons. Expression was negatively correlated with plant tissue nitrogen content and positively correlated with a plant carbon/nitrogen ratio. Bark tissue from ring nematodeinfested trees had significantly higher concentrations of total soluble phenolic compounds and carbon/nitrogen ratios than bark samples from trees without nematodes, and canker size was significantly greater in trees growing in ring nematode-infested soil compared with noninfested soil. Nitrogen fertilization significantly decreased the plant carbon/nitrogen ratio, which was positively correlated with the concentration of total soluble phenolic compounds. Canker size developing after bacterial inoculation was positively correlated with higher plant carbon/nitrogen ratios and total soluble phenolic compounds. These results support the hypothesis that one reason why nitrogen fertilization decreases host susceptibility to bacterial canker is by either reducing the amount of plant metabolites that can induce syrB gene expression, or producing or increasing the concentration of compounds that antagonize syrB inducing compounds.

C/N Ratio and Nutrient Content in Peach Bark Related to Peach Tree Short Life

“…Differences in results between this study and literature (cAO et al, 2005) may be due to the sampling time, tissue type, plant age and cultural practices, as already reported by Reighard et al (2014). Additionally, it should be considered that all orchards sampled in this study had varietal mixtures of seeds of different scion cultivars as rootstock (table 1); therefore, with unknown genetic identity, which may have influenced the nutrient content of the sampled tissue.…”

“…Foliar applications of ca(NO 3 ) 2 increase concentrations of nitrogen in peach leaves and calcium in peach bark, but showed no effect in reducing susceptibility to infection by Pseudomonas syringae pv. syringae (cAO et al, 2013).…”

“…considering that inadequate plant nutrition (SHARPe et al, 1989) and high c / N ratio (cAO et al, 2005) have been mentioned as factors that may favor the occurrence of PtSl and lack of information on the subject in Brazilian literature, this study was aimed to evaluate the association of PtSl with the c / N ratio and nutrient content in peach bark in nine commercial orchards in the region of Pelotas.…”

Effect of calcium and nitrogen fertilization on bacterial canker susceptibility in stone fruits

“…It has been well documented that ring nematode infestation reduces root growth, and causes nitrogen deficiency and water deficit in tree hosts [18,22,23]. Nitrogen fertilization has been shown to reduce the severity of bacterial canker in peach and prune [8,10,19,20]. Fertilization with balanced nitrogen, phosphorus and potassium fertilizers significantly reduced disease severity in a problem 'French' prune orchard [24].…”

“…Increased calcium levels in bark tissues have also been associated with bacterial canker resistance in apricot and peach [11][12][13]. Previously, supplements of nitrogen for stone fruit trees that have been stressed with nematodes have demonstrated some beneficial effects in reducing peach susceptibility to bacterial canker, although supplements of calcium have no clear effects [19,20].…”