Effects of continuous dark upon ultrastructure, bacterial populations and accumulation of phytoalexins during interactions between Xanthomonas campestris pv. malvacearum and bacterial blight susceptible and resistant cotton

• Published in: Physiological and molecular plant pathology Vol. 32; no. 1; pp. 141 - 162
• Main Authors: Morgham, Alia T., Richardson, P.E., Essenberg, M., Cover, E.C.
• Format: Journal Article
• Language: English
• Published: London Elsevier India Pvt Ltd 1988; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Bacterial plant pathogens; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Generalities; Genetics and breeding of economic plants; Pathology. Damages, economic importance; Pest resistance; Phytopathology. Animal pests. Plant and forest protection; Plant viruses and viroids; Varietal selection. Specialized plant breeding, plant breeding aims; Em; HR; LCME; DHC; LC; Malvaceae; Pseudomonadales; Continuous; Phytopathogen; Xanthomonas malvacearum; Fiber crop; Microorganism resistance; Ultrastructure; Dicotyledones; Sesquiterpenes; Angiospermae; Bacteria; Pseudomonadaceae; Obscurity; Light effect; Terpenoid; Microorganism growth; Pathophysiology; Metabolism; Transmission electron microscopy; Sensitivity resistance; Phytoalexin; Spermatophyta; Gossypium hirsutum; Biological accumulation
• ISSN: 0885-5765; 1096-1178
• DOI: 10.1016/S0885-5765(88)80012-2

Fourth and fifth leaves of susceptible (Ac 44) and highly resistant (Im 216) cotton plants were inoculated with a suspension of Xanthomonas campestris pv. malvacearum. Tissue responses were studied by means of electron microscopy. Half the plants were maintained in continuous dark after inoculation, the other half in 14 h light/10 h dark. Fibrillar structures enveloped the bacteria in leaf tissue of Im 216 plants under both conditions. Enveloping structures also formed in Ac 44 leaves which had been kept in continuous dark, but not in leaves maintained in a light/dark cycle. At 2 days post-inoculation, envelopes that formed in Ac 44 which had been kept in the dark ruptured, as they do in cotton lines of intermediate resistance under a light/dark cycle. Plasma membrane, cytoplasm and chloroplast degeneration occurred more rapidly than in Ac 44 kept under the light/dark cycle. Wall appositions were frequent in Im 216 in continuous dark and rare in the other interactions. Although the ultrastructural reactions of Ac 44 and Im 216 plants maintained in the dark resembled the hypersensitive response, bacteria multiplied to levels typically found in susceptible plants maintained in a light/dark cycle. The initial envelopment of bacteria and rapid tissue degeneration observed under such conditions were evidently not sufficient to cause inhibition of bacterial growth. Sesquiterpenoid phytoalexins accumulated as previously observed in Im 216 under the light/dark cycle; however, only low levels of these compounds were present in Im 216 held in continuous dark or in Ac 44 maintained under either light regime. When coinoculated with X. campestris pv. malvacearum into Im 216, the saprophyte Pseudomonas fluorescens also multiplied in continuous dark to a level typical of a compatible pathogen. Thus the mechanisms which inhibit a phytopathogen and a saprophyte failed to function during the disruptive changes that occurred in continuous dark following inoculation with X. campestris pv. malvacearum.