PATHOGENESIS OF PSEUDOMONAS SYRINGAE PV. SESAMI ASSOCIATED WITH SESAME (SESAMUM INDICUM L.) BACTERIAL LEAF SPOT  

SYEDA SADIQA FIRDOUS1, REHANA ASGHAR1*, MUHAMMAD IRFAN UL-HAQUE2, ABDUL WAHEED, SYED NADEEM AFZAL2 AND MUHAMMAD YASIN MIRZA3

Abstract: Sesame bacterial leaf spot caused by Pseudomonas syringae pv. sesami was observed to cause severe symptoms on sesame crop during the monsoon season in barani areas of Pakistan. Histological study was conducted to elucidate the mode of infection of the causal bacterium by incubating leaves or discs in bacterial suspension and by infiltration methods. Infected leaves were cleared in lactophenol: ethanol solution. Periodic histology of cleared inoculated discs from infected leaves showed that bacterial cells resided and multiplied in depressions and around trichome bases for 24 h before penetration through stomata and trichome basal cells. When pin-point-sized spots first appeared at 3 days after inoculation, chloroplast membrane was damaged at this stage. With the early appearance of small necrotic spot symptoms at 4 days after inoculation, the bacterium was detected in parenchymatous tissues and apparently moved from parenchymatous tissues to transverse vascular systems. This systematic infection process in sesame indicated the involvement of any secondary metabolite/s. With the appearance of typical leaf spot symptoms comprised of brown lesions 5 to 6 days after inoculation, no further histopathological changes were observed using infected cleared disc technique. Bacterial infection was confirmed in tolerant and susceptible genotypes by both methods and it was shown that mode of infection in two genotypes was same but infection was delayed in tolerant genotype.
 

¹Department of Botany, PMAS Arid Agriculture University, Rawalpindi, Pakistan

²Department of Plant Pathology, PMAS Arid Agriculture University, Rawalpindi, Pakistan

³Oil seed Programme, National Agriculture Research Council, Islamabad, Pakistan