Archivio Journal of Plant Pathology

Abstract:

In February 2012, several plants of physic nut (Jatropha curcas) growing in Assiut Governorate (Egypt) showed shedding of the leaves, blackening and decaying of the collar region of the stem and necrotic lesions on branches. A fungus was consistently isolated on potato dextrose agar (PDA) from symptomatic branches. Single-spore fungal cultures produced white, aerial mycelium that became dull gray after a week in culture. The mycelium was fast spreading, branched and septate. Pycnidia from 30-day-old pure cultures produced dark brown, oval conidia that were two celled, thin walled, and oval with longitudinal striations. The average size of the conidia was 23.64×12.73 μm with a length/width ratio of 1.86. Conidia were initially unicellular, hyaline, thick-walled with granular content. Based on conidial morphology, the fungus was identified as Lasiodiplodia theobromae. To confirm the identity of the mycete the internal transcribed spacer (ITS) region was amplified with ITS1/ITS4 primers and sequenced. Sequences of the isolates were 99% identical to two L. theobromae accession from GenBank (HM008598 and HM999905). Five 1-year-old healthy plants of J. curcas were inoculated inserting a 10-mm PDA plug of mycelium into the wound and wrapping the inoculation site with wetted cotton wool and Parafilm. Ten non-inoculated plants served as control. After 6 days, all inoculated plants produced the same symptoms. while controls remained symptomless. The pathogen was reisolated from inoculated branches, fulfilling Koch's postulates. L. theobromae has been reported to cause cankers and dieback in Malaysia (Sulaiman and Thanarajoo, 2012) and India (Latha et al., 2009). To our knowledge, this is the first report of stem canker associated with L. theobromae of physic nut in Egypt.