First Report of Collar and Root Rot of Physic Nut (Jatropha curcas) Caused by Neoscytalidium dimidiatum in Brazil

Abstract

Physic nut (Jatropha curcas L.; Euphorbiaeae) has become important in Brazil due to its potential as a feedstock for biodiesel production. In October 2010, during routine monitoring of fields in the state of Piauí, several plants were observed with symptoms of collar and root rot. Initially, plants appeared withered and chlorotic, and later became defoliated. Roots and collars of affected plants also appeared rotten with black fungal structures directly observed. Symptomatic tissue fragments of 5 mm diameter were washed with 70% ethanol, 1% sodium hypochlorite, and sterilized water, before being placed in petri dishes containing potato dextrose agar (PDA) and incubated at 25°C. Pure cultures were then obtained by single-spore isolation. The fungus isolated was grown on plates containing 2% water agar overlaid with sterilized corn straw or pine twigs and incubated at 25°C under a photoperiod of 12 h for 4 weeks to induce the formation of fruiting bodies. Thirty measurements of all of the relevant morphological characters were made using a light microscope for the identification of the species. On PDA, isolates initially appeared white and became dark after 7 days. The aerial mycelia formed chains of zero- to one-septate arthroconidia, oblong to globose, initially hyaline that became brown and with a thick wall with age. The dimensions of arthroconidia were 4 to 12 × 2.5 to 8 μm. The formation of pycnidia was observed on the plates with corn straw and pines twigs. These were dark, with a globose base up to 250 μm and a neck up to 810 μm. Conidiogenous cells were holoblastic, lageniform to ampulliform, hyaline, and 6 to 10 × 1.5 to 2.5 μm. Conidia were hyaline, ellipsoid to nearly fusiform, and 8 to 12 × 4 to 5 μm. Septate and dark conidia were not observed. DNA was extracted from one isolate following Wizard Genomic DNA Purification Kit procedures and amplified using primers ITS1 and ITS4. Products were directly sequencing by Macrogen, Korea. The 856-bp sequence obtained was deposited in GenBank (Accession No. JQ927342). The sequence was 99% similar to Neoscytalidium dimidiatum (Penz.) Crous & Slippers, further supporting the identification by morphology. Pathogenicity tests were conducted by using 6 mm disks removed from the outer bark of the collar region of healthy plants using a sterile cork borer, and 6-mm diameter plugs were placed in each wound. Five plants were inoculated with the isolate and five plants inoculated with an isolate-free agar plug. Below these, pieces of moistened cotton were placed and covered with Parafilm. After 60 days, all inoculated plants reproduced the symptoms observed in the field, and the pathogen was successfully reisolated. All non-inoculated plants remained healthy. The genus Neoscytalidium includes species having Scytalidium-like synanamorphs in the aerial mycelia and Fusicoccum-like conidia in the pycnidia (1). Currently, this species is reported to cause diseases in fig, mango, and orange (2,3). To our knowledge, this is the first report of collar and rot root caused by N. dimidiatum in J. curcas and of this fungus in Brazil. It seems likely the disease exists in areas beyond Piauí and could cause important losses for biodiesel production. References: (1) P. W. Crous et al. Stud. Mycol. 55:235, 2006. (2) G. Polizzi et al. Plant Dis. 93:1215, 2009. (3) J. D. Ray et al. Austral. Plant Dis. Notes 5:48, 2010.