The physic nut (Jatropha curcas L.) is used as a living fence, due to its fast spreading, handling, and quick growth. It is studied worldwide as a bioenergy crop to obtain biodiesel, which helps reduce the emission of greenhouse gases and mitigate global warming (^{Zamarripa and Solís, 2013}). In Arriaga, Chiapas, since 2009, commercial plantations have been observed to contain dead 1- and 2-year old physic nut plants, which presented symptoms of wilting and basal stem rot. The aim of this study was to determine the etiology of the wilting and basal stem rot in the physic nut plant in Arriaga, Chiapas.

Samples with symptoms of wilting and basal stem rot were gathered in two physic nut plantations located in Arriaga, Chiapas: 1) a 90 ha lot with physic nuts from India, planted from seeds in 2008 in Rancho San Jacinto, located at 16° 13' 18" latitude north and 94° 01' 07" longitude west, at an altitude of 50 masl; 2) 3 ha lot with physic nut from Chiapas, planted from seeds in 2010, property of the Autonomous University of Chiapas, located at 16° 11' 05" latitude north and 93° 55' 57" longitude west, at an altitude of 38 masl. The samples were processed and analyzed under laboratory conditions. Cross sections of 5 mm of diseased plant material were obtained, disinfected superficially with 1 % sodium hypchlorite, rinsed with sterile distilled water and planted in Petri dishes with B King. The dishes were incubated at 28 °C for 48 hours; the culture formed was transferred to a new culture medium, using an inoculation loop, using the Streak Plate Method. Different tests were carried out with pure cultures, including: the hypersensitivity reaction test, with the infiltration of a bacterial solution at 1.2x10⁹ UFC/mL in tobacco (Nicotiana tabacum L. cv. Xanthi) leaves from 60-day old plants. Concentration was calculated using the ^{McFarland scale (1907)}, a test of rotting in potato tubercula of the cv. Alpha, by inoculations of bacterial growth in incision in slices under aseptic conditions; auxiliary biochemical identification tests in a triphenyl tetrazolium chloride (TTC) culture media, Gram staining, KOH test, production of the enzyme cytochrome oxidase, production of the enzyme catalase with hydrogen peroxide (H₂O₂), production of the enzyme urease in a Christensen culture media, oxidative and/or fermentative metabolism of glucose in a Hugh and Leifson culture media (^{Denny and Hayward, 2001}).

The plants gathered from commercial fields displayed symptoms of wilting on leaves, bacterial rot on the base of the stem and root. This corresponds with the description of symptoms reported by ^{Hendroko et al. (2008)}, ^{Ginting and Maryono (2009)}, and ^{Hidayah and Yulianti (2009)}. Up to 85 % less plants aged 1 to 2 years died in a time lapse of 20 to 30 days after the beginning of the epidemic. The incidence of the disease fell noticeably when the crop reached its third year of age. From the samples gathered on the field, 16 strains were obtained, 11 of which were discarded using the test of hypersensitivity on tobacco and the biochemical tests applied on it. Strains 1 and 3B showed positive results on the hypersensitivity test on tobacco after 48 h (Figure 1), and strain P3 also showed positive results or variables after 72 h; in this sense, ^{Ji et al. (2007)} mentioned that R. solanacearum shows variability in the response to hypersensitivity. Finally, negative results were obtained for this test with strains P1 and P2.

Figure 1 Positive result after 48 h for the hypersensitivity test on tobacco (Nicotiana tabacum L.) cv. Xanthi, performed on the isolated strain 1 of physic nut. 

In the potato tubercule rotting tests, results were positive for all five bacterial strains, which coincides with ^{Rodríguez (2012)}, who mentioned that for isolated bacterias from organisms with rotting, pathogenicity can be valued with this test.

The five isolated bacterial strains from physic nut were positive in a TTC media, with the growth of colonies colored red with white edges, distinctive features of colonies infected with R. solanacearum (Figure 2). These results coincide with reports by ^{Perea et al. (2011)}, who reported that the growth of R. solanacearum colonies in a TTC growth media are characterized by a red color with white edges. The Gram staining and biochemical tests for oxidase, catalase, urease, coincide with reports by ^{Yabuuchi et al. (1995)}, ^{Denny and Hayward (2001)}, ^{Dhital (2001)}, EPPO (2004), ^{Rahman et al. (2010)}, ^{Perea et al. (2011)}, ^{Marques et al. (2012)} and ^{Rodríguez (2012)} (Table 1).

Figure 2 Growth in a TTC media of the P1 isolated strain of Jatropha curcas with symptoms of wilting and bacterial rotting; a red color is observable, surrounded by a white area, typical of R. solanacearum cultures. 

Table 1 Biochemical and pathogenicity tests performed on five bacterial strains of Jatropha curcas. 

¹Control = Isolated reference strain from tomato (Solanum lycopersicum L.) identified and provided by the Lab. Of Plant Disease, Dept. of Microbiology, Natinal School of Biological Science, Instituto Politécnico Nacional, Mexico City.

²Response of R. solanacearum, according to según ^{Denny y Hayward (2001)}, ^{Dhital (2001)}, ^{EPPO (2004)}, ^{Rahman et al. (2010)}, ^{Perea et al. (2011)}, ^{Marques et al. (2012)}, ^{Rodríguez (2012)}.

³V = Vaiable.

The wilting and basal rotting of Jatropha curcas in Arriaga, Chiapas, Mexico are characterized by symptoms of flabbiness in petioles, wilting and loss of leaves, rotting in the root and base of the stem, production of adventitious roots and senescence 20 to 30 days after the first symptoms. Out of 16 isolated bacterial strains in physic nut plants that underwent the tobacco hypersensitivity test, three strains coincide with the characteristics for R. solanacearum. Although Koch's postulates were not fulfilled, this is the first report on the relation of Ralstonia solanacearum in wilting and basal rotting of the physic nut plant in Chiapas, Mexico.