First Report of Curvularia lunata on Jatropha curcas in Mexico.

Abstract

The Mexican nut or Jatropha curcas (Euphorbiaceae) is considered an alternative biodiesel source (2). This species is native to Mexico, but is widely distributed in Latin America, Africa, India, and Southeast Asia. Mexico has 6 million hectares with potential for cultivation of this crop (4). In Tamaulipas, Mexico, several adaptation trials have been conducted since 2008. In 2009, symptoms of Curvularia leaf spot were observed on basal leaves of 1-year-old J. curcas plants of the ecotype 'Yautepec' growing in El Mante, Tamaulipas. Spots with yellow borders originated on the edge of leaves, coalesced, and often resulted in approximately 20% leaf abscission on infected plants. Symptomatic leaves were sectioned into small pieces (0.5 cm) and gently washed with a 3:1 solution of 5% sodium hypochlorite to water and rinsed three times with sterilized distilled water. The leaf pieces were dried for 24 h on sterile filter paper, cultured on potato dextrose agar (PDA), and incubated at 27°C under continuous light for 7 days. Cultures produced pale brown conidia, relatively fusiform and cylindrical (25.6 ± 2.6 to 14.0 ± 1.6 μm) with a central cell that was slightly curved and larger and darker than the end cells. Conidia were loosely arranged on conidiophores sparsely distributed or in closer verticils (1). On the basis of the morphological characteristics, the fungus was identified as Curvularia lunata. A fraction of the mycelium grown on solid medium was inoculated into potato dextrose broth and grown for 72 h and DNA extraction was performed. PCR with primers designed for 26S and internal transcribed spacer (ITS) region were used to amplify and sequence 16S rRNA and the D2 region. This analysis resulted in 100% identity of the test isolate to GenBank Accession No. GQ328852.1 and the sequence of our isolate was submitted with Accession No. JF798505.1. Dried specimens were sent to the USA National Collection BPI. Koch's postulates were completed by testing for pathogenicity on 20 70-day-old Jatropha plants grown under greenhouse conditions. A conidial suspension (1 × 106 conidia ml-1) was prepared from monosporic cultures and hand sprayed onto test plants. Twenty plants were treated only with sterile water and used as controls. Symptoms appeared 2 weeks after inoculation, and 40 days later, all inoculated plants showed the same symptoms as those recorded in the field. Control plants did not show any disease symptoms. C. lunata was reisolated from 70% of the inoculated leaves. In Mexico, C. lunata was found on leaves of Quercus, Liquidambar, and Ananas, and was reported on cassava (Manihot esculentum), another member of the Euphorbiacea (3). To our knowledge, this is the first report of C. lunata on Jatropha in Mexico.