Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502 Vol. 2(ISC-2012), 110-115 (2013) Res.J.Recent.Sci. International Science Congress Association 110 Genetic variability of Macrophomina phaseolina Affecting Sesame: phenotypic traits, RAPD markers and interaction with the Crop Martínez-Hilders Andrea, Mendoza Yuraima, Peraza Dasybel and Laurentin Hernán Departamento de Ciencias Biológicas, Decanato de Agronomía, Universidad Centroccidental Lisandro Alvarado, Barquisimeto, VENEZUELA Available online at: www.isca.in Received 04 th August 2012, revised 26 th January 2013, accepted 07 th February 2013 Abstract Macrophomina phaseolina is a fungus which affects more than 300 cultivated species. It is one of the most important biotic stresses on sesame (Sesamum indicum L.). A successful control strategy, especially plant resistance management, depends on comprehensive knowledge about genetic variability for both fungus and plant. To evaluate genetic diversity of M. phaseolina affecting sesame in the most important crop production region of Venezuela, seven isolates were characterized by means of phenotypic traits, and RAPD markers. Four of these isolates were used for evaluating the interaction with four sesame genotypes in two ways: interaction in vivo by inoculation, and effect of root and stem extracts on fungus growth. Variability for growth velocity (optical density ranged between 1.69 to 2.32 at 96 hours of growing) (P≤0.05) and microsclerotia production (18-56 in 100 μL) (P≤0.05), was observed. Ten primers used were able to amplify the DNA, generating 81 bands (100% polymorphic). Ordination of the seven isolates by means of principal coordinates analysis based on RAPD did not show a consistent relationship with phenotypic attributes or geographical origin. After inoculation, length lesion produced by the four isolates did not show statistical differences, but germination percentage did (P≤0.01). One of the fungus is olates reduced up to almost 70% average germination of the four sesame genotypes. Mycelial growth of four isolates was inhibited in 17 – 32 % as compared to the control. These results indicate it is difficult to manage charcoal rot by means of obtaining resistant cultivars because of the fungus variability found in all the levels evaluated.. Keywords: DNA, charcoal rot, sesame, inoculation, morphological traits. Introduction Charcoal rot is a disease caused by the fungus Macrophomina phaseolina (Tassi) Goid. On more than 300 cultivated species, causing obstruction at root tissue 1 . It is an important threat to sesame (Sesamum indicum L.) production in Venezuela 2 . Sesame season in Venezuela (November - April) is characterized by high temperatures and dry soils because of lack of rain, which are favorable conditions for charcoal rot 3 . In Venezuela, losses in sesame due to this fungus have been evaluated, resulting up to 65% of seed weight reduction for affected plants 4 . M. phaseolina survives in the soil by means of sclerotia, which have been quantified in Venezuelan soils of sesame production areas up to 200 g -1 of soil 5 . Suitable identification of plant pathogens is a key factor for establishing disease control strategies 6 , for that, genetic and morphological characterization is needed. Characterization of individuals in a population is defined as the description based on phenotype or molecular traits 7 , and both strategies are complementary according to the information provided 8 . One of the strategies for controlling the pathogen is the use of genetic resistance, but for using it, it is necessary a wide knowledge about genetic variability for both Macrophomina phaseolina and Sesamum indicum. Furthermore, knowledge about interaction between isolates of the fungus and sesame cultivars is required. Interaction host-pathogen could be studied in vivo and in vitro. Studies of interaction in vivo need an efficient inoculation protocol to ensure the pathogen reaches to the host, and the host is able to respond. Studies of interaction sesame-M. phaseolina has been previously reported (e.g. 9,10 ). For in vitro studies, an approach used is to confront the pathogen to plant extracts and to evaluate the effect of this extract on pathogen growth. If extracts have some biochemical compounds which are toxic to the pathogen, the fungus will inhibit the growth. This kind of evaluation could have a huge potential. Number of plant species is about 500,000 but only few of them have been studied according to antimicrobial activity of extracts 11 . Effect of cultivated plant extracts (sunflower) on M. phaseolina have been reported (e.g. 12 ), but never sesame extracts effect on this fungus has been evaluated. The objective of this investigation was to evaluate genetic diversity of Macrophomina phaseolina coming from Venezuelan sesame production, in four different ways by means of: a. phenotypic attributes, b. molecular markers (RAPD), c. ability to cause disease on four sesame genotypes, d. growth with sesame extracts. Material and Methods Fungus isolates: Tissue presenting the disease collected from plants in the field was obtained to get seven isolates (table 1).