Selection and Analysis of Polymorphisms in Somaclonal Variants of <i>Agave americana</i> Resistant to <i>Fusarium oxysporum</i> via an Ethyl Methanesulphonate Treatment

Agave americana L. callus were exposed to different concentrations of ethyl methanesulphonate (EMS) 0, 15, 30, 45 and 60 mM and to different times of exposure (2 and 4 h). The viability and capacity of shoot formation were shown to be affected when the callus were exposed to high concentrations (30–60 mM). Only the callus exposed to 15 mM EMS presented shoot formation; the exposure time of two hours produced the largest quantity of shoots regenerated per callus (21 shoots/callus). In order to generate somaclonal variants resistant to Fusarium oxysporum, a selection pressure was applied through of a culture filtrate (CF) of 100 ppm of the fungus. This was made in callus obtained in the treatment with 15 mM EMS during 2 h of exposure. The CF caused oxidation and necrosis in 71.25% of the callus; however, they were capable of generating shoots (3.5 shoots/callus). Molecular markers type RAPD, ISSR and DAMD were used to evaluate the genetic variation arising from the mutations caused by EMS on control plants and 16-month-old somaclonal variants. The polymorphic information content (PIC) for each one of the initiating groups was: 0.28 (DAMD), 0.09 (ISSR) and 0.14 (RAPD). DAMD revealed a greater percentage of polymorphism than RAPD and ISSR. Polymorphic bands were detected in the somaclonal variants. This indicated that the EMS caused genetic variation in the regenerated plants conferring resistance to them against Fusarium oxysporum.