COMMON BEAN GENETICALLY MODIFIED WITH THE RECOMBINANT DEFENSIN pdf1.2 TOLERANT TO ROOT ROT DISEASE

Abstract

Pathogenic fungi are responsible for root rot in common beans. However, an efficient control of this situation has not been possible, either because the genetic diversity of common beans lacks resistance genes or because control methods have a limited effectiveness. Lines of common  bean (Phaseolus vulgaris L.) cv. Flor de Mayo Anita (FMA) —genetically modified with the defensin gene (pdf1.2) from Arabidopsis thaliana— were evaluated under confinement conditions to determine their protective capacity against the Fusarium oxysporum and F. lateritium fungi. Twenty-five plants from five homozygous lines (T4 FMA-pdf1.2 L2, L3, L4, L7, and L9) were placed in 1-L pots containing Sunshine Mix^® No. 6. Then they incubated with 2.0 × 10⁵ conidia mL^-1 of Fusarium oxysporum and, 21 days later, with 2.5 × 10⁵ conidia mL^-1 of F. lateritium. The non-genetically modified controls were FMA common bean plants and cv. Montcalm, incubated and non-incubated with pathogens. The plants were evaluated 21 d after each inoculation, based on a semiquantitative evaluation scale. The evaluation of the plants inoculated with F. oxysporum indicated that the five FMA-pdf1.2 lines showed a significantly lower severity than the control plants; likewise, lines L3 and L9 had a better performance. Meanwhile, F. lateritium damaged up to 25 % of the hypocotyl and root tissues of all the FMA-pdf1.2 common bean lines; this percentage is significantly lower (p ≤ 0.05) than the damage percentage in the control plants, which reached 50 % of the tissues. There was an inverse correlation between the transcriptional expression levels of the pdf1.2 gene and the protection degree conferred (R² = -0.93): the five FMA-pdf1.2 lines were less severely damaged by F. oxysporum and F. lateritium (within the tolerance margin).