The effect of β-aminobutyric acid (BABA) on root knot nematode and soft rot pathogen disease complexes in Solanum tuberosum plants

The efficacy of three elicitors, DL-β-aminobutyric acid (BABA), Acibenzolar-S-methyl (Bion) and Messenger (Harpin) on potato plants inoculated with Meloidogyne incognita second stage juveniles (J2s) was investigated in this study. The efficacy of each elicitor was evaluated based on galling index, egg numbers, total root knot nematode (RKN) population numbers, number of juveniles and the percentage of females in respective extracted populations per treatment at 28 and 56 dpi. There was a significant decrease in galling indices of all treated compared to untreated control plants. The highest percentage reduction was observed for 20 mM BABA-treated plants (33 %) followed by 5 mM BABA (23 %), 50 mg/l Bion (18 %), 100 mg/l Bion (15 %) and Messenger (8 %). The number of eggs extracted from plants treated with 20 mM BABA was significantly lower (66 %) compared to untreated controls. Furthermore, treating plants with 20 mM BABA decreased the total RKN population numbers by 55 % whilst the decrease observed for Bion and Messenger was between 24 and 39 %. Of the three tested elicitors, 20 mM BABA was found to be the most effective elicitor at both 28 and 56 dpi. Hence, it was selected for further testing against RKN and Pectobacterium carotovorum subsp. brasiliense (Pcb) disease complex. Efficacy was tested by comparing the colony forming units (cfu) of Pcb from treated and untreated control plants inoculated with M. incongita and Pcb simultaneously. The concentration of Pcb from untreated plants inoculated with both pathogens was significantly higher (3.3 × 10³ cfu/ml) compared to their treated counterparts (8.71 × 10² cfu/ml). This suggests that BABA has the potential to decrease soft rot bacterial infections in RKN disease complexes by decreasing the rate of RKN infection. This is the first report where BABA is shown to decrease the infection rate of RKN as a primary causal agent in combination with a secondary pathogen.