Abstract:
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
5mM BABA (23%), 50mg/L Bion (18%), 100mg/L Bion (15%) and Messenger (8%). The
number of eggs extracted from plants treated with 20mM BABA was significantly lower
(66%) compared to untreated controls. Furthermore, treating plants with 20mM BABA
decreased the total RKN population numbers by 55% whilst the decrease observed for Bion and Messenger was between 24-39%. Of the three tested elicitors, 20mM 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 × 103cfu/ml) compared to their treated
counterparts (8.71 × 102cfu/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.
