Amino acid drenches suppress early invasion and reproduction of Meloidogyne incognita in tomato with associated root biochemical and elemental shifts

Meloidogyne incognita causes severe yield losses in tomato, and several amino acids have shown activity against root-knot nematodes in vitro and in whole-plant studies. However, whole-plant evaluations have rarely integrated early juvenile abundance with galling and reproduction. This study evaluated eight amino acids and related derivatives applied as soil drenches at 2,000 mg L⁻¹ in tomato, with inoculated positive and a non-inoculated negative control. Juveniles abundance in roots was monitored at 1, 3, 7 and 14 days after inoculation, whereas galling, egg production, and reproduction factor were assessed at 30 days. Leaf pigments were quantified, and bulk-root biochemical and elemental profiles were analyzed using ATR-FTIR and ED-XRF. L-cysteine achieved reproduction factors below one in both experimental runs and maintained the lowest juvenile abundance from 1 to 14 days after inoculation. L-cysteine hydrochloride monohydrate, L-methionine, and L-lysine also reduced juvenile abundance, egg production, and reproduction factor relative to the positive control, whereas DL-methionine, L-arginine, L-histidine, and N-acetyl-L-histidine monohydrate produced weaker responses. Leaf pigment contents and roots profiles varied among treatments. These profiles provided physiological context, but did not consistently match nematode rankings. L-cysteine showed the most consistent suppression across early juvenile abundance and final reproduction.