Controlled mild water stress as a priming tool to inherent defense mechanisms of navel orange against citrus nematode, Tylenchulus semipenetrans

Abstract

Citrus nematode, Tylenchulus semipenetrans Cobb, 1913 is a major economically important plant-parasitic nematode responsible for citrus slow decline worldwide. This study aimed to evaluate the efficacy of controlled mild water stress on priming defences in navel orange (Citrus sinensis “Navel”) seedlings and to model nematode-host interactions under stress. Five greenhouse treatments were applied: negative control (C-, 100% field capacity), positive control (C+, 100%), pre-infection water stress (T1, 40%), post-infection water stress (T2, 40%), and continuous water stress (T3, 70%). Nematode reproduction criteria, plant growth and physiological and biochemical parameters were evaluated. Results indicate that the controlled mild water stress significantly (p ≤ 0.05) reduced nematode reproduction. The final nematode population (Pf) and reproduction factor decreased from 6.176 to 2.47 in positive control to 2.034 and 0.81 in continuous water stress. Shoot length and fresh weight declined from 31.47 cm to 29.22 g in negative control to 7.30 cm and 6.58 g in continuous water stress. Regression based model indicated that a strong positive correlation between nematode final population and orange seedlings growth performance (R2 = 0.995–0.999), demonstrated that the controlled mild water stress plays a critical role in mediating the interaction between T. semipenetrans and its host plant. Stressed plants accumulated higher flavonoids (up to 4.563 mg QE g− 1 FW), phenolics (6.498 mg g− 1 FW min− 1), and proline (11.50 mg g− 1 FW), while chlorophyll a and b decreased to 0.607 and 0.207 mg g− 1 FW, respectively. These findings suggest that controlled mild water stress, particularly when applied as a pre- or post-infection, can reduce T. semipenetrans reproduction and enhance citrus defense mechanisms. However, continuous water stress limits plant growth, highlighting a balance between nematode suppression and host adaptation for sustainable management.