Impact of rhizobacteria community of citrus root on Tylenchulus semipenetrans and on Citrus plant growth

Tylenchulus semipenetrans Cobb, is a parasitic nematode of citrus, causing significant reduction in citrus growth and yield. Biological antagonists including bacteria and fungi have been used to control citrus nematodes. Citrus rhizosphere bacteria were collected from mature orchards in Tunisia and they have been studied to evaluate their nematicidal potentials on citrus nematode and abilities to stimulate plant root growth. Sixty bacterial strains isolated from egg masses of citrus nematode, citrus roots and associated to nematode trapping fungi, were tested for their abilities to parasitize T. semipenetrans and their impact on citrus growth parameters. The data analysis revealed that Bacillus weihenstephanensis, Lysinibacillus sphaericus, Bacillus subtilis, Bacillus thuringiensis, Bacillus pumilus and Bacillus cereus showed the highest effectiveness on T. semipenetrans juvenile (J2) causing up to 85% mortality of juveniles (J2) after 6 days of exposure in vitro. B. subtilis, B. amyloliquefaciens, B. pumilus and B. weihenstephanensis also inhibited egg hatching of citrus nematode in vitro. Furthermore, the majority of these rhizobacteria significantly stimulated citrus growth parameters. The application of B. weihenstephanensis, B. cereus, B. mycoides, B. thuringiensis, L. sphaericus, and Alcaligenes faecalis stimulated sour orange root growth in vitro compared to the control. Citrus rhizosphere bacteria must be studied further due to their diversity, abundance, and ability to effectively control T. semipenetrans.