Morphological responses of Eucalyptus demonstrate the potential of Trichoderma harzianum to promote resistance against Leptocybe invasa.

Abstract

The gall wasp Leptocybe invasa Fisher & La Salle (Hymenoptera: Eulophidae) is a major limiting factor in the cultivation of eucalyptus both in Brazil and across the world. This insect induces a gall formation on the principal veins of leaves, apices and petioles. This study investigated the impact of inoculating the fungus T. harzianum on plant growth and defense responses of Eucalyptus to Leptocybe invasa. Two hybrid eucalypt clones (Eucalyptus tereticornis Sm. × Eucalyptus camaldulensis Dehnh.) were used to produce seedlings. Plants were inoculated by spraying the T. harzianum conidial suspension onto the fourth, fifth and sixth fully expanded leaves. Evaluations of ovipositions and galls were carried out 7 and 44 days after infestation (d.a.i), and growth parameters were assessed at six points during the experiment: 15, 30, 45, 60, 75 and 90 d.a.i. Our findings show that susceptible and resistant non-inoculated Eucalyptus plants infested by L. invasa developed galls. However, only oviposition marks were observed in inoculated plants without gall formation, indicating that T. harzianum inoculation enhances Eucalyptus resistance to L. invasa. Additionally, inoculated plants showed increased height, leaf count and branch growth. The findings of this study suggest that T. harzianum has significant potential for controlling L. invasa infestations in susceptible Eucalyptus plantations and the added advantage of enhanced plant growth.