Leaf Anatomical Characteristics of the Eucalyptus Clones Tolerating to Gall Wasp (Leptocybe invasa Fisher & LaSalle)

Abstract

Leptocybe invasa, a gall wasp, is a devastating of Eucalyptus plantation in Thailand and other countries. The study was to determine the Eucalyptus tolerant and susceptible to gall wasp. Six Eucalyptus clones were selected, H4 and T5 were tolerant clones while K7, K25, K51 and CT76 were gall wasp susceptible clones. Rooted cutting material of H4 and CT76 were from Siam Forestry company, SCG, The other from stump coppices of the mature trees standing at the Faculty of Forestry, Kasetsart University. Leaf samples of 1-2 weeks old were collected and preserved in 3% glutaraldehyde in water. Thin sections of petiole, leaf laminar and mid-rib were obtained by free hand cutting with razor blades. The sections were further stained with safranin O and investigating under a compound microscope

            Anatomical structure of laminar was similar for six studied clones of which epidermis was one layer, mesophyll was bifacial type with two layers palisade parenchyma at both side. The gall wasp did not damage the leaf laminar. The anatomical structure of petiole and mid-rib were similar of which composed epidermis, ground tissue and vascular tissue. The epidermis was similar for both petiole and mid- rib and for all clones while epidermal height varied from 12.625 µm Ground tissues of both petiole and mid-rib differed between adaxial and abaxial . Angular collenchyma 3-7 layers were found at the adaxial ground tissue of both petiole ground tissues differed between the gall wasp tolerant and susceptible clones, the susceptible clones consist of only thin wall parenchyma while the tolerant clones, H4 and T5, consist of 7-12 layers of angular collenchyma and few layers of parenchyma .Vascular bundle was at the middle between ground tissues. Xylem was flanked by phloem called bicollateral bundle.

Width of ground tissues and cell size in ground tissues of both petiole and mid-rib and of all clones did not correlate to gall wasp tolerance. Double wall thickness was thin, 2.263- 3.493 µm for the susceptible clones while was very thick, 7.60 µm and 6.27 µm for the tolerant clones of H4 and T5, respectively. Therefore, the present of collenchyma and increasing wall thickness in ground tissue exhibited gall wasp tolerance in the tolerant clones.

Keywords: Eucalyptus, Gall Wasp, Leptocybe invasa, Leaf anatomy