SUSCEPTIBILITY OF 32 WALNUT VARIETIES TO GNOMONIA LEPTOSTYLA AND XANTHOMONAS CAMPESTRIS PV JUGLANDIS

The aim of this research is to compare the susceptibility to Gnomonia leptostyla (Fr.) Ces.et De Not and Xanthomonas juglandis (Pierce) Dowson of 32 walnut varieties: 7 were Italian (I), 8 French (F), 7 Spanish (S), 1 Portuguese (P), 2 Greek (G) and 7 American (A). Plant material consists of 3–5 trees virus free per each accession of a collection of 70 walnut varieties (Fruit Tree Research Institute in Caserta). Data were collected in two different periods, June and October 1994, in order to study disease evolution.

To detect the level of Gnomonia leptostyla infection, 100 leaves per variety were sampled at random on 3–5 limbs.
The number of necrosis with acervuli was determined and data were analyzed with a multiple range test (with conf. int. of 95%).

Incidence of Xanthomonas juglandis was estimated as percentage of leaves infected with the bacteria.
The necrosis with the diameter smaller than 3 mm were analyzed by a light microscope.

The 32 accessions were included in 5 different classes of susceptibility to G. leptostyla depending on the number of necrosis with acervuli.
The fungus did not infected Hartley (A) and Mayette (F), while J. Jefe (S) and VZ5 (S) are the most susceptible.

During vegetative season one quarter of the 32 accessions showed the bacterial presence on the 20% of the necrosis analyzed.

In October, Payne (A), Xerta 119 (S), Xerta 122 (S), VZ4 (S), VZ5 (S) and FK5 (G) and TR8 (I) showed the highest percentage of infection of X. juglandis.

In the 1995 we will continue this research to confirm these preliminary data.

III International Walnut Congress

M. Pastore, D. Consoli, G. Cristinzio

https://doi.org/10.17660/ActaHortic.1997.442.60