Inoculated excised leaf disk technique allows decomposition of poplar partial resistance to Melampsora larici-populina leaf rust into key epidemiological components such as latent period (LP), uredinia number (UN), uredinia size (US), and spore production (SP) for a given M. larici-populina strain under controlled environmental conditions. Three hundred thirty-six genotypes from an interspecific Populus deltoides × P. trichocarpa F1 progeny segregating for complete resistance to M. larici-populina strain 93ID6 were inoculated with M. larici-populina strain 93CV1. This strain was able to infect the whole family, except few probable recombinants. LP, final UN, and final US after one infectious cycle proved to be relevant complementary descriptors of partial resistance. Area under the disease progress curve and other parameters of uredinia appearance dynamics did not yield additional information. Indirect assessment of SP by US scoring was reliable and easy to access compared with direct spore count...

Partial Resistance to Melampsora larici-populina Leaf Rust in Hybrid Poplars: Genetic Variability in Inoculated Excised Leaf Disk Bioassay and Relationship with Complete Resistance.

Histological studies on the mycoparasitism of Cladosporium tenuissimum on urediniospores of Uromyces appendiculatus

https://air.unimi.it/bitstream/2434/7815/1/Cladosporium%20su%20phytochemistry.pdf

Secondary mould metabolites of Cladosporium tenuissimum, a hyperparasite of rust fungi.

Selected isolates of Cladosporium tenuissimum were tested for their ability to inhibit in vitro aeciospore germination of the two-needle pine stem rusts Cronartium flaccidum and Peridermium pini and to suppress disease development in planta. The antagonistic fungus displayed a number of disease-suppressive mechanisms. Aeciospore germination on water agar slides was reduced at 12, 18, and 24 h when a conidial suspension (1.5 x 10(7) conidia per ml) of the Cladosporium tenuissimum isolates was added. When the aeciospores were incubated in same-strength conidial suspensions for 1, 11, 21, and 31 days, viability was reduced at 20 and 4 degreesC. Light and scanning electron microscopy showed that rust spores were directly parasitized by Cladosporium tenuissimum and that the antagonist had evolved several strategies to breach the spore wail and gain access to the underlying tissues. Penetration occurred with or without appressoria. The hyperparasite exerted a mechanical force to destroy the spore structures (spinules, cell wall) by direct contact, penetrated the aeciospores and subsequently proliferated within them. However, an enzymatic action could also be involved. This was shown by the dissolution of the host tell wall that comes in contact with the mycelium of the mycoparasite, by the lack of indentation in the host wall at the contact site, and by the minimal swelling at the infecting hyphal tip. Culture filtrates of the hyperparasite inhibited germination of rust propagules. A compound purified from the filtrates was characterized by chemical and spectroscopic analysis as cladosporol, a known beta -1,3-glucan biosynthesis inhibitor. Conidia of Cladosporium tenuissimum reduced rust development on new infected pine seedlings over 2 years under greenhouse conditions. Because the fungus is an aggressive mycoparasite, produces fungicidal metabolites, and can survive and multiply in forest ecosystems without rusts, it seems a promising agent for the biological control of pine stem rusts in Europe.

Antagonism of the Two-Needle Pine Stem Rust Fungi Cronartium flaccidum and Peridermium pini by Cladosporium tenuissimum In Vitro and In Planta.

Summary Responses by quarantine and forestry authorities to the inadvertent introduction to Australia of seven economically important pests and pathogens of forest trees, or forest products, from the time of introduction to the present are described. Eradication was achieved only in the case of European house borer (Hylotrupes bajulus). but not for West Indian drywood termite (Cryptotermes brevis), five-spined bark beetle (Ips grandicollis). Sirex wood wasp (Sirex noctilio), poplar rusts (Melampsora medusae and M. larici-populina) and Dothistroma needle blight (Dothistroma septospora). It has not been possible to quantify the economic cost of eradication attempts, or of control measures including research, for any of the case histories presented. It is argued that the Australian Agricultural Health and Quarantine Service should be actively involved in control campaigns until effective pest or disease management strategies have been developed.

Development of contingency plans for use against exotic pests and diseases of trees and timber. 3. Histories of control measures against some introduced pests and diseases of forests and forest products in Australia

SUMMARY Clones of Populus spp. growing in a relatively uniform field environment near Canberra appear to differ in the form and degree of resistance to the two leaf rusts Melampsora medusae Thum, and M. larici-populina Kleb. There is evidence of considerable racial specialisation in both rust species and this has importance in future breeding strategies for poplar. Although both rust species occurred at low and high latitudes in eastern Australia in 1975, in midsummer M. medusae was most common on clones at low latitudes while M. larici-populina was most frequent on the same clones at higher latitudes. Fungal hyperparasites of both rusts are common in the field in autumn. A programme for further research on poplar rusts is outlined.

Some Aspects of Poplar Rust Research in Australia

Conidia of Cladosporium sp. are frequently present in large numbers in collections of uredospores of Melampsora larici-populina made in the field at Canberra in late autumn. The presence of these conidia considerably reduces the viability of the uredospores and consequently infection of leaves of Populus nigra var. italica under controlled conditions. Lysis of germinated and ungerminated uredospores under experimental conditions by the mycelium of Cladosporium sp. has been demonstrated. The potential for control of leaf rust of poplar by hyperparasitism is discussed.

Parasitism of uredospores of Melampsora larici‐populina Kleb. by Cladosporium sp.

Six mono-uredospore isolates (races) of Melampsora medusae Thiim. produced qualitatively distinct reactions, in vitro, when incubated at 15 °C on leaf disks of certain cultivars of Populus deltoides Marsh. The infection types in some race-cultivar combinations were very temperature sensitive with less distinct reactions when incubated at 20 or 25°C. The significance of differential race-cultivar-temperature interaction in the epidemiology of M. medusae is discussed.

Temperature sensitivity of qualitative race‐cultivar interactions in Melampsora medusae Thüm. and Populus species

The first record of infection of Populus alba var. hickeliana by the American rust, Melampsora medusae Thum. is reported. The morphology of uredospores of rust on P. alba is compared with that of other Melampsora spp. infecting white poplars. The implications of these observations for the widespread establishment in the future of white × black hybrid poplars are discussed.

Infection of Populus alba var. hickeliana by Melampsora medusae Thüm.

A water soluble inhibitor of germination is present on the surfaces of freshly collected spores of Marssonina brunnea (Ell et Ev.) P. Magn. Spores of this pathogen have a high potential for germination even in the absence of external substrates. Among the poplar clones examined there was no correlation between spore germination on leaf discs and the disease reaction of the discs under controlled conditions. However under these conditions the disease development on leaf discs taken from clone I-69/55 was correlated with the high resistance of this clone to Marssonina leaf spot in the field.

W. A. Heather

Papers

Some Aspects of Poplar Rust Research in Australia

Parasitism of uredospores of Melampsora larici‐populina Kleb. by Cladosporium sp.

Temperature sensitivity of qualitative race‐cultivar interactions in Melampsora medusae Thüm. and Populus species

Infection of Populus alba var. hickeliana by Melampsora medusae Thüm.

In vitro and in vivo germination of spores of Marssonina brunnea (Ell. et Ev.) P. Magn.