Farzad Jahromi

Early infection process of Damasonium minus by the potential mycoherbistat Rhynchosporium alismatis

Rhynchosporium alismatis is a fungal pathogen that promises to be a suitable biological control agent to manage the rice weed, starfruit (Damasonium minus). Light and scanning electron microscopy were used to study the infection process. Conidial germination, appressorium formation, and penetration by R. alismatis were compared at 25 and 30°C on starfruit leaves, and in separate experiments, conidial germination and appressorium formation were compared at both temperatures on cellophane paper. Appressorium formation was significantly (P < 0.005) higher at 25 than 30°C after 8 h on leaves and after 10 h on cellophane paper. Sessile appressoria were frequently observed on leaves, while no such structures were observed on cellophane paper. Penetration through stomata appeared to be a random event. Subepidermal hyphae were frequent after 24 h, and conidial formation was observed 48 h after inoculation of leaves at 25°C. Deformation of the leaf surface around the appressoria indicated signs of physical pressure. Fast conidial germination, penetration, and infection is an advantage, since the fungus is not exposed for long periods of time to adverse environmental conditions. The formation of conidia on the leaves can lead to further disease spread.

The interaction between Plectosporium alismatis and sublethal doses of bensulfuron-methyl reduces the growth of starfruit (Damasonium minus) in rice

Abstract Plectosporium alismatis is a fungal pathogen that is being investigated as a biocontrol agent for suppressing starfruit (Damasonium minus), a significant weed of Australian rice fields. The aim of this research was to study the effect of the fungus on weed competition and its interactions with chemical herbicides. Conidial germination was significantly reduced by Londax® (bensulfuron-methyl), while MCPA had no effects. Glasshouse trials showed evidence of synergism between the fungus and 1.56% of the recommended dose of Londax®, in reducing the weed growth. The application of inoculum (conidia suspended in water) in the glasshouse eliminated weed competition with rice. In the field, the reduction in weed growth caused by the fungus did not significantly eliminate starfruit competition with rice. This is thought to be due to the presence of other weeds.

Factors Affecting Disease Development by Rhynchosporium alismatis in Starfruit (Damasonium minus), a Weed of Rice

The fungal pathogen Rhynchosporium alismatis is being developed for biological control of starfruit (Damasonium minus), an important aquatic weed in Australian rice fields. The development of R. alismatis in starfruit differs between juvenile and adult plants. Juvenile starfruit plants are stunted as a result of fungal infection, while in adult plants, the main effect is necrosis and chlorosis of floating leaves. A conidial concentration of 1×104 conidia mL−1 was adequate to cause disease symptoms on floating leaves, but the stunting effect on juveniles was caused by concentrations of at least 1×105 conidia mL−1. To successfully inoculate juvenile plants, the water must be drained before inoculation to expose plants to the inoculum. The artificial addition of dew periods did not enhance disease development in plants. The stunting of juvenile starfruit plants caused by the infection of R. alismatis may give rice plants a competitive advantage over the weed at the seedling stage

Effect of environmental factors on disease development caused by the fungal pathogen Plectosporium alismatis on the floating-leaf stage of starfruit (Damasonium minus), a weed of rice

Abstract Starfruit, Damasonium minus (R. Br.) Buch, is a herbicide-resistant, aquatic-weed occurring in Australian rice fields. The fungal pathogen Plectosporium alismatis (Oudem) W.M. Pitt, W. Gams & U. Braun is a potential mycoherbicide for the control of this weed. Previous work showed that the fungus can suppress the growth of starfruit juvenile plants. This paper reports the effect of environmental factors on the disease development on starfruit at the floating-leaf stage. Fungal inoculation of plants in advanced phases of floating leaf stage reduced significantly (P<0.05) the green leaf area, but only when the percentages of diseased areas were deducted. However, inoculation when the first floating leaf was emerging reduced significantly (P<0.001) both, plant dry above-ground biomass and leaf area.

Molecular Phylogeny Inferred from 18S rRNA Gene Sequences of Nematodes Associated with Cernuella virgata, a Pest Snail in Australia

Pest snails are economically important pests of the grain industry. Nematode based bioagent appears to be a hope for controlling pest snails in an environment friendly way. Based on the dataset of 18S rRNA gene sequences, we propose a molecular phylogeny of nematodes baited with Cernuella virgata in soils collected from southern states of Australia. A total of 12 species (representing eight genera of nematodes) were identified and the inferred phylogenetic trees (Neighbor-Joining and Minium Evolution) placed them within three (I, IV and VII) out of the seven clades, indicating the possibility of multiple origins of snail parasitism. In Clade I and Clade VII, nematodes associated with Cernuella virgata formed sister group relationships with some slug – parasitic nematodes. We assume that snail – parasitic nematodes and slug - parasitic nematodes might share common ancestors in their evolutionary histories.