Plant fungal pathogens

Introduction

Fungi is a kingdom of eukaryotic, heterotrophic organisms that live parasitically or as saprobes (derive their nutrition from the dead remains of other organisms), including mushrooms, yeasts, smuts, molds, etc. Fungi reproduce either sexually or asexually, and have life cycles that range from simple to complex.

The primary phyla dealt with in plant pathology are Chytridiomycota (chytrids), ZygomycotaAscomycota (sac fungi or ascomycetes), and Basidiomycota (basidiomycetes).

Usually fungal infections cause necrosis, distortion and other abnormalities in plant tissue. Most distinctive signs of fungal infections is appearance of hyphae, mycelia, fruiting bodies and spores.

 

Basidiomycota

A phylum of fungi that produce their sexual spores (basidiospores) on the outside of the basidium. It includes forms commonly known as mushrooms, boletes, puffballs, earthstars, stinkhorns, bird’s-nest fungi, jelly fungi, bracket or shelf fungi, and rust and smut fungi.

cellular organisms – Eukaryota – Opisthokonta – Fungi – Dikarya – Basidiomycota –

Organism Disease Transmission Management
Pucciniomycotina – Pucciniomycetes – Pucciniales – Phakopsoraceae – Phakopsora – Phakopsora pachyrhizi
Common name: Soybean Asian rust
An obligate parasite of soybean; originated in Asia-Australia; was first reported in the 1990s in Hawaii and, since 2001, it has been found in South America and in 2004 in continental USA. Infects leaf tissue of a broad range (at least 31 species in 17 genera) of leguminous plants. At the beginning, small, tan-coloured lesions, restricted by leaf veins, can be observed on infected leaves. Lesions enlarge and, 5–8 days after initial infection, rust pustules (uredia, syn. uredinia) become visible. The uredia open with a round ostiole through which uredospores are released. The pathogen is able to defoliate soybean fields within a few days and may lead to complete crop failure. Invasive species kudzu serve as a reservoir of the overwintering pathogen. Pustules formed on the leaves of infected plants produce spores which can be disseminated by wind over very long distances. Not known to be spread by seed. Under conditions of warm temperatures and high humidity, new infections can arise every 9-10 days. At present, can be controlled by use of several fungicides and breeding for resistance. Resistant cultivars generally develop reddish-brown lesions with little or no sporulation. None of the soybean cultivars in present commercial production is resistant to all P. pachyhrizi isolates.
Pucciniomycotina – Pucciniomycetes – Pucciniales – Pucciniaceae – Puccinia – Puccinia triticina
Common name: wheat leaf rust
The fungus is an obligate parasite capable of producing infectious urediniospores as long as infected leaf tissue remains alive. Characterized by the uredinial stage. Orange to brown uredinia scattered on both leaf surfaces produce infectious urediniospores. Cuases the most common rust disease of wheat. Symptoms are often seen in the autumn on early-sown crops as individual orange to brown pustules usually seen on leaves. When leaves begin to senesce, a ‘green island’ develops around individual pustules. Towards the end of the season dark teliospores are sometimes produced. Yield losses are usually the result of decreased numbers of kernels per head and lower kernel weights. Urediniospores can be wind-disseminated and infect host plants hundreds of kilometres from their source plant, which can result in wheat leaf rust epidemics on a continental scale. In warm climates, leaf rust infections that over-summer on volunteer wheat can serve as resevoirs of inoculum for the autumn-planted winter wheat. Destruction of volunteers will help to prevent carry-over of the disease. Fungicides and planting resistant cultivars are most common control measures.
Ustilaginomycotina – Ustilaginomycetes – Ustilaginales – Ustilaginaceae – Ustilago – Ustilago tritici
Common name: loose smut
Smuts are characterized by large numbers of dark, thick-walled and dust-like teliospores. The word “smut” originates from from a Germanic word for dirt. Cuases most common and detructive smut disease in barley. The smutted heads usually emerge a day or two earlier than healthy heads. The medium- to dark-brown, powdery spore masses are enclosed within a fragile, silvery gray membrane that soon ruptures releasing the pale yellow-brown spores which are lighter in color on one side. By harvest, an erect and naked spike is all that remains of the head. Seed-borne: fungus survives between crop cycles as dormant mycelium in the embryo and endosperm of diseased seed. Indirect systemic infection is possible via stigma to embryo by pollen tube. Cannot be controlled by cleaning seed surfaces. Hot water or heat with adequate temperature can kill the fungus and not the plant. Further possibilities to control it are the application of systemic fungicides, cultivar resistance, and cultural practices. Sow certified, smut-free barley seed of resistant varieties are recommended.