Host specificity testing and assessment of the pathogenicity of the rust, Puccinia abrupta var. partheniicola, as a biological control agent of Parthenium weed (Parthenium hysterophorus)

Abstract

Parthenium hysterophorus, a native of Central America, is a problem weed of Australian rangeland, particularly in Queensland. Following field surveys in Mexico, the rust fungus Puccinia abrupta var. partheniicola was selected as a potential biological control agent. One isolate was chosen for further investigation after infection studies with one Kenyan and five Mexican isolates. Assessment of inoculation conditions showed that temperatures of less than 20° C and dew periods of more than 6 hours were required for abundant pustule production. Infection with the rust hastened leaf senescence, significantly decreased the life span and dry weight of Parthenium plants, and reduced flower production 10‐fold. Subsequent host‐range studies against 120 species and varieties, with further screening against a limited number of species conducted under a range of environmental regimes, indicated the rust to be sufficiently host‐specific to be considered for introduction. Additional host‐range tests against sunflowers demonstrated that resistance to P. abrupta var. partheniicola was not modified by prior inoculation with P. helianthi.

Host Range of Puccinia psidii, a Potential Biological Control Agent of Melaleuca quinquenervia in Florida

“…It has been suggested that host specificity tests of microbial pathogens should be conducted under controlled conditions to facilitate optimum infection and disease development on test plants (Watson, 1985). However, these artificial conditions can predispose plants to infection and may artificially increase the perceived host range of the organism being tested (Adams, 1988;Parker et al, 1994;Watson, 1985). Other Puccinia spp.…”

Microscopic observations of a compatible host/pathogen interaction between a potential biocontrol agent (Uromyces pencanus) and its target weed (Nassella neesiana)

“…The technique is easy to perform and has the advantage of allowing a relatively rapid examination of the rust infection process on leaf samples of weeds and cultivated plants (Bruzzese and Hasan 1983). It has been shown to work very well with whole leaf portions of the flat leaves of dicotyledonous species (Bruzzese and Hasan 1986;Evans and Tomley 1994;Parker et al 1994) or of some grass species such as Dactylis glomerata (Bruzzese and Hasan 1983), maize, oat, or wheat (personal observations).…”

“…The whole leaf clearing-staining technique proposed by Bruzzese and Hasan (1983) has been included in the host range testing of many rust fungi selected as prospective candidates in biological control programs, especially in projects in which a high number of species must be tested against the pathogen (Bruzzese and Hasan 1986;Evans and Tomley 1994;Parker et al 1994). The technique is easy to perform and has the advantage of allowing a relatively rapid examination of the rust infection process on leaf samples of weeds and cultivated plants (Bruzzese and Hasan 1983).…”

Selection of pathogen agents in weed biological control: critical issues and peculiarities in relation to arthropod agents

“…Nonetheless, such native-range studies are seldom carried out to assist the selection process of pathogens. While controlled-environment experiments are also sometimes performed to measure the pathogen's impact (Parker et al 1994;Shishkoff & Bruckart 1996;Evans & Bruzzese 2003;Berner & Bruckart 2005), results are generally inadequate to make sound predictions of field impact under varying and often less than optimum conditions. Only once has a limited field trial of an exotic pathogen (Puccinia carduorum Jacky) in the introduced range of the target weed (musk thistle; Carduus nutans) been approved prior to large-scale releases (Baudoin et al 1993).…”