Field Resistance in Three Native Monocotyledon Species That Colonize Indigenous Sclerophyll Forest After Invasion by Phytophthora cinnamomi

Abstract

Lepidosperma laterale (Cyperaceae), Gahnia radula (Cyperaceae) and Poa sieberana (Poaceae) colonize bare ground of dry sclerophyll forest after disease due to P. cinnamomi. To determine their resistance, plants grown in divided root boxes were inoculated with 150-200 zoospores of the pathogen. Infected roots ceased growth. In the small necrotic lesions produced, the pathogen remained viable and capable of providing a source of inoculum for disease extension. Fungal growth was usually limited to the lesion but in some cases a few hyphae were observed in adjacent tissue. Away from the lesion there was a rapid reduction of fungal material and of the associated cellular disintegration. Rates of root production and root growth were not stimulated by infection but uninfected lateral roots replaced the root tip in some plants; in others, a new root tip emerged from the necrotic zone, enabling the plant to outgrow the fungal attack.

False-negative isolations or absence of lesions may cause mis-diagnosis of diseased plants infected with Phytophthora cinnamomi

“…It is important to recognise that symptomless plants having viable P. cinnamomi may, under conducive conditions, become diseased in the future and may provide a source of inoculum to contaminate otherwise disease-free sites. This concern has also been raised in root inoculation studies of Abies fraseri (Kenerley and Bruck 1983) and natural sedges (Phillips and Weste 1984), and in stem inoculations of jarrah (O'Gara et al 1997). …”

“…Other wound inoculation studies (Shea et al 1982;Phillips and Weste 1984;Davison et al 1994) have isolated P. cinnamomi in advance of lesions, although it was Davison et al (1994) who first described this as a hemibiotrophic interaction. With time, this initial biotrophic interaction became necrotrophic.…”

“…The presence of Phytophthora cinnamomi Rands is usually indicated by a lesion in the plant host, which is then confirmed by plating the tissue onto agar selective for Phytophthora (Tippett et al 1983;Robin 1992;Bunny et al 1995). Some reports indicate that P. cinnamomi is not confined to lesions as it has been isolated from symptomless tissue up to 30 mm in front of the lesion margin (Shea et al 1982;Phillips and Weste 1984;Davison et al 1994;Hüberli 1995). More important, however, is the recent isolation of P. cinnamomi from symptomless Eucalyptus marginata Donn.…”

Assessment of Australian native annual/herbaceous perennial plant species as asymptomatic or symptomatic hosts of Phytophthora cinnamomi under controlled conditions

“…). However, tolerant or resistant plant species could nevertheless host the pathogen (Phillips and Weste ; Sieler et al. ; McDougall ; Cahill et al.…”

Why are hairy root clusters so abundant in the most nutrient-impoverished soils of Australia?

“…This includes most members e x a m i n e d in the t r i b e s C a r i c e a e and R h y n c h o s p o r e a e of the C y p e r a c e a e both in Australia and elsewhere (Davies et al, 1973;Lamont, 1974;Phillips and Weste, 1984). The rootlets are swollen (dauciform) with obvious gaps between them but appear even hairier than proteoid roots.…”