The biology of Endophyllum osteospermi, and its use for the biological control of Chrysanthemoides monilifera ssp. monilifera

Wood, A. R. (Alan Robert) (2004-12)

Dissertation (PhD Agric)--University of Stellenbosch, 2004.

Thesis

ENGLISH ABSTRACT: Chrysanthemoides monilifera ssp. monilifera is a shrub indigenous to South Africa, which has become a serious weed of native vegetation in Australia. Endophyllum osteospermi is a microcyclic, autoecious, rust fungus that induces witches' brooms on C. monilifera ssp. monilifera. This rust is considered as a candidate biocontrol agent for use against C. monilifera ssp. monilifera in Australia. The vegetative growth and reproductive output of healthy branches on bushes with different levels of E. osteospermi infections were measured at three sites. The growth of healthy branches on infected bushes was 26- 81% less than that of healthy branches on uninfected bushes. The number of buds, flowering capitulae, fruiting capitulae, and cypselas on healthy branches of infected bushes was 35-75%, 45-90%, 15-99%, and 15-90% less, respectively, than those on uninfected bushes. At five sites, the infection levels and number of witches' brooms were determined every two months. The increase in number of witches' brooms per bush ranged between o and 282 within one year, with an average increase per bush of28 (SE ± 4.8) and 39 (SE ± 9.2) during two years. The average simple interest rate (rs) increase of infection levels for all bushes was 0.015 month-I (s.e. ± 0.0041, n = 72) and 0.0098 month" (s.e. ± 0.0073, n = 43) during two years. Aecidioid teliospores germinated between 10 and 20oe, with 15°e as optimum. Light, and particularly near-uv light, stimulated germination. A period of 6 to 8 hours of light was needed to obtain optimum germination levels. The temperature requirements for basidiospore development differed from that of aecidioid teliospore germination. Optimum was at 15°e, but a rapid decrease in basidiospore production occurred at higher temperatures, few developed at 19°e. Two nuclear divisions occurred within 12 hours of germination to produce a metabasidium with three or four nuclei. A third nuclear division occurred in the basidiospores between 24 and 48 hours. Plants inoculated under controlled conditions took 5 to 24 months before witches' brooms began to develop. A Geographic Information System (GIS) approach was used to model the potential distribution of E. osteospermi in South Africa, based on monthly average climate surfaces with parameters derived from the above experiments. The same model was applied to Australia to suggest a potential distribution of the rust if released in Australia. This potential distribution was similar to one generated using the climate matching computer programme CLIMEX©, but gave greater spatial accuracy. Both approaches indicate that E. osteospermi should establish in temperate Australia. Chrysanthemoides species, as well as other South African asteraceaus plants, were monitored for E. osteospermi between 1992 and 2003. Endophyllum osteospermi was recorded on C. monilifera ssp. monilifera, C. monilifera ssp. pisifera, C. monilifera ssp. rotundata, C. monilifera ssp. canescens, C. monilifera ssp. subcanescens, C. incana, an undescribed taxon of Chrysanthemoides, Osteospermum ciliatum, 0. polygaloides and 0. potbergense. Endophyllum dimorphothecae sp. nov. is described on Dimorphotheca cuneata. Aecidium elytropappi, which was recorded on Elytropappus rhinocerostis and Stoebe plumose, is transferred to Endophyllum as E. elytropappi comb. nov. Germination of aecidioid teliospores and penetration by basidiospores were observed on the surface of excised leaves of 32 plant species at 4 days after inoculation. Germinating aecidioid teliospores aborted on 14 plant species, whilst no penetration was attempted on a further 12. Penetration only occurred on 9. Therefore only these 9 plant species need to undergo traditional host specificity testing. Pending these results, E. osteospermi could be safely released in Australia for the biological control of C. monilifera ssp. monilifera.

AFRIKAANSE OPSOMMING: Chrysanthemoides monilifera ssp. monilifera 'n meerjarige wat inheems in Suid Afrika is, het 'n belangrike onkruid in Austalië geword. Endophyllum osteospermi 'n mikrosikliese, autoecious roesswam, induseer heksebesems op C. monilifera ssp. monilifera. Hierdie roesswam word as 'n potensiële biologiese beheeragent teen C. monilifera ssp. monilifera in Austalië beskou. Die vegetatiewe groei en voortplanting van gesonde takke op struike met verskillende vlakke van E. osteospermi infeksies is by drie lokaliteite gemeet. Groei van gesonde takke op geinfekteerde bosse was 26-81 % minder as die van gesonde takke op ongeïnfekteerde bosse. Die aantalokselknoppe, blommende capitulum, vrugdraende capitulum en pitvrugte op individuele gesonde takke van geïnfekteerde bosse was onderskeidelik 35-75%, 45-90%,15-99%, en 15-90% minder, as die op ongeïnfekteerde bosse. By vyf lokaliteite is die infeksievlakke en die aantal heksebesems elke twee maande vasgestel. Die toename in heksebesems van elke plant was tussen 0 en 282 binne eenjaar, met 'n gemmidel van 28 (SE ± 4.8) en 39 (SE ± 9.2) geduurende twee jaare. Die gemiddelde eenvoudige rentekoers (rs) toename in infeksievlakke van al die struike was 0.015 maand" (s.e. ± 0.0041, n = 72) en 0.0098 maand-1 (s.e. ± 0.0073, n = 43) gedurende twee jaare. Ontkieming van aecidioidteliospore het tussen 100e en 200e met 15°e as die optimum. Lig en veral naby-uv lig het ontkieming gestimuleer, terwylontkieming relatief swak was onder donker toestande. 'n Periode van 6 tot 8 uur lig was nodig vir optimale ontkiemingsvlakke. Die temperatuurvereistes vir basidiospoor ontwikkeling het verskil van die van aecidioid teliospoor ontkieming. Optimale was by 15°e, maar 'n vinnige afname in basidiospoorproduksie het by hoër temperature voorgekom, min het by 19°e voorgekom. Twee kernverdelings het binne 12 ure van die begin van ontkieming voorgekom om 'n metabasidium te produseer met drie of vier kerne. 'n Derde kern verdeling het in die basidiospore tussen 24 en 48 uur voorgekom. Plante wat onder beheeerde toestande geïnokuleer is het heksebesems 5 tot 24 maande na inokulasie ontwikkel. 'n Geografiese Inligtings Sisteem (GIS) benadering is gebruik om 'n model vir die potensiële verspreiding van E. osteospermi in Suid Afrika te ontwikkel, gebasseer op die maandelikse gemiddelde klimaatoppervlaktes met parameters wat vanaf bogenoemde eksperimente verkry is. Dieselfde model is in Austalië toegepas om 'n potensiële verspreiding van die roesswam voor te stel. Hierdie potensiële verspreiding was soortgelyk aan 'n program wat met die klimaats vergelykende rekenaarsprogram CLIMEX© ontwikel is, maar dit het groter ruimtelike akkuraatheid gemaak. Beide benaderings het aangedui dat E. osteospermi in Austalië behoort te vestig. Chrysanthemoides spesies, asook ander inheemse plante van die Asteraceae, is tussen 1992 en 2003 vir die voorkoms van E. osteospermi in Suid Afrika waargeneem. Endophyllum osteospermi is op C. monilifera ssp. monilifera, C. monilifera ssp. pisifera, C. monilifera ssp. rotundata, C. monilifera ssp. canescens, C. monilifera ssp. subcanescens, C. incana, 'n onbeskryfde taxon van Chrysanthemoides, Osteospermum ciliatum, a. polygaloides en a. potbergense waargeneem. Endophyllum dimorphothecae sp. nov. is beskryf op Dimorphotheca cuneata. Aecidium elytropappi, wat op Elytropappus rhinocerostis en Stoebe plumosa voorkom, is by Endophyllum ingesluit as E. elytropappi comb. nov. Ontkieming van aecidioidteliospore en penetrasie deur basidiospore op die oppervlak van verwyderde blare van 32 plant spesies 4 dae na inokulasie is waargeneem. Ontkiemende aecidioidteliospore het op 14 toets plant spesies ge-aborteer, terwyl geen penetrasie op 'n verdere 12 gepoog is nie. Penetrasie het slegs op 9 voorgekom. Derhalwe hoef slegs die 9 plant spesies tradisionele gasheer spesifisiteitstoetse te ondergaan. Afhangende van die resultate kan E. osteospermi dus met veiligheid in Austalië vir die biologiese beheer van C. monilifera ssp. monilifera vrygelaat word.

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