Invasiveness Assessment - Lesser broomrape (Orobanche minor) in Victoria

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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.

Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here.

The following table provides information on the invasiveness of Lesser broomrape.

A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:

Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Lesser broomrape
Scientific name: Orobanche minor

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Germination will occur after the seeds have been exposed to a period of preconditioning; have been stimulated by root exudates of host or false host species and exposed to seasonal temperature and moisture levels (Koncalocá & Kropác 1997).	MH	H
Establishment requirements?	Needs to be in the vicinity of the roots of a host plant (Evans 1962).	ML	H
How much disturbance is required?	Establishes in growing crops including clover, tobacco and broad bean (Foy et al 1989).	MH	H
Growth/Competitive
Life form?	Other; an annual or perennial herbaceous obligate root parasite (Holm et al 1997).	L	H
Allelopathic properties?	Does reduce the host plants vigour, however there is allelopathy reported.	L	M
Tolerates herb pressure?	In Europe it is considered unpalatable by stock as it smells and has a bitter taste, however it has been reported to be grazed in Australia (Evans 1962). Grazing by sheep has reportedly resulted in death of those plants grazed, can be eliminated with heavy grazing (Southwood 1971). Grazing may kill plants but seeds of other Orobanche sp. have been reported to remain viable after passing through a sheep (Foy et al 1989). Therefore under moderate grazing the species is considered to be still capable of sexual reproduction.	MH	H
Normal growth rate?	As a parasite Orobanche clearly has a competitive advantage over any of its host species, it can effectively stop the host plant growing (Eizenberg, Colquhoun & Mallory-Smith 2005). Once the plant emerges it will flower, set seed and die back in the space of a few months (Holm et al 1997). Therefore the species is considered to be competitive with other fast growing annual and perennial herbs.	MH	H
Stress tolerance to frost, drought, w/logg, sal. etc?	Unknown, probably dependent on host species.	M	L
Reproduction
Reproductive system	Produces seed through self pollination (Elias et al 2006).	L	H
Number of propagules produced?	Jones (1991) report a maximum theoretical seed production of 111,780 seeds, if the plant produced 90 flowers which was the maximum number produced by a plant during their study and each capsule contained 1242 seeds which was also the maximum found during their study. The seed production is deemed high as to produce more than 200 seeds, either the plant with 90 flowers only need to produce 25 seeds per capsule or two capsules with the maximum number of seeds of 1242.	H	H
Propagule longevity?	There are reports that the species seeds can remain viable for more than 10 years, it is unknown however what proportion remain viable. Seeds can remain viable in the soil for more than 10 years (Elias et al 2006). Seed remains viable in the soil for 10-15 years (Edwards 1972).	M	M
Reproductive period?	Under favourable conditions can have two periods of reproduction, however most commonly acts as an annual (Evans 1962).	ML	H
Time to reproductive maturity?	The species is treated as an annual however the seedlings may live in the soil for a number of years before emerging (Mussleman 1994).	H	H
Dispersal
Number of mechanisms?	Seeds are very small and can be dispersed by wind, water, grazing animals and accidental human dispersal though contamination (Elias et al 2006).	H	H
How far do they disperse?	Not specifically known; however with the range and number of dispersal agents it is likely that some seeds will disperse more than 1km.	H	M

Note: Phyla canescens has previously been regarded as a synonym of P. nodiflora, and although the two species are similar and closely related, they are separate species (Julien et al 2004, Munir 1993).

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