Difference between "biotroph" and "parasitic"

Question

In the studying process for my exam I learned about ways of life of pathogenes in plants. There, it was mentioned, they can live nekrotrophic, hemibiotrophic or biotrophic. As far as I understand, a biotrophic way of living includes being completly dependent on your host. Therefore, those pathogenes do not kill their host.

That sounds like a parasitic way of life. However, I neither found a source that proved me that this is the same nor did I found a source that specifically explained the difference.

I would be very grateful, if some one can explain this to me! Thank you in advance!

Answer 1

I think the Wiktionary definition of biotrophic is enlightening (emphasis mine):

Describing a parasite or symbiont that needs its host in order to stay alive.

So, all non-necrotrophic obligate parasites are biotrophic, but not all biotrophic organisms are parasites.

Fungi of the lineage Glomeromycota (also called arbuscular mycorrhizal fungi) may be considered biotrophic plant symbionts. Association of these fungi with roots improves plant acquisition of nutrients from soil and, in exchange, allows the fungi to obtain photosynthesis-derived carbon sources from the plant.¹ Textbook sources corroborate that such fungi are biotrophic.²

These fungi have a low, or negligible, saprophytic ability and can apparently produce viable propagules only upon the biotrophic colonization of a susceptible host root.

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References

1. Corradi N, Bonfante P. The arbuscular mycorrhizal symbiosis: origin and evolution of a beneficial plant infection. PLoS Pathog. 2012;8(4):e1002600.
2. Azcón-Aguilar C, Bago B, Barea JM. Saprophytic Growth of Arbuscular Mycorrhizal Fungi. In: Varma A, Hock B. (eds) Mycorrhiza. Springer, Berlin, Heidelberg. 1999.