Abstract:
Pitch canker, caused by Fusarium circinatum (teleomorph Gibberella circinata), is regarded
as one of the most severe phytopathogenic diseases affecting commercial Pinus plantations
worldwide, and is anticipated to be aggravated by the increase in temperature and humidity
associated with climate change. In South Africa, the preferred commercial pine species has
been Pinus patula. The fungus causes Fusarium-wilt on seedlings and has drastically decreased
the post-planting survival of seedlings. Hybridisation of P. patula with Fusarium-tolerant
species such as Pinus tecunumanii, has led to the development of an alternative planting stock.
However, the mechanisms underlying P. tecunumanii’s relative resistance remains
inconclusive. Previous research has highlighted the putative involvement of terpene synthases
in defence against Fusarium spp., as their regulation is significantly altered early in response
to this pathogen. RNA-seq reference transcriptomes for P. patula and P. tecunumanii have
provided the much-needed genetic resources necessary to interrogate the putative defence
related genes undergoing differential expression due to F. circinatum infection. The aim of this
study was to determine whether observed differences in resistance between these two hosts, is
correlated with induced terpene synthase gene expression profiles, and to resolve the implicated
orthologs. The differential expression patterns of genes identified as terpene synthase orthologs
was assessed for their potential to contribute to resistance. While the two host species, P. patula
and P. tecunumanii, did appear to respond dissimilarly, this is not indicative of terpene
synthesis playing a causal role in defence.