Abstract
Fusarium circinatum is the causal agent for the disease, pitch canker, in Pinus patula. Commercial forestry incurs large economic losses from the pathogen, primarily as a result of post-planting mortality resulting in increased re-establishment costs. One means of enhancing defense is through pretreatment of seedlings with chemicals or biologically derived compounds that stimulate defense responses; a process collectively known as induced resistance. We compared the efficiency of ten inducers in improving defense against F. circinatum in P. patula seedlings. Chitosan (10mg/ml) was effective in reducing and delaying disease symptoms of pitch canker in seedlings. Under both nursery and greenhouse conditions, chitosan application resulted in reduced lesion lengths in treated plants compared to non-treated plants over a period of six weeks (p<0.05, Kruskal–Wallis). Reverse transcription-quantitative PCR expression analysis revealed that the reduction in lesion size in treated seedlings was accompanied by a four-fold increase in transcript abundance of the phenylalanine ammonia lyase transcript, which encodes an enzyme involved in the first committed step of the phenylpropanoid pathway. We suggest that the application of chitosan as part of an integrated management strategy, be further investigated for an effective approach to induce resistance in P. patula seedlings against F. circinatum.
Highlights
The fungal pathogen, Fusarium circinatum, affects a range of commercially important hosts worldwide
This study aimed to investigate the effectiveness of various chemical and biologicallyderived inducers in reducing disease symptoms caused by F. circinatum on P. patula and to subsequently determine the activation of induced resistance in P. patula at the molecular level
Two important findings have emerged from our observations i.e. (i) chitosan treatment of P. patula seedlings resulted in reduced F. circinatum disease symptoms and (ii) the application of chitosan resulted in enhanced expression of PpaPAL in P. patula, suggesting the onset of induced resistance
Summary
The fungal pathogen, Fusarium circinatum, affects a range of commercially important hosts worldwide (reviewed by Wingfield et al, 2008). Current disease management strategies are based on an integrated approach focusing on the use of appropriate nursery hygiene practices and the use of planting stock that are more tolerant to the pathogen (Mitchell et al, 2011). An alternative disease management strategy exploits the phenomenon of induced resistance in plants, which is potentially useful in improving resistance against a subsequent challenge by a pathogen (Eyles et al, 2009; Vallad and Goodman, 2004). The use of induced resistance has been explored extensively in agriculturally important crop plants such as maize, wheat and tomatoes (reviewed in Sticher et al, 1997; Vallad and Goodman, 2004)
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