Abstract
Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cubense, especially by tropical race 4 (Foc TR4), is threatening the global banana industry. Musa acuminata Pahang, a wild diploid banana that displays strong resistance to Foc TR4, holds great potential to understand the underlying resistance mechanisms. Microscopic examination reports that, in a wounding inoculation system, the Foc TR4 infection processes in roots of Pahang (resistant) and a triploid cultivar Brazilian (susceptible) were similar by 7 days post inoculation (dpi), but significant differences were observed in corms of both genotypes at 14 dpi. We compare transcriptomic responses in the corms of Pahang and Brazilian, and show that Pahang exhibited constitutive defense responses before Foc TR4 infection and inducible defense responses prior to Brazilian at the initial Foc TR4 infection stage. Most key enzymatic genes in the phenylalanine metabolism pathway were up-regulated in Brazilian, suggesting that lignin and phytotoxin may be triggered during later stages of Foc TR4 infection. This study unravels a few potential resistance candidate genes whose expression patterns were assessed by RT-qPCR assay and improves our understanding the defense mechanisms of Pahang response to Foc TR4.
Highlights
Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cubense (Foc), is a destructive soil-borne banana disease which is threatening the global banana industry[1,2]
The lesion size in corms (Fig. 1g) and disease index (Fig. 1h) of Pahang was significantly less than that of Brazilian at 14 dpi. It suggested that in a wounding inoculation system, the infection processes in roots of Pahang and Brazilian were similar by 7 dpi, but significant differences occurred in corms of both banana genotypes at 14 dpi
We focused on the response to Foc TR4 of corm tissues, which link roots to the pseudostem and leaves, rather than the roots because significant differential symptoms were displayed in corms due to Foc TR4 infection, and this is the first report where the corm is analysed during the banana-Foc TR4 interaction
Summary
Fusarium wilt disease, caused by Fusarium oxysporum f. sp. cubense (Foc), is a destructive soil-borne banana disease which is threatening the global banana industry[1,2]. After Foc infection, bananas undergo a series of changes in physiology, biochemistry and molecular biology, such as accumulating H2O2 sharply in the root cells[16]; strengthening root cell walls through accumulation of lignin and phenolics[17,18,19]; secreting root exudates to inhibit spore germination and hyphal growth[20]; activating salicylic acid (SA) or jasmonic acid (JA) metabolism and signal transduction[21,22]; up-regulating cell-death genes like MusaBAG123 and β-1,3-glucanase genes[24] to inhibit the growth of the pathogen These studies focused on the banana-Foc interaction, the molecular mechanisms underlying resistance to Fusarium wilt remained unclear. RT-qPCR assays further indicated the high reliability of RNA-seq data
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