Differential Colonization Patterns of Bananas (Musa spp.) by Physiological Race 1 and Race 4 Isolates of Fusarium oxysporum f.sp cubense

摘要

Fusarium oxysporum f.sp. cubense (Foc) is the causative agent of Fusarium wilt of bananas (Musa spp.). To clarify the colonization patterns of Foc in bananas, two green fluorescent protein-tagged isolates, NT320 (race 1) and B2-gfp (race 4), were used to follow infection of the banana varieties Pisang Awak and Brazil. Penetration and colonization of both isolates in roots of these two banana varieties were observed within 6days, but sporulation in xylem vessels was not observed until day 30 postinoculation. Interestingly, B2-gfp penetrated into xylem vessels of Pisang Awak banana roots more quickly than NT320, implying that the race 4 isolate is more virulent than the race 1 isolate. This result was further confirmed by comparing the disease severity of plants inoculated with NT320 with that of plants inoculated with B2-gfp. Quantitative real-time PCR revealed that some pathogenicity-associated genes, including Fga1, Fhk1, Fow2 and Ste12, were upregulated by B2-gfp during exposure to Brazil bananas, while they were either downregulated by NT320 or not significantly changed. These data might partly explain why the race 4 isolate was more virulent than the race 1 isolate.