Fusarium wilt disease of banana, caused by the notorious soil-borne pathogen Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), is extremely difficult to manage. Manipulation of soil pH or application of synthetic iron chelators can suppress the disease through iron starvation, which inhibits the germination of pathogen propagules called chlamydospores. However, the effect of iron starvation on chlamydospore germination is largely unknown. In this study, scanning electron microscopy was used to assemble the developmental sequence of chlamydospore germination and to assess the effect of iron starvation and pH in vitro. Germination occurs in three distinct phenotypic transitions (swelling, polarized growth, outgrowth). Outgrowth, characterized by formation of a single protrusion (germ tube), occurred at 2 to 3 h, and a maximum value of 69.3% to 76.7% outgrowth was observed at 8 to 10 h after germination induction. Germination exhibited plasticity with pH as over 60% of the chlamydospores formed a germ tube between pH 3 and pH 11. Iron-starved chlamydospores exhibited polarized-growth arrest, characterized by the inability to form a germ tube. Gene expression analysis of rnr1 and rnr2, which encode the iron-dependent enzyme ribonucleotide reductase, showed that rnr2 was upregulated (p < 0.0001) in iron-starved chlamydospores compared to the control. Collectively, these findings suggest that iron and extracellular pH are crucial for chlamydospore germination in Foc TR4. Moreover, inhibition of germination by iron starvation may be linked to a different mechanism, rather than repression of the function of ribonucleotide reductase, the enzyme that controls growth by regulation of DNA synthesis.

香蕉枯萎病，由臭名昭著的土传病原体尖孢镰刀菌引起。 sp。 cubense Tropical Race 4 (Foc TR4) 极难管理。控制土壤pH值或使用合成铁螯合剂可以通过铁饥饿来抑制疾病，铁饥饿会抑制称为厚垣孢子的病原体繁殖体的萌发。然而，缺铁对厚垣孢子萌发的影响在很大程度上尚不清楚。在这项研究中，使用扫描电子显微镜组装了厚垣孢子萌发的发育序列，并评估了体外铁饥饿和pH的影响。发芽发生在三种不同的表型转变中（肿胀、极化生长、生长）。发芽的特征是形成单个突起（胚芽管），发生在发芽诱导后 2 至 3 小时，并且在发芽诱导后 8 至 10 小时观察到最大发芽率，为 69.3% 至 76.7%。发芽表现出随 pH 值的可塑性，因为超过 60% 的厚垣孢子在 pH 3 和 pH 11 之间形成芽管。缺铁的厚垣孢子表现出极化生长停滞，其特征是无法形成芽管。对编码铁依赖性酶核糖核苷酸还原酶的rnr1和rnr2进行基因表达分析表明，与对照相比，缺铁厚垣孢子中rnr2表达上调 (p < 0.0001)。总的来说，这些发现表明铁和细胞外 pH 对于 Foc TR4 中厚垣孢子的萌发至关重要。 此外，铁饥饿对发芽的抑制可能与不同的机制有关，而不是与核糖核苷酸还原酶功能的抑制有关，核糖核苷酸还原酶是通过调节DNA合成来控制生长的酶。