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Banana is the most popular and most exported fruit and also a major food crop for millions of people around the world. Despite its importance and the presence of serious disease threats, research into this crop is limited. One of those is Panama disease or Fusarium wilt. In the previous century Fusarium wilt wiped out the “Gros Michel” based banana industry in Central America. The epidemic was eventually quenched by planting “Cavendish” bananas. However, 50 years ago the disease recurred, but now on “Cavendish” bananas. Since then the disease has spread across South-East Asia, to the Middle-East and the Indian subcontinent and leaped into Africa. Here, we report the presence of Fusarium oxysporum f.sp. cubense Tropical Race 4 (Foc TR4) in “Cavendish” plantations in Laos, Myanmar, and Vietnam. A combination of classical morphology, DNA sequencing, and phenotyping assays revealed a very close relationship between the Foc TR4 strains in the entire Greater Mekong Subregion (GMS), which is increasingly prone to intensive banana production. Analyses of single-nucleotide polymorphisms enabled us to initiate a phylogeography of Foc TR4 across three geographical areas—GMS, Indian subcontinent, and the Middle East revealing three distinct Foc TR4 sub-lineages. Collectively, our data place these new incursions in a broader agroecological context and underscore the need for awareness campaigns and the implementation of validated quarantine measures to prevent further international dissemination of Foc TR4.

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Stable isotopes of N provide a new approach to the study of algal production in the ocean, yet know!edge of the isctopc fractionation (c) in various oceanic regime5 is i d~k i~~y .tiere w e report large and rapid changes in isotope composit~on (6'") of 2 coastal diatoms and 2 clones (open and coastal) of a coccolithophore grown in the simultaneous presence of nitrate, ammonium and urea under varylng conditions of N availability (i.e. N-sufficiency and N-starvation followed by N-resupply) and hence different physiological states. Du.ring N-sufficiency, the SI5N of particulate organic N (PON) was well reproduced, uslng a model derived from Rayleigh distillation theory, with constant E similar to that for growth on each individual N source. However, following N-resupply, the variations in S15NpoU could be well explained only in the case of the open ocean Emiliania huxleyi, with E similar to N-sufficient conditions. It was concluded that the mechanism of isotope fractionation changed rapidly with N availability for the 3 coastal clones. However, in the case of E. huxleyi isolated from the Subarctic Pacific Ocean, no evidence of a change in mechanism was found, suggesting that perhaps open ocean species can quickly recover from N-depleted conditions.

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