Fusarium oxysporum f. sp. cubense (Foc) causes Fusarium wilt in banana (Musa AAA). Foc Race 1 devastated the subgroup Gros Michel during the first half of the twentieth century. The Gros Michel was largely replaced by the resistant subgroup Cavendish in the 1950s. However, in the 1980s, Foc Tropical Race 4 started to spread affecting Cavendish bananas. No proper control measures have been found to deal with the disease. This paper re-takes an important research line from the 1950s to evaluate the potential of soil management for Fusarium wilt management. The role of soil properties on Fusarium wilt in bananas was studied in two greenhouse experiments. It was evaluated whether the influence of two main soil properties (pH and N) on Fusarium wilt is similar for Race 1 and Tropical Race 4. Two soil pH levels (lower than 5.2 and higher than 6.0) respectively ensured through acidification and liming; and three levels of N (ammonium nitrate, 33.5% N) weekly doses (low:0 N g, medium: 0.08 N g and high: 0.25 N g per plant) were achieved. The first experiment in Costa Rica confirmed the earlier results about the influence of soil pH and nitrogen on Fusarium wilt (Race 1) on Gros Michel bananas. The second experiment in The Netherlands evaluated the influence of pH and N on interactions between Foc (both Race 1 and Tropical Race 4) and Cavendish bananas. Results in both experiments showed that soil pH affected crop development and the disease. Besides, the interaction of the lower pH x the higher N accelerated the infection and reduced plant development. As such, the results showed that soil management has the potential to reduce the impacts of Fusarium wilt while dealing with Race 1 and Tropical Race 4 although it requires confirmation and further evaluation under field conditions.

In the last century, Fusarium wilt of banana (FWB) destroyed the banana cultivar Gros Michel. The Cavendish cultivars saved the global banana industry, and currently they dominate global production (~50%) and the export trade (~95%). However, a new strain called Tropical Race 4 (TR4) surfaced in the late 1960’s, spread globally and greatly damages Cavendish plantations as well as manifold local varieties that are primarily grown by small holders. Presently, there is no commercially available replacement for Cavendish and hence control strategies must be developed and implemented to manage FWB. Here, we studied whether it is possible to induce resistance to TR4 by pre-inoculations with different Fusarium spp. Only pre-treatments with an avirulent Race 1 strain significantly reduced disease development of TR4 in a Cavendish genotype and this effect was stable at various nutritional and pH conditions. We then used transcriptome analysis to study the molecular basis of this response. Several genes involved in plant defence responses were up-regulated during the initial stages of individual infections with TR4 and Race 1, as well as in combined treatments. In addition, a number of genes in the ethylene and jasmonate response pathways as well as several gibberellin synthesis associated genes were induced. We observed upregulation of RGA2 like genes in all treatments. Hence, RGA2 could be a key factor involved in both R1 and TR4 resistance. The data support the hypothesis that activating resistance to Race 1 in Cavendish bananas affects TR4 development and provide a first insight of gene expression during the interaction between various Fusarium spp. and banana.

Aims This study looks whether the response of soil management (liming and nitrogen fertilization) on the incidence of Fusarium wilt (Foc Race 1) in Gros Michel banana (Musa AAA) is influenced by soil types. Methods The effect of inoculation with Foc Race 1 was studied in a factorial greenhouse trial with eight representative soil types of the Costa Rican banana region, two pH levels; and three levels of N-fertilization. After an 8-week period, plant biomass, leaf area, and a disease index were measured.Results There were significant effects of soil pH and N, and their interactions on disease expression. Low pH levels and high N-fertilization increased the disease expression. The response to changes in soil pH and N-fertilization differed considerably between the different soil types. Conclusions Although soil pH and N influence Fusarium wilt in banana, each soil type differs in its response to these soil properties. This complicates the development of standard soil management strategies in terms of e.g., N-fertilization and liming to mitigate or fight the disease.

Introducción. Las rizobacterias promotoras de crecimiento vegetal (RPCV) podrían ser utilizadas como una fuente alternativa al uso de fertilizantes nitrogenados convencionales en el cultivo de banano (Musa AAA). Es necesario la búsqueda de bacterias adaptadas a las condiciones de los suelos de Costa Rica y del cultivo del banano. Objetivo. Evaluar el efecto de la inoculación de cuatro aislamientos de Bacillus cereus sobre el crecimiento y el contenido de nitrógeno (N) de plántulas de banano en condiciones de invernadero. Materiales y métodos. Se realizaron dos experimentos simultáneos entre abril y septiembre 2020, en el Centro de Investigaciones de la Corporación Bananera Nacional (CORBANA), La Rita, Limón, Costa Rica. Se inocularon cuatro aislamientos de B. cereus en plantas de banano a las cuales se les fertilizó con cuatro dosis de nitrógeno semanalmente. El diseño consistió en parcelas divididas, donde la parcela principal estuvo conformada por cuatro niveles de N: 0, 33, 66, 100 % de la dosis; y la parcela pequeña por los aislamientos bacterianos y el testigo. Se midieron las variables altura de planta, contenido de clorofila, el área foliar de la tercera hoja, peso fresco y seco de raíces, cormo, pseudotallo y hojas, así como el contenido de nitrógeno en cada órgano. Resultados. El experimento 1: las plantas inoculadas con el aislamiento SER-23 presentaron el mayor peso seco total. En el experimento 2: el mayor peso seco total se observó en las plántulas inoculadas con el aislamiento BF-98. La aplicación de las bacterias SER-23 y BF-98 aumentó significativamente el contenido de nitrógeno en todos los órganos evaluados. Conclusiones. La inoculación de los aislamientos de Bacillus cereus SER-23 y BF-98 estimuló el aumento de la biomasa y contenido de nitrógeno en las plantas de banano, este incremento dependió de la disponibilidad de nitrógeno y el tipo de suelo.