The Development of Thematic Core Collections in Cassava Based on Yield, Disease Resistance, and Root Quality Traits

Thematic collections (TCs), which are composed of genotypes with superior agronomic traits and reduced size, offer valuable opportunities for parental selection in plant breeding programs. Three TCs were created to focus on crucial attributes: root yield (CC_Yield), pest and disease resistance (CC_Disease), and root quality traits (CC_Root_quality). The genotypes were ranked using the best linear unbiased predictors (BLUP) method, and a truncated selection was implemented for each collection based on specific traits. The TCs exhibited minimal overlap, with each collection comprising 72 genotypes (CC_Disease), 63 genotypes (CC_Root_quality), and 64 genotypes (CC_Yield), representing 4%, 3.5%, and 3.5% of the total individuals in the entire collection, respectively. The Shannon-Weaver Diversity Index values generally varied but remained below 10% when compared to the entire collection. Most TCs exhibited observed heterozygosity, genetic diversity, and the inbreeding coefficient that closely resembled those of the entire collection, effectively retaining 90.76%, 88.10%, and 88.99% of the alleles present in the entire collection (CC_Disease, CC_Root_quality, and CC_Disease, respectively). A PCA of molecular and agro-morphological data revealed well-distributed and dispersed genotypes, while a discriminant analysis of principal components (DAPC) displayed a high discrimination capacity among the accessions within each collection. The strategies employed in this study hold significant potential for advancing crop improvement efforts.

Improvements in the Resistance of the Banana Species to Fusarium Wilt: A Systematic Review of Methods and Perspectives

The fungus Fusarium oxysporum f. sp. cubense (FOC), tropical race 4 (TR4), causes Fusarium wilt of banana, a pandemic that has threatened the cultivation and export trade of this fruit. This article presents the first systematic review of studies conducted in the last 10 years on the resistance of Musa spp. to Fusarium wilt. We evaluated articles deposited in different academic databases, using a standardized search string and predefined inclusion and exclusion criteria. We note that the information on the sequencing of the Musa sp. genome is certainly a source for obtaining resistant cultivars, mainly by evaluating the banana transcriptome data after infection with FOC. We also showed that there are sources of resistance to FOC race 1 (R1) and FOC TR4 in banana germplasms and that these data are the basis for obtaining resistant cultivars, although the published data are still scarce. In contrast, the transgenics approach has been adopted frequently. We propose harmonizing methods and protocols to facilitate the comparison of information obtained in different research centers and efforts based on global cooperation to cope with the disease. Thus, we offer here a contribution that may facilitate and direct research towards the production of banana resistant to FOC.

Members of Gammaproteobacteria as indicator species of healthy banana plants on Fusarium wilt-infested fields in Central America

Culminating in the 1950's, bananas, the world's most extensive perennial monoculture, suffered one of the most devastating disease epidemics in history. In Latin America and the Caribbean, Fusarium wilt (FW) caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (FOC), forced the abandonment of the Gros Michel-based export banana industry. Comparative microbiome analyses performed between healthy and diseased Gros Michel plants on FW-infested farms in Nicaragua and Costa Rica revealed significant shifts in the gammaproteobacterial microbiome. Although we found substantial differences in the banana microbiome between both countries and a higher impact of FOC on farms in Costa Rica than in Nicaragua, the composition especially in the endophytic microhabitats was similar and the general microbiome response to FW followed similar rules. Gammaproteobacterial diversity and community members were identified as potential health indicators. Healthy plants revealed an increase in potentially plant-beneficial Pseudomonas and Stenotrophomonas, while diseased plants showed a preferential occurrence of Enterobacteriaceae known for their plant-degrading capacity. Significantly higher microbial rhizosphere diversity found in healthy plants could be indicative of pathogen suppression events preventing or minimizing disease expression. This first study examining banana microbiome shifts caused by FW under natural field conditions opens new perspectives for its biological control.

Identification, transcriptional and functional analysis of heat-shock protein 90s in banana (Musa acuminata L.) highlight their novel role in melatonin-mediated plant response to Fusarium wilt

As one popular fresh fruit, banana (Musa acuminata) is cultivated in the world's subtropical and tropical areas. In recent years, pathogen Fusarium oxysporum f. sp. cubense (Foc) has been widely and rapidly spread to banana cultivated areas, causing substantial yield loss. However, the molecular mechanism of banana response to Foc remains unclear, and functional identification of disease-related genes is also very limited. In this study, nine 90 kDa heat-shock proteins (HSP90s) were genomewide identified. Moreover, the expression profile of them in different organs, developmental stages, and in response to abiotic and fungal pathogen Foc were systematically analyzed. Notably, we found that the transcripts of 9 MaHSP90s were commonly regulated by melatonin (N-acetyl-5-methoxytryptamine) and Foc infection. Further studies showed that exogenous application of melatonin improved banana resistance to Fusarium wilt, but the effect was lost when cotreated with HSP90 inhibitor (geldanamycin, GDA). Moreover, melatonin and GDA had opposite effect on auxin level in response to Foc4, while melatonin and GDA cotreated plants had no significant effect, suggesting the involvement of MaHSP90s in the cross talk of melatonin and auxin in response to fungal infection. Taken together, this study demonstrated that MaHSP90s are essential for melatonin-mediated plant response to Fusarium wilt, which extends our understanding the putative roles of MaHSP90s as well as melatonin in the biological control of banana Fusarium wilt.

Heat shock transcription factors in banana: genome-wide characterization and expression profile analysis during development and stress response

Banana (Musa acuminata) is one of the most popular fresh fruits. However, the rapid spread of fungal pathogen Fusarium oxysporum f. sp. cubense (Foc) in tropical areas severely affected banana growth and production. Thus, it is very important to identify candidate genes involved in banana response to abiotic stress and pathogen infection, as well as the molecular mechanism and possible utilization for genetic breeding. Heat stress transcription factors (Hsfs) are widely known for their common involvement in various abiotic stresses and plant-pathogen interaction. However, no MaHsf has been identified in banana, as well as its possible role. In this study, genome-wide identification and further analyses of evolution, gene structure and conserved motifs showed closer relationship of them in every subgroup. The comprehensive expression profiles of MaHsfs revealed the tissue- and developmental stage-specific or dependent, as well as abiotic and biotic stress-responsive expressions of them. The common regulation of several MaHsfs by abiotic and biotic stress indicated the possible roles of them in plant stress responses. Taken together, this study extended our understanding of MaHsf gene family and identified some candidate MaHsfs with specific expression profiles, which may be used as potential candidates for genetic breeding in banana.