Genetic diversity and population structure in banana (Musa spp.) breeding germplasm.

Bananas (Musa spp.) are one of the most highly consumed fruits globally, grown in the tropical and sub-tropical regions. We evaluated 856 Musa accessions from the breeding programs of the International Institute of Tropical Agriculture of Nigeria, Tanzania, and Uganda; the National Agricultural Research Organization of Uganda; the Brazilian Agricultural Research Corporation (Embrapa); and the National Research Centre for Banana of India. Accessions from the in vitro gene bank at the International Transit Centre in Belgium were included to provide a baseline of available global diversity. A total of 16,903 informative single nucleotide polymorphism markers were used to estimate and characterize the genetic diversity and population structure and identify overlaps and unique material among the breeding programs. Analysis of molecular variance displayed low genetic variation among accessions and diploids and a higher variation among tetraploids (p < 0.001). Structure analysis revealed two major clusters corresponding to genomic composition. The results indicate that there is potential for the banana breeding programs to increase the diversity in their breeding materials and should exploit this potential for parental improvement and to enhance genetic gains in future breeding efforts.

Striking variation in chromosome structure within Musa acuminata subspecies, diploid cultivars, and F1 diploid hybrids.

The majority of cultivated bananas originated from inter- and intra(sub)specific crosses between two wild diploid species, Musa acuminata and Musa balbisiana. Hybridization and polyploidization events during the evolution of bananas led to the formation of clonally propagated cultivars characterized by a high level of genome heterozygosity and reduced fertility. The combination of low fertility in edible clones and differences in the chromosome structure among M. acuminata subspecies greatly hampers the breeding of improved banana cultivars. Using comparative oligo-painting, we investigated large chromosomal rearrangements in a set of wild M. acuminata subspecies and cultivars that originated from natural and human-made crosses. Additionally, we analyzed the chromosome structure of F1 progeny that resulted from crosses between Mchare bananas and the wild M. acuminata 'Calcutta 4' genotype. Analysis of chromosome structure within M. acuminata revealed the presence of a large number of chromosomal rearrangements showing a correlation with banana speciation. Chromosome painting of F1 hybrids was complemented by Illumina resequencing to identify the contribution of parental subgenomes to the diploid hybrid clones. The balanced presence of both parental genomes was revealed in all F1 hybrids, with the exception of one clone, which contained only Mchare-specific SNPs and thus most probably originated from an unreduced diploid gamete of Mchare.

Datasets from fertilized improved and local varieties of cassava grown in the highlands of South Kivu, Democratic Republic of Congo.

The use of mineral fertilizer and organic inputs with an improved and local variety of cassava allows (i) to identify nutrient limitations to cassava production, (ii) to investigate the effects of variety and combined application of mineral and organic inputs on cassava growth and yield and (iii) to evaluate the profitability of the improved variety and fertilizer use in cassava production. Data on growth, yield and yield components of an improved and local variety of cassava, economic analysis, soil and weather, collected during two growing cycles of cassava in farmer's fields in the highlands of the Democratic Republic of Congo (DR Congo) are presented. The data complement the recently published paper "Increased cassava growth and yields through improved variety use and fertilizer application in the highlands of South Kivu, Democratic Republic of Congo" (Munyahali et al., 2023) [1]. Data on plant height and diameter were collected throughout the growing period of the crop while the data on the storage root, stem, tradable storage root, non-tradable storage root and harvest index were determined at 12 months after planting (MAP). An economic analysis was performed using a simplified financial analysis whereby additional benefits were calculated relative to the respective control treatments; the total costs included the purchasing price of fertilizers and the additional net benefits represented the revenue from the increased storage root yield due to fertilizer application. The value cost ratio (VCR) was calculated as the additional net benefits over the cost of fertilizer purchase.

Unravelling the diversity in water usage among wild banana species in response to vapour pressure deficit.

The rise in global temperature is not only affecting plant functioning directly, but is also increasing air vapour pressure deficit (VPD). The yield of banana is heavily affected by water deficit but so far breeding programs have never addressed the issue of water deficit caused by high VPD. A reduction in transpiration at high VPD has been suggested as a key drought tolerance breeding trait to avoid excessive water loss, hydraulic failure and to increase water use efficiency. In this study, stomatal and transpiration responses under increasing VPD at the leaf and whole-plant level of 8 wild banana (sub)species were evaluated, displaying significant differences in stomatal reactivity. Three different phenotypic groups were identified under increasing VPD. While (sub)species of group III maintained high transpiration rates under increasing VPD, M. acuminata ssp. errans (group I), M. acuminata ssp. zebrina (group II) and M. balbisiana (group II) showed the highest transpiration rate limitations to increasing VPD. In contrast to group I, group II only showed strong reductions at high VPD levels, limiting the cost of reduced photosynthesis and strongly increasing their water use efficiency. M. acuminata ssp. zebrina and M. balbisiana thus show the most favourable responses. This study provides a basis for the identification of potential parent material in gene banks for breeding future-proof bananas that cope better with lack of water.

Genetic Mapping, Candidate Gene Identification and Marker Validation for Host Plant Resistance to the Race 4 of Fusarium oxysporum f. sp. cubense Using Musa acuminata ssp. malaccensis.

Fusarium wilt of banana is a devastating disease that has decimated banana production worldwide. Host resistance to Fusarium oxysporum f. sp. Cubense (Foc), the causal agent of this disease, is genetically dissected in this study using two Musa acuminata ssp. Malaccensis segregating populations, segregating for Foc Tropical (TR4) and Subtropical (STR4) race 4 resistance. Marker loci and trait association using 11 SNP-based PCR markers allowed the candidate region to be delimited to a 12.9 cM genetic interval corresponding to a 959 kb region on chromosome 3 of 'DH-Pahang' reference assembly v4. Within this region, there was a cluster of pattern recognition receptors, namely leucine-rich repeat ectodomain containing receptor-like protein kinases, cysteine-rich cell-wall-associated protein kinases, and leaf rust 10 disease-resistance locus receptor-like proteins, positioned in an interspersed arrangement. Their transcript levels were rapidly upregulated in the resistant progenies but not in the susceptible F2 progenies at the onset of infection. This suggests that one or several of these genes may control resistance at this locus. To confirm the segregation of single-gene resistance, we generated an inter-cross between the resistant parent 'Ma850' and a susceptible line 'Ma848', to show that the STR4 resistance co-segregated with marker '28820' at this locus. Finally, an informative SNP marker 29730 allowed the locus-specific resistance to be assessed in a collection of diploid and polyploid banana plants. Of the 60 lines screened, 22 lines were predicted to carry resistance at this locus, including lines known to be TR4-resistant, such as 'Pahang', 'SH-3362', 'SH-3217', 'Ma-ITC0250', and 'DH-Pahang/CIRAD 930'. Additional screening in the International Institute for Tropical Agriculture's collection suggests that the dominant allele is common among the elite 'Matooke' NARITA hybrids, as well as in other triploid or tetraploid hybrids derived from East African highland bananas. Fine mapping and candidate gene identification will allow characterization of molecular mechanisms underlying the TR4 resistance. The markers developed in this study can now aid the marker-assisted selection of TR4 resistance in breeding programs around the world.

Identification of a Major QTL-Controlling Resistance to the Subtropical Race 4 of Fusarium oxysporum f. sp. cubense in Musa acuminata ssp. malaccensis.

Vascular wilt caused by the ascomycete fungal pathogen Fusarium oxysporum f. sp. cubense (Foc) is a major constraint of banana production around the world. The virulent race, namely Tropical Race 4, can infect all Cavendish-type banana plants and is now widespread across the globe, causing devastating losses to global banana production. In this study, we characterized Foc Subtropical Race 4 (STR4) resistance in a wild banana relative which, through estimated genome size and ancestry analysis, was confirmed to be Musa acuminata ssp. malaccensis. Using a self-derived F2 population segregating for STR4 resistance, quantitative trait loci sequencing (QTL-seq) was performed on bulks consisting of resistant and susceptible individuals. Changes in SNP index between the bulks revealed a major QTL located on the distal end of the long arm of chromosome 3. Multiple resistance genes are present in this region. Identification of chromosome regions conferring resistance to Foc can facilitate marker assisted selection in breeding programs and paves the way towards identifying genes underpinning resistance.

First Report of the Root-Knot Nematode Meloidogyne enterolobii Parasitizing Plantain (Musa spp., AAB) in Nigeria.

Plantain (Musa spp., AAB), an important staple food in Africa with West Africa accounting for 32% of global production, is prone to numerous pests and diseases of which plant-parasitic nematodes are a key concern. This includes root-knot nematodes (RKN; Meloidogyne spp.), which infect the roots, causing them to become galled, deformed and swollen. The nematode Meloidogyne enterolobii is considered a global threat to production of many important agricultural crops due to its extremely virulent and aggressive nature (Philbrick et al. 2020). In 2019, during a survey to identify the diversity of nematodes associated with Musa spp. in Nigeria, RKN females (n = 13) were isolated from a heavily galled root (50-75% galling) from a single plantain cv. Agbagba (Musa spp., AAB) plant in Onne, Rivers State, Nigeria (4°43'08.8"N 7°10'37.5"E). Genomic DNA was extracted from three females and processed individually using worm lysis buffer and proteinase K (Bert et al. 2008). The females were identified as M. enterolobii based on Nad5 mtDNA (Janssen et al. 2016), with GenBank accession no. ON010028, ON010027, ON010026, and were 100% homologous to the M. enterolobii sequences MW965454, KU372358 and KU372359 (Supplementary Figure S1). The sampled plant did not show any specific above-ground symptoms but swellings were apparent on the secondary and tertiary roots, which were associated with RKN females that were embedded in the root tissue. All the life stages were found clustered together in the root cortex, where they created necrotic brown-black lesions. A mean value of 2,604 ± 820 (mean ± standard deviation) males, eggs and second-stage juveniles (J2) were extracted from 5 g of root sub-samples (n = 6) using the Hussey and Barker (1973) NaOCl method. On average 39 females were hand-picked (n = 6) from 5 g fresh root. Pure cultures were established from single egg masses and maintained on RKN-susceptible tomato plants (Solanum lycopersicum cv. Marmande). To conduct Koch's postulates, two-month old plantlets of plantain cv. Agbagba (n = 5) were inoculated with 8000 J2s and eggs (initial population) of M. enterolobii pure cultures in 8 L pots in a screenhouse in Nigeria. Non-inoculated plantlets were included as negative controls. The nematode reproduction factor (RF = final density / initial population) and root damage symptoms were assessed 90 days post-inoculation. All the inoculated plantlets had similar galling symptoms and extensive necrosis as was observed in the field (Supplementary Figure S2), with an average RF = 25.9. No symptoms were observed on control plants. Adult females (n = 2) removed from the roots were identified as M. enterolobii based on Nad5 mtDNA (ON532789, ON532790) confirming that plantain cv. Agbagba is a host of M. enterolobii. In Nigeria, M. enterolobii has been reported to be associated with four plant species belonging to four plant families: Euphorbiaceae (Oyetunde et al. 2022), Cucurbitaceae (Bello et al. 2020), Dioscoreaceae (Kolombia et al. 2016), and Solanaceae (dos Santos et al. 2019). To our knowledge, this is the first report of M. enterolobii on a member of the Musaceae in Nigeria and globally the first report on plantain (Musa spp., AAB). The impact of M. enterolobii on plantain productivity has yet to be determined but given the RF value obtained in the pathogenicity test, plantain is a suitable host. This calls for a comprehensive RKN diversity study to evaluate the geographic spread of M. enterolobii on this important staple food crop in West Africa.

Comparative study of physicochemical, nutritional, phytochemical, and sensory properties of bread with plantain and soy flours partly replacing wheat flour.

Plantain flour (PLF) and soy flour (SF) were used to substitute wheat flour (10% and 20% w/w) in composite bread. Physicochemical, phytochemical, and sensory properties were investigated. Partial substitution by PLF significantly increased (p < .05) starch, amylose, ascorbic acid, and potassium content in bread samples. In contrast, a significant improvement (p < .05) in protein, fat, amylopectin, and calcium content was observed with SF substitution. Composite bread with PLF and SF together lowered the hydrolysis index (HI) and glycemic index (GI) as compared with whole wheat flour. The molar phytate to minerals (iron, zinc, and calcium) ratio in all composite loaves was lower than reported critical values, except for phytate to iron. Significant differences (p < .05) were found in color, specific volume, and texture characteristics of loaves made from partial substitution with PLF and SF. Sensory evaluation revealed that bread with 10% PLF exhibited better scores for appearance and willingness to pay than the control. In contrast, SF negatively affected (p < .05) the appearance, texture, color, overall acceptance, and willingness to pay. The trade-off analysis indicated that PLF can be utilized to produce bread that meets consumers' demands, while incorporating SF as an alternative high-nutrient density bread will be beneficial to health.

Phylogeography and conservation gaps of Musa balbisiana Colla genetic diversity revealed by microsatellite markers.

Collection and storage of crop wild relative (CWR) germplasm is crucial for preserving species genetic diversity and crop improvement. Nevertheless, much of the genetic variation of CWRs is absent in ex situ collections and detailed passport data are often lacking. Here, we focussed on Musa balbisiana, one of the two main progenitor species of many banana cultivars. We investigated the genetic structure of M. balbisiana across its distribution range using microsatellite markers. Accessions stored at the International Musa Germplasm Transit Centre (ITC) ex situ collection were compared with plant material collected from multiple countries and home gardens from Vietnam. Genetic structure analyses revealed that accessions could be divided into three main clusters. Vietnamese and Chinese populations were assigned to a first and second cluster respectively. A third cluster consisted of ITC and home garden accessions. Samples from Papua New Guinea were allocated to the cluster with Chinese populations but were assigned to a separate fourth cluster if the number of allowed clusters was set higher. Only one ITC accession grouped with native M. balbisiana populations and one group of ITC accessions was nearly genetically identical to home garden samples. This questioned their wild status, including accessions used as reference for wild M. balbisiana. Moreover, most ITC accessions and home garden samples were genetically distinct from wild populations. Our results highlight that additional germplasm should be collected from the native distribution range, especially from Northeast India, Myanmar, China, and the Philippines and stored for ex situ conservation at the ITC. The lack of passport data for many M. balbisiana accessions also complicates the interpretation of genetic information in relation to cultivation and historical dispersal routes. Supplementary Information: The online version contains supplementary material available at 10.1007/s10722-022-01389-4.

First Report of Lasiodiplodia theobromae Causing Dieback Symptoms on Plantain (Musa AAB subgroup) in Nigeria.

Bananas (banana and plantains) rank sixth among staple food crops (FAO 2018), with production challenged by biotic factors, mainly fungal diseases that may cause a total loss in some orchards (Jones 2018). In April 2017, dieback symptoms (progressive blackening and necrotic aerial plant parts, leaves, fruits and peduncles) were observed on plantain (Musa AAB subgroup), in Onne, Rivers State, Nigeria (4°42'55.4012″N, 7°10'35.92128″E). Diseased plants (n=112) were either wilted with blackened necrotic areas, or dead (Fig. S1). Nearly 10% of the plants had blackened pseudostems and fruits with slate gray to black internal tissues when sliced (Fig. S1) and black, erumpent pycnidia were observed on diseased fruits. A fungal species was consistently isolated when surface disinfected pieces of diseased samples were cultured on PDA plates. Plates were incubated at 25±2°C for 4 to 15 d to observe conidia. Isolates had colonies and conidia consistent with members of the Botryosphaeriaceae family (Phillips et al. 2013). Immature conidia were single-celled, ellipsoidal and hyaline while mature conidia were two-celled, had a thick wall, a central septum, longitudinal striations, and a dark brown, cinnamon-like color. Size of mature conidia (n = 20) ranged 22.9 to 30.0 × 14.2 to 18.4 µm ( = 27.0 × 15.6 µm; Fig. S1). DNA templates of three isolates (23688-2_R16; 19144-18_R15 and PITA_22-1) were amplified using primers ITS1 and ITS4 for the ITS locus, EF1-688F and EF1-1251R for the translation elongation factor 1-α (TEF-1α) locus (Phillips et al. 2013) and sequenced (GenBank accession Nos. MZ413346, MZ413347, and MZ413348 for ITS; and MZ420177, MZ420178, and MZ420179 for TEF-1α). BLASTn query showed 100% identity with reference sequences of various isolates of Lasiodiplodia theobromae. Based on morphological characters and nucleotide homology, the isolates were identified as L. theobromae (Fig. S1 & S2). To fulfil Koch's postulates, 4-month-old plants of plantain hybrid PITA 24, and mature fruits from three genotypes (PITA 24, plantain cultivar Obino L'ewai) were inoculated with mycelial plugs from the margins of 5-d-old cultures of the three L. theobromae isolates. Pseudostems were drilled with a sterile 5 -mm cork borer, a mycelial plug placed down into the wound, covered with sterilized cotton, and sealed with parafilm. Sterile water was injected every third day to maintain moisture at the inoculated area. Toothpicks containing mycelia were used to inoculate fruits, placed in plastic Crisper boxes. Sterile PDA plugs or toothpicks were used for the controls. Inoculated plants and fruits were kept in a screenhouse at room temperature (~26°C) for 14 d. All inoculated materials developed symptoms similar to the diseased plants in the field. Control plants and fruits remained asymptomatic. L. theobromae was re-isolated from the artificially inoculated plant parts and its identity was confirmed. The fungus L. theobromae is distributed in tropical and subtropical regions and has a wide host range (Phillips et al. 2013; Mehl et al. 2017). This fungus was previously reported in grey literature as the causal agent of Musa spp. basal rot at Onne, Nigeria (Mwangi et al. 2005) but its molecular identification was not conducted; it was unknown whether the isolates were indeed L. theobromae or other cryptic species (L. pseudotheobromae or L. parva) (Alves et al. 2008). Over 15 years later, the present study confirms L. theobromae as the causal agent of basal rot of bananas based on nucleotide homology, and to our knowledge, this is the first report of L. theobromae causing dieback disease on plantain in Nigeria and in Africa. There is need to conduct a more comprehensive distribution surveys and develop appropriate control strategies in Nigeria.

Banana seed genetic resources for food security: Status, constraints, and future priorities.

Storing seed collections of crop wild relatives, wild plant taxa genetically related to crops, is an essential component in global food security. Seed banking protects genetic resources from degradation and extinction and provides material for use by breeders. Despite being among the most important crops in the world, banana and plantain crop wild relatives are largely under-represented in genebanks. Nevertheless, banana crop wild relative seed collections are in fact held in different countries, but these have not previously been part of reporting or analysis. To fill this gap, we firstly collated banana seed accession data from 13 institutions in 10 countries. These included 537 accessions containing an estimated 430,000 seeds of 56 species. We reviewed their taxonomic coverage and seed storage conditions including viability estimates. We found that seed accessions have low viability (25% mean) representing problems in seed storage and processing. Secondly, we surveyed 22 institutions involved in banana genetic resource conservation regarding the key constraints and knowledge gaps that institutions face related to banana seed conservation. Major constraints were identified including finding suitable material and populations to collect seeds from, lack of knowledge regarding optimal storage conditions and germination conditions. Thirdly, we carried out a conservation prioritization and gap analysis of Musaceae taxa, using established methods, to index representativeness. Overall, our conservation assessment showed that despite this extended data set banana crop wild relatives are inadequately conserved, with 51% of taxa not represented in seed collections at all; the average conservation assessment showing high priority for conservation according to the index. Finally, we provide recommendations for future collecting, research, and management, to conserve banana and plantain crop wild relatives in seed banks for future generations.

Drying banana seeds for ex situ conservation.

The ability of seeds to withstand drying is fundamental to ex situ seed conservation but drying responses are not well known for most wild species including crop wild relatives. We look at drying responses of seeds of Musa acuminata and Musa balbisiana, the two primary wild relatives of bananas and plantains, using the following four experimental approaches: (i) We equilibrated seeds to a range of relative humidity (RH) levels using non-saturated lithium chloride solutions and subsequently measured moisture content (MC) and viability. At each humidity level we tested viability using embryo rescue (ER), tetrazolium chloride staining and germination in an incubator. We found that seed viability was not reduced when seeds were dried to 4% equilibrium relative humidity (eRH; equating to 2.5% MC). (ii) We assessed viability of mature and less mature seeds using ER and germination in the soil and tested responses to drying. Findings showed that seeds must be fully mature to germinate and immature seeds had negligible viability. (iii) We dried seeds extracted from ripe/unripe fruit to 35-40% eRH at different rates and tested viability with germination tests in the soil. Seeds from unripe fruit lost viability when dried and especially when dried faster; seeds from ripe fruit only lost viability when fast dried. (iv) Finally, we dried and re-imbibed mature and less mature seeds and measured embryo shrinkage and volume change using X-ray computer tomography. Embryos of less mature seeds shrank significantly when dried to 15% eRH from 0.468 to 0.262 mm3, but embryos of mature seeds did not. Based on our results, mature seeds from ripe fruit are desiccation tolerant to moisture levels required for seed genebanking but embryos from immature seeds are mechanistically less able to withstand desiccation, especially when water potential gradients are high.

From fruit growth to ripening in plantain: a careful balance between carbohydrate synthesis and breakdown.

In this study, we aimed to investigate for the first time different fruit development stages in plantain banana in order gain insights into the order of appearance and dominance of specific enzymes and fluxes. We examined fruit development in two plantain banana cultivars during the period between 2-12 weeks after bunch emergence using high-throughput proteomics, quantification of major metabolites, and analyses of metabolic fluxes. Starch synthesis and breakdown are processes that take place simultaneously. During the first 10 weeks fruits accumulated up to 48% of their dry weight as starch, and glucose 6-phosphate and fructose were important precursors. We found a unique amyloplast transporter and hypothesize that it facilitates the import of fructose. We identified an invertase originating from the Musa balbisiana genome that would enable carbon flow back to growth and starch synthesis and maintain a high starch content even during ripening. Enzymes associated with the initiation of ripening were involved in ethylene and auxin metabolism, starch breakdown, pulp softening, and ascorbate biosynthesis. The initiation of ripening was cultivar specific, with faster initiation being particularly linked to the 1-aminocyclopropane-1-carboxylate oxidase and 4-alpha glucanotransferase disproportionating enzymes. Information of this kind is fundamental to determining the optimal time for picking the fruit in order to reduce post-harvest losses, and has potential applications for breeding to improve fruit quality.

Datasets from harmonised metabolic phenotyping of root, tuber and banana crop.

Biochemical characterisation of germplasm collections and crop wild relatives (CWRs) facilitates the assessment of biological potential and the selection of breeding lines for crop improvement. Data from the biochemical characterisation of staple root, tuber and banana (RTB) crops, i.e. banana (Musa spp.), cassava (Manihot esculenta), potato (Solanum tuberosum), sweet potato (Ipomoea batatas) and yam (Dioscorea spp.), using a metabolomics approach is presented. The data support the previously published research article "Metabolite database for root, tuber, and banana crops to facilitate modern breeding in understudied crops" (Price et al., 2020) [1]. Diversity panels for each crop, which included a variety of species, accessions, landraces and CWRs, were characterised. The biochemical profile for potato was based on five elite lines under abiotic stress. Metabolites were extracted from the tissue of foliage and storage organs (tuber, root and banana pulp) via solvent partition. Extracts were analysed via a combination of liquid chromatography - mass spectrometry (LC-MS), gas chromatography (GC)-MS, high pressure liquid chromatography with photodiode array detector (HPLC-PDA) and ultra performance liquid chromatography (UPLC)-PDA. Metabolites were identified by mass spectral matching to in-house libraries comprised from authentic standards and comparison to databases or previously published literature.

High-throughput phenotyping reveals differential transpiration behaviour within the banana wild relatives highlighting diversity in drought tolerance.

Crop wild relatives, the closely related species of crops, may harbour potentially important sources of new allelic diversity for (a)biotic tolerance or resistance. However, to date, wild diversity is only poorly characterized and evaluated. Banana has a large wild diversity but only a narrow proportion is currently used in breeding programmes. The main objective of this study was to evaluate genotype-dependent transpiration responses in relation to the environment. By applying continuous high-throughput phenotyping, we were able to construct genotype-specific transpiration response models in relation to light, VPD and soil water potential. We characterized and evaluated six (sub)species and discerned four phenotypic clusters. Significant differences were observed in leaf area, cumulative transpiration and transpiration efficiency. We confirmed a general stomatal-driven 'isohydric' drought avoidance behaviour, but discovered genotypic differences in the onset and intensity of stomatal closure. We pinpointed crucial genotype-specific soil water potentials when drought avoidance mechanisms were initiated and when stress kicked in. Differences between (sub)species were dependent on environmental conditions, illustrating the need for high-throughput dynamic phenotyping, modelling and validation. We conclude that the banana wild relatives contain useful drought tolerance traits, emphasising the importance of their conservation and potential for use in breeding programmes.

Diversity of Fusarium associated banana wilt in northern Viet Nam.

Fusarium is one of the most important fungal genera of plant pathogens that affect the cultivation of a wide range of crops. Agricultural losses caused by Fusariumoxysporumf.sp.cubense (Foc) directly affect the income, subsistence, and nourishment of thousands of farmers worldwide. For Viet Nam, predictions on the impact of Foc for the future are dramatic, with an estimated loss in the banana production area of 8% within the next five years and up to 71% within the next 25 years. In the current study, we applied a combined morphological-molecular approach to assess the taxonomic identity and phylogenetic position of the different Foc isolates collected in northern Viet Nam. In addition, we aimed to estimate the proportion of the different Fusarium races infecting bananas in northern Viet Nam. The morphology of the isolates was investigated by growing the collected Fusarium isolates on four distinct nutritious media (PDA, SNA, CLA, and OMA). Molecular phylogenetic relationships were inferred by sequencing partial rpb1, rpb2, and tef1a genes and adding the obtained sequences into a phylogenetic framework. Molecular characterization shows that c. 74% of the Fusarium isolates obtained from infected banana pseudostem tissue belong to F.tardichlamydosporum. Compared to F.tardichlamydosporum, F.odoratissimum accounts for c.10% of the Fusarium wilt in northern Viet Nam, demonstrating that Foc TR4 is not yet a dominant strain in the region. Fusariumcugenangense - considered to cause Race 2 infections among bananas - is only found in c. 10% of the tissue material that was obtained from infected Vietnamese bananas. Additionally, one of the isolates cultured from diseased bananas was phylogenetically not positioned within the F.oxysporum species complex (FOSC), but in contrast, fell within the Fusariumfujikuroi species complex (FFSC). As a result, a possible new pathogen for bananas may have been found. Besides being present on several ABB 'Tay banana', F.tardichlamydosporum was also derived from infected tissue of a wild Musalutea, showing the importance of wild bananas as a possible sink for Foc.

Corrigendum to: Drying banana seeds for ex situ conservation.

[This corrects the article DOI: 10.1093/conphys/coab099.].

Continuous Mapping Identifies Loci Associated With Weevil Resistance [Cosmopolites sordidus (Germar)] in a Triploid Banana Population.

The first step toward marker-assisted selection is linking the phenotypes to molecular markers through quantitative trait loci (QTL) analysis. While the process is straightforward in self-pollinating diploid (2x) species, QTL analysis in polyploids requires unconventional methods. In this study, we have identified markers associated with weevil Cosmopolites sordidus (Germar) resistance in bananas using 138 triploid (2n = 3x) hybrids derived from a cross between a tetraploid "Monyet" (2n = 4x) and a 2x "Kokopo" (2n = 2x) banana genotypes. The population was genotyped by Diversity Arrays Technology Sequencing (DArTSeq), resulting in 18,009 polymorphic single nucleotide polymorphisms (SNPs) between the two parents. Marker-trait association was carried out by continuous mapping where the adjusted trait means for the corm peripheral damage (PD) and total cross-section damage (TXD), both on the logit scale, were regressed on the marker allele frequencies. Forty-four SNPs that were associated with corm PD were identified on the chromosomes 5, 6, and 8, with 41 of them located on chromosome 6 and segregated in "Kokopo." Eleven SNPs associated with corm total TXD were identified on chromosome 6 and segregated in "Monyet." The additive effect of replacing one reference allele with the alternative allele was determined at each marker position. The PD QTL was confirmed using conventional QTL linkage analysis in the simplex markers segregating in "Kokopo" (AAAA × RA). We also identified 43 putative genes in the vicinity of the markers significantly associated with the two traits. The identified loci associated with resistance to weevil damage will be used in the efforts of developing molecular tools for marker-assisted breeding in bananas.

Using seminatural and simulated habitats for seed germination ecology of banana wild relatives.

Ecologically meaningful seed germination experiments are constrained by access to seeds and relevant environments for testing at the same time. This is particularly the case when research is carried out far from the native area of the studied species.Here, we demonstrate an alternative-the use of glasshouses in botanic gardens as simulated-natural habitats to extend the ecological interpretation of germination studies. Our focal taxa were banana crop wild relatives (Musa acuminata subsp. burmannica, Musa acuminata subsp. siamea, and Musa balbisiana), native to tropical and subtropical South-East Asia. Tests were carried out in Belgium, where we performed germination tests in relation to foliage-shading/exposure to solar radiation and seed burial depth, as well as seed survival and dormancy release in the soil. We calibrated the interpretation of these studies by also conducting an experiment in a seminatural habitat in a species native range (M. balbisiana-Los Baños, the Philippines), where we tested germination responses to exposure to sun/shade. Using temperature data loggers, we determined temperature dynamics suitable for germination in both these settings.In these seminatural and simulated-natural habitats, seeds germinated in response to exposure to direct solar radiation. Seed burial depth had a significant but marginal effect by comparison, even when seeds were buried to 7 cm in the soil. Temperatures at sun-exposed compared with shaded environments differed by only a few degrees Celsius. Maximum temperature of the period prior to germination was the most significant contributor to germination responses and germination increased linearly above a threshold of 23℃ to the maximum temperature in the soil (in simulated-natural habitats) of 35℃.Glasshouses can provide useful environments to aid interpretation of seed germination responses to environmental niches.

Use of timelapse photography to determine flower opening time and pattern in banana (Musa spp.) for efficient hand pollination.

Sterility and low seed set in bananas is the main challenge to their conventional genetic improvement. The first step to seed set in a banana breeding program depends on pollination at the right time to ensure effective fertilization. This study aimed at determining bract opening time (BOT) to enhance efficient pollination and seed set in bananas. A Nikon D810 digital camera was set-up to take pictures of growing banana inflorescences at five-minute intervals and time-lapse movies were developed at a speed of 30 frames per second to allow real-time monitoring of BOT. Genotypes studied included wild banana (1), Mchare (2), Matooke (4), Matooke hybrid (1), and plantain (1). Events of bract opening initiated by bract lift for female flowers (P < 0.01) started at 16:32 h and at 18:54 h for male flowers. Start of bract rolling was at 18:51 h among female flowers (P < 0.001) and 20:48 h for male flowers. Bracts ended rolling at 02:33 h and 01:16 h for female and flowers respectively (P < 0.05). Total time of bract opening (from lift to end of rolling) for female flowers was significantly longer than that of male flowers (P < 0.001). On average, the number of bracts subtending female flowers opening increased from one on the first day, to between one and four on the fourth day. The number regressed to one bract on day eight before start of opening of bracts subtending male flowers. There was a longer opening interval between bracts subtending female and male flowers constituting spatial and temporal separation. Bract rolling increased from partial to complete rolling from proximal to the distal end of the inflorescence among female flower. On the other hand, bracts subtending male flowers completely rolled. Differences in BOT of genotypes with the same reference time of assessment may be partly responsible for variable fertility. Hand pollination time between 07:00 and 10:00 h is slightly late thus an early feasible time should be tried.