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A. Tenkouano

This study aimed to assess the persistence and horticultural value of bunch dichotomy in plantain. Meristematic tissue was collected from a plant of the cultivar UNN showing a double-bunch phenotype and cultured in vitro. Ninety-five seedlings were acclimatized for 6 to 8 weeks in a greenhouse, prior to transfer to the field. Field evaluation was carried out at three experimental farms (Abuja, Ibadan, and Onne) of the International Institute of Tropical Agriculture, in Nigeria. Micropropagated plants of two plantain accessions, `Agbagba' and `Obino l'ewai', that produce single bunches were included as controls. Reversal of the double-bunch phenotype to a single-bunch phenotype was observed. Few plants underwent an additional dichotomization event to produce three bunches. This suggests that branching may be due to random genetic events instead of a stable mutation. Furthermore, field performance data were not significantly different for phenological or yield traits between clones producing one, two, or three bunches. Thus, selection for increased number of bunches may not be warranted in this Musa population.

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K.P. Baiyeri, B.N. Mbah, and A. Tenkouano

The additive main effects and multiplicative interaction (AMMI) model was used to evaluate the stability patterns of 36 Musa genotypes in four cropping environments for bunch weight, pulp weight, and dry matter content. Alleycropping generally induced higher means for all traits than did sole cropping. The triploid plantains produced smaller bunch weights and were less stable than dessert and cooking bananas. In this ploidy group, bunch weight was highest for the cooking bananas `Cardaba' and `Fougamou', but only `Fougamou' was stable across environments. Among the hybrids, only `FHIA23' (dessert banana) expressed high and stable bunch weights, while other high-yielding hybrids displayed specific adaptation to alleycropping. Pulp weight was lower but more stable in plantains than in other triploid genotypes. Among the hybrids, pulp weight was high and stable for one cooking banana (`FHIA3'), one dessert banana (`FHIA1'), and three plantains (`PITA1', `PITA2', and `PITA7'). Dry matter content was highest in plantains and lowest in dessert bananas at both triploid and tetraploid levels, and was also more stable than the other traits. Thus, the adaptation patterns of genotypes across environments varied according to the trait studied. When rank changes were not observed across traits for a given genotype, differences were still noted in the relative magnitude of the IPCA1 score. Hence, both farm gate traits and postharvest processing traits should be considered in selecting for broad or specific adaptation. Determination of the genetic relationships between processing traits and farm gate traits could allow Musa breeders to construct selection indices that would facilitate multiple trait selection and enhance breeding efficiency, with respect to cultivar stability and adaptation across environments.

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A. Tenkouano, J.H. Crouch, H.K. Crouch, and D. Vuylsteke

We attempted to determine ploidy level in the gametophyte and the sporophyte of Musa using pollen and chloroplast characteristics, respectively. In the gametophyte, interploidy differences accounted for 63.8% of the genetic variance for pollen diameter and 87.5% for pollen stainability, the remainder being attributable to intraploidy differences among clones. While pollen count and stainability effectively separated triploid accessions from diploids or tetraploids, they did not discriminate between diploids and tetraploids. In the sporophyte, the relative contributions of interploidy and intraploidy differences to genetic variation in the number of chloroplasts in stomatal guard cells were 70.8% and 29.2%, respectively. Although pollen diameter and chloroplast number increased with ploidy, the use of the sporophytic parameter appears to provide a more satisfactory means of estimating ploidy status in Musa.

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A. Tenkouano, D. Vuylsteke, J. Okoro, D. Makumbi, R. Swennen, and R. Ortiz

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H.O. Oselebe, A. Tenkouano, M. Pillay, I.U. Obi, and M.I. Uguru

The majority of edible bananas (Musa L.) are triploid (2n = 3x = 33) cultivars known as dessert, plantain, or cooking bananas with predominant AAA, AAB, and ABB genomes, justifying the aim of breeding programs to develop improved hybrids of the different utilization classes in the triploid background. This usually involves crossing 3x landraces to 2x accessions that are donors of resistance genes, selecting 4x and 2x primary hybrids from the 3x-2x progenies, and crossing 4x-2x hybrids to produce secondary 3x hybrids. Ploidy and genome segregation routinely occurs during this process and constitutes a major hindrance for selection because this is not easily detectable at the morphological level. This study was carried out to assess the potential of early screening for discriminating ploidy and genome classes in 4x (AAAB)-2x (AA) breeding populations, based on flow cytometry and genome-specific RAPD analysis. Results indicate that progenies of 4x-2x crosses produced predominantly 3x progenies (94.1%). RAPD analysis identified seven genomic classes, dominated by AAA and AAB configurations segregating 1:1 (χ2 = 0.21, P = 0.05). Plant size and bunch weight increased with ploidy level, justifying ploidy-based grouping of progenies for homogenous field evaluation. Similarly, genome-based grouping within ploidy classes is recommended to allow proper evaluation of progenies according to targeted postharvest utilization. Thus, ploidy analysis by flow cytometry and genome determination by RAPD open prospects for enhancing breeding efficiency in the development of triploid bananas or plantains.