Floral biology, Field Controlled Pollination and Hybrid Obtention of Dioscorea Dumetorum (Kunth) Pax) in Cameroon
Introduction- There is very little literature on the floral biology, synchronization of maturity of male and female flowers, flowering phenology and controlled pollination of Dioscorea dumetorum (D. dumetorum). However, the genetic improvement of this yam species, which is widely consumed in Cameroon and has exceptional nutritional qualities, cannot be achieved without knowledge and understanding of these biological attributes or phenomena. The aim of this study was to (1) – examine the sexual reproductive biology of D. dumetorum; (2) – study the phonology of flowering in this plant species; and (3) – develop a pollination method in order to obtain hybrid seedlings. • Materials and Methods: Forty seven cultivars of D. dumetorum collected in the main yam growing regions of Cameroon were used; (1) – In order to study the floral biology and synchronization of maturity of male and female flowers, two repetitive observations of floral characteristics of yam were undertaken. Data were collected on the stages of stem emergence, first bud emergence, first flower opening and flowering pattern within a day; (2)- For flowering study, the flowering records of the 47 cultivars collected over a three-year period; (3)- For the determination of the best pollination method, three methods were tested. Materials used include syringe, wire brush, bamboo splinter, scissors, pencil, notepad, alcohol, vials, razor blade, and roll of thread. • Data analysis: Five types of data analysis were done in this study. (1) – ANOVA, for quantitative data, when the hypothesis of normality of data is confirm by Kolmogorov test, including data related to (a) – flower morphology. These are: inflorescence Number (InfN), Inflorescence Length (InfL), Flowers Numbers (FlwN), Flower Length (FwrLg), Flower Diameter (FlwD) and Density; (b) – data related to flowering pattern including Days to Emergence (DE); Days to First Bud emergence (DFB), Days to First Flower Opening (DFFO), Days to First Bud emergence to First Flower Opening (DFB-DFFO), Number of Flowered Plants (NFP) and Maturation Time (MT) over three years evaluation. (2) – Mean separation. Means were separated using LSD or DUNCAN according to the number of means to separate. This was done at 5% threshold and (3) – Relationship establishment with Pearson correlation coefficient. In the case of abnormality of data, Mann Whitney test according to Monte Carlo method at 99% confidence interval was performed. (4) – For qualitative data, Binomial logistic regression analysis was performed with Monte Carlo permutation in order to establish the relation between flowering, year and sex and lastly (5) – Kendall correlation coefficients at 5%. • Results and discussion: This study has confirmed that D. dumetorum is a gynodioecious plant. The female fruit is a spike and the male fruit a panicle. The spike is on average 10 times longer than the panicle. The mean number of inflorescences (16) is comparable between male and female and male cultivars. The floral density is fifteen times greater on male cultivars; this could be interpreted as a strategy of this yam species to favor fruit bearing by female flowers. Sex influences most of the floral traits. There is an average lag of 16 days between the maturation of male and female flowers, with the males maturing earlier. Flowering monitoring of 47 D. dumetoum cultivars confirmed the erratic nature of flowering to the extent that the chance of flowering of a cultivar in one year to the next can be multiplied by 4. Sex could also influence flowering. Pollination with a syringe is an efficient method that allows up to 64% fructification. These fruits produce viable seeds that germinate according to a sigmoid curve, which starts to slope on day twenty-five and reaches its peak on day forty-four, marking the end of germination. This information is useful for strategic planning of genetic improvement of Dioscorea dumetorum by sexual means.
