Reproductive biology, phenology, pollen viability and germinability in Kersting's groundnut (Macrotyloma geocarpum (Harms) Maréchal & Baudet, Fabaceae)

Abstract

Knowledge gap on the reproductive biology of orphan crops is a major challenge to their cultivar development and genetic improvement. This study described the reproductive organs and phenology, assessed receptivity of stigma versus anther dehiscence, and examined pollen viability and germination in Kersting's groundnut. Experiments were conducted on nine morphotypes in a randomized complete block design with three replications in a screenhouse. Phenological observations were made on 1026 flower buds. Anther dehiscence was determined through microscopic observations while receptivity of the stigma was assessed using the hydrogen peroxide test. Pollen viability was assayed using histochemical staining. In vitro germination and pollen tube growth were assessed for up to 72h. Flowers were bisexual and incompletely protogynous, and spontaneous self-pollination was favoured by style bending. Flowering and fruiting were classified into six developmental stages each. Timing of all stages differed significantly (P<0.001) among morphotypes. The stigma was receptive 1-2 days before anther dehiscence and remained so until each flower wilted. Anthesis started 3 days from young bud appearance and lasted between 2–4 days depending on the morphotype. Pollen viability rates were very high (88–98%) and differed among morphotypes (P<0.001). Pollen germination rates were low (8–37%) and varied among morphotypes and anthesis stages (P<0.05). Pollen tube growth varied significantly among morphotypes, anthesis stages and incubation time. The morphotype ZHLA-2 exhibited the highest reproductive vigour and could be recommended as pollen donor for hybridization. The study provides information on the best time and stage for emasculation and is expected to help breeders optimise a hybridisation protocol.