Abstract
AbstractIn Bambara groundnut [Vigna subterranea (L) Verdc], long photoperiods can cause a decline in pod and seed number. While negative photoperiod effects on pod yield have been reported, positive effects and the existence of genotypes less sensitive for photoperiod have not been reported. Ten geographically diverse genotypes were evaluated over 3 years under short and long photoperiod for yield‐related traits (pod number, pod weight, seed number, seed weight, and 100 seed weight), pod growth habit (geocarpic or ageocarpic pods), peduncle elongation and soil penetration, and pod set/abortion. Anatomical sections of gynophores and embryonic pod development of a highly photoperiod sensitive genotype “Ankpa‐4” from Nigeria were examined. A strong photoperiodic effect on yield component traits (pod number, pod weight, seed number, seed weight, and 100 seed weight) was observed and with considerable variation between genotypes. Three classes of photoperiod effect on pod yield were identified, (a) qualitative short‐day types; (b) quantitative short‐day types; and (c) quantitative long‐day types. In long photoperiods, above‐ground vegetative biomass and the length of lateral branches in some genotypes increased by at least twofold. Morphological and anatomical characterization of gynophores and developing pods of the most sensitive line shows continuous geocarpic growth, but with healthy embryonic pods failing to enlarge after soil penetration. Results from the yield patterns of the three phenotypic classes confirm that pods and seeds are high priority sinks, and long photoperiod alters the balance in assimilate distribution between competing yield forming processes and vegetative sinks. By exploiting the genetic variation characterized here for photoperiod requirement for pod filling, the geographical range of this crop could be extended beyond current growing regions. In the near future, we anticipate that Bambara groundnut will become a significant contributor to global food, nutritional, and environmental security once these photoperiod issues are resolved.
Highlights
An increasing worldwide demand for more nutritious food in the face of a rapidly changing climate has placed new emphasis on breeding future crops with higher yields, improved tolerance to abiotic stresses and, critically, better dietary nutritional content
The only genotype that had a significant delay of 6–7 days to the onset of flowering under the long photoperiod was Ankpa4 from Nigeria (7°N), and this selection has been previously reported to show daylength sensitivity for days to flowering (Brink, 1997, 1999; Linnemann, 1993, 1994)
We have shown that there were strong photoperiodic effects on the yield component traits in Bambara groundnut and considerable differences were observed to exist between genotypes derived from different landraces under long photoperiods
Summary
An increasing worldwide demand for more nutritious food in the face of a rapidly changing climate has placed new emphasis on breeding future crops with higher yields, improved tolerance to abiotic stresses and, critically, better dietary nutritional content. Bambara groundnut is a potential future crop that could lend greater resilience to agricultural production under a rapidly changing climate. Seed yields can be low and/or unstable due to the lack of improvement by controlled cross-breeding. Variation in final yield has been attributed to different planting dates (Karikari, Sebolai, & Munthali, 1996; Karikari et al, 1997; Linnemann & Craufurd, 1994), and low/unstable yields are more pronounced when landraces from equatorial regions are transferred and grown under long-day conditions away from the equator (Linnemann, 1994; Linnemann & Azam, 1993; Nishitani, Muraki, & Inoue, 1988; Sesay, Magagula, & Mansuetus, 2008)
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