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AOBPreview published online on January 30, 2006
Annals of Botany, doi:10.1093/aob/mcl002
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received September 21, 2005
Revised October 20, 2005
Accepted December 5, 2005

Article

Phases of Dormancy in Yam Tubers (Dioscorea rotundata)

E. I. ILE 1, P. Q. CRAUFURD 2 *, N. H. BATTEY 3, and R. ASIEDU 4

1 Plant Environment Laboratory, The University of Reading, Reading RG2 9AF, UK; School of Biological Sciences, The University of Reading, Whiteknights, Reading RG6 6AS, UK
2 Plant Environment Laboratory, The University of Reading, Reading RG2 9AF, UK
3 School of Biological Sciences, The University of Reading, Whiteknights, Reading RG6 6AS, UK
4 International Institute of Tropical Agriculture, Oyo Road, Ibadan, Nigeria

* To whom correspondence should be addressed.
P. Q. CRAUFURD, E-mail: p.q.craufurd{at}rdg.ac.uk


  Abstract

• Background and Aims The control of dormancy in yam (Disocorea spp.) tubers is poorly understood and attempts to shorten the long dormant period (i.e. cause tubers to sprout or germinate much earlier) have been unsuccessful. The aim of this study was to identify and define the phases of dormancy in Dioscorea rotundata tubers, and to produce a framework within which dormancy can be more effectively studied.

• Methods Plants of ‘TDr 131’ derived from tissue culture were grown in a glasshouse simulating temperature and photoperiod at Ibadan (7°N), Nigeria to produce tubers. Tubers were sampled on four occasions: 30 d before shoot senescence (149 days after planting, DAP), at shoot senescence (179 DAP), and twice during storage at a constant 25 °C (269 and 326 DAP). The development of the apical shoot bud was described from tissue sections. In addition, the responsiveness of shoot apical bud development to plant growth regulators (gibberellic acid, 2-chloroethanol and thiourea) applied to excised tuber sections was also examined 6 and 12 d after treatment.

• Key Results and Conclusions Three phases of tuber dormancy are proposed: Phase I, from tuber initiation to the appearance of the tuber germinating meristem; Phase II, from the tuber germinating meristem to initiation of foliar primordium; and Phase III, from foliar primordium to appearance of the shoot bud on the surface of the tuber. Phase I is the longest phase (approx. 220 d in ‘TDr 131’), is not affected by PGRs and is proposed to be an endo-dormant phase. Phases II and III are shorter (<70 d in total), are influenced by PGRs and environmental conditions, and are therefore endo-/eco-dormant phases. To manipulate dormancy to allow off-season planting and more than one generation per year requires that the duration of Phase I is shortened.

Keywords: Dioscorea rotundata, yam, dormancy, phases of dormancy, plant growth regulator, primary thickening meristem, tuber germinating meristem, shoot apical meristem.
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