INDUCTION OF SPROUTING IN DORMANT YAM (DIOSCOREA SPP.) TUBERS WITH INHIBITORS OF GIBBERELLINS

Abstract

A reliable means to induce sprouting in dormant seed tubers of yams (Dioscorea species) is required to enhance flexibility in planting date and rate of propagation of the crop. Experiments were conducted to assess the potential of two gibberellin inhibitors, Uniconazole-P and Prohexadione-calcium, to induce sprouting in tubers from three varieties of D. rotundata and four of D. alata. Uniconazole-P and Prohexadionecalcium shortened the period of dormancy in tubers of some varieties. In others, they either had no effect or extended dormancy. The varietal responses were also influenced by whether the tubers were treated at harvest (before shoot senescence) or four weeks after harvest by which time shoots had senesced fully. Tubers stored in darkness at a constant temperature of 30 • C sprouted earlier but lost weight faster than did those stored under natural daylight and ambient temperature. The apparent slow action of Uniconazole-P and Prohexadione-calcium, and their variable effectiveness in relation to variety, would limit their usefulness in seed or breeding programmes, or in determining treatment timing and the best storage environment for the tubers after treatment. I N T RO D U C T I O NTuber dormancy is an important mechanism for adaptation of yams (Dioscorea spp.) to their natural environments (Craufurd et al., 2001) and, because yams are purchased predominantly as fresh tubers for food preparation, long dormancy is very important for shelf life. Hence, long dormancy of tubers is a desirable attribute in yam breeding and selection programmes. It complicates the use of the tuber for propagation, however. Irrespective of when a yam seed tuber is planted, the critical starting point of the growing season is when dormancy ends and sprouts are produced. There is a period of about four months after harvest during which tuber losses are incurred in storage but propagation of the planting material would not be successful. In some environments, early planting could largely obviate losses incurred during seed-yam storage if there was more flexibility in the control of sprouting date through effective means of artificially terminating dormancy. Successful protocols for this would have a tremendous impact on yam cultivation. They could lead to more uniformity in sprouting, off-season propagation of planting materials, multiple cropping cycles of early maturing varieties per year and better control over planting date. Developing such protocols has been rather challenging (Barker et al., 1999a;b;Craufurd et al., 2001).

Influence of exogenous gibberellin inhibitors on tuber sprouting in yam

“…The variable responses of varieties of D. rotundata and D. alata to UP and PC are in line with the results of Shiwachi et al (2003) in which tubers of the same varieties were treated with the gibberellin inhibitors four weeks after harvest. Again TDa 99/00049 had the greatest response.…”

“…Moreover, UP obstructed the effect of GAs on tuber growth. Shiwachi et al (2003) applied UP and PC four weeks after harvest to induce tuber sprouting in D. rotundata and D. alata: they shortened the period of dormancy in some varieties, but either extended it or had no significant effect in others. Probably the tubers were at different stages of dormancy.…”

“…H Shiwachi et al In Experiment 2, six varieties (excluding TDa 95/00328) were planted on 9 April 2001 in the same field as Experiment 1. On 8 November, tubers were harvested from plants that had nearly senesced and soaked in 5 mg/l UP or 10 mg/l of PC for 24 h. These concentrations were based on those of Shiwachi et al (2003). Tubers soaked in water were the control, treated tubers were buried in coco-peat boxes and kept on the shelves of a yam barn, covered with transparent plastic sheet to maintain a warmer air temperature than ambient but giving natural light.…”

Effects of planting methods and tuber weights on growth and yield of yam cultivars (Dioscorea rotundata Poir.) in Gabon

“…Variability in the duration of dormancy has been attributed to differences in species, variety crop management, data of tuber harvest, growth, and storage (Hamadina and Asiedu, 2015). Long dormancy of tubers is a desirable attribute in yam breeding and selection programs (Shiwachi et al 2003). It permits a better storage but it complicates the use of the tuber for propagation.…”

Effect of Provenance and Storage Agroecology on Duration of Yam (Dioscorea rotundata Poir.) Tuber Dormancy

“…Results from thousands of tubers evaluated in this study showed that the earliest time of sprouting occurred in late December, but mostly within the first three months of the year ( [16], [17], [18]). The occurrence of sprouting at a defined period or season (at end of the Harmattan season to the beginning of the rains) in the year in Nigeria such as between late December of previous year and April of the next year, suggests that landraces have developed life cycles/stages that fit the annual seasonal cycle.…”