The Effect of some Growth Regulators on Sprouting and Field Performance of Three White Yam Varieties (Dioscorea Rotundata) Poir.

Abstract

A study was carried out at the University of Ghana from January 2001 to January 2002 to find out if Labreko and Pona yam varieties treated exogenously with some growth regulators will respond to yam minisett technique. Six experiments were set up consisting of three yam minisett sprouting studies and three field assessments of the sprouted mini setts The objective of the study was to use growth regulators to enhance sprouting of Labreko and Pona minisetts and to improve field performance of the sprouted minisetts. In Experiment 1, different levels of the growth regulators naphthalene acetic acid (0, 50, 100 and 200 mg/1), ethrel (0,100, 500 and 1000 ppm) and coconut milk (water and undiluted coconut milk) were applied to the head, middle and tail sections of Labreko, Pona and Dakpaan white yam varieties (Dioscorea rotundata) Poir. The treated minisetts were dusted with dithane M45 fungicide, air-dried and then planted in moist sterile sawdust kept in baskets. They were inspected fortnightly to take data. In Experiment 2, NAA was dropped from the treatments used in Experiment 1. In Experiment 3, 500 ppm o f ethrel and undiluted coconut milk were applied to Labreko and Pona. The sprouted minisetts from the three experiments were transplanted to the field. In the first field experiment (Experiment 4) the effects of developmental stage of sprouted minisetts from Experiment 1 at transplanting and the growth regulators on field performances were studied. In Experiment 5, the effect of the different concentrations o f the growth regulators on field performance was studied. The last experiment looked at the effects of 500 ppm of ethrel and coconut milk on field performances. It was found that coconut milk and ethrel promoted sprouting while NAA suppressed sprouting. The improvement of coconut milk over the control in sprouting was in the range of 13-30 % and that of ethrel was 7-8 %. Three months after storage, the highest percentage sprouting of the varieties, 6 and 10 weeks after nursing, were 18.9 and 69 % respectively. Six months after storage, sprouting increased to 88 % for Pona. Therefore, dormancy ought to be sufficiently broken (that is more than 3 months after harvest), before some varieties such as Pona and Labreko could respond to sprouting. The higher the concentration of NAA, the higher its suppression effects on sprouting. Minisetts from the head and tail sections interacted positively with coconut milk. Lower concentrations of ethrel were required to induce more sprouting in the head and tail sections in the first experiment. However, as the release of dormancy progressed higher levels were required to make a difference between the ethrel levels and the control. Stage 1 (with vine length of up to 2 cm) and Stage 2 (with vine length of 2.1-4.0 cm) sprouted minisetts survived better than Stage 3 (with vine length o f 4.1-6.0 cm, with some having 2 leaves). Stage 2 sprouted minisetts produced the highest tuber yield. Among the three varieties Pona recorded the lowest percentage survival on the field.