Control of rhizome growth in Alstroemeria
Increases of temperature in the range from 8 to 18°C in vivo, significantly enhanced the dry weights of lateral rhizomes, roots and shoots. At the higher temperatures dry weight production was often seen to decrease. Decreases in irradiance from 100 to 50 per cent in vivo, produced significant decreases in the dry weights of lateral rhizomes, roots and shoots. In contrast, the numbers of lateral rhizomes, tubers and shoots were largely unaffected by temperature and irradiance treatments. Day length treatments of 8 to 16 hours light in a 24 hour period in vivo produced few significant changes in either the dry weights or numbers of plant parts produced. However, day length had a strong influence over the time of flowering. For maximum rhizome production a temperature of between 13 and 18°C, a high irradiance and a short day length were required. Increases of temperature in the range 8 to 18°C in vitro, caused significant increases in the number of lateral rhizomes and shoots produced. At the highest temperature the numbers produced often decreased. The number of roots produced was unaffected by temperature. Decreases in irradiance from 100 to 25 per cent and increases in day length from 8 to 20 hours light in a 24 hour period, produced no significant changes in the number of lateral rhizomes, roots or shoots produced in vitro. Low irradiance, however, caused etiolation of the shoots. For a good multiplication rate the requirements for the culture environment were a temperature of 15°C, an irradiance of 5 Win- 2 with a day length of 8 hours of light in a 24 hour period. The presence or absence of tubers and damage suffered by `splits' prior to planting were found to be important factors in the establishment of plants in vivo. Subculture of rhizome explants without aerial shoot or rhizome apices and of rhizome explants divided into single internodes with or without aerial shoots, enhanced the rhizome multiplication rate. Addition of the plant growth regulators triiodobenzoic acid, thidiazuron, α-naphthaleneacetic acid, gibberellic acid and paclobutrazol to culture media, with and without BAP, caused no significant changes in the numbers of lateral rhizomes, shoots or roots produced. However, paclobutrazol produced changes in explant morphology, i.e. shoot size was reduced and the diameter of roots was increased.