Abstract
Streptocarpus formosus (Hilliard & B.L. Burtt) T.J. Edwards is a flowering herbaceous perennial indigenous to South Africa and is part of the rosulate group of herbaceous acaulescent plants within the Gesneriaceae family. According to the National Assessment database for the Red List of South African Plants version 2020.1., the plant is listed as rare. The ornamental use of S. formosus has untapped commercial potential as a flowering indoor pot plant, an outdoor bedding plant for shade and as a cut flower for the vase, all of which are limited by a five-month eco-dormancy period during the late autumn and all through the cold season in the short-day winter months. Viable commercial production will require cultivation techniques that produce flowering plants all year round. This study investigated the effectiveness of applying root zone heating to S. formosus plants grown in deep water culture hydroponics during the eco-dormancy period in preventing abscission layer formation and in encouraging flowering and assessed the growth activity response of the plants. The experiment was conducted over eight weeks during the winter season in the greenhouse at Kirstenbosch Botanical garden in water reservoirs, each maintained at five different experimental temperature treatments (18, 22, 26—control, 30 and 34 °C) applied to 10 sample replicates. The results showed that the lowest hydroponic root zone temperature of 18 °C had the greatest effect on the vegetative growth of S. formosus, with the highest average increases in fresh weight (1078 g), root length (211 cm), overall leaf length (362 cm) and the number of newly leaves formed (177 = n), all noted as statistically significant when compared with the other water temperature treatments, which yielded negative results from reduced vegetative growth. Findings from the study also revealed that while all heated solutions significantly prevented the formation of abscission layers of S. formosus, they had a less significant effect on inflorescence formation, with only 18 °C having the greatest positive effect on flower development.
Highlights
Within the Gesneriaceae, Streptocarpus form part of an economically important ornamental plant group with other significant members such as Saintpaulia spp. (AfricanViolets), Gloxinia spp. and Sinningia spp. [1], all of which are herbaceous perennials known for the beauty of their flowers [2,3]
The results showed that the lowest hydroponic root zone temperature of 18 ◦ C had the greatest effect on the vegetative growth of S. formosus, with the highest average increases in fresh weight (1078 g), root length (211 cm), overall leaf length (362 cm) and the number of newly leaves formed (177 = n), all noted as statistically significant when compared with the other water temperature treatments, which yielded negative results from reduced vegetative growth
Findings from the study revealed that while all heated solutions significantly prevented the formation of abscission layers of S. formosus, they had a less significant effect on inflorescence formation, with only 18 ◦ C having the greatest positive effect on flower development
Summary
Within the Gesneriaceae, Streptocarpus form part of an economically important ornamental plant group with other significant members such as Saintpaulia spp. (AfricanViolets), Gloxinia spp. and Sinningia spp. [1], all of which are herbaceous perennials known for the beauty of their flowers [2,3]. S. formosus grows naturally in a summer rainfall locality with very little irrigation through precipitation during the cold season [4] This abiotic combination of reduced water and low temperatures triggers a survival tactic where the nutrients and carbohydrate reserves in the leaves are transported and remobilized to actively growing 4.0/). Horticulturae 2021, 7, 120 parts of the plant causing yellowing of the part, or all, of the leaves [5,6] before the plants enter a survival state of eco-dormancy [7] This annual process in Streptocarpus with flowering occurring mostly under 15 h long days as compared to 8 h short days [8] and combined with the slowed short-day growth processes of eco-dormancy and the shedding of leaf mass through unsightly abscission layers severely limits the ornamental commercial use of Streptocarpus formosus. Manipulating root zone temperature to keep plant crops and ornamentals actively growing for commercial out-of-season production has been comprehensively researched purposely to meet market demands [17,18,19,20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
