Studies of Vegetative Growth, Inflorescence Development and Eco-Dormancy Formation of Abscission Layers in Streptocarpus formosus (Gesneriaceae)

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.

Frost Damage in Poplar on the Prairies

Frost cankers in poplar are freeze-killed areas of bark and wood around which woody calluses develop and form burls and frost ribs. Frost dieback is a freeze-killed segment of the stem at the base, tip, or mid-portion of a branch or leader. It may or may not enhance natural pruning of poplar branches depending on whether the basal parts are damaged or alive and able to form abscission layers. In addition to abscission, low temperature affects increment, growth patterns, and vigor of poplar. Tree become stunted from persistent leader dieback. Suckers, crooks, and sweeps also characterize many stands of poplar. These characteristics of frost damage in mature forest stands are valuable in assessing the hazard of frost if the stands are to be clear-cut and reforested. The effects of frost damage are controlled somewhat in amenity, parks, and recreational areas because pruning is necessary to prevent wind breakage of staghead and frost-cankered trees.