Height and time of summer pruning of greenhouse-grown ‘Mercedes’ roses were examined for effect on flower production in the subsequent season. The interaction of pruning severity and the flower cutting procedure also was tested. It was found that pruning in mid-July is preferable to mid-May and that severe (50 cm) pruning combined with “underhook cut” during the winter has an adverse effect on plant productivity. Summer picking of flowers followed by high (120 cm) pruning in mid-July represents an attractive alternative if a commercial outlet can be found for the flowers, since the subsequent winter harvest is better than that resulting from present practice and comparable to that resulting from gradual pruning in mid-July.
Tissue culture plantlets of Saintpaulia ionantha and Peperomia grisco-argenta were grown for 120 days in growth boxes placed in a greenhouse. The filtercovered tops of the boxes were sloped facing south, the direction of the sun, while the walls were constructed of white styrofoam board Four types of light filters covered the frames. Two blue celluloid sheets were used to alter the sunlight spectrum: one filtered out the red (B + FR), and the other removed most of the red and far-red, FR (B - FR). Two polyethylene films were formulated as light filters and diffusers: one scattered all the transmitted light and decreased the R: FR ratio (W), while the other was neutral in respect to the sunlight spectrum and did not cause light scattering (A). Vegetative growth of Saintpaulia plants was enhanced under the light-diffusing filters, resulting in higher fresh weight and larger leaves. Saintpaulia plants flowered first under the W filter, then the A filter, and last under the B + FR filter; no flowering occurred in the absence of FR light (B - RR). There was no significant difference in the development of Peperomia plants grown under the different filters. The results are discussed in relation to plant adaptation to various environments.
Root promotion activity in avocado leaf extracts was determined by the mung bean bioassay. Ten different clones representing a wide range of rooting abilities were compared. Following chromatography of methanol extracts in 8 isoprapanol : 2 water (v/v), a positive correlation was found between rooting ability of avocado cuttings and a mung bean rooting promoter at Rf 0.9–1.0 of the chromatograms. The same zone inhibited the straight growth of wheat coleoptile.
Cuttings of 10 different clones of avocado (Persea americana Mill.) were rooted under intermittant mist. A wide range in rooting capability was noted. Rooting percentage of clones was found to be correlated with number of leaves retained on the cuttings. Speed of rooting within the same clone was also determined by number of leaves retained. Carbohydrate content in leaves and cutting bases at the beginning was not associated with rooting capability. Starch accumulation at the cutting bases occurred while cuttings were under mist; this was correlated with the rooting capability. Mineral (N, P, K, Ca, Mg, Na, Cl, B, Fe, Zn, Mn) content of the leaves at the beginning and after a while under the mist did not show any association with rooting except for Mn, which was negatively correlated with rooting capability.
Leaf shedding (LS) of 3 avocado (Persea americana Mill.) clones (‘Northrop 28/5’, ‘Fuchs 20’ and ‘Nahlat 7’) differing in rooting ability was studied. Two distinct processes, leaf blade senescence and formation of the abscission layer, were found to be associated with LS. The rate of these processes differs among the 3 clones, and their combination determines the speed of LS. Leaf senescence was simulated by measuring chlorophyll destruction over time in leaf discs incubated in the light. The speed of abscission layer formation was estimated by measuring the time required for petioles to shed from incubated internodes. The results obtained in these tests were in agreement with the behavior of LS from cuttings of the 3 clones under mist. Auxin and cytokinin alone, or in combination, as measured in the 2 test systems, affected these leaf blade senescence and abscission layer formations at different rates. Six cuttings of the clone ‘Fuchs 20’ were sprayed weekly with combinations of NAA and BA. The optimal combination (1.10-4m NAA + 5.10-4m BA) caused a significant delay in LS and improvement in rooting. Relatively simple tests of leaf senescence and petiole abscission are discussed as potential methods for predicting rooting ability of leafy cuttings.
Rose (Rosa sp.) plants (`Mercedes') were grown in yellow tuff (YT) (volcanic ash, scoria) and pumice from Italy (PI) and Greece (PG) for which physical and hydraulic characteristics were determined. The differences among the measured retention curves of these materials result in significant differences among their relative hydraulic conductivity functions. The hydraulic conductivity of YT is much higher than that of PI, which is higher than that of PG. The plants were subjected to optimal growth and nutrition conditions. Irrigation was controlled using electronic tensiometers, at suction values well within the range of easily available water: 13 cm for YT and 8 cm for the two pumice types. Nonetheless, yields were significantly higher in YT than in PI; yields were even lower in PG. We suggest that the limiting factor was the dynamic water availability to the plants, which is affected mainly by the unsaturated hydraulic conductivity. The relative hydraulic conductivity of YT at 13 cm is more than an order of magnitude higher than that of PI at 8 cm. The relative hydraulic conductivity of PG at 8 cm is two orders of magnitude lower than that of YT at 13 cm. It seems that the current concept of easily available water, based on a predetermined suction range, independent of the hydraulic characteristics of the media, is not an appropriate parameter for irrigation management in soilless culture. The unsaturated hydraulic conductivity, being a characteristic function of the medium and highly sensitive to moisture variation, indicates better the actual availability of water to the roots. Therefore, it should be used for irrigation control in containers filled with porous substrates.
Rose plants (cv. Kardinal, grafted on Natal Brier) were grown in UC mix (42% fir bark, 33% peat, and 25% sand) and in coir. Water tension in the media was maintained within a predetermined narrow range using electronic tensiometers. Whole plant net photosynthesis as a function of the water tension in the medium was determined and the results were later normalized to measured leaf area. Simultaneous measurements of metabolic heat and respiration rate were carried out on detached young (FW = 10-20 mg.) leaflet samples, using differential scanning calorimeter (model 4100, Calorimetry Sciences, Provo, Utah). Only a small amount of plant material is removed for analyses so the assay is essentially non-destructive for the whole plant. Physical characteristics of the media greatly affect the relationship between water tension and water availability to plants. At similar tension values, water availability is much lower in coir than in UC mix. The effects of water availability on net photosynthesis, metabolic heat rate, and respiration will be discussed in relation to their effect on productivity.