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- Author or Editor: Daniel J. Cantliffe x
Presowing seed treatments were devised to improve emergence and crop uniformity of two sweet corn (Zea mays L.) cultivars [`Crisp N' Sweet 711' (CNS-711) and `How Sweet It Is' (HSII)] that carry shrunken-2 (sh2) mutant endosperm. The treatments included a fungicide combination, sodium hypochlorite (SH), solid matrix priming (SMP), and SMP combined with SH during treatment (SMPSH). Seed germination was tested in a laboratory cold test. Emergence percentage, emergence rate index (ERI), and seedling dry weight were calculated from field trials. CNS-711, in the cold test and field trials, had a higher germination rate, ERI, final emergence, and seedling dry weight than HSII. In both cultivars, SMPSH significantly improved germination in the cold test and final emergence and ERI in the field trials for HSII compared to nontreated seeds. There was no significant difference between the fungicide and SMPSH treatments regardless of cultivar. These results suggest that the combination of SMP and disinfection with SH can be an alternative seed treatment to fungicides to improve uniformity and stand establishment in sh2 sweet corns.
Abstract
Seeds of 2 corn (Zea mays L.) endosperm mutants, shrunken-2 (sh2) and sugary (su), were produced in the field and greenhouse and harvested 18 to 46 days postpollination (dpp). Seeds of su accumulated dry weight rapidly after 26 dpp, while sh2 seeds had nearly attained their final weight by this stage. This resulted in a larger endosperm in su. Greenhouse-grown sh2 seeds weighed more than field-grown sh2 throughout development. Germination and seedling growth of greenhouse-grown sh2 seeds under optimum conditions were greater than that of field-grown sh2 when seeds were older than 26 days. Greenhouse-grown sh2 seeds 26 days and older germinated as well as field- and greenhouse-grown su with comparable seedling growth. Germination of field-grown sh2 seeds was much higher throughout development in the cold rolled-towel test compared to the cold soil test. Viability and vigor differences between immature seeds of both genotypes were not distinguishable by the cold, rolled-towel test, but were very noticeable in the cold soil test. Under cold soil test conditions, greenhouse-grown sh2 seeds had significantly greater emergence than did field-grown sh2 38 dpp and older. Mature greenhouse-grown sh2 and su seeds were of equal viability and vigor in the cold soil test.
Abstract
Field- and greenhouse-grown seeds of 2 sweet corn (Zea mays L.) endosperm mutants—shrunken-2 (sh2) and sugary (su)—were harvested 18 to 46 days postpollination (dpp). Mature sh2 seeds had a greater imbibition and leakage rate than did su. Leachate conductivity was greater from field-grown sh2 seeds than greenhouse-grown sh2 at maturity. No difference in carbohydrate leakage was observed between genotypes at maturity. Leakage generally decreased in all seed types with increasing maturity. Cracking of the pericarp was not noticeable in either sh2 or su during development. In mature seeds of both genotypes, the pericarp appeared to be thicker and adhered more tightly to the aleurone layer than in immature seeds. Dry seeds of sh2 contained considerably less total carbohydrates and starch than su 18 to 46 dpp. Field-grown su seeds accumulated more total carbohydrates during development than greenhouse-grown su or sh2. The lowest amounts of sugars in dry seeds occurred at maturity with no difference noted between field- and greenhouse-grown sh2 and field-grown su. Immature fresh kernels (freeze-dried) of su and sh2 contained 2 to 3 times, respectively, more sugars than immature dry kernels. At maturity, fresh and dry kernels of either genotype had equal amounts of sugars, but fresh kernels contained more starch.
A rapid and reliable predictor of sweet corn seed field emergence is required to produce high-quality, uniform crops. Field emergence of seven sh2 sweet corn cultivars grown at 3 geographic locations in Florida over 2 planting periods (fall and spring) was correlated with laboratory vigor tests. Factor analysis was used to separate non-collinear vigor tests for subsequent multiple regression models. The best single predictor test (R2=0.93***) was an index based on conductivity of the leachate and germination percentage after complex stressing vigor test incubated at 15°C. Leakage conductivity after 3 h soaking at 25 or 30°C (R2=0.90***), cold test in soil (R2=0.90***), mean alternate temperature stress conductivity test (R2=0.88***), standard germination test incubated at 30°C (R2=0.88***), and the index incubated at 25°C (R2=0.88***) were also good predictors of field emergence. Non-collinear tests including the towel germination test at 25°C and an alternate temperature stress conductivity test generated the highest most significant two factor predictor (R2=0.89***), and with glutamic acid decarboxylase activity (GADA) the best three factor predictor (r2=0.93***). The index of conductivity and complex stressing vigor test (ICS) proposed as a predictor of seed emergence considered two main factors affecting emergence in sh2 sweet corn: the condition of the membrane of the seeds and potential pathogen infection.
Abstract
Cotyledons of 3 cultivars of pickling cucumber (Cucumis sativus L.) were partially or wholly removed during early seedling development to determine the effect of reduced seedling vigor on subsequent sex expression. Under winter conditions in the greenhouse, removal of 11/2 to 2 cotyledons led to reduced seedling vigor, an increase in the number of staminate flowers, and a reduction in the number of pistillate flowers on the first 10 nodes of the hybrid cultivars ‘Pioneer’ and ‘Pickmore’. During spring trials, removal of the cotyledons led to a vigor reduction in young seedlings, but mature plants were not stunted. Under conditions which were more favorable for plant growth, sex expression was unaltered in the plants. Sex expression was generally unaffected by cotyledon removal in an inbred line ‘MSU 713-5’ in both winter and spring trials, although the number of pistillate flowers produced was reduced by removal of both cotyledons 3 or 6 days after emergence in the spring trials. It appears that major loss of cotyledonary tissue can lead to an alteration of sex expression in hybrid cucumbers grown under less than optimum conditions for plant growth.
For many years, the former Vegetable Crops Department, now the Horticultural Sciences Department, at the University of Florida offered a vegetable crop industries course. This one-credit course is offered each year as a 3- to 5-day field trip into vegetable production areas of Florida in the spring semester during spring break. The intent of the course is to give undergraduate students an extensive on-site evaluation of the application of scientific principles learned in lectures related to Florida's commercial vegetable industry. A new, innovative approach to structuring this course was initiated recently wherein only alumni of the department interacted with the students on all phases of commercial vegetable agriculture in Florida. These alumni had obtained degrees at the BS, MS, or PhD level and represented many professional backgrounds related to producing, handling, and marketing vegetables. Students were exposed to real-life situations and were encouraged to discuss and seek employment opportunities during the farm visitations. Student expenses were offset by donations from the Florida vegetable industry.
Mini or “baby” vegetables have become increasingly popular items for restaurant chefs and retail sales. Squash (Cucurbita pepo) are generally open-field cultivated where climate, insect, and disease pressures create challenging conditions for growers and shippers who produce and market this delicate, immature fruit. In order to overcome these challenges, in Spring 2003 and 2004, 18 squash cultivars, including zucchini, yellow-summer, patty pan/scallop, and cousa types, were grown hydroponically in a passively ventilated greenhouse and compared for yield of “baby”-size fruit. Squash were graded as “baby” when they were less than 4 inches in length for zucchini, yellow-summer, and cousa types and less than 1.5 inches diameter for round and patty pan/scallop types. In both seasons, `Sunburst' (patty pan) produced the greatest number of baby-size fruit per plant, while `Bareket' (green zucchini) produced the least. The zucchini-types produced between 16 and 25 baby-size fruit per plant in 2003. The yellow summer squash-types produced on average 45 baby fruit per plant. The production of the patty pan/scallop types ranged from 50 to 67 baby-size fruit per plant depending on cultivar. The cousa types produced approximately 30 baby-size fruit. Total yields were lower in 2004 due to a shortened season. Squash plants will produce numerous high quality baby-sized fruit when grown hydroponically in a reduced pesticide environment of a greenhouse where they can be harvested, packaged, and distributed to buyers daily. The cultivars Hurricane, Raven, Gold Rush, Goldy, Sunray, Seneca Supreme, Supersett, Butter Scallop, Sunburst, Patty Green Tint, Starship, Magda, and HA-187 could be used for hydroponic baby squash production.
Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, Crisp N' Sweet 711 and How Sweet It Is were used to analyze seed quality factor differences between the cultivars. Negative correlations occurred among germination percentage and imbibition, electric conductivity, potassium concentration and total soluble sugars of the seed leachate. Imbibition and total soluble sugar in the leachate significantly increased as imbibition temperature increased from 5°C to 25°C in both cultivars. A significant increase in conductivity of the leachate also occurred in `Crisp N' Sweet 711' when temperature increased. Cracks in the seed coat were more frequent in `How Sweet It Is' than `Crisp N' Sweet 711'. The higher concentrations of soluble sugars in the seed, greater imbibition rate, leakage conductivity, potassium and sugar concentration in the leachate may have been directly related to the poorer seed quality of `How Sweet It Is'. The alteration in cell membrane structure caused by a rapid water uptake in `How Sweet It Is' may have led to the high concentration of electrolytes in the seed leachate. This, in turn, might provide a greater nutritive subtrate for fungi development.
A physiological disorder in greenhouse-grown pepper (Capsicum annuum L.) plants was observed in Florida, wherein the base of the main stem becomes swollen below the cotyledonary node level and crack-like wounds develop at the base of the stem's epidermis. The disorder may predispose the plant to a localized rot and result in a sudden plant wilt. The effects of soilless media type, transplant depth, and amount of nutrient solution applied per day were studied to evaluate the development of what was termed “Elephant's Foot” disorder, on a greenhouse-grown bell pepper crop in Gainesville, Fla. The percentage of plants with epidermal wounds at the base of the stem was highest (83%) on plants transplanted at half of the cell height (3.8 cm), compared to plants transplanted to the cotyledonary node level (6%) and the second leaf node (0%). Salts were washed from the surface of basal stem epidermis and electrical conductivity measured in the washing solution was expressed per unit area of epidermal sample (ECA). The ECA in the solutions from plants transplanted at half of the cell height was higher than that from plants transplanted to the cotyledonary node level and to the second leaf node. There was a positive linear relationship (r = 0.81) between the percentage of plants with epidermal wounds and the ECA of the solution obtained from washing the epidermal tissues. Salts deposited on the epidermis beneath the cotyledonary node provoked a tissue injury that may predispose the plant to a Fusarium infection. Simple management practices, such as transplanting deep, using cultivars with lower susceptibility to salt damage, and gradually moving back the emitter from the base of the plant after transplanting (to reduce humid conditions near the base of the stem) would help reduce the appearance of this basal stem disorder in soilless-grown peppers.
Cell size and media density can modify plant quality of greenhouse grown transplants through variation in light competition among plants, water and nutrient retention and root growth volumes required to fill the cells Thus, `South Bay' lettuce (Lactuga sativa L.) seedlings were grown in the greenhouse during different seasons to investigate the effect of different cell size and media packing density on transplant quality and yield for lettuce grown on sand and muck soils at different latitudes. Four Speedling flat cell sizes (882, 392, 242, 124 cells/flat) and two media packing densities (unpacked and packed - 1.5 times in weight) were tested in all the trials. Few seedling data parameters had an interaction between cell size and media density at transplanting. The larger cell size (242, 124 cells/flat) and greater media density led to increase leaf area, leaf length, shoot and total dry weight, RGR and LWR Conversely, RWR and the root:shoot ratio had the opposite trend, reaching the greater values with smaller cell size and less media density. High root growth can improve the pulling of the plants from the tray at transplanting and quicker establishment in the field. The treatments did not affect yield of plants grown on organic soil. When plants were grown on sandy soil head weights were greater from plants grown in 392, 242, or 124 cells/flat compared to 882 cells/flat.