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Thomas Björkman

Buckwheat has historically been used to suppress weeds and improve soil condition, but many of the tricks to success have been lost to history. Buckwheat is inexpensive and particularly effective in short windows between crops. We are documenting the techniques of existing experts and complementing that with research. We surveyed northeastern vegetable and strawberry growers to identify what information they need in order to feel confident that they could succeed with a buckwheat cover crop. Top questions include seed availability, types of weeds controlled, relation to other cover crops, volunteer management, and herbicide tolerance. One question tested experimentally was how to establish a full stand with minimum cost. We tested the minimum tillage requirement following pea harvest. No-till resulted in good emergence but slow growth, and dominance by weeds. Disk incorporating the pea residue resulted in excellent growth, which was not further enhanced by chisel plowing before disking. Buckwheat seedlings are intolerant of waterlogging, so deeper tillage may be important in wet years. Sowing buckwheat immediately after tillage resulted in emergence of 35%, leaving gaps large enough for weeds to grow. Waiting 1 week gave an 80% stand and complete weed suppression. Waiting 2 weeks also gave an 80% stand, but weed growth was advanced enough that weed suppression was incomplete. Therefore, a buckwheat cover crop following early vegetables requires light tillage to permit root growth, and up to a week of decomposition. If those provisions are made, complete weed suppression is obtainable.

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Thomas Björkman

Brushing is an effective method to control hypocotyl elongation in cucumbers (Cucumis sativus L. `Turbo') grown in plug trays for transplanting. The amount of daily brushing and the number of days to brush for best performance was determined. Treatment with 10 strokes per day for the 4 days of maximal hypocotyl elongation was sufficient to reduce final hypocotyl length by 25%. More brushing did not meaningfully reduce elongation further. Inhibition of dry weight gain, which is detrimental, was minor (<10%) compared with the height control achieved. Despite seasonal differences in absolute elongation, the effects of brushing were the same.

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Denise Duclos and Thomas Björkman

The genetic factors that control reproductive development in B. oleracea remain a mystery. Broccoli differs from cauliflower in its floral development stage at harvest. We are studying the role of meristem identity genes (MIGs) in the transition from inflorescence meristem (cauliflower) to floral buds (broccoli). The objectives are to determine stage-specific roles of MIGs during reproductive development and to check whether expression of flowering genes in heading B. oleracea is as predicted by the Arabidopsis flowering model. We tested a model of arrest in B. oleracea that incorporates FUL, a redundant gene of AP1 in controlling inflorescence architecture and floral meristem identity, the meristem gene TFL1, the flowering gene LFY, and AP1/CAL, and genes involved in flower transition. Conclusions. 1) Arrest at the inflorescence meristem stage is highly correlated with a decrease in LFY to TFL1 ratio, given by a decrease in TFL1 expression. 2) Transcription of AP1c is stimulated at the time of floral primordium initiation, suggesting a role in floral transition but not in floral organ specification. Plants recessive for AP1a, AP1c, and CAL formed normal floral buds containing all four whorls of organs, and did not necessarily form curd. We suggest that their ability to flower could be related with the ectopic expression of FUL by affecting TFL1 expression. FUL paralogs were highly expressed at all stages of development of the triple mutant plants. 3) The lack of upregulation in AP1 transcripts at the floral bud stage, and the absence of an A-function mutant phenotype imply that other genes act redundantly with AP1 in the specification of sepal identity and questions the role of AP1a and AP1c as A-function genes in B. oleracea.

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Thomas Björkman and Stephen Reiners

Starter phosphorus (P) is often recommended for warm-season vegetables sown in cool soil, even if soil P index levels are already high. The cost and environmental risk associated with excessive P fertilization justify re-examination of the practice. The objective of the study was to confirm that performance of early plantings of snap bean (Phaseolus vulgaris L.) is improved by starter P application and to test whether solubilizing soil P with potassium bicarbonate (KHCO3) can serve as an alternative in western New York soils. Addition of starter fertilizer at either recommended (15 kg·ha−1) or supraoptimal (35 kg·ha−1) P rates did not generally improve seedling tissue P concentration, early growth (biomass at flowering), or pod yield. Starter P application increased tissue P in only two of 11 experiments, and it never increased yield. Application of 6 kg·ha−1 KHCO3 to release soil-bound phosphate was not phytotoxic to snap beans. In the two experiments in which starter P increased tissue P, KHCO3 application had a smaller effect in one and no effect in the other. KHCO3 application did not increase yield in any of the six experiments where it was tested. A direct test of the contribution of P limitation to the poorer performance of early plantings showed that neither starter P nor KHCO3 application increased yield at early planting. Seasonal differences in crop performance could not be attributed to mineralization of soil phosphate after soil warmed. Water-extractable soil P was not lower in the spring than in summer, remaining constant at all 11 bean fields that were sampled from mid-April through mid-July. In these trials, P was likely not growth-limiting in the cool soils tested. Because starter P may not be necessary in vegetable soils testing high or very high for P, vegetables would also not likely benefit from bicarbonate application under high P conditions.

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Thomas Bjorkman and Karen Pearson

Production of broccoli in areas where summer temperatures exceed 30C is difficult because the head may not form properly. The high temperature causes an unevenness in the head due to widely differing sizes of buds. The sensitive stage of development was determined for the early maturing variety `Galaxy' by exposing it to 1-week at 36C at varying developmental stages, and subsequently analyzing the head structure. The injury is a cessation of bud enlargement during the high-temperature exposure. There is no corresponding cessation of bud initiation at the apex. The patter of injury is consistent with susceptibility over a relatively small range of bud development: even with a 1-week exposure, only about 1/3 of the buds will be affected. The plant's most developmental stage at this sensitive period still appears vegetative, but the youngest leaves are just beginning to reorient as a consequence of the reduced stem elongation rate. The meristem is less than 1 mm wide, and scanning electron micrographs show floral primordia just forming, still subtended by leaf primordia. The injury is fully expressed when the head is first exposed (≈10 mm wide), though it becomes more apparent as the head matures. The buds that were delayed in development by the high temperature developed into fertile flowers, albeit about a week late.

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Lauren C. Garner and Thomas Björkman

Stretching is a problem in high-density transplant production. Mechanical conditioning provides good height control for many crops, but information concerning the dosage and timing of stimulation, and possible effects on field performance are necessary for successful commercial implementation. Mechanical conditioning was applied to processing tomatoes (`Ohio 8245') grown in #288-deep flats (≈2000 plants/m2). Brushing was applied by daily gentle stroking of the plant canopy with a Styrofoam planter flat. The appropriate dose as determined by stroking 0, 10, 20, or 40 times daily back and forth. Twenty strokes provided sufficient height control with minimal plant damage. The interval between strokes was also varied, using 0.6 6, 60, or 600 s. These intervals were all equally effective in reducing the growth rate of the canopy. This broad range provides flexibility in commercial use of this technique. To test for effects on field performance, two methods of conditioning were used: brushing and impedance. Brushing was 20 continuous strokes daily. The impeded plant canopy was compressed slightly by a piece of Plexiglas suspended overnight. The treatments were applied from canopy closure until transplanting to the field. At transplanting, brushed and impeded plants were significantly shorter than control plants without a reduction in shoot dry weight. The treatments did not affect the speed at which the plants grew in the field. Within 5 weeks after transplanting, there were no significant differences between treatments in any measured parameter, including final yield. Therefore, both brushing and impedance provide a flexible and effective method for controlling tomato transplant height without adversely affecting establishment or yield.

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Denise V. Duclos and Thomas Björkman

Cauliflower (Brassica oleracea var. botrytis) and broccoli (B. oleracea var. italica) differ in the developmental stage of the reproductive meristem at harvest. A cauliflower head is formed by arrest at the inflorescence meristem stage and broccoli at the flower bud stage, and the horticultural value of the crop depends on synchronous development across the head. In other plant species, gibberellin (GA) can promote floral development and is therefore a candidate for providing the early developmental cues that shape the curd morphology. This research investigated the effect of GAs on the two horticulturally important transitions of the reproductive meristem: initiation of the inflorescence meristem and initiation of floral primordia on the proliferated inflorescence meristems. GA is known to affect the former in many species, but effects on the latter have not been determined. It is also not known whether one or both active forms produced by the two GA biosynthetic pathways is involved in the reproductive transitions in this crop. GAs from the early-13 hydroxylation pathway (GA3) and the non-13 hydroxylation pathway (GA4+7) were applied to the shoot apical meristems of cauliflower and broccoli at three developmental stages: adult-vegetative, curd initiation, and curd enlargement. GAs applied during the adult vegetative stage caused the curd to form faster and after fewer additional nodes in both cauliflower and broccoli. GAs applied to the inflorescence meristem did not cause floral primordia to form nor did the expression of transition-associated genes change. Integrator genes BoLFY and SOC1 had constant expression over 24 hours, and meristem-identity genes BoAP1-a and BoAP1-c remained undetectable. However, GAs applied early during the reproductive phase increased bract development in cauliflower curds. This study shows that GAs from both pathways can trigger the vegetative-to-reproductive transition in both cauliflower and broccoli, resulting in earlier curd formation. However, GAs did not advance the inflorescence-meristem-to-floral-primordium transition; on the contrary, they increased bract incidence in cauliflower, a sign of reversion toward the vegetative stage, suggesting that another pathway is responsible for this second transition in cauliflower and broccoli.

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Mark W. Farnham and Thomas Bjorkman

Breeding a vegetable crop for adaptation to a temperature regime that is higher than the recognized optimum for the species in question is an example of breeding for abiotic stress tolerance. Before embarking on a project to breed for such stress tolerance, we propose that several critical considerations or questions must be addressed. These considerations include the following: 1) What is the effect of the abiotic stress on the crop to be improved; 2) what will be the conditions of the selection environment; 3) what germplasm is available that contains the necessary genetic variation to initiate improvement; 4) what breeding scheme will be used to facilitate improvement; and 5) what will be the specific goals of the breeding effort? We use a case study with broccoli to breed for adaptation to high-temperature environments to provide examples of how each of these considerations might be addressed in developing an improvement effort. Based on documented success with this case study in which broccoli quality and performance under high-temperature summer environments has been improved, insights are provided that should be useful to future attempts to breed vegetables more tolerant of an abiotic stress.

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Mark W. Farnham and Thomas Björkman

Broccoli (Brassica oleracea L. Italica Group) is a vegetable crop requiring relatively cool conditions (e.g., less than 23 °C) to induce and maintain vernalization and to allow normal floral and head development to proceed. In general, this requirement is a major limiting factor to production of broccoli in eastern states where growing seasons are often interrupted by high temperature spikes. The USDA, ARS, U.S. Vegetable Laboratory (USVL) is conducting a program to breed broccoli varieties adapted to summer conditions of the southeastern United States. The goal of the current study was to compare performance of three experimental broccoli hybrids from that program with some commonly raised commercial hybrids (‘Packman’, ‘Marathon’, ‘Arcadia’, ‘Greenbelt’, ‘Patron’, and ‘Gypsy’) by conducting trials in summer environments as well as in more conventional growing environments (e.g., in fall). All hybrids produced marketable heads with high quality ratings in fall field trials (2006, 2007, and 2008). Under the high temperatures that were characteristic of the summer (2007, 2008, and 2009) trials in South Carolina, the commercial hybrids ‘Marathon’, ‘Greenbelt’, ‘Arcadia’, and ‘Patron’ failed to produce broccoli heads at all. The remaining hybrids produced heads with similar mean head mass, stem diameter, and bead size in South Carolina summer trials. However, the three experimental hybrids produced marketable quality heads, but ‘Gypsy’ and ‘Packman’ did not. The primary flaws in ‘Gypsy’ and ‘Packman’ heads were increased yellow color, flattening of the dome, increased roughness, and non-uniformity of bead size. In New York trials, all tested hybrids developed heads, but ‘Packman’ and ‘Marathon’ produced relatively poor-quality heads when maturing in summer and better quality heads when maturing in the fall. The experimental hybrids exhibited more consistent quality across different maturity times in the New York tests. Results of this research indicate that broccoli response to summer conditions of the eastern United States is dependent on the cultivar grown. Many cultivars are not adapted to extreme summer conditions of the Southeast because they will not be effectively vernalized and will therefore not head. Others such as ‘Gypsy’ and ‘Packman’ will head, but non-uniform bud development results in a rough-appearing curd in which flower buds are at various stages of development. The experimental hybrids that are single crosses of inbreds selected for adaptation to southeastern summer conditions represent a unique class of broccoli hybrids that combine early maturity and the ability to produce heads under summer conditions of South Carolina. Additional tests of these latter hybrids in New York indicate that they may be generally adapted to summer environments of the eastern United States.

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Lauren C. Garner and Thomas Bjorkman

Stretching is a problem in high-density transplant production. Mechanical conditioning provides good height control for many crops, but there may be adverse effects on field performance. Mechanical conditioning was applied to processing tomatoes (Ohio 8245) grown in #288-deep flats (=2000 plants/m2) using two methods, brushing and impendance. Brushing was applied by gently stroking the plant canopy with a Styrofoam planter flat 20 times back and forth every morning. The impeded plant canopy was compressed slightly by apiece of Plexiglas suspended overnight. The treatments were applied from canopy closure until transplanting to the field. At transplanting, brushed plants were 31% (1993) and 12% (1994) shorter than control plants, and impeded plants were 25% (1993) and 24% (1994) shorter than control plants. In both years, the caliper of impeded transplants was significantly larger than that of both the control and brushed plants. There was also no reduction in dry weight and no noticeable difference in plant quality between treatments. The treatments did not affect the speed at which the plants recovered from transplant shock or the rate at which they grew in the field. Within 5 weeks after transplanting, there were no significant differences between treatments in biomass, leaf area estimates, stem caliper, flowering, early set, or field yield, despite differences in size at transplanting. Therefore, both brushing and impendance result in sturdy, high-quality transplants without adversely affecting establishment or yield.