Flower senescence in many plants is associated with a significant increase in ethylene production. This ethylene has been shown to play a regulatory role in the demise of the petals. The regulation of petal senescence by ethylene is thought to facilitate the ordered breakdown and remobilization of cellular constituents to other plant and flower organs. In order to gain insight in the remobilization of cellular constituents, we investigated changes in P, Ca, Mg, Mn, Cu, Fe, and Co concentrations in petunia corollas from flowers at anthesis through senescence. Our results showed that all elements in our study were present in lower concentrations in corollas than mature leaves. Phosphorus concentration decreased from ≈2000 mg·kg-1 in presenescent corollas to 1500 mg·kg-1 in senescing tissue, a change correlated to increases in ethylene production by the corollas. Increases in Ca, Mg, and Mn concentrations were noted during development of corollas from anthesis to senescence. However, no clear correlation exists between these changes and the ethylene climacteric since increases were gradual and continuous from anthesis to senescence. Calcium concentrations increased 3- to 4-fold from anthesis to senescence. Changes in Mg and Mn concentrations were less pronounced and were limited to 2- to 3-fold increases for Mn and a 2-fold increase for Mg. Concentrations of Cu, Fe, and Co fluctuated throughout development and ranged from 2 to 14, 88 to 544, and 0 to 4 mg·kg-1, respectively.
To observe changes in the nutritional status of corollas during development and senescence, Petunia ×hybrida cv. Mitchell corollas were analyzed for macronutrient and micronutrient content, dry weight, fresh weight, and ethylene production. Carbon content decreased at slightly lower rates than dry weight during corolla development between anthesis and senescence, while fresh weight and ethylene production followed patterns expected of climacteric flowers. Nitrogen, phosphorus, and potassium content declined during development. Both phosphorus and potassium content gradually declined throughout development with overall losses of about 75% and 40%, respectively. Nitrogen content declined 50% during development but losses occurred only during the final stages of senescence. No significant changes were observed in sulfur, calcium, magnesium, and micronutrient content of the corollas during development. Most elements were present in much lower concentrations in corollas than in leaves. The concentrations of calcium, magnesium, and manganese were about 1-, 5-, and 15-fold lower in corollas than in leaves, respectively. Results indicate that remobilization of selected macronutrients from corollas occurred before and during senescence. Taken together with the presence of low concentrations of macronutrients, my data support the contention that petunia corollas are nutritionally in expensive and therefore easily disposable organs.
Tiffany Fess and Sven Verlinden
Three different control methods, row cover, staggered plantings, and the release of a parasitic wasp, Pediobiusfoveolatus, were used to test effectiveness at controlling Mexican bean beetle (MBB) infestations on snap beans. The study consisted of six plots, on five different farms in the Morgantown, W. Va. area, three with and three without the application of the control methods. Releases of 15 adults and 100 larvae during flowering of the bean crop occurred at each plot. Weekly counts of the three MBB life stages, parasitized MBB larvae, and bean yields were taken. The results showed that the release of the parasitic wasp maintained the MBB populations below economic thresholds throughout the growing season. The average yield from plots that received wasp treatments was 34.2 kg, compared to 15.2 kg harvested from untreated plots. Plots that received row cover treatments were shown to be slightly more effective than staggered plantings at controlling MBB populations. Row cover plots yielded an average of 15.3 kg, in comparison to the 11.8 kg yield from untreated plots, while staggered plantings in treated plots yielded 9.5 kg, compared to 6.0 kg from untreated plots. End of season MBB populations in treated plots consisted of 75 adults, 57 pupae, 275 larvae, and 94 parasitized larvae compared to untreated populations, 98 adults, 214 pupae, 420 larvae on average. In conclusion, increased yields can likely be correlated to decreased MBB populations, indicating the release of P. foveolatusas a viable option for control of MBB, especially in organic systems.
Sven Verlinden and William R. Woodson
Ethylene plays a key regulatory role in carnation flower senescence. Flower senescence is associated with a significant increase in ethylene production. Continued perception of this ethylene by the flower is necessary to sustain the climacteric rise in ethylene and the expression of senescence related genes associated with senescence. In addition, increased sensitivity by the flower to ethylene during development and senescence has been observed. In order to study the perception of ethylene at the molecular level, an ethylene receptor gene was cloned from carnation petals. The clone, CARETR, shows 68% homology at the nucleic acid level with the Arabidopsis ethylene receptor gene, ETR1. Northern blot analysis revealed that CARETR is present as a low abundant transcript in petals, styles, and ovaries. Further analysis also showed that CARETR is upregulated during flower senescence. Treatment with the ethylene action inhibitor norbornadiene (NBD) resulted in decreased levels of CARETR transcripts. These data suggest that CARETR plays a role in the increased sensitivity of carnation flowers to ethylene during flower development and is involved in staging the rapid and orchestrated death of the flower.
Sven Verlinden and William R. Woodson
High-temperature treatments can be used for disinfestation of a variety of horticultural crops. Carnation flowers were subjected to a heat treatment in order to determine if it is a viable option for disinfestation of this crop. Flowers were exposed to 45°C for 24 hr in the dark, while control flowers were held at RT for 24 hr in the dark. Subsequently, the flowers were held at RT in the light and monitored for ethylene production, an indicator of imminent floral senescence. In the heat-treated flowers, the ethylene climacteric occurred at 96 hr after the heat treatment, a delay of 12 hr when compared to the control. Peak ethylene production was decreased by 25% to 30% in heat-treated flowers. Northern blot analysis of the ethylene biosynthetic pathway genes, ACC synthase, and ACC oxidase, showed that the expression of these genes is delayed by 8 to 16 hr in heat-treated flowers. This indicates that the delay and decrease in ethylene production is at least, in part, due to a delay or reduction in the expression of these genes. Further investigation revealed a decreased responsiveness of the petals to ethylene. Petals from heat-treated and control flowers were exposed to 1 ppm ethylene for 0, 0.5, 1, 2, 4, 6, 12, and 32 hr. The heat-treated petals again showed a delay and a decrease in maximum ethylene production after exposure to ethylene. A delay in expression of ACC synthase and ACC oxidase was also observed. The beneficial effects of exposing carnation flowers to high temperatures, a delay in ethylene production, and reduced responsiveness to ethylene, suggest that heat treatments could be used for disinfestation of this crop.
James E. Faust, Sven Verlinden and Royal D. Heins
Rapid reduction in temperature for two to three hours starting at sunrise reduces stem elongation compared to elongation of plants maintained under constant temperatures during the day. This experiment was designed to determine if syringing plants with water at sunrise would substitute for a reduction in air temperature or enhance the response to the drop in temperature. Easter lily (Lilium longiflorum Thumb.) plants were exposed to constant 20°C or to 20°C and then 16°C for a 3-hr period following sunrise. Half the plants in each temperature regime were syringed at 30-minute intervals with 20°C water for 3 hr starting 20 minutes before sunrise. Shoot-tip temperature during the three-hr pulse time averaged 20.0 and 17.3°C for the dry plants and 17.3 and 14.7°C for the syringed plants. Total elongation for the dry plants at 20°C was 30 cm and for the temperature-pulsed plants, 4.8 cm less; for the syringed plants, 3.3 and 5.8 cm less, respectively. While shoot-tip temperature of dry plants averaged 0.9°C above air temperature during the remaining hours of the day, syringed plants averaged 1.0°C cooler than the same air temperature even though plants had dried. The data indicate the reduction in stem elongation from a low-temperature pulse at sunrise can be enhanced by evaporative cooling.
Sven Verlinden, Louis McDonald, James Kotcon and Silas Childs
In 1999, West Virginia University (WVU) established an organic farming systems project with a market garden section consisting of 32 plots measuring 16 × 25 ft arranged in a completely randomized design. Sixteen of these plots were managed as high-input and 16 as low-input plots. High-input plots received 10 tons/acre per year of dairy manure and a rye-vetch (Secale cereale and Vicia villosa) cover crop during each winter season since the inception of the experiment in 1999. Fertility in low-input plots was managed solely with an annual rye-vetch cover crop while both treatments also received 5 tons/acre of mixed species hay used as mulch in 2 of every 4 years. A 4-year rotation of crops, green bean (Phaseolus vulgaris), zucchini (Cucurbita pepo), tomato (Solanum lycopersicum), green pepper (Capsicum annuum), and lettuce (Lactuca sativa) in the Fabaceae, Cucurbitaceae, Solanaceae, and Asteraceae families, was established in 1999 and has been maintained ever since. Soil organic matter (SOM) in the upper 6 inches of the soil profile (4.4% in 1999) has remained unchanged in low-input plots at 5.2% in 2004 and 5.4% in 2014, the year following transition and most recent data collection, respectively. During this same time period, significant increases in SOM from 6.4% in 2004 to 8.7% in 2014 were observed in high-input plots. Bulk density was lower in high-input plots than low-input plots in 2014. Despite these improvements in soil quality, high-input plots showed very high levels of phosphorus and potassium. Over the duration of the experiment, yearly manure application increased yields by 22% in all crops combined; however, individual crops responded quite differently. The yield was 9%, 25%, 24%, and 24% higher in high-input plots than in low-input plots for tomato, pepper, zucchini, and green bean, respectively. Manure application in addition to green manures and hay mulch incorporation was found to result in significant economic returns.
Silvanda Silva, Sven Verlinden, Robert Herner and Randolph Beaudry
Base-to-tip profiles of sucrose, glucose, fructose, and respiration rate were measured for asparagus (Asparagus officinalis L.) spears stored at 0C. Fructose content was ≈3-fold and 4-fold higher than glucose and sucrose, respectively. The highest level of fructose was found in the base and was ≈15-fold higher than the tip. The changes in asparagus metabolism were characterized by loss of sucrose and a high rate of respiration within the first hours after harvest. Sucrose was more rapidly lost than the other sugars during this period. The respiration rate was measured along the length of intact spears at 0.5, 1, 2, and 3 h after harvest. Subsequent measurements were taken after larger time intervals for 23 days. The respiration rate declined rapidly to ≈60% of the initial rate within 12 h, decreasing more slowly thereafter. Initially, the respiration rate of the tip was about four times that of the base, but, after 23 days, the respiration rate of the tip was only twice that of the base. Sucrose content and respiration rates were closely correlated.
Silvanda Silva, Sven Verlinden, Robert Herner and Randolph Beaudry
Asparagus spears (Asparagus officinalis L.) were placed in solutions of six different concentrations of sucrose (0%, 1%, 2%, 4%, 8%, and 16%) plus citric acid at 0C for 24 h following harvest. The profiles of sucrose, fructose, glucose, and respiration rate along the length of the spear were evaluated throughout storage. The effect of carbohydrate loading on the rate of respiration, sucrose loss, and the shelf life of asparagus was determined. For all treatments, sugars decreased and respiration rate increased from the butt to the tip. The 4% sucrose treatment enhanced the sugar level in the tip ≈5-fold relative to the control. For the 8% and 16% treatments, sucrose tended to accumulate in the base. Spears loaded with higher sucrose concentrations had higher respiration rates than controls up to 3 h after loading. After this time, no significant differences were observed between treatments. For all treatments, respiration rates declined rapidly following harvest, stabilizing in ≈24 h. Weight gain and growth increased as the treatment sucrose concentration decreased. Solution uptake was enhanced by loading at lower humidity levels.
Sven Verlinden, Silvanda M. Silva, Robert C. Herner and Randolph M. Beaudry
The rate of respiration and the concentrations of sucrose, glucose, and fructose were measured along the length of intact asparagus (Asparagus officinalis cv. Jersey Giant) spears during storage at 0 °C. Carbon dioxide production by each of five sections along the spear was initially high but underwent a rapid and extensive decline within the first 24 hours after harvest with the rate of decline slowing thereafter. The respiration rate was highest at the tip (Section 1), decreasing as the distance from the tip increased (Sections 2 through 5 with Section 5 being more basal). Initially, the respiration rate of the tip was approximately four times that of the base, but after 23 days at 0 °C, the respiration rate of the tip was only twice that of the base. Sugar levels were measured in Sections 1 through 4. Sugar levels declined with time, but increased, unlike respiration, with distance from the tip. Sucrose underwent a rapid decline within the first 24 hours of storage in the tip and Sections 3 and 4. Sucrose depletion was most extensive in the tip, reaching more than 95% by Day 23. Glucose underwent the most rapid decline in Section 2. The relatively higher rate of glucose depletion in Section 2, the zone of rapid cell elongation, may have been to support a relatively higher rate of cell wall biosynthesis in this section. For the first day after harvest, sugar depletion far outstripped hexose equivalents respired as CO2. Afterward, however, the rate of respiration (as hexose equivalents) was similar to the rate of sugar depletion for all sections except the most basipetal, which lost carbohydrate faster than could be accounted for by respired CO2. The data suggest that hexoses were exported from more basipetal tissues to support the metabolic activity of more acropetal sections.