Overview
My program is centered in the identification and understanding of plant morphological and physiological adaptation mechanisms to environmental stresses and in the development of sustainable vegetable cropping systems. The current focus is on five integrated areas: 1) stand establishment, seed germination and transplant quality, shoot/root growth and physiological responses to drought and temperature stresses; 2) water conservation strategies, deficit irrigation and nitrogen impact on plant growth, development, and product quality; 3) cultural strategies for traditional and novel crops that contain high phytochemical content for human health and with adaptability to water-restricted regions, 4) plant growth regulators (PGRs) to modify vegetative and reproductive development of economically important vegetable crops, and 5) screening and selection of Texas AgriLife Research pepper, onion, and melon genotypes and commercial spinach cultivars.
Stand Establishment | Water Conservation |
Deficit Irrigation - Nitrogen - Novel Crops & Phytochemicals | PGR's
ABA and transplant stress tolerance
Understanding how containerized transplants respond to exogenous stressors at morphological and physiological levels provides the basis for elucidating the complex mechanisms underlying pre- and post-transplant stress tolerance. The ability for young transplants to tolerate stress and resume growth is linked to the balance of leaf transpiration, photosynthesis, root water uptake, and shoot/root growth. However, vegetable species have wide variation in the ability to acclimatize to water and temperature stresses. We are focusing on abscisic acid (ABA) methods of application to vegetable seedlings exposed to cycles of desiccation and comparing the efficacy of ABA with physical antitranspirants. We are also interested to investigate whether ABA-treated transplants would control growth prior to transplanting and prolong their stress tolerance when exposed to high temperature, drought stress or low light conditions. The objective is to determine if signaling, metabolic and/or physical compounds have the potential to modulate seedling development, control shoot growth at transplanting, enhance stress tolerance and ultimately improve field establishment of vegetable transplants. View Photos
Irrigated vegetable crops are economically important in the Wintergarden. However, increased regulations restricting water use, competition for underground and surface water with large urban areas, like the city of San Antonio, coupled with extreme temperatures and drought has placed a large strain on water resources and on the livelihood of farming communities in southwest Texas. Currently growers are allowed to pump only 24 inches/acre per year from the Edwards Aquifer. We expect that water pumping restrictions will increase in the near future. Growers have a great interest in the implementation of efficient irrigation systems such as Center pivot, LEPA, subsurface drip (SDI) and the recently developed low pressure drip system (LPS). These technologies, when integrated with new genetic materials that have drought tolerance, high nutritional components and adapted to our environmental conditions, could provide ‘branded products’ for shippers and growers, and consequently create new opportunities to increase market shares. This project aims at developing efficient irrigation strategies to enhance quality of vegetable crops while saving water in the Edwards Aquifer region. We are also developing water-crop strategies using deficit irrigation (less than 100% ETc) and applying crop coefficients (Kc) for the region. State of the art facilities such as 7 large in-ground lysimeters and automatic drip systems are in placed at the Center. The goal of our program, which is integrated with the Agronomy program aims at reaching 25% water savings for most vegetable crops including spinach, watermelon, onion and peppers. View Photos
3. Deficit Irrigation - Nitrogen - Novel Crops & Phytochemicals
3.1. Deficit irrigation and plant population in spinach
The objective of this project was to determine yield, leaf quality, and water use efficiency to irrigation rates and plant population. Three irrigation regimes were imposed with a center pivot system, 100%, 75%, and 50% crop evapotranspiration rates (ETc), at four plant populations: 655, 815, 988 and 1,149 thousand seeds/ha on cv. DMC 16. During the first year, marketable yield was reduced by deficit irrigation. However, water use efficiency was significantly higher for 50% ETc compared to 100% ETc, but similar to 75% ETc. Deficit irrigation also decreased the % stem weight. Despite a slight increase in the % of yellow leaves but not in % of stem weight, marketable yield and water use efficiency were significantly higher at 1,149 thousand seeds/ha. This study showed that deficit irrigation in combination with increased plant population has the potential to increase yield and water savings, without adversely affecting leaf quality.
3.2. Deficit irrigation and slow release nitrogen
Field studies are being conducted to compare N rates and sources (UAN and slow release N fertilizers) under optimum and deficit irrigation practices (less than 100% crop evapotranspiration rates, ETc) for cool season crops (spinach, onion and carrots). We are focusing on changes in soil/plant nitrate and ammonium content during crop development, marketable yield, sensory and phytochemical quality attributes. View Photos
3.3. Deficit irrigation, nitrogen rates and phytochemicals in artichoke
Artichoke (Cynara scolymus L.), a newly introduced crop in southwest Texas, is an excellent source of antioxidant phenolic compounds, including chlorogenic acid and cynarin. The edible part of the artichoke immature flower (head) is also known as a good source of minerals and dietary fibers. To investigate whether pre-harvest crop strategies can improve yield and nutritional quality of artichoke, a two-year field experiment was conducted with three irrigation regimes (50, 75 and 100 % crop evapotranspiration, ETc) and four N rates (0, 60, 120 and 180 kg N ha-1). Seedlings of artichoke cv. Imperial Star were transplanted in the 2005-2006 season, and off-shoots were allowed for re-growth in the 2006-2007 season. Differential irrigation was applied after stand establishment with a subsurface drip system. Nitrogen fertilizer was applied as NH4NO3 by side dressing in two equal split doses at stand establishment and head initiation each year. Yield, total head number, average head weight and size were highest at 100 % ETc, while 35% and 20% yield reduction occurred at 50 % ETc in the first and second season, respectively. Overall, nitrogen had small effects on head growth and yield. Total phenolics and chlorogenic acid content significantly increased with deficit irrigation, especially at late harvests. Cynarin content also showed similar trends, but they were not statistically significant. Conversely, soluble sugar and fiber content were similar among treatments but decreased as time of harvest progressed. Considering the sugar composition, the sucrose to monosaccharide (glucose and fructose) ratio increased during harvesting time. In this biennial production system, deficit irrigation strategies (lower than 100 % ETc) had a stronger impact than nitrogen rates on yield and the nutritional quality of artichoke heads. View Photos
3.4. Irrigation systems on Poblano or ancho peppers
Yield and fruit quality of poblano pepper (Capsicum annuum L. cv. Tiburon) were evaluated in response to deficit irrigation rates and irrigation systems. The experiment was conducted at the Texas Agr. Exp. Station in Uvalde with a Center pivot in a 2.5 ha block using three irrigation rates, 100%, 80% and 60% evapotranspiration rates (ETc). Six-week containerized transplants were mechanically transplanted on beds 1.0 m between centers with plants within rows 45 cm apart. We also compared production efficiency of four irrigation systems in an urban-rural environment near San Antonio. Beds were 0.9 m between centers of single-row beds or 1.8 m between centers of double-row beds and plants within rows 45 cm apart. Irrigation systems were: 1) furrow irrigation with one line/single beds, 2) subsurface drip (SDI)-no mulch, with one line/single bed, 3) SDI-no mulch, with two lines/double beds, and 4) SDI drip-white mulch with two lines/double beds. Summer ratooning of the spring-planted crop under deficit irrigation (less than 100% ETc) allowed a fall crop with a 2.0 fold yield increase, larger fruit size (greater than 10 cm length) and significantly lower defects caused by sunburn or blossom end rot compared to summer production. SDI drip-white mulch had a 2.4 fold yield increase and 76 mm water savings compared to furrow. Fruit vitamin C content was not affected by irrigation, however, mature red fruits had a 3.6 fold increase compared to mature green fruits. Combining deficit irrigation with ratooning we were able to produce fancy poblano fruits. Additional water savings and increased yield were demonstrated by SDI technology. View Photos
3.5. Deficit irrigation and lycopene content in watermelon
Past experiments were conducted to determine the effects of deficit irrigation and environments on lycopene content, quality, and yield of diploid and triploid watermelon. Irrigation rates were 1.0 evapotranspiration (ET), 0.75 ET and 0.5 ET. Diploid cvs. were ‘Summer Flavor 710’ and ‘Summer Flavor 800’, and triploid cvs. were ‘Summer Sweet 5244’ and ‘Super Seedless 7187’. The experiments were conducted in three Texas locations: Uvalde, Weslaco, and Lubbock. All experiments used similar cultural strategies (plant spacing, subsurface drip, black plastic mulch, and containerized transplants), except for transplanting and harvesting dates. Deficit irrigation reduced total marketable yield by about 30% in Uvalde and Lubbock, and it increased the yield of small fruits (< 5 kg). Individual fruit size was more variable for diploid than triploids at 0.75 ET and 0.50 ET. Soluble solid content (SSC) was lower at 1.0 ET rate for triploids, but not diploids. Generally deficit irrigation did not decrease SSC, and significantly increased flesh firmness in triploids compared to diploids. Fruit lycopene content increased with maturity at all irrigation rates and cultivars. This work across three diverse Texas locations demonstrated that deficit irrigation directly reduced yield, but had less effect on lycopene development and fruit quality of triploid watermelon.
4. Plant growth regulators: Ethylene inhibitors
4.1. 1-MCP dipping in melon
The objective of this study was to determine the effects of 1-MCP post-harvest dipping application rates and timings on cantaloupe fruit quality. Cantaloupe cv. Mission was grown in a commercial field on a silty clay loam following standard cultural practices for the Wintergarden of Texas. Three consecutive experiments were conducted. First we evaluated 1-MCP rates (0 to 10 ppm) at three levels of maturity (fruits attached, half slip and full slip), second we evaluated 1-MCP rates (0 to 10 ppm) at four dipping times (0.5, 1, 2 and 5 min), and thirdly we evaluated 1-MCP rates (0 to 1 ppm) at two storage times (10 and 20 days) and two temperatures (4 and 8 ˚C). After fruits remained in cold storage (10 days in exps. 1 and 2) they were transferred to room conditions (23 ˚C) and evaluated 1, 3, and 5 days after storage (DAS). Fruits treated with 1 or 10 ppm 1-MCP were firmer than control fruits 1, 3 and 5 DAS. Fruits tended to be less yellow and with less sunken discoloration areas with 10 ppm 1-MCP compared to control (water) or adjuvant (0 ppm). Dipping melon fruits in 1 ppm 1-MCP for 5 min or 10 ppm 1-MCP for 1 min gave the least decay ratings. In the last experiment, 1 ppm 1-MCP for 5 min provided significant benefit in maintaining fruit firmness, 22% and 43% compared to control fruits stored at 4°C and 8°C, respectively. Fruit soluble solid content was minimally affected by the treatments. Integrating the three experiments, we conclude that post-harvest dipping in 1 ppm 1-MCP for 2 or 5 min appears a reliable method to maintain pre-harvest fruit quality and extend the shelf life of cantaloupe cv. Mission. View Photos
4.2. Pre-harvest AVG spray on melon
Studies were conducted to determine whether aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, would synchronizeharvest, increase yield and improve overall at harvest and postharvest quality of melon. Field experiments were conducted during two seasons with AVG (124 g a.i. ha-1) applied as spray or soil-injected into the root zone with a single or double application between 7 and 21 days before harvest. AVG spray, but not AVG injection, delayed harvest at two timings in the first season and only once in the second season. Total marketable yield increased with AVG injection but not with the AVG spray method of application. Regardless of method of application, AVG did not affect fruit firmness, rind thickness, netting, or soluble solids content when measured at harvest, but AVG spray decreased fruit size and seed cavity in one season. Similarly, pre-harvest application of AVG spray did not affect fruit quality after storage, except for an increase in fruit firmness with the AVG injection method. Our data suggests that yield and fruit quality responses to AVG spray application timing and method were weak and inconsistent to be used for melon field production.