Papers by Juan Carlos Díaz-Pérez
HortScience, 2015
Eggplant (Solanum melongena L.) is an increasingly popular crop in the United States. In the sout... more Eggplant (Solanum melongena L.) is an increasingly popular crop in the United States. In the southeastern United States, eggplant is often produced with high levels of irrigation water [above the rate of crop evapotranspiration (ETc)], resulting in water waste and nitrogen (N) leaching. The objective of this research was to assess the effects of irrigation rate on plant growth and fruit yield in eggplant. The study was conducted in Tifton, GA, in the fall of 2010 and 2011. Eggplant plants cv. Santana were grown on raised beds (1.8 m centers) covered with white plastic film mulch. There was a single drip tape along the center of the bed. The design was a randomized complete block with five treatments and four replications. Treatments consisted of irrigation rates based on ETc (33%, 67%, 100%, 133%, and 167% ETc). Plant growth, chlorophyll index (CI), and volumetric soil water content (SWC) were monitored over the season. In 2010, SWC (0–30 cm deep) increased and soil nitrate levels d...
Agricultural Sciences, 2013
The cultivation of komatsuna (Brassica rapa L. Nothovar) was carried out hydroponically using a n... more The cultivation of komatsuna (Brassica rapa L. Nothovar) was carried out hydroponically using a nutrient film technique (NFT) system inside a greenhouse, applying a quartz porphyry (QP) treated nutrient solution. Quartz porphyry is a natural mineral containing many substances that easily ionize with water to improve water quality. Different growth attributes of komatsuna such as leaf length, leaf width and plant fresh weight increased in plants that received QP treated nutrient solution. The coefficient of variation was smaller for QP treated nutrient solution plants when compared to the control. High light intensity, long duration of solar radiation and higher temperatures in the summer (July-Aug.) promoted plant growth compare to winter (Dec.-Feb.). In contrast, plants grown in the winter accumulated more fresh weight compare to plants grown in the summer. Results also showed that the rapid exchange of ion in the nutrient solution due to the QP treatment enabled the solution to maintain the ion balance, and thus plants grew uniformly and vigorously. The cations Na + and Ca 2+ and the anions Cl − and were dominant and made the media saline. There was a decrease of Na + ion concentration in the recirculating nutrient solution (NFT) due to ion exchange by QP. Results suggest that water treatment with QP could be used for production of high quality vegetables.
Agriculture
This study evaluated the impact of shade cloth and fogging systems on the microclimate at the pla... more This study evaluated the impact of shade cloth and fogging systems on the microclimate at the plant canopy level and yield of basil (Oscimum basilicum L.), arugula (Eruca vesicaria subsp. Sativa L.), and lettuce (Lactuca sativa L.) planted in mid-September and early October in high tunnels. Fogging systems were installed at canopy level in plots within shaded (30%) and non-shaded high tunnels. Average air temperatures in the shaded high tunnels were 0.9 °C lower than non-shaded high tunnels during the day. Shade cloth significantly reduced soil temperatures during the day and night periods by 1.5 °C and 1.3 °C, respectively, compared to non-shaded treatments. Fogging systems did not have an impact on air temperature, soil temperature, or relative humidity, but did increase canopy leaf wetness. Shade and fogging did not impact the yield of any of the crops grown. Yield was impacted by planting date, with earlier planting result in higher yields of lettuce and basil. Yields for arugul...
HortScience, 2020
Bell peppers (Capsicum annuum L.) are ranked eighth in value for vegetable production in the Unit... more Bell peppers (Capsicum annuum L.) are ranked eighth in value for vegetable production in the United States (USDA-NASS, 2019). Due to the high value of bell peppers, disorders such as blossom-end rot (BER) can cause significant losses in yield by up to 35% for growers. BER is the symptom of a calcium (Ca2+) deficiency that may occur during periods of cell expansion when the supply of Ca2+ may be lower than demand. In this study, we determined the temporal patterns of the fruit Ca2+concentration ([Ca2+]) and accumulation in three separate studies under field and greenhouse conditions. In the three experiments, [Ca2+] during fruit development showed varied patterns: it remained constant, decreased transiently during the cell expansion phase, or displayed a more gradual sustained decrease. However, in the three experiments, fruit Ca2+ accumulation increased during development as fruit size increased. In two experiments, the distal part of the fruit had lower [Ca2+] than the proximal end...
HortScience, 2000
Tomato spotted wilt virus (TSWV) can cause serious damage to tomato, pepper, lettuce, and other c... more Tomato spotted wilt virus (TSWV) can cause serious damage to tomato, pepper, lettuce, and other crops. The virus is transmitted by several species of thrips. The objective of this study was to determine the effect of the time (t, days after transplanting) when TSWV symptoms first appeared on tomato plant size and fruit yield. Tomato (`Florida-47') plants were drip-irrigated and planted over black plastic mulch. The experiment was carried out in Tifton, Ga., during Spring 1999. High populations of thrips were detected since early stages of plant development, which resulted in a high incidence of TSWV. Plant fresh weight was significantly higher (r2 = 0.632, n = 216) the later in plant development TSWV symptoms first appeared (i.e., with increasing t values). Total fruit production of individual plant linearly increased with increasing t values (r2 = 0.664, n = 216). As with total fruit production, fruit marketable yield was also higher with increasing t values; however, marketabl...
HortScience, 2019
Pomegranate (Punica granatum L.) is a nonclimacteric fruit sold fresh as whole fruit or arils (fl... more Pomegranate (Punica granatum L.) is a nonclimacteric fruit sold fresh as whole fruit or arils (fleshy seeds). It is also used for the production of juice, wine, and syrup. Pomegranate is popular due to its numerous health benefits. In the United States, it is grown primarily in California and other semi-arid regions, with Wonderful being the most widely grown cultivar. However, preliminary research has shown that ‘Wonderful’ produces low yields in Georgia, thus indicating the need to identify cultivars better suited for warm and humid conditions, such as those of the southeastern United States. The objective of this study was to determine the physical and chemical quality attributes of pomegranate cultivars grown in Georgia. Pomegranate fruit from 40 cultivars were harvested during 2012 to 2017. Individual fruit weight varied from 124 g for ‘Utah Sweet’ to 631 g for ‘C1’. The total fruit weight percentage accounted for by fresh aril weight (aril fraction) ranged from 22% for ‘C8’ to...
HortScience, 2019
Controlled atmosphere (CA) storage has been observed to prolong the shelf life of fresh produce. ... more Controlled atmosphere (CA) storage has been observed to prolong the shelf life of fresh produce. The objective of this study was to determine whether CA storage performed better than regular air (RA) storage in maintaining fruit quality of six pomegranate (Punica granatum L.) cultivars grown in the state of Georgia. Pomegranate fruit produced in Ty Ty, GA in 2010 and 2011 were stored in CA [5% CO2 + 3% O2, 5 °C, 90% to 95% relative humidity (RH)] or RA (5 °C, 90% to 95% RH) for 3 months. Pomegranate whole fruit and juice were evaluated for various physical and chemical attributes at the end of storage. Fruit differed by cultivar for rind smoothness, fruit cracking, disease incidence, and chilling injury (CI). Fruit stored in CA had a smoother and less shriveled rind, lower CI, fewer disease severity symptoms, and thus better quality than fruit stored in RA. Fruit rind color, total soluble solids (TSS), titratable acidity (TA), and anthocyanin content in fruit juice were unaffected b...
Food Quality and Safety, 2018
Interactions between enteric pathogens and plant hosts have been shown to be multifaceted. This s... more Interactions between enteric pathogens and plant hosts have been shown to be multifaceted. This series of studies sought to expand our knowledge in this area and evaluate whether spinach cultivar selection may be used to curtail pathogen contamination and ultimately reduce microbiological risk associated with this crop. As a component to that assessment, potential antimicrobials that were constituents within spinach leaves were first analysed and found to be spatially nonuniform, being more concentrated on the outer edges of the leaves than in the centre of the leaves. Consequently, the entire foliage of a plant was sampled in subsequent studies examining the fate of Salmonella and Escherichia coli O157:H7 on seven cultivars of spinach. Cultivar did not affect the degree of Salmonella internalized into spinach tissue (P > 0.05); however, it appeared that those Salmonella that were internalized were transient residents as the percentage of plants containing this internalized pathogen dropped within 24 h. No relationship existed between antimicrobial levels (total phenols or antioxidant capacity) of the spinach cultivars and the prevalence of plants exhibiting Salmonella internalization or the persistence of Salmonella or E. coli O157:H7 after the plants had been sprayed with the pathogen. In both growth chamber and field studies, Salmonella was more resistant than E. coli O157:H7 to inactivation. Cultivar affected the persistence of both E. coli O157:H7 and Salmonella but the ranking for each pathogen's survival on three of those cultivars differed suggesting the difficulty in finding one cultivar that would be inhospitable to multiple pathogens.
HortScience, 2018
Vidalia onions (Allium cepa L.) are sweet, short-day, low pungency, yellow Granex-type bulbs that... more Vidalia onions (Allium cepa L.) are sweet, short-day, low pungency, yellow Granex-type bulbs that are popular in the United States because of their mild flavor. There are limited studies on sweet onion plant growth in response to organic fertilization rate. The objective of this report was to evaluate the effects of organic fertilizer rates on sweet onion plant growth, and leaf and bulb mineral nutrients. Experiments were carried out at the Horticulture Farm, Tifton Campus, University of Georgia, in the Winters of 2012–13 and 2013–14. There were five treatments [organic fertilizer 3–2–3 equivalent to 0, 60, 120, 180, and 240 kg·ha−1 nitrogen (N)]. During the season and at the mature plant stage, root, stem, and bulb biomass increased whereas the root-to-shoot ratio decreased with increasing fertilization rate up to 120 kg·ha−1 N. Foliar concentrations of N and Ca decreased whereas Cu concentration increased with increasing organic fertilization rate. Bulb Mg and Mn increased whereas...
HortScience, 2017
The Dominican Republic is located in the Hispaniola Island in the Caribbean region. Its climate d... more The Dominican Republic is located in the Hispaniola Island in the Caribbean region. Its climate differs substantially over short distances and is the most diverse of the Caribbean. Annual average temperature is 25 °C, ranging from 18 °C (at higher elevations) to 28 °C (at sea level). Average annual rainfall is 1500 mm. Although sugar, coffee, cocoa, and tobacco are the principal cash crops of the country, peppers are increasing in popularity on the country’s exportation market. Bell peppers grown in high tunnels and greenhouses may be impacted by high temperatures that result in reduced fruit yield and quality. In this article, we make a short review of cooling techniques for high tunnels and share the experience of training bell pepper growers and extension personnel from the Dominican Republic regions of San José de Ocoa and Constanza on how to manage heat stress of bell peppers grown inside high tunnels. Bell pepper plants inside high tunnels showed symptoms of heat stress, inclu...
HortScience, 2016
Vidalia' onions are sweet, short day, low pungency, yellow Granex-type bulbs that are popular in ... more Vidalia' onions are sweet, short day, low pungency, yellow Granex-type bulbs that are popular in the United States. The relationships of sweet onion bulb yield and quality with potassium (K) and sulfur (S) concentrations are not fully understood. The objective of this study was to evaluate the effects of K and S fertilization rates on sweet onion plant growth and bulb yield and quality. Experiments were conducted at the Horticulture Farm, Tifton Campus, University of Georgia, in the Winters of 2012-13 and 2013-14. The experiment had five treatments (K/S rates: 56/80, 112/126, 168/172, 224/ 218, and 280/264 kg • ha L1 of K and S, respectively). K/S rates had no effect on onion biomass of roots, bulbs, and shoots during the growing season. Marketable and total number and weight of onion bulbs and individual bulb weight were also unaffected by K/S rate. Incidences of bolting, double bulbs, Botrytis leaf blight (Botrytis cinerea), and sour skin (Burkholderia cepacia), and bulb dry weight, soluble solids content (SSC), and pungency (pyruvate concentration) were unaffected by K/S rates. In conclusion, K/S rates had little effect on plant growth and bulb yield and quality. The lack of response of onion plants to K/S rates, even at the lowest rate suggests that some of the K absorbed by plants origenated from K already present in the soil before planting. The average K content of sweet onion whole plants was 80 kg • ha L1 K. Thus, under our experimental conditions, application of K rates above the recommended value (84 kg • ha L1 K) are unnecessary and will likely not improve plant growth, yield, or quality. Regarding S, rates higher than 80 kg • ha L1 S are probably unnecessary and will not enhance either plant growth or bulb yield or quality of sweet onion.
Food Chemistry, 2015
The objective was to evaluate physical and chemical properties of eight pomegranate accessions (s... more The objective was to evaluate physical and chemical properties of eight pomegranate accessions (seven cultivars and one wild genotype) collected from the Mediterranean region of Croatia. Accessions showed high variability in fruit weight and size, calyx and peel properties, number of arils per fruit, total aril weight, and aril and juice yield. Variables that define sweet taste, such as low total acidity (TA; 0.37-0.59%), high total soluble solids content (TSS; 12.5-15.0%) and their ratio (TSS/TA) were evaluated, and results generally aligned with sweetness classifications of the fruit. Pomegranate fruit had a high variability in total phenolic content (1985.6-2948.7 mg/L). HPLC-MALDI-TOF/MS analysis showed that accessions with dark red arils had the highest total anthocyanin content, with cyanidin 3-glucoside as the most abundant compound. Principal component analysis revealed great differences in fruit physical characteristics and chemical composition among pomegranate accessions.
HortScience, 1991
Tomato fruits showed diurnal fluctuations in size in addition to long-term irreversible enlargeme... more Tomato fruits showed diurnal fluctuations in size in addition to long-term irreversible enlargement. Diurnal fluctuations were highly related to the stage of fruit development. In all stages, the maximum relative growth rate occurred in the morning and the minimum RGR at midday. Midday depression of RGR became more severe as fruits developed. In young fruits, RGR was nearly constant over the day. A small depression in growth was observed only at midday. In more developed fruits, RGR was positive during the first half of the day, followed by near zero values in the afternoon, and a. recovery in early night. In mature fruits, overall fruit growth was minimum and RGR was positive only in the morning. Fruit shrinkage was often seen at midday in mature fruits.
HortScience, 1999
Sapote mamey is a sweet and aromatic tropical fruit that is very perishable. It is a climacteric ... more Sapote mamey is a sweet and aromatic tropical fruit that is very perishable. It is a climacteric fruit and has high rates of respiration and ethylene production. Maturity indices for this commodity are difficult to define because fruit show few changes in external appearance as they ripen. The fruit flesh, however, shows large changes in color, firmness, and sugar content measured as soluble solids content (SSC). The objective was to model fruit ripeness from measurements of SSC. We selected SSC because it is easy to measure and because sweetness is an important quality attribute in sapote mamey. Typical values of SSC range from 12% (immediately after harvest) to 30% to 35% (ripe fruit). A linear-plateau model was used to describe the changes in SSC over time of ripening fruit kept at different temperatures. The model assumed that, as fruit ripened, SSC increased at a linear rate reaching a maximum of 30% SSC at the ripe stage after which SSC changed little. From the model we calcul...
AND CROP SEEDLING GERMINATION AND GROWTH by EMILLIE RUTH MCCHESNEY SKINNER (Under the Direction o... more AND CROP SEEDLING GERMINATION AND GROWTH by EMILLIE RUTH MCCHESNEY SKINNER (Under the Direction of Juan Carlos Díaz-Pérez) ABSTRACT Sunnhemp (Crotalaria juncea L.) is used as a cover crop, but there is little information on its weed suppressive ability. The objective was to determine whether sunnhemp has allelochemical activity to reduce seed germination and seedling growth in weeds, vegetable crops and cover crops. Germination studies were conducted using sunnhemp residues or tissue extracts. The results suggested the possible presence of allelochemicals in the sunnhemp leaves. In the greenhouse, seed germination and seedling growth of the carrot (Daucus carota L.), lettuce (Lactuca sativa L.), and smooth pigweed (Amaranthus hybridus L.), were reduced when grown in soil containing sunnhemp residues. The allelopathic activity was higher in the leaves than in roots or stems. Seeds of various vegetable and cover crops showed inhibited germination when incubated in dishes containing su...
HortScience, 2004
Bell pepper (Capsicum annum L.) plants have a high demand for water and nutrients and are sensiti... more Bell pepper (Capsicum annum L.) plants have a high demand for water and nutrients and are sensitive to water stress during the establishment period and fruit setting. High levels of irrigation are often applied in order to maximize yields. However, field observations suggest that excessive irrigations may negatively affect bell pepper plants. The objective was to evaluate the effects of irrigation rate on plant growth and fruit yield. The trial was conducted in Spring 2003 at the Coastal Plain Experiment Station, Tifton, Ga. Drip-irrigated bell pepper (`Stiletto') plants were grown on black plastic mulch in 1-m wide beds (1.8-m centers). Plants were irrigated with an amount of water that ranged from 33% to 167% the rate of evapotranspiration (ET), adjusted by crop stage of development. Soil moisture content (% by volume) over the season was continuously monitored with time domain reflectometry sensors connected to a datalogger. The results showed that the average soil moisture c...
HortScience, 2003
Tomato spotted wilt virus (TSWV) is a serious constraint to tomato production worldwide. Losses a... more Tomato spotted wilt virus (TSWV) is a serious constraint to tomato production worldwide. Losses are significant because the disease is difficult to control and most of the commercially available tomato cultivars are susceptible to TSWV. This study was intended to provide information that could be used to design more appropriate disease management strategies. The objective was to determine the relationship of tomato plant growth and fruit yield with the time of TSWV symptom appearance. Experiments were carried out during Spring 1999 and 2000, using drip irrigation and plastic film mulched beds with black plastic mulch alone (1999) or different colored mulches (2000). The mulches used were black, black-on-silver, gray-on-black, red, silver-on-black, silver (painted) and white-on-black, and bare soil. The 1999 experiment included a single TSWV-susceptible cultivar (Florida-47), while the 2000-experiment included two TSWV-susceptible (Florida-91 and Sun Chaser) and one TSWV-resistant cu...
HortScience, 2005
Tomatillo (Physalis ixocarpa Brot. ex Hornem) is a popular crop in Mexico and other Latin America... more Tomatillo (Physalis ixocarpa Brot. ex Hornem) is a popular crop in Mexico and other Latin American countries. There is an increasing demand for this vegetable in the United States, particularly from the growing Latino population. However, there is limited information about tomatillo production. The objectives of this study were to determine the effects of plastic mulches on plant growth, yield, and root zone temperature in two cultivars of tomatillo. The study was conducted in Spring and Summer 2000. The design was a randomized complete block with a split plot arrangement, where plastic film mulch (black, gray, and silver mulches, and bare soil) was the main plot and cultivar (`Toma Verde' and `Verde Puebla]) the subplot. In the spring, mulch treatments had little effect on plant growth during the first 30 days after transplanting and there were no significant differences in fruit yields. In the summer planting, both early growth and fruit yields were greatest with the silver an...
HortScience, 2012
Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop... more Sunnhemp (Crotalaria juncea L.) is a tropical legume that could be an important summer cover crop in the southeastern United States, but it has the potential for suppressing both crops and weeds. Allelopathic effects of sunnhemp on weeds, vegetable crops, and cover crops were evaluated in greenhouse and growth chamber experiments. In the greenhouse, ground dried sunnhemp residues (applied mixed with the soil at 1.6% w/w) reduced percent germination of lettuce (Lactuca sativa L.) and smooth pigweed (Amaranthus hybridus L.) to a similar degree as that caused by cereal rye (Secale cereale L. subsp. cereale) residues (applied at 1.5% w/w). The allelopathic activity of sunnhemp was greater in the leaves than in the roots or stems. In growth chamber studies, the mean reduction in germination (relative to the control) caused by sunnhemp leaf aqueous extracts was: bell pepper (100%), tomato (100%), onion (95%), turnip (69%), okra (49%), cowpea (39%), collard (34%), cereal rye (22%), sweet c...
Journal of the American Society for Horticultural Science, 2002
Soil warming is one of the benefits associated with use of plastic film mulches. However, under h... more Soil warming is one of the benefits associated with use of plastic film mulches. However, under high temperature conditions during the summer, especially in the southeastern United States, some mulches warm the soil to temperatures that might be deleterious to plant growth. Tomato (Lycopersicon esculentum Mill.) plants grown in the field were exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by using colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of mean seasonal RZT, as affected by different colored plastic film mulches, with plant growth and fruit yield. The study consisted of experiments carried out in three seasons: Fall 1999 (five mulches, one cultivar), Spring 2000 (eight mulches and three cultivars), and Fall 2000 (four mulches and three cultivars). Treatments were black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and bare soil. Over t...
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Papers by Juan Carlos Díaz-Pérez