Numerous studies have evaluated the effect of high-energy radiation as means to increase nutritional quality of lettuce (Lactuca sativa). However, most research has focused on providing constant radiation quality or quantity throughout the production cycle, which typically results in yield reductions or increases in production costs. End-of-production (EOP) radiation is a cost-effective, preharvest practice that can allow growers to manipulate product quality and thus increase market value of lettuce without negatively affecting plant growth. The objective of this study was to quantify and compare growth and accumulation of secondary metabolites from ‘Rouxaï RZ’ and ‘Codex RZ’ red-leaf lettuce grown indoors and exposed to different strategies of EOP high-energy radiation. Plants were grown for 24 days under an average daily light integral (DLI) of 15.8 mol·m‒2·d‒1 (220 µmol·m‒2·s‒1 for 20 h·d−1) using red:blue light-emitting diode (LED) lamps. Four days before harvest (36 days after sowing), plants were exposed to one of three EOP treatments added to red:blue LEDs: 1) ultraviolet-A (EOP-ultraviolet); 2) high blue (EOP-B); or 3) high-intensity (EOP-H) radiation. A fourth treatment was included as a control, with no EOP. Except for EOP-H, all treatments provided a DLI of 15.8 mol·m‒2·d‒1; EOP-H provided a DLI of 31.7 mol·m‒2·d‒1. No treatment differences were measured for shoot fresh weight (FW) of ‘Rouxaï RZ’ but shoot FW of ‘Codex RZ’ was negatively affected by EOP radiation, indicating potential changes in lettuce yield from applying EOP high-energy radiation during active plant growth. In general, EOP treatments did not affect total phenolic content and total carotenoid concentration of plants, but anthocyanin content and antioxidant capacity were positively influenced by EOP-B and EOP-H, whereas EOP-ultraviolet resulted in similar nutritional quality to control. Findings from this study indicate that EOP high-energy radiation, especially EOP-B, has significant potential to improve the nutritional quality of red-leaf lettuce grown in controlled environments.
Celina Gómez and Juan Jiménez
Juan A. Villanueva-Jiménez and Marjorie A. Hoy
Florida citrus nursery growers were surveyed to learn about their citrus leafminer (Phyllocnistis citrella Stainton) (CLM) management practices as a preliminary step in developing an integrated pest management (IPM) program. All responses were kept anonymous. Survey responses from growers producing ≈4.2 million trees annually were obtained, which represents most of the estimated 5.2 million trees required to annually replant Florida groves. Large nurseries (20%) each produced ≥100,000 trees per year and jointly provided 88% of the trees produced annually. Small nurseries (80%) each produced <100,000 trees per year. The citrus leafminer was ranked the most important pest in nurseries during 1995. Pesticides used for CLM control included avermectin, azadirachtin, imidacloprid, fenoxycarb, diflubenzuron, and sulfur, in order of importance. Oil and soap also were used. Growers were concerned about the possibility that the CLM will develop resistance to pesticides. Producers potentially were willing to monitor CLM populations, switch pesticide types to improve survival of parasitoids of the CLM, and leave untreated trees inside the nursery to serve as refuges for CLM parasitoids. In order of importance, pest management advice was provided by private chemical companies, the Florida Citrus Pest Management Guide produced by the University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS), UF/IFAS personnel, grower magazines, private consultants, the Florida Citrus Nurserymen's Association, and other growers.
Juan Carlos Díaz-Pérez, Kelly St. John, Mohammad Yamin Kabir, J. Alberto Alvarado-Chávez, Ania M. Cutiño-Jiménez, Jesús Bautista, Gunawati Gunawan, and Savithri U. Nambeesan
Colored shade nets may affect plant growth and fruit yield of horticultural crops. The understanding of how colored shade nets influence plants, however, is far from complete. The objective of this study was to determine the effects of colored shade nets on bell pepper fruit yield, postharvest transpiration, color, chemical composition, and antioxidant capacity. The experiment was conducted in Tifton, GA, during the spring of 2015 and 2016. The experimental design was a randomized complete block with four replications and five colored shade net treatments (black, red, silver, and white nets, and an unshaded control). The nets were placed on the top of wooden rectangular structures (15 m wide × 6 m long × 5 m high), leaving the sides of the structures uncovered. Results showed that in both 2015 and 2016, marketable and total fruit number, yield, and individual fruit weight were reduced under the unshaded treatment. There were inconsistent differences in marketable and total fruit number, yield, and individual fruit weight among colored shade nets. Postharvest fruit transpiration and skin permeance were also reduced in unshaded conditions, and no differences were found among colored shade nets. Fruit color L* and b* values were highest, and a* value was lowest in unshaded conditions. Fruit soluble solids, total phenols, flavonoids, and antioxidant capacity [Cupric Reducing Antioxidant Capacity (CUPRAC) and Trolox Equivalent Antioxidant Capacity (TEAC)] responded differently among colored shade nets in the 2 years. Total phenols, flavonoids, and TEAC, however, were among the highest in unshaded conditions. In conclusion, results of the present study support previous findings that shade nets increase fruit yield and quality in bell pepper compared with fruit produced in unshaded conditions. Nevertheless, there were no consistent differences in fruit total and marketable yield and postharvest fruit transpiration and chemical composition of fruit produced under colored shade nets.
José M. López-Aranda, Luis Miranda, Juan J. Medina, Carmen Soria, Berta de los Santos, Fernando Romero, Rosa M. Pérez-Jiménez, Miguel Talavera, Steve A. Fennimore, and Bielinski M. Santos
Field trials were conducted in two locations in Spain to determine the effect of methyl bromide (MBr) alternatives on soilborne diseases and nematodes, and strawberry (Fragaria ×ananassa) yields under high-tunnel conditions. Fumigant treatments were applied to the same plots each year. Treatments were MBr + chloropicrin (Pic) (50:50, v/v) at a rate of 400 kg·ha−1; 1,3-dichloropropene (1,3-D) + Pic (65:35, v/v) at 300 kg·ha−1; Pic at 300 kg·ha−1; dimethyl disulfide (DMDS) + Pic (50:50, v/v) at 500 kg·ha−1; propylene oxide at 550 kg·ha−1; dazomet at 400 kg·ha−1; and calcium cyanamide (Ca-cyanamide) at 700 kg·ha−1. A nontreated control was also included. Fumigation with MBr + Pic, 1,3-D + Pic, Pic, and DMDS + Pic consistently improved early and total marketable strawberry yields in both locations. This response was caused by successful soilborne fungus and nematode control, improving strawberry growth and development, which resulted in increased plant canopy diameters and higher strawberry early and total yield.