The effects of three plasma-activated water generation systems on lettuce seed germination

Irrigation water treatment using plasma technology is a new approach to improve productivity. In this study the generation of plasma-activated water (PAW) as a novel subject in agriculture is investigated. Three water treatment systems were designed and evaluated: 1^st PAW generation from vapor and injection into the water, 2^nd PAW generation using electrical discharge on the water surface and 3^rd PAW generation in the aeration path into the water. The lettuce seeds were irrigated with PAW. The germination rate and mean germination time were measured after 6 days. The seedlings weight and the number of seedlings with a length of more than 3 cm were also recorded after 8 days. The results showed that PAW had a significant effect on the germination rate and length of seedlings. Electrical discharge on the water surface had the best results. Germination rate and the number of seedlings with a length of more than 3 cm increased by 11 and 36% respectively. While injection of plasma-treated air into the water significantly reduced the number of seedlings longer than 3 cm, compared to the control. In conclusion, the PAW application can improve some attributes of lettuce germination depending on the PAW system.

Lignocellulosic wastes of Carya illinoinensis (Juglandaceae) inhibit germination and seedling develop-ment of Lactuca sativa (Asteraceae)

The study evaluated the effect of Carya illinoinensis plant extracts on lettuce seed germination and development. Experiment was carried out in a completely randomized experimental design with five treatments and replications. Plant extracts were prepared from the dry ground vegetable waste. The concentration was adjusted to 10% m.v-1. The treatments were classified into: heterogeneous pruning residues (HPR), leaves residues (LR), epicarp residues (ER), mesocarp residues (MR), and control treatment (CT, 100% water). The variables evaluated were: first germination count (GP4%), final germination count (GP7%), germination speed index (GSI), germination inhibition (PGI), frequency of abnormal seedlings (FAS), root length (RL), shoot length (SL), and total length of seedling (TLS). Extracts obtained from residues of C. illinoinensis decreased the lettuce seed germination, but their effect depends on the plant tissue (e.g. leaf, epicarp or mesocarp) used at production of plant extracts. Plant extracts from HPR and MR do not result in drastic allelochemical effects. Aqueous extracts from LR and ER reduced significantly the seed germination and the normal development of lettuce seedlings, with an absolute reduction in germination of 90.2% and 79.2%, respectively. Only plant extracts from leaf residues and epicarp residues from C. illinoinensis inhibit the germination and seedling development of L. sativa.

Allelopathy of aqueous extracts of Paubrasilia echinata (Lam.) Gagnon and H.C. Lima and G.P Lewis in lettuce seed germination

O pau-brasil é uma espécie nativa ameaçada de extinção com potencial para uso em programas de reflorestamento, porém, há pouca informação sobre seu efeito alelopático na germinação de sementes de outras espécies. Sendo assim, objetivou-se com esse trabalho avaliar o efeito alelopático de extratos aquosos de Paubrasilia echinata L. na germinação de sementes de alface, visando a sua utilização em programas de reflorestamento. Amostras de folhas frescas e secas foram trituradas em liquidificador, acrescentando-se, posteriormente, 400 mL de água destilada e, após 10 minutos, as soluções foram filtradas. A partir desses extratos brutos, foram feitas diluições em água destilada e obteve-se os seguintes tratamentos: 0%, 25%, 50% , 75% e 100% dos extratos de folhas frescas e secas. Foi feito o teste de germinação das sementes de alface embebidas nos extratos, seguindo as recomendações das Regras para Análise de Sementes (RAS) (BRASIL, 2009). Foi feita a contagem diária, avaliando-se o índice de velocidade de germinação (MAGUIRE, 1962), a velocidade de germinação (EDMOND; DRAPALLA, 1958 apud FERREIRA; BORGUETTI, 2004) e a porcentagem de germinação, sendo consideradas germinadas as sementes com 2 mm de comprimento de radícula. As análises estatísticas foram realizadas usando o programa GRAPHPAD PRISM. Concluiu-se que P. echinata exerce efeito alelopático na germinação de sementes de alface. O uso de P. echinata em programas de reflorestamento deve ser criterioso, com a adoção de medidas que minimizem a alelopatia em plantas circunvizinhas.

Water-Soluble Carbon Nanoparticles Improve Seed Germination and Post-Germination Growth of Lettuce under Salinity Stress

Seed germination is a critical developmental phase for seedling establishment and crop production. Increasing salinity stress associated with climatic change can pose a challenge for seed germination and stand establishment of many crops including lettuce. Here, we show that water soluble carbon nanoparticles (CNPs) can significantly promote seed germination without affecting seedling growth. Twenty-seven varieties of lettuce (Lactuca sativa) were screened for sensitivity to germination in 150 and 200 mM NaCl, and six salt-sensitive varieties (Little Gem, Parris Island, Breen, Butter Crunch, Muir, and Jericho) were selected and primed with 0.3% soluble carbon nanoparticles. Pretreatment with CNPs significantly improved seed germination under 150 mM NaCl and high temperature. CNP treatment slightly inhibited the elongation of primary roots but promoted lateral root growth and accumulation of chlorophyll content of seedlings grown under salt stress. Despite different lettuce varieties exhibiting a distinct response to nanoparticle treatments, results from this study indicate that soluble nanoparticles can significantly improve lettuce seed germination under salinity stress, which provide fundamental evidence on the potential of nanoparticles in agricultural application to improve crop yield and quality under stressful conditions.

Hydrogen Peroxide for Insect and Algae Control in a Lettuce Hydroponic Environment

Insects and algae demonstrate adaptability in hydroponic environments. Algae attract flies, Bradysia spp. (Diptera: Sciaridae) and Scatella stagnalis (Diptera: Ephydridae), called fungus gnats and shore fly, respectively. Flies feed on algae, damaging seedlings radicellae, and may transmit pathogens to lettuce plants. Little information on the management of flies and algae is known. A paradox in the face of the expansion of hydroponics. The objective was to evaluate the potential of hydrogen peroxide (H2O2) as an insecticide and algaecide agent. Entomopathogenic fungi were also evaluated as an alternative control to flies. The experiment was conducted in a commercial hydroponic system under a randomized complete block design with 5 treatments and 4 replicates. The treatments, sprayed on the phenolic foam plates, immediately after lettuce seed deposition, were: H2O2, Beauveria bassiana, Metarhizium anisopliae, Spinosyn and water, as control. The quality of the lettuce seedlings (cv. Brida), the presence of flies and algae evolution in the phenolic foam plates were recorded daily. H2O2 and Spinosyn affected lettuce seed germination, but were able to reduce adult flies on the phenolic foam cells. The highest number of larvae was observed with both fungi, and only water, compared to H2O2. No larvae were found in Spinosyn sprayed phenolic foam cells. However, lettuce seedlings from Spinosyn sprayed plates were those with lower fresh weight. H2O2 severely retained algae infestation in phenolic foam cells over a 15-day observation period. The present work demonstrates the potential that H2O2 can play as an insecticidal and algaecide agent in hydroponic environments.

Allelopathic effect of Passiflora alata Curtis extracts on seed germination

Many plant chemical compounds can interfere on seed germination and on the development of other plants. Thus, this research aimed to verify the effect of sweet passion fruit seeds (Passiflora alata Curtis) extracts, under lettuce seed germination and lettuce seedlings growing. The experiment was carried out in a controlled environment. The treatments were: T1-distilled water as a control; T2-embryo extract; T3- tegument extract; T4- whole grain extract; T5- soaking solution. Lettuce seed (Lactuca sativa L.) cv. Babá de Verão, was used as a bioindicator of the allelopathic effect. When the treatment of embryo extract of sweet passion fruit was applied, a lower germination percentage and lower speed emergence rate of lettuce seeds were observed. The largest number of abnormal seedlings was observed from seeds germinated in the embryo extract (T2) and the soaking solution (T5). The sweet passion fruit embryo extract discloses compounds that are able to inhibit the germination and can negatively influence the development of lettuce seedlings.