Leaf yield and polyphenols of artichoke (Cynara cardunculus L.) influenced by harvest frequency and herbicide stress
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Artichoke is a traditional vegetable plant grown and used in subtropical and Mediterranean regions. Artichoke leaves and flower buds contain high concentration of polyphenols, which are attributed to nutritional and pharmacological effects. These compounds include caffeoylquinic acids (chlorogenic acid, caffeic acid and cynarin), flavonoids (scolymoside, cynaroside and luteolin) and sesquiterpene lactones.Although, artichoke has enormous importance in the Mediterranean region, certain climatic limitations discourage its cultivation in Central Europe. Yet, in Germany it is cultivated as a commercial annual leaf crop. Cultivation in Germany is focused on the production of rosette leaves which contain high contents of polyphenols that are used for dyspeptic complaints.Contrary to the vegetable production of artichoke, only a few research work on its importance as leaf crop has been done. This research area needs a focus on the influence of the environmental conditions and agronomic factors on yield and polyphenols contents of artichoke leaves under field conditions in Germany.Keeping these points into consideration, research was conducted at University Giessen to study the effect of plant density (4, 8, 12 and 16 plants m-2) and harvest frequency (LHF- low harvest frequency with 3 harvests, MHF- medium harvest frequency with 5 harvests and HHF- high harvest frequency with 6 harvests per growing season) on plant growth, yield and polyphenols of artichoke leaves. Simultaneously, a second experiment to study the impact of different post-emergence herbicides (Haloxyfop, Phenmedipham, Pyridate, Quizalofop-P, Prosulfocarb, Carfentrazone, Rimsulfuron, Aclonifen and Clomazone) on leaf yield and the concentration of polyphenols (CQA and flavonoids) was conducted. The experiments were conducted at experimental research stations Gross-Gerau and Giessen, respectively. Cultivar Gobbo di Nizza was sown manually in 75 cm apart rows with 25 cm intra-row distance at 2 cm soil depth. The field trials were designed in RCBD in factorial arrangement (plant density x harvest frequency) and one factor RCBD (herbicides) with 4 replications. Obtained results were analyzed statistically by the PIAF (Programm Information Auswertung Feldversuche - Statistical program for evaluation of field trials).On the basis of the results obtained in three experimental years, it was found that LHF (3 harvests per growth season) in combination with higher plant densities (12-16 plants m-2) led to best growth and yield parameters (plant height, leaves per unit area, leaf yield) and highest concentration of polyphenols. High harvest frequency (6 harvests per growth seasons) led to lower leaf yield and lower concentration of caffeoylquinic acids and flavonoids in the leaves. Additionally differential response of the interaction of plant density x harvest frequency to some yield parameters was also observed. These differences in growth and yield parameters may be attributed to the specific growth conditions (air temperature, light interception, day length) during leaf formation of artichoke. Plant densities lower than 8 plants m-2 failed to compensate the loss in leaf yield by producing more leaves as that of higher plant densities.Post-emergence application of Pyridate, Aclonifen and Clomazone resulted in reduction of leaf yield in both growth phases of artichoke. Chlorophyll fluorescence data determined that Pyridate reduced chlorophyll fluorescence and electron transport rate in artichoke leaves significantly, showing a stress to the plants. Phenmedipham, Aclonifen and Clomazone also showed the same negative effects after their application to artichoke leaves. These negative effects of the post emergence herbicides used in the study appeared at 1 DAA (days after application) to maximum of 1 WAA (week after application). The physiological symptoms of stress measured in the form of chlorophyll fluorescence and ETR were not visible at 4 WAA or later. Only Pyridate and Aclonifen showed some adverse effects on the concentration of CQA (up to 1 WAA) in artichoke leaves. CQA and flavonoids determined at harvest of artichoke leaves did not show any adverse effects of the post emergence herbicides used in the research project. Recovery of artichoke against he adverse effects of herbicides may be attributed to the regeneration and formation of new leaves.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Giessen : VVB Laufersweiler