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Articles by J. L. Christiansen
Total Records ( 2 ) for J. L. Christiansen
  S. T. Jorgensen , A. Pookpakdi , S. Tudsri , O. Stolen , R. Ortiz and J. L. Christiansen
  A field study was conducted in Thailand under a rain-fed environment to determine the effect of four different cutting heights above ground level and two closing dates on dry matter (DM) production, yield components, and fodder quality of five different cultivars of Napier grass (Pennisetum purpureum Schumach), all treatments cut with the same frequency of approximately 4 weeks. Eighteen quantitative trait measurements were used to investigate the interactions between cultivar diversity and cutting regimes. Principal-component analysis (PCA) showed a clustering of two distinct cultivars and another group of cultivars in one cluster without obvious structure. There was also a clear clustering of the control (0 cm cutting height) across all cultivars whereas other cutting heights affected growth differently according to cultivar. The optimal cutting regime for obtaining high DM yield depended on the genetic background and did not relate to a reduction in the number of vegetative buds for the cultivars with a basal shooting pattern. For the cultivars with higher DM yield arising from high stubble height, the DM was differently distributed into leaf and stem material. Before cuttings, the tiller number was reduced in the control plots but not in the plots with more lenient cutting height. Average tiller yield increased with increasing cutting height to reach a maximum at 20-cm cutting height. Average harvested culm length was constant for the four cutting heights. The variation in a number of plant traits, arising from cultivar diversity, can be altered by agronomic practices, thereby causing potentially contradictory results. Defining specific interactions of cultivar-by-cutting height treatments and analysing these with PCA proved to be a useful approach for visualising clusters from multiple measurements. The proposed approach for analysing data could serve as a model for other trials with similar interactions between cultivar diversity and agronomic treatments.
  J. L. Christiansen , S. -E. Jacobsen and S. T. Joslashrgensen
  Sensitivity to photoperiod in quinoa (Chenopodium quinoa Willd.) was studied under controlled conditions to enhance crop adaptation to environments outside its centre of origin. Two varieties, a traditional variety from Bolivia (Real), which will not mature under Danish conditions, and an early maturing variety (Q52), developed for Danish climatic conditions, were used in this reciprocal transfer experiment. Plants were moved from a short daylength of 10 h (SD) to a long daylength of 18 h (LD) and vice versa at set intervals from sowing to 100 days after sowing (DAS). A reaction of LD in time to flowering was observed only in the Bolivian variety Real. Under SD both varieties flowered after 39 DAS. For Real the LD regime resulted in a moderate increase in time to flowering to 44 DAS. The non-sensitive, juvenile period in Real was estimated to be approximately 16 days. In Q52 a moderate increase in the number of leaves was formed on the main stem after flowering at LD, which indicates that some daylength sensitivity remains. The most striking difference occurred during seed filling, when going from SD to LD. In Q52 the time from the end of flowering to maturity increased from 39 to 52 days. Under SD, Real had a seed-filling period similar to Q52, but at LD Real remained with green leaves during seed filling. Hard seed was observed in the still green perigonium 57 days after end of flowering. At this moment re-shooting occurred from the inflorescence, and seed maturity was not reached at the termination of the experiment at 150 DAS. This study shows that flower induction is not a major problem for adaptation of quinoa to North European conditions but that a very strong, daylength sensitive, stay green reaction is the main cause of the late maturity of South American introductions.
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