| Sumario: | Megathyrsus maximus is a forage species widely used in livestock production systems due to its high biomass yield, good nutritional quality, and ease of propagation. Understanding the response of the species’ genetic diversity to growth under shade conditions is essential for assessing its potential use in silvopastoral systems. These systems represent a sustainable alternative to mitigate the negative impacts of monoculture forage production on soil health, animal welfare, and the environment.
This dataset includes information on the response of M. maximus genotypes to shade conditions. To generate the data, vegetative propagules from 33 genotypes were established under two light environments in a glass greenhouse: full sunlight (no shade) and 75% shade. Each experimental unit (genotype × shade condition) was replicated three times. The dataset comprises weekly measurements collected over a six-week period, including SPAD values, plant height, stem height, gas exchange parameters, and chlorophyll fluorescence. In addition, reference measurements of red light, far-red light, and photosynthetically active radiation (PAR) were recorded under each shade condition. Final harvest data include leaf area, number of leaves, biomass partitioning, root-to-shoot ratio, and specific leaf area.
This dataset provides valuable information for breeding programs aimed at selecting M. maximus genotypes with potential for use in silvopastoral systems. Moreover, it offers a useful resource for plant scientists seeking to better understand the physiological and morphological mechanisms underlying shade adaptation in this species.
Methodology:Plant material, experimental design, and study site: Vegetative propagules of 33 Megathyrsus maximus genotypes from the germplasm collection of the Alliance Bioversity and CIAT Tropical Forages Breeding Program were used in this study. Plants were established in a sandy loam Vertisol characterized by high fertility and a pH of 7.5. The experiment followed a split-plot design with a 33 × 2 factorial arrangement, where genotype (33 levels) and shade condition (75% shade and full sunlight) were the experimental factors. Shade treatment was assigned to the main plots, while individual plants constituted the experimental units. Each plant was grown in a 3-L pot, and each genotype × shade combination was replicated three times. The trial was conducted in a glass greenhouse located on the CIAT campus in Palmira, Valle del Cauca, Colombia. Red and far-red radiation were measured using a LightScout Red/Far Red Meter (Spectrum Technologies, USA), while photosynthetically active radiation (PAR) was measured using a SpectraPen Mini (Photon Systems Instruments, Czech Republic).
Gas exchange and chlorophyll fluorescence: Stomatal conductance, transpiration rate, and the effective quantum yield of photosystem II were measured using a LI-600 porometer/fluorometer (LI-COR, Lincoln, NE, USA). Measurements were taken weekly on the third fully expanded leaf of each plant, from the initiation of shade treatments until 45 days after treatment establishment.
Plant growth: From the onset of treatments until day 45, SPAD values were recorded weekly using a SPAD 502 Plus chlorophyll meter (Spectrum Technologies, Aurora, IL, USA), with measurements taken on the third fully expanded leaf. Plant height was measured from the stem base to the tip of the longest leaf, while stem height was measured from the base to the apical meristem of the most vigorous stem per plant. At 45 days after treatment initiation, a final destructive harvest was conducted. Leaf area was determined using an LI-3100 area meter (LI-COR, Lincoln, NE, USA). The number of leaves per plant was recorded, and stems (including inflorescences), leaves, and roots were separated and oven-dried in paper bags at 60 °C for 72 hours. The root-to-shoot ratio was subsequently calculated, and specific leaf area was estimated as the ratio of leaf area to leaf dry mass.
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