Seed Potassium Concentration Decline During Maturation Is Inversely Related to Subsequent Germination of Primrose

Abstract

It has been reported previously that seed potassium (K) concentrations were negatively correlated with the seed's germination capacity in randomly sampled commercial seed lots of primrose (Primula vulgaris Huds.). To explain this relationship, hypotheses about a causal role for the seed maturation level at harvest date and the possible environmental and genetic stability of the correlation were explored. Mineral composition and quality of Primula seeds were investigated (1) as to how they were affected by maturation stage with weekly seed harvests from the 7th to the 15th week post-anthesis (WPA), and (2) using a nutrient solution culture of gonophores varying in K supply (0, 1.5, 3, and 6 mmol K L−1) during reproductive growth. Concentrations of minerals [K, nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg)] in leaves and whole seeds were analyzed, as were selected seed characteristics (embryo and endosperm development, seed mass, viability, and germination) of two parental lines (pin and thrum morph of genotypes 45 and 48) for hybrid-seed generation. Leaf-mineral composition and vegetative growth were mostly affected by K supply. In contrast, mineral concentrations per gram dry seed mass of seeds harvested at mature stage (15 WPA) were not influenced (i.e., K, Mg), or only slightly so (i.e., N, P, Ca), by differential K supply to gonophore plants. However, seeds harvested at the premature stage (8 WPA) revealed concentrations of K, Ca, and Mg at evidently increased levels, with K and Mg clearly reflecting the differential K availability. During further maturation, the seed N and P concentrations remained relatively constant in respect to the considerable growth in single seed mass. In contrast, concentrations of K, Ca, and Mg decreased markedly and simultaneously with rapid seed growth. Irrespective of the different growth rates of seed mass between the genotypes, the decreasing seed concentrations (31% decline) strongly correlated with increasing percentage germination (40% rise) from 9 to 14 WPA (r = −0.81; n = 21; p < 0.01). However, weaker negative correlations between germination and seed Ca or Mg concentrations resulted from pronounced genotypic differences in levels of these two seed elements. Taken together, seed K concentration is the most reliable measure to indicate maturity and to act as a marker for low germination capacity due to premature seed harvest. In addition, possible interactions between climate impact, phytohormones, and seed mineral dynamics during maturation should be explored.