Investigations into the potential use of physical-chemical properties of crop seeds as indicators of seed germinability and early seedling growth
Electrical conductivity of soakwater was measured for individual seeds from a range of crop species. Conductivity was expected to increase with loss of germinability since deterioration is thought to degrade membrane permeability in seeds leading to increased loss of cellular contents during imbibition. Non-terminable seeds had, on average, higher soakwater conductivities per seed than germinable seeds. Heavier seeds tended to have higher conductivities per seed than lighter seeds, partly explaining overlaps between the soakwater conductivity distributions of germination categories. Re-expressing conductivity on a unit weight basis reduced the effect of seed size (weight) and led to improved differentiation between seed germination categories, but their conductivity distributions still overlapped. Genera, cultivar or seed lot, and soak time also influenced soakwater conductivity and the differentiation between seed germination categories. Tetrazolium vital staining of radish and onion seeds revealed that small areas of damage on crucial tissue sites could cause non-germinability with low soakwater conductivity. Seeds with extensive damage away from these sites could be germinable with high soakwater conductivities. Such instances accounted for some of the overlap in conductivity distributions. Larger graded seeds were more susceptible to imbibition damage than smaller graded seeds. The smallest hand graded seeds of onion and Brussels sprout showed reduced germination percentage and seedling growth compared with larger graded seeds. K+ was present in soakwater of individual pea and soyabean seeds in far greater amounts than Mg2+ or Ca2+ and, along with UV absorbance at 210nm and 260nm, tended to have higher values for non-germinable compared with germinable seeds. These soakwater measurements were no more effective than electrical conductivity at differentiating between seed germination categories.