Individual seed electrolyte leakage tests and evaluation of soaking injury using maize

Abstract

Determination of seed viability has traditionally involved germination, which is obviously destructive to the seed and also labor intensive. Both are far from being cost effective. The development of non-destructive or at least less injurious methods of testing seed quality i.e. viability and vigor determination using electroconductivity measurements of single seed leachate solutions could effectively replace the standard germination test. The objectives were to compare five indices of seed quality, all of which are based on individual seed leachate conductivity tests. Additionally, if the soak period is brief enough, there should be little injury to the seeds allowing for successive soaks on the same sample. Seeds of Zea mays L. were aged using two methods to obtain varying levels of viability and vigor for comparisons. The first method, modified controlled deterioration, involved placing two samples of seeds in separate desiccators over a saturated NaCl solution for 16 and 20 days for seed lots 88-2i and 88-1d, respectively. The seeds were sealed in aluminum foil packets, 110 per packet, and aged for 120 hours at 45°C. The second method involved placing two samples of seeds in separate desiccators over H2SO4 at 35°C for 238 and 484 days, respectively for desiccators one and two. After aging, seeds from each desiccator were kept in aluminum foil packets. Electroconductivity testing was done on samples of 100 seeds from each of the aging methods. The seed samples were soaked for six hours during which time 29 scans of data were obtained. The samples were dried at room temperature for seven days after which time they were germinated using the rolled paper towel method. An additional 100 unsoaked (control) seeds were germinated at the same time. Radicle lengths were measured at the end of 72 hours and final germination was counted at the end of seven days. Relative vigor was calculated as a ratio of the soaked seed radicle lengths divided by the unsoaked control seed radicle lengths. Electroconductivity data were concatenated and made compatible with the UNIX format. Five indices were derived from the data for determination of their ability to predict maize seed quality. Internal Slope (IS) and mean and median μAmps after five hours of imbibition were derived from a Richards function program, the Initial Leach Rate (ILR) was derived from the rectangular hyperbola and the Average Absolute Leach Rate (AALR) was derived from another Richards function program. The second aging method did not produce the desired range of seed quality and so the results discussed are based on the first aging technique. Internal Slope was the best predictor of seed viability, r2 = 0.91, followed very closely by the median μAmp value, r2 = 0.87, and the mean μAmp value, r2 = 0.81. The ILR and AALR indices did not predict seed quality with r2 values of 0.01 and 0.03, respectively. Relative vigor was not estimated as well as viability, probably due to the artificial aging. A second experiment was designed to study the effect of five successive soak cycles (C) and five cycle durations (CD) of 2, 4, 6, 7 and 8 hours on viability and vigor loss response. All subsets regression plus consideration between bias and random error led to the choice of the following two best subset models: YVIA = 99.14 - 0.0609 (CD*C2), R2 = 0.62, and YRV = 0.99 + 0.0229 (CD) - 0.0101 (CD*C), R2 = 0.52. Response surfaces were generated which suggested that 4 C of 5 hours each resulted in only an 8% loss of viability but a 20% loss of relative vigor. Conductivity measurements taken at the end of each CD for each C showed that 45% of the readily leachable electrolytes leached during the first soak period. Furthermore, a priming effect, invigoration, was observed when the seeds were soaked for a total of ten hours, taking into consideration both the number of cycles and the duration of each cycle.