Agriculture Reference
In-Depth Information
damage during harvest and drying than other sweet corn genotypes (Wann, 1986). The type of seed injury
also may reduce the ability of the conductivity test to accurately predict seed vigor. Herter and Burris (1989)
showed that conductivity test results were not correlated with ield emergence for corn seeds subjected to
drying injury. Seed enhancements such as priming inluence conductivity results. Primed tomato seeds leak
less than non-primed seeds (Argerich and Bradford, 1989). This is attributed to the washing off of external
solutes during priming. Primed lettuce seeds lost less K
+
ions than those not primed (Weges and Karssen,
1990).
Because of the value of the conductivity test, its speed in acquiring results, and its presentation of
quantitative data, many differing approaches to conductivity testing have been proposed. For example,
single seed conductivity results determined by the ASAC-1000 were superior to bulk test results (Tyagi
1992; Hepburn et al., 1984). However, the enormous data generated from the evaluation of individual seeds
has stimulated research to simplify the interpretation of results. Furman et al. (1987) interfaced the ASAC-
1000 with a microcomputer and Wilson (1992) developed a mathematical model to apply to individual
sweet corn seed readings.
Other investigators have focused on what is leaked from seeds rather than relying on composite con-
ductivity readings. Deswal and Sheoran (1993) found that the optical density of individual seed leachates at
260 nm obtained after 6 or 10 h soaking was correlated with conductivity values. Dias et al. (1996) reported
that determination of K
+
leakage using a lame photometer was a more sensitive measure of soybean seed
vigor than the bulk conductivity test and Custodio and Marcos-Filho (1997) determined that K
+
leach-
ate after 30 min at 30°C distinguished differing quality levels among soybean seed lots. Woodstock et al.
(1985) found that leaching of individual minerals was a better indicator of cotton seed quality than total
release of electrolytes, with K
+
and Ca
++
being signiicantly correlated with seed vigor. The predominant
amino acids leaked from non-germinable leek, onion, and cabbage seeds were alanine, glutamic acid, and
arginine (Taylor et al., 1995). Others have used the principle of seed leakage and the type of compound
leaked to physically upgrade seed vigor. Taylor et al. (1991) found that sinapine, a luorescent compound,
leaked more from deteriorated than non-deteriorated
Brassica
seeds. Lee et al. (1997) coated the seeds with
an adsorbent that trapped the sinapine during imbibition, redried the seeds, and then sorted them into luo-
rescent (non-viable) and nonluorescent (viable) grades.
As solutes leak from seeds, they also modify the pH of the seed steep water. This can be detected by
adding sodium carbonate-phenolphthalein, which changes the soak water to a pink color for viable seeds
and no color for non-viable seeds (Peske and Amaral, 1994). The pH partition point has been identiied as
5.8 for viable vs. non-viable seeds (Peske and Amaral, 1986).
Hampton (1995) indicated that variables in the conductivity test were:
1. Water purity and cleanliness of equipment;
2. Injured/damaged seeds;
3. Seed treatments;
4. Pathogens;
5. Initial seed moisture content;
6. Cultivar;
7. Seed size; and
8. Uniformity of seed lot.
Figures 8.4 and 8.5 show the effect of temperature, soaking time, and seed lot age on electrical conductivity
(Sorensen et al., 1995).
