(pp. 122-135)
Problems in Evaluating Viability of Soybean Infected With Phomopsis Spp.1
J.B. Franca Neto and S.H. West2
ABSTRACT:
The detrimental effects of Phomopsis spp. on seed germination of soybean [Glycine max (L.) Merrill] are broadly recognized. Rolled paper toweling is the most widely used method for testing germination of soybean seed. The validity of the rolled-paper-towel test to determine the actual viability of soybean seed infected with Phomopsis spp. was examined.
Seventy-three seed samples of 23 soybean cultivars produced in Florida in 1986 were analyzed for germination, vigor [tetrazolium (TZ) test], and pathogens. Phomopsis spp. were the fungi most frequently associated with soybean seed (up to 77% seed infection). Infection by these microorganisms was mainly restricted to the seedcoat. Deep-seated infection was rare (mean 0.5%). Viability, as obtained by the standard germination test (rolled paper toweling) was drastically reduced by high (>33%) levels of Phomopsis spp. These detrimental effects were not observed when germination was examined in sand, if conditions were adequate for fast emergence. When seed were tested in sand, the infected seedcoats remained in or on the sand upon emergence, thus the seedlings escaped much of the detrimental effects of infected seedcoats. Therefore, rolled paper toweling was not the best substrate to evaluate germination of soybean seed infected with high levels of Phomopsis spp. Emergence in sand or the TZ test provided more realistic estimates of viability for seed lots infected with these fungi. Nevertheless, it was noted that as the vigor level expressed by the TZ test decreased, the level of infected seedlings and damping-off tended to increase.
Additional index words: Germination, Emergence, Vigor, Glycine max (L.) Merrill, Tetrazolium test.
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(pp. 136-149)
Effects of Colletotrichum truncatum and Cercospora kikuchii on Viability and Quality of Soybean Seed1
J.B. Franca Neto and S.H. West2
ABSTRACT:
Seventy-three seed samples of 23 soybean (Glycine max [L.] Merr.) cultivars produced in Florida in 1986 were analyzed for germination, vigor [tetrazolium (TZ) test], and presence of seedborne pathogens. Thirty percent of the samples contained from 5 to 20% (high) infection by Colletotrichum truncatum (Schw.) Andrus & Moore. Infection was mainly restricted to the seed coat, but 50% of the seed lots with high levels of infection had embryo infection from 1 to 10%. Although C. truncatum infected fewer seeds than Phomopsis spp., it caused more damping-off, regardless of seed vigor level.
As the pathogen incidence increased, the amount of damping off also increased. These detrimental effects were observed on the standard germination test (rolled paper towels) which also was severely affected by high levels of Phomopsis spp. The TZ test values were not affected by the presence of these fungi, thus giving the highest percent germination. Sand emergence provided estimates of germination for seed lots with high incidence of infection by C. truncatum that more nearly simulated what would be expected in the field under ideal conditions. Seventeen percent of the samples contained high levels (7 to 33%) of infection by Cercospora kikuchii (Matsu. & Tomoyasu). This pathogen was almost exclusively restricted to the seed coat. An antagonistic effect was observed between C. kikuchii and Phomopsis spp. infecting soybean seeds: the higher the level of seed infection by C. kikuchii, the lower the seed infection by Phomopsis spp. No detrimental pathogen effects of seed infection of this pathogen were observed on germination, emergence, and vigor of soybean seed with the natural levels of C. kikuchii infected seeds used in this study.
Additional index words: Germination, Emergence, Vigor, Damping-off, Glycine max (L.) Merrill, Tetrazolium test, Phomopsis spp., Purple seed stain.
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(pp. 150-168)
Factors Affecting the Outcome and Usefullness of Seed Heterogeneity Tests1
Dan Niffenegger, Duane lsely and L.E. Everson2
ABSTRACT:
Heterogeneity testing of commercial seed lots before bagging could substantially reduce the number of "stop sales" on seed lots having numbers of noxious weed seeds or percentages of weed or other crop seeds in inspection samples out of tolerance with labeled numbers. However, because of high costs of testing and presently unavoidable delays in obtaining results, heterogeneity tests are seldom made. Experiments were run to determine what might be done to increase the use and usefulness of heterogeneity tests.
Poorly-, intermediate-, and well-mixed batches of alfalfa and rape seed were tested for heterogeneity with respect to indicator seeds (seeds identical to the principal seed but marked for easy detection). Alfalfa seed was also tested for heterogeneity with respect to three weed seed species. Two controllable variables were found to be critical to the outcome of a heterogeneity test: (1) average number of indicator or weed seeds per sample and (2) the number of samples examined in a heterogeneity test. Small numbers in either category can lead to wrong declarations of homogeneity in lots that are truly heterogeneous. The hypothesis is advanced that indicator seed heterogeneity test results can be used as a reliable predictor of heterogeneity with respect to weed seed count, hard seed percentage, or count or percentage of any other seed lot component or attribute. Heterogeneity testing of a seed lot with indicator seeds can lead to a high degree of probability that seed tags will correctly describe the seed in each bag of the lot.
Additional Index Words: Homogeneity, Uniformity, Bagging, Tolerances, Seed statistics, Sample size, Indicator seeds, Marketing, Stop sale, Noxious weed seeds, Sampling, Blending, Mixing.
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(pp. 169-176)
Effects of Seed Size and Density Separation on Thickspike Wheatgrass Dimensions, Rate of Imbibition, and Respiration1
H.R. Armstrong, and L.E. Wiesner2
ABSTRACT:
Seed size separations have been traditionally used to increase seedling vigor. Examination of naked caryopses of a combination of size and density separations revealed that seed mass could be used to describe the physical dimensions of the caryopsis and embryo of 'Critana' thickspike wheatgrass (Agropyron daystachyum (hook.) Schribn .). No differences were found between hydration curves for small-light (S-L) and large-heavy (L-H) seed separations for whole seeds, naked caryopses, endosperm and embryos. Greater respiration rates were found for LH seeds than S-L seeds on a seed basis for whole seeds, naked caryopses and embryos.
Additional index words: Vigor, Germination, Elymus lanceolatus
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