Volume 17, No. 1, 1993

Download Cover and Contents

(pp. 1-11)
Sorghum (Sorghum bicolor L. Moench) Seed Internal Morphology Related to Seed Specific Gravity, Weathering, and Immaturity
A. Susana Goggi, James C. Delouche, and Lynn M. Gourley
ABSTRACT:
Germination and vigor problems in sorghum are usually related to weathering during the post-maturation, pre-harvest period and to drought induced seed immaturity. Weathering and immaturity also lowers the specific gravity of the seeds. To examine the effects of weathering and immaturity on the internal morphology of seeds varying in specific gravity, sorghum [Sorghum bicolor (L.) Moench] seeds (Wheatland cv.) from panicles harvested at physiological maturity, exposed to field weathering or to artificially induced immaturity, were separated into high (>1.30) and low (>1.20) specific gravity levels.

Scanning electron microscope photomicrographs revealed cavities and profuse fungal growth in the  placental sac area and in the embryo of seeds from the intense weathering treatment and low specific gravity class. Similar cavities were observed in the immature seeds. Endosperm cells in the immature seeds were not completely filled with starch granules, and the epithelial and aleurone layers were not fully developed. The presence of cavities reduced the density of the seeds, consequently their specific gravity was lower. Seeds of low specific gravity also occurred among those harvested at physiological maturity, and they also exhibited morphological features of weathered or immature seeds or both.
Additional index words: sorghum, seed specific gravity, seed weathering, seed immaturity, scanning electron microscopy.
Download entire article

(pp. 12-21)
Phomopsis Seed Decay in Soybean with Dense Pubescence1
P.R. Thomison, D.L. Jeffers, W.J. Kenworthy, and P.B. Cregan2
ABSTRACT:
Phomopsis seed decay is a major cause of poor soybean [Glycine max (L.) Merr.] seed quality in regions where the climate is warm and humid during and after seed maturation. Increasing pubescence density on soybean plants may increase retention of moisture in pods and seeds, and thereby influence seed infection by Phomopsis Iongicolla Hobbs, The objective of this study was to evaluate the effect of increased pubescence density on seed infection by P. longicolla and germination.

Near-isogenic lines of two soybean cultivars, Clark and Harosoy, differing in pubescence density (normal vs. dense) were evaluated for seed-borne disease In 12 environments across four years (1985-88) in Maryland, Pennsylvania and Ohio. There were no significant differences between normal and dense pubescence isolines for seed infection by P. longicolla in nine environments and seed germination in 11 environments. In three environments where significant pubescence effects on seed infection were found, infection varied depending on the genetic background into which the dense pubescence gene has been introduced. Dense pubescence was generally associated with delayed maturity (nine of 12 environments) and increased plant height {eight of 12 environments). There was also slightly greater lodging in the plants with dense pubescence than in the normal pubescence isolines (four of 12 environments). Growing dense pubescence soy bean in the eastern United States should not increase the potential for seed disease problems due to P. longicolla.
Additional index words: GIycine max, seed germination, seed-borne diseases, Phomopsis spp., Diaporfhe phaseolorum, Phomopsis longicolla, trichome, isogenic lines, morphology.
Download entire article

(pp. 22-28)
Relationship of Uniformity of Soybean Seedling Emergence to Yield1
D.B. Egli2
ABSTRACT:
A field experiment was conducted for two years at Lexington, KY to evaluate the effect of  variation in the time of seedling emergence within the plant community on soybean [Glycine max (L.) Merr.] yield. Variation in time of emergence was created by planting alternate seeds in the row either 4 or 7 d after the initial plantings. In the control treatment, all seeds were planted when the initial plantings were made. All seeds were planted by hand in 0.76 m rows at a population of 26 plants m-2 (51 mm between plants in the row).

Plants from the initial and delayed plantings were harvested separately. The rate of dry matter accumulation from R1 to R5 (g plant-1 d-1) of the delayed plants in the mixed plantings was less (32 to 74%) than the rate of plants from the initial planting. The same effect was shown for yield (26 to 76% less) and seeds per plant. However, the rate of dry matter accumulation per unit area (g m-2 d-1), yield per unit area and seeds per unit area were the same for all treatments. Thus, variation in time of emergence, which created differences in plant size and individual plant yield in the community, had no effect on yield per unit area in soybean.
Additional index words: Glycine max (L.) Merr., plant size, crop growth rate, seed vigor.
Download entire article

(pp. 29-37)
Accelerated Aging Techniques for Evaluating Sorghum Seed Vigor1
A.E. Ibrahim, D.M. TeKrony* and D.B. Egli2
ABSTRACT:
Accelerated aging is an established seed vigor test for a number of crop species. This  investigation examined the effects of aging temperatures and duration of exposure on the germination of treated and untreated sorghum (Sorghum bicolor L. Moench) seed. Three temperatures (41°C, 43°C and 45°C) and three exposure periods (24, 48 and 72 h) were tested using seed lots of "Topaz" of different ages and two seed treatments (Captan and rnethoxychlor; Captan, methoxychlor and Concept II).

Seed moisture increased with longer aging durations with little differences between seed lots. Seed moistures of 29-30% were reached after 72 h aging at both 43 and 45°C. Seed germination was almost unaffected by aging at 41°C but declined at higher temperatures and after longer test durations. Seed from a freshly harvested high vigor seed lot had higher accelerated-aging germination than carryover lower vigor seed lots. Seed treated with Captan and Methoxychlor germinated similar lo the untreated seed following aging, however when Concept II was added the seed showed greater sensitivity to aging stress especially in carryover seed lots. Seed lots were effectively separated by aging for 72 h, 43°C and 48 h, 45°C. Both aging treatments showed high correlations with soil emergence across three field plantings, however, the 72 h, 43°C treatment is recommended because it showed the most consistent germination results across treated and untreated seed lots.
Additional index words: cold test, field emergence, seed safeners, seed treatment.
Download entire article

(pp. 38-41)
Occurence and Frequency of Twin and Triplet Peanut (Arachis hypogaea L.) Seedlings1
W.D. Branch and W.R. Guerke2
ABSTRACT:
Cooperative research was conducted between the University of Georgia, Coastal Plain Experiment Station and the Georgia Department of Agriculture, Seed Laboratory in Tifton to study the occurrence and frequency of twin and triplet peanut (Arachis hypogaea L.) seedlings. Twin and triplet peanut seedlings were easily observed fallowing standard germination tests, however the occurrence of each was very low.

For twins, estimated frequency was <0.01% and for triplets <0.001%. Progenies from individual twin and triplet plants did not exhibit any inherited polyembryony characteristics. Based on these findings, the potential to readily identify twin-derived haploids would not appear promising for a peanut breeding program.
Additional index words: Groundnut (Arachis hypogaea L.), haploid breeding, and polyembryonic seed.
Download entire article