Seed Coat Cracking Research Articles

Mechanical Properties Related to Soybean Seedcoat Cracking During Drying

ABSTRACT THE ultimate tensile stress and relaxation modulus of the soybean seedcoat were evaluated in two orthogonal directionsparallel and perpendicular to the hilum. An Instron Universal Testing Machine fitted with an environmental chamber was used to measure these mechanical properties for different drying conditions. Both properties were found to decrease as seedcoat moisture content and temperature increased. A three-term Maxwell model was found to adequately characterize the tensile viscoelastic behavior of the seedcoat. The seedcoat was found to be hydro-rheologically simple. Loading perpendicular to the hilum resulted in approximately 50% higher ultimate stess than loading parallel to the hilum. This anisotropic behavior may explain why over 90% of cracks in soybean seedcoat formed during drying extend from the hilum out; a situation representing loading parallel to the hilum.

Effects of freezing to −196 °C and thawing on Setaria lutescens seeds

The effects of single and repeated freezing and thawing of Setaria lutescens seeds in liquid nitrogen were investigated. One freeze to −196 °C followed by a slow thaw, increased seed germination from 40 to 70%, but additional freeze-thaw cycles reduced germination to 30%. Using a scanning electron microscope, evidence was produced that seed coat cracking did not cause either initial increased, or subsequent reduced germination. Observations with a transmission electron microscope revealed that disruption of the integrity of lipid bodies accompanied increased damage from repeated freezing at −196 °C and thawing. Repeated freezing and thawing of seeds stored in liquid nitrogen should be done with care to avoid loss of the germplasm.

Testing Methods, Variation, Morphological and Genetic Studies of Seed-coat Cracking in Dry Beans (Phaseolus vulgaris L.)1

Abstract Seed-coat cracking injury was determined in Great Northern (GN) dry bean lines in 1977, 1978 (also Pintos in 1978) using 3 methods as follows: Vogel small plot thresher (field), seed dropping, and a controlled rotating impact disk machine. Differences in susceptibility for seed-coat cracking were observed within each testing method. Overall, ‘GN Emerson’, near-isogenic determinate ‘GN Nebraska #1’ and ‘Pinto UI 111’ had the best resistance to seed-coat cracking. A genotype × year interaction for seed injury occurred with the Vogel thresher but not with the other 2 methods. The other 2 methods gave consistent results but the rotating disk machine method was preferred because of ease, rapidity of operation and standardization of the rotation speed. The early and late maturing determinate near-isogenic lines of ‘GN Nebraska #1’ had less seed-coat injury than the early and late indeterminate lines using the Vogel and rotating impact disk method. The early determinate line had the least amount of seed-coat injury for all three methods. ‘Pinto UI 111’, ‘Bulgarian White’, and ‘GN D-88’, which exhibited the best resistance to seed-coat cracking in the 7 parent diallel crossing study, had the most uniform seed-coat thickness as well as having thick seed coats. The cultivars which had thin or thick but non-uniformly thick seed coats were susceptible to seed-coat cracking. Differences in thickness in macrosclerid, os-teosclerid and parenchyma cell layers of the seed coat were observed between cultivars, but no relationship between these cell layers and the seed-coat cracking response was established. Seed-coat cracking was quantitatively inherited. ‘Bulgarian White’, ‘Pinto UI 111’ and ‘GN D-88’ showed high combining ability for resistance to seed-coat cracking. The estimates of the genetic effects indicated that additive effects were mainly involved.

Effect of Some Seed Characteristics on Mechanically Induced Seedcoat Damage in Navy Beans (Phaseolus vulgaris L.)

AbstractNavy bean seeds were evaluated for their response to mechanical abuse. Seed of all lines was hand threshed and equilibrated to a constant moisture content prior to damaging.Highly significant differences were found among lines in their reaction to seedcoat cracking. Seed weight, shape, density and seedcoat anatomy were examined as components contributing to seedcoat damage. Seedcoat cracking increased as the seed weight increased. Normal within‐line weight differences were small and self‐compensating, but between lines weight variation had a highly significant effect on cracking. Cracking also increased as the shape became more nonspherical. Increased seed density improved seedcoat tolerance to mechanical abuse but caused a nonsignificant increase in cotyledon splitting. Tolerant bean lines generally had a thinner parenchymatous layer underlying the osteosclerids. There was no difference in the thickness of the osteosclerid and macrosclerid layers between tolerant and susceptible lines.