Sclerotinia minor (Jagger) Kohn is serious and increasingly prevalent pathogen of peanut (Arachis hypogaea L.). Peanut stem tissues were reported to differ in their resistance to S. minor, but field performance is not always correlated with laboratory evaluations of resistance to Sclerotinia diseases in other crops. Differences in genotype performance in field and laboratory results may reflect differences in mechanisms of resistance. The objective of this study was to characterize mechanisms of resistance to S. minor in selected peanut genotypes by using agar culture tests, wounded and nonwounded stem inoculations, and field trials. For the culture test, sap was expressed from five genotypes with different levels of field‐resistance toS. minor. Each extract was incorporated into an agar medium, which was overlaid with a dialysis membrane. The fungus produced distinctive infection hyphae on the media. Genotype extracts differentially affected size of terminal and secondary hyphae and the number of hyphae per organized cluster. Nine genotypes were evaluated for resistance to S. minor in two stem inoculation tests. Inoculation sites were wounded in the first method, and were not wounded in the second method. Significant differences in lesion size were found with both methods, but more differences were found among genotypes in the nonwounded inoculation. Genotype performance in culture and stem inoculation tests was not correlated with performance in the field. These studies demonstrated that although some genotypes had resistance to stem colonization by S. minor, other mechanisms account for most of the resistance expressed in the field.
Peroxidative changes in seed lipids are thought to be a major cause of seed deterioration during storage. This study was conducted to determine the fatty‐acid composition of soybean [Glycine max (L.) Merr.] seeds, axes, and mitochondria during the early stages of deterioration. High‐quality seed lots of ‘Union’ and ‘Desoto’ soybean were stored at 25 °C and 115 g kg‐1 seed moisture for 10 and 12 months, respectively. Seeds were sampled at frequent intervals and the fatty‐acid composition of storage and membrane lipids from seeds, axes, and mitochondria were determined. There were no detectable changes in the fatty‐acid composition of storage lipids from whole seeds or axes during the storage period for either seed lot, despite the substantial decline in seed vigor. There was a slight decrease in the percentage of unsaturated fatty acids in the membrane lipids of excised axes from Desoto seeds. The percentage of unsaturated fatty acids in the mitochondria from excised axes declined early during storage. The double‐bond index (DBI) of lipids from mitochondria of the Union axes fell from 1.76 at the beginning of storage to 1.60 after 10 months. Similar declines of 1.79 to 1.70 after 1 yr in storage were seen for the Desoto axes. Mitochondria! respiration and DBI were highly correlated for both seed lots. These data suggest that the decreases in mitochondrial respiration during storage may be associated with peroxidative changes in mitochondrial lipids and that these changes occurred prior to loss in seed vigor.
The number of cultivars of perennial ryegrass (Lolium perenne L.) continues to grow. Accurate and rapid laboratory techniques to differentiate between cultivars has become increasingly important for both consumer protection and plant variety protection. The purpose of our work was to develop an electorphoretic procedure for ryegrass seed which would differentiate cultivars of perennial ryegrass. Proteins were extracted from ground seeds of 28 perennial ryegrass cultivars. Extracts were analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDSPAGE) procedures. A total of 27 bands were present with many of the bands common for the 28 cultivars. Cultivars were characterized by presence or absence of specific bands and by band intensity ratios calculated from densitometer scans. The cultivars Pennant and Premier were not successfully differentiated from each other nor was ‘Omega’ found to be different from the cultivar Birdie. All other cultivars were differentiated by unique banding patterns. Banding patterns from SDS‐PAGE of proteins were not affected by year and location of production, class of certified seed, or viability and vigor of the seed.
Understanding the cause of soybean [Glycine max (L.) Merr.] seed deterioration during storage will assist in the development of accurate laboratory tests to evaluate seed vigor. This study was designed to investigate the changes that occur in mitochondria! respiration during the early stages of soybean seed deterioration. High‐quality seed lots of ‘Desoto’ and ‘Union’ soybean were stored at 25 °C and 115 g kg‐1 seed moisture. Seed quality (germination and vigor) and conductivity of leachate from embryonic axes were measured at monthly intervals during storage. Mitochondrial State 3 (ST 3) respiration rates and respiratory control ratios (RCR) were measured from excised axes of samples after 24 h of imbibition. Germination remained high for seeds of both cultivars throughout storage; however, seed vigor (as measured by accelerated aging) declined significantly after 7 and 10 months for Union and Desoto, respectively. Conductivity of the leachate from excised axes for both cultivars increased early during storage prior to detectable changes in whole seed vigor. State 3 respiration rates of mitochondria from axes decreased throughout storage and RCR values declined after 2 months for Union and after 4 months for Desoto. Decreases in ST 3 respiration rates and RCR in both cultivars preceded measurable declines in whole‐seed vigor and correlated with increases in the conductivity of axes leachate.
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