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Freezing hardiness was evaluated for several winter wheat (Triticum aestivumL.) cultivars and eight selections under controlled freezing conditions. High and low intensity freezing was achieved by decreasing the temperature slowly in hardened wheat crowns containing high and low amounts of water respectively. Freezing hardiness was assessed in terms of lower peripheral crown meristem (root) regrowth on a 0 (dead) to 5 (undamaged) scale. The standard deviation for the freezing test was approximately one meristem rating unit when the number of pots/replication were less than four. Standard deviation increased when the number of pots/replication increased. Different genotypes were easily differentiated when freezing hardiness was evaluated in terms of meristem rating and each genotype replicated 50 times. Many tests were required over a wide range of test temperatures to obtain satisfactory LD50values. Significant interaction in freezing hardiness evaluated either as meristem ratings or as percent survival was found between eight winter wheat selections and freezing condition, but not between 14 wheat cultivars and freezing condition.

Plant breeders are greatly concerned with the number and location of test sites necessary to assess cultivar performance. Yield trials rarely contain the same entries over sites and years, and this greatly reduces the flexibility needed to compare advanced germplasm with current commercial cultivars over a period of time. In this paper we provide an alternative method to the statistical procedures normally used to compare cultivars. Winter wheat (Triticum aestivumL.) nurseries in Michigan were used to develop the concept of a gene pool base, which allows comparisons over years and sites without regard to particular entries in the sample. It is proposed that as long as entries in the test are a representative sample of the population gene pool, the sample mean can be used as an index of comparison. Yearly additions and subtractions to the gene pool over the relatively short time span of six years did not greatly affect the average reaction to the environment. The regression of cultivar mean yield on nursery mean yield demonstrated that 53 to 95% of the variation in cultivar performance could be explained by site mean performance, with most cultivars falling in the 70 to 85% range. The data points were distributed in a continuum from high to low yielding sites. In graphing the regression of a cultivar on site mean yields, the designation of points by location could be used to suggest which cultivars should be grown in each environment and yield potential range. Locations were identified that had consistently high, low, intermediate, or extremely variable yield ranges over years. Any minimal set of test sites should include the extremes to provide an adequate estimate of the regression line.

During controlled water stress applied at the threeleaf stage, the barley (Hordeum vulgareL.) cultivars ‘Proctor’ and ‘Excelsior’ showed different rates of free proline accumulation and leaf‐firing. Both processes were faster in Proctor (a drought‐susceptible cultivar) than in Excelsior (a drought‐resistant cultivar). The different rates of proline accumulation during stress in Proctor, in Excelsior, and in a wild barley (H. spontaneumC. Koch) could be attributed to differences in the rate of decline of leaf water potential (ψleaf); at the same ψleafvalue, all three genotypes contained similar amounts of free proline. After non‐destructive screening of the F2generation from a Proctor ✕ Excelsior cross for proline‐accumulating capacity under controlled water stress conditions, F3seed from plants selected for high and low proline accumulation was obtained. When F3plants were tested for proline accumulation during controlled stress, the selection for proline accumulation was found to have been effective. Reselection among F3plants and subsequent testing of the F4generation confirmed this result. Among individual plants of the F3generation (which was segregating for the prollne accumulation trait) there was a positive association between the amount of free proline accumulated during stress and the severity of leaf‐firing. Massive proline accumulation is a symptom of severe internal water stress in barley and apparently has no survival value during drought. Although there is heritable variation in the amount of proline accumulated during stress, it is not of practical value in breeding for drought resistance.

Forty‐one genotypes (seven cultivars and 34 breeding lines) of winter wheat (Triticum aestivumL.) were planted in eight locations in each of 2 years. Test weight data were used to group locations according to their similarity of genotype ✕ location (G✕L) effects by cluster analysis. The results indicated that deletion of only one location from the variance analysis resulted in a group within which G ✕ L interaction was not significant. Such an analysis would be useful for the selection of testing sites for early generation testing and for development of genotypes with wide or narrow adaptability. The cultivars were also grouped into 10 clusters with respect to their test weight similarity across the 16 environments (2 years and eight locations). Further, stability parameters, i.e., mean, regression coefficient, and deviations from regression were calculated for each genotype. Cluster analysis effectively grouped genotypes according to their stability responses. Three broad categories of genotypes were identified with respect to their stability characteristics. Cluster analysis could be a useful supplementary tool for the analysis of adaptation reactions of wheat genotypes for test weight.

A quantitative investigation of the relationship between freeze‐damaged plant crowns and the percent moisture of the crowns was conducted. ‘Wong,’ ‘Hudson,’ and ‘Dicktoo’ barleys (Hordeum vulgareL.) and ‘Genesee,’ ‘Illinois 59‐884’ (CI 14023), and ‘Redcoat’ wheats (Triticum aestivumL.) were the cultivars studied. Artificial freezing tests, over a temperature range of —18 to —7 C and over a range of adjusted plant crown moisture percentages of 55 to 75%, were used. Crown damage was assessed as a root regrowth rating on an arbitrary scale of 0 to 9. Equations were obtained for each cultivar relating root regrowth to crown moisture and killing temperature. Predicted root regrowth was plotted against crown moisture and killing temperature as curves representing several levels of survival. The close relationship which exists between moisture content and freezing injury at specific temperatures was clearly demonstrated. Dicktoo barley and Illinois 59‐884 wheat were the cultivars most resistant to freeze‐damage. Macroscopic pictures of freeze‐damaged plant crowns are included.

The genotype‐environmental interaction of test weight and its components in Eastern soft winter wheat, Triticum aestivumL. em ‘Thell,’ was studied at seven locations in 2 years. Significant effects of location and years for test weight indicate that breeders should include a sample of years and locations when selecting for this character. By removing the differential effects of density, an environmental characteristic, from test weight and dealing only with packing efficiency, a varietal characteristic, a definite gain in genetic variance was obtained. Although test weight and kernel weight under different environments were highly correlated, a covariance analysis demonstrated no genetic correlation between them. This suggests that there are no genes in common controlling test weight and kernel weight in the varieties studied. Utilizing a combined regression analysis to examine genotype stability of test weight, cultivars and advanced breeding lines that had a significant interaction with the nursery means over different environments were identified. These lines were relatively indifferent to environmental variation and always had good test‐weight performance. The analysis also identified genotypes with average sensitivity and lines with extreme or undesirable sensitivity.

Test weight is defined as the weight of grain that fills a given volume. It is the product of kernel density and volume of grain occupying the container. The latter component, when expressed as percentage of the volume of the container, is referred to as packing efficiency and was shown to be a cultivar characteristic. Of the two components packing efficiency has a greater effect on test weight when comparing soft winter wheats (Triticum aestivumL. em Thell). There was a negative correlation between test weight and the kernel length‐width ratio (kernel shape). When the length‐width ratio remained constant, there was no increase in test weight when kernel volume increased. Kernel width was correlated more than length with kernel volume. Test weight and flour yield were not correlated within or among cultivars. Kernel protein was related to kernel size within cultivars.

The activity of freezing kinetics inhibitors was characterized by a visual rating technique for several wheat (Triticum aestivumL.) cultivars. The procedure allowed a single test of a cultivar with a minimum of 13 g of seed, and 10 tests per day with the equipment available. Comparisons between several replications of kinetic inhibitor ratings and cultivar survival of high‐intensity freezing showed expected relationships. The activity of kinetic inhibitors from some cultivars was commensurate with survival ability. However, other cultivars exhibited better kinetic inhibitor activity than indicated by their survival rating. The ability to identify cultivars with high activity with no confounding effect by plant weaknesses in other areas that can affect survival, is a distinct advantage of this test. All wheat cultivars tested had lower ratings than ‘Rosen’ rye, the standard for the maximum rating. A large number of cultivars with varied genetic backgrounds are now being screened for improved kinetic inhibitor activity using this technique. As an initial inquiry leading to the screening technique, the validity of using seed as the polysaccharide source in the kinetic inhibitor tests was substantiated by hydrolysis and chromatography. Monosaccharide components were similar for polysaccharides extracted from crown tissues, the important area of freezing resistance, and from seed tissue. Purifying the polysaccharide extracts has proved difficult. In the best preparations, no compositional differences were seen between those polysaccharides exhibiting activity as kinetic inhibitors and those showing inactivity.