The grouping of accessions into clusters is achieved by a classification strategy that partitions the original col-When forming core subsets, accessions from a collection are classilection into groups with maximum distances between fied into clusters, and then samples are drawn from the clusters with accessions located in different groups and minimum disthe aim of maintaining the diversity of the collection. In a stratified tances between accessions located in the same group. sampling strategy, the allocation method provides a criterion for determining the number of accessions to be selected from each cluster. Franco et al. (1998Franco et al. ( , 2002 and Franco and Crossa This paper proposes an allocation method (D method) and compares (2002) proposed a sequential Ward-Modified Location it with three other allocation methods (L, LD, and NY methods). In Method (MLM) strategy in which the Gower (1971) these allocation methods, the number of accessions sampled per clusdistance is used as a measure of similarity (or distance) ter is proportional to (i) the mean of the Gower's distance between among accessions considering all continuous and cateaccessions within the cluster (D method), (ii) the logarithm of the gorical variables. The initial groups were formed by the cluster size (L method), (iii) the product of the cluster size times the Ward (1963) method, and then the MLM was used to mean Gower distance (NY method), and (iv) the product of the loga-J. Franco, Facultad de Agronomía, Universidad de la Repú blica, Av.

Conservation of plant genetic resources is achieved by protection of populations in nature (in situ) or by preservation of samples in gene banks (ex situ). The latter are essential for users of germplasm who need ready access. Ex situ conservation also acts as a back-up for certain segments of diversity that might otherwise be lost in nature and in human-dominated ecosystems. The two methods are complementary, yet better understanding of this interrelation and the role of ex situ conservation in global environmental considerations is needed. Inclusion of ex situ conservation efforts within current environmental policies conserving global diversity would focus greater international attention on the safeguarding of these efforts.

Oat (Avena sativa L.) investigations are of current interest because of the high quality protein present in the oat groat. In this study, groats were analyzed individually from single panicles selected from three replicates each of ‘Dal,’ ‘Froker,’ and ‘Orbit’ oats grown in the nursery and in the greenhouse. Grain weight, groat weight, groat percent, protein percent, and protein content per groat were determined, and relative position on the panicle was recorded. Within a panicle, groat weight decreased and groat percent increased from primary to secondary to tertiary kernels. Protein percent varied only slightly between primary and secondary groats, but was less in the tertiary of Dal and Froker. About 60% of the total protein was in the primary groats of Dal and Froker. Orbit contained many doubles in which the primary groat was not formed; hence the primary groats contained only about 45% of the total protein. Position of the groat on the oat panicle had an effect on the kernel characteristics. Correlations between groat distance from the panicle base and kernel weight, groat weight, and protein weight were positive and highly significant. Between groat distance from the base and protein percent, the relation was negative and generally highly significant.

each observation with p traits measured in each environment is normally distributed. For r environments, the Classification methods are used in genetic resource conservation vector of each observation has dimensions 1 ϫ rp, where and plant breeding. The two-stage Ward-Modified Location Model (Ward-MLM) clustering strategy defines initial groups by the Ward rp ϭ trait-environment combinations (variables). method and the MLM is then used to improve those groups. The Lawrence and Krzanowski (1996) used the Location three-way clustering strategy considers the same trait measured in Model (LM), originally proposed by Olkin and Tate different environments as different variables (environment-trait com-(1961), for classifying n individuals when p continuous bination), so that the resulting clusters of cultivars have a small traits and q categorical traits are measured in one envigroup ϫ environment interaction (GEI) for all the traits included in ronment. The LM combines the levels of all q categorical the study. An important component of the GEI is the imperfect traits in one multinomial variable, W, with m levels (w ϭ genotypic correlation or crossover interaction (COI). This study used 1,2,…,m). Franco et al. (1998) modified the LM and the three-way Ward-MLM clustering strategy in three different data proposed the Modified Location Model (MLM), by assets with the objectives of (i) evaluating the ability of the Ward-MLM suming that the m levels of the W variable and the pmethodology for clustering cultivars into groups with low COI, (ii) obtaining a graphical representation of the variables in a low dimen-multinormal variables for each subpopulation, are indesional scatter plot produced by the multidimensional scaling method pendent. The authors proposed using the MLM in a (MDS) in which the GEI of continuous and categorical traits and two-stage clustering strategy where initial groups are environments can be visualized, and (iii) studying how the relationship defined by the Ward (or any other hierarchical clusterbetween a pair of traits changes across environments. The three-way ing strategy) method and the MLM is then used with Ward-MLM strategy produced groups of cultivars with low levels of those groups (Ward-MLM). COI. The increment of the correlation coefficient values betweenFranco et al. (1999) extended the Ward-MLM stratgroups with respect to the total correlation coefficients indicated that egy to the case of clustering three-way data of cultivar ϫ the groups formed by the three-way Ward-MLM strategy comprised environment ϫ trait. Thus, the vector of each observasubsets of individuals that had similar trait responses across envition for r environments is 1 ϫ (rp ϩ 1). The three-way ronments. Ward-MLM clustering strategy considers the same trait measured in different environments as different variables (environment-trait combinations). Since the Abbreviations: GM, Gaussian Mixture; LM, Location model; MLM, when all measured traits are continuous. The authors Modified location model; EM, Expectation maximizatio...

Correlations among several chemical and agronomic characteristics were determined in 1970 and 1971 for 10 Avena sativa L. cultivars and for 46 F4‐F6 backcross “N” lines derived from a complex interspecific cross involving a 6x amphiploid. In 1971, groat protein percentage was significantly and negatively correlated with yield in both series, but in 1970 a nonsignificant positive r of 0.37 existed in the A. sativa series. A strong negative association existed between groat protein percentage and kernel weight in the A. sativa and 46 “N” line series in 1971 (−0.71** and −0.28*, respectively), when kernel weights were considerably higher than in 1970. Correlation coefficients between groat protein and lipid percentages were negative, though nonsignificant, for the A. sativa series in both years, but were near zero or positive in the “N” series. ‘Dal’ was high in both groat protein and lipid percentages, illustrating that departures from the general relationship exist. Lines such as ‘Lodi,’ with higher lipid and lower protein percentages, contribute strongly to a negative association.The correlation between lipid percentage and grain yield was significant and positive only in 1971. While r values between lipid percentage and kernel weight were significantly positive in the A. sativa series in both years, the relationship in the “N” series was significant and negative in 1970 and near zero in 1971. Groat protein percentages varied more from year to year within selections than did lipid percentages.The association between groat protein percentage and four of the six fatty acids differed in the A. sativa series from that in the “N” series. The relationship between lipid percentage and the fatty acids were considerably more in agreement for the two series. Lipid percentage was positively associated with percentages of stearic and oleic acids, but negatively correlated with myristic, palmitic, and linoleic acids.