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hande, 1957; Nyquist, 1991). This approach is based on the assumption that both random and systematic Inexpensive estimates of broad-sense heritability (BSH) may be environmental variation within a planting containing a valuable in plant breeding. This research evaluated two methods for estimating BSH with data from stands of equidistantly spaced geno-single genotype follows an inverse logarithmic function types. Both methods depend on the assumption that genetic and of the number of individual plants within a plot (x), environmental contributions to plot variance (plot ϭ group of contiguwhere a plot is a group of contiguous plants (Smith, ous plants) change at different rates as plot size changes if genetic 1936). Given a measure of environmental variation on variation is distributed randomly. For the method proposed by V.J. an individual basis (V 1), Smith (1936) showed that the Shrikhande, variances among plot means are computed and leastpattern of environmental variation on a plot mean basis squares regression used to estimate environmental and genetic vari-(V x) in such a planting could be represented by the ances and the change in a plot variance with changes in plot size. The regression coefficient b (termed the heterogeneity coefother method involves the same approach, but uses a two-parameter ficient) of the function (Smith's Law): model suggested by G.H. Freeman but not previously used to estimate BSH. Both methods produce biased BSH estimates since genotypic and genotypic ϫ environmental components of variation are insepara-V x ϭ V 1 x b [1] ble. Our objectives were to: (i) develop software to calculate variances for the methods, and (ii) compare BSH estimates generated using In a planting where environmental variation changes these methods with each other and with those from analysis of variance abruptly, phenotypic correlations between neighboring (ANOVA) of data from families grown in the same environment. plants and mean plot variance would decrease rapidly Data were from a perennial herb, Sphaeralcea emoryi Torr. grown as plot size increases and b approaches zero. More conin Tucson, AZ. Shrikhande's method produced parameter estimates sistent environmental effects would be associated with with large variances and BSH estimates that averaged 3.6 times larger a more gradual decline in plot variance and b values than those from Freeman's method. Only BSH estimates from Freeapproaching one. man's method agreed well with those from ANOVA for most traits. Freeman's method may be useful for rapidly and inexpensively gener

In southern Mali and throughout the semiarid tropics, small-scale family farmers are faced with the challenge of producing adequate harvests in difficult biophysical and socioeconomic environments. Professional plant breeders have had much difficulty developing modern varieties that outperform farmers' traditional varieties in these environments, in part because of an incomplete understanding of why farmers choose the varieties they grow. Improved understanding of farmers' varietal choices can contribute to collaboration between farmers and formal plant breeders. Based on a 15-month field study in Dissan, Mali, we examine farmer's choices among their traditional sorghum varieties in terms of one or more than one variety, and short-cycle or long-cycle varieties, and the interaction between these two choices. Results support our general hypothesis that farmers choose varieties to optimize outputs in the face of variation in the growing environment and in human managed inputs such as labor and tools.

There is much discussion of the probability of transgene flow from transgenic crop varieties to landraces and wild relatives in centers of origin or diversity, and its genetic, ecological, and social consequences. Without costly research on the variables determining gene flow, research on transgene frequencies in landrace (or wild relative) populations can be valuable for understanding transgene flow and its effects. Minimal research requirements include (1) understanding how farmer practices and seed systems affect landrace populations, (2) sampling to optimize Ne/n (effective/census population size), (3) minimizing variance at all levels sampled, and (4) using Ne to calculate binomial probabilities for transgene frequencies. A key case is maize in Mexico. Two peer-reviewed papers, based on landrace samples from the Sierra Juárez region of Oaxaca, Mexico, reached seemingly conflicting conclusions: transgenes are present (Quist and Chapela, 2001, Nature 414: 541-543; 2002, Nature 416: 602) or "detectable transgenes" are absent (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA 102: 12338-12343 and 18242). We analyzed these papers using information on Oaxacan maize seed systems and estimates of Ne. We conclude that if Quist and Chapela's results showing presence are accepted, Ortiz-García et al.'s conclusions of no evidence of transgenes at detectable levels or for their introgression into maize landraces in the Sierra de Juárez of Oaxaca are not scientifically justified. This is because their samples are not representative, and their statistical analysis is inconclusive due to using n instead of Ne. Using estimates of Ne based on Ortiz-García et al.'s n, we estimate that transgenes could be present in maize landraces in the Sierra Juárez region at frequencies of approximately 1-4%, and are more likely to be present in the 90% of Oaxacan landrace area that is not mountainous. Thus, we have no scientific evidence of maize transgene presence or absence in recent years in Mexico, Oaxaca State, or the Sierra Juárez region.

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Fifteen microsatellite loci were used to genotype 108 accessions of cultivated olive, Olea europaea L. ssp. europaea var. europaea, and eight of O. europaea L. ssp. cuspidata (Wall. ex G. Don) Ciferri, from the germplasm collection of the United States Department of Agriculture in Davis, California. Number of alleles per locus ranged from 3, for locus IAS-pOe12_A, to 16, for locus ssrOeUA-DCA11, with an overall mean of 9.93. Observed heterozygosity ranged from 0.175, for locus UDO99-019, to 0.937, for locus GAPU89, with a mean of 0.640. The cluster analysis using the Unweighted Pair Group Method using Arithmetic mean (UPGMA) method displayed thirteen clusters within seven main groups that can be partially described by common geographic origin or fruit use, though overlap among these groups was common. The locus-wise total gene diversity (H T ) ranged from 0.319, at UDO99-019, to 0.847, at ssrOeUA-DCA3, with an overall mean of 0.696. Most of the gene diversity was partitioned within clusters, with proportions (H S /H T ) ranging from 0.633, at IASpOe12_B, to 0.848 at GAPU89 per locus, with a mean of 0.759. The principal components analysis explained 24.8% of the total variation along the first two components. Projection of accessions onto the first two principal components produced affinities generally in agreement with the results of the UPGMA cluster analysis. The California cultivar 'Mission' clustered closely with Iberian cultivars and may represent clonal selections adapted to local growing conditions. The results show significant diversity but low levels of differentiation among olive cultivars within the collection.