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North American soybean [Glycine max (L.) Merr.] is derived from a narrow genetic base. Plant introductions (PI) and cultivars from the northern USA may be sources of diversity for southern U.S. cultivars. Screening diverse lines for agronomic value may identify potential parents that facilitate breeding for diversity. The objectives of this research were to evaluate the association of agronomic value and genetic diversity of selected PIs and to conduct a preliminary comparison of their value in the South with that of selected northern U.S. cultivars. Field evaluations of 31 PIs, 11 populations derived from cross of five northern cultivars × southern lines, and 15 southern lines were conducted at five environments in Arkansas. Restriction fragment length polymorphism (RFLP) data from 60 loci were collected from all PIs, parents of the populations, and 57 southern elite lines. The agronomic value of most PIs was low because of excessive shattering, lodging, and/or poor yield. Exceptions were noted. The estimated yield potential of most of the northern cultivars exceeded the mean yield of the PIs and they had less shattering than the PIs. The PIs and the northern cultivars were genetically divergent from the southern elite population and from each other. The agronomic value and relative diversity of the PIs were independent. Diverse PIs with above average agronomic value were identified. These PIs may serve as sources of genetic diversity that can be exploited through simple breeding schemes. The southern PIs and northern lines may act as complementary gene pools to provide desirable genes for diversifying southern U.S. soybean.

Estimates of among and within half-sib family varl. ance components for disease scores in each of two corn (Zea mays L.) populations were obtained from artificially inoculated experiments in 1, 2, or 3 years. These estimates were used to predict response to mass, half-sib, and Ss election for resistance to northern corn leaf blight (caused by Helminthosporium turcicum Pass.), Diplodia stalk rot [caused by Diplodia maydis (Berk.) Sacc.], and anthracnose leaf blight and stalk rot [caused by Col. letotrichum graminlcola (Ces.) Wils.]. In addition, among half-sib family variance component estimates for yield were obtained from unlnoculated experiments for the same families.Genetic correlations among yield and reactions to the four diseases were estimated.Per-year predicted gains in ieaf blight resistance for mass selection with pollen control were greater than for either S~ or half-sib family selection (with 20 plants per family). Per-year predicted gain for mass selection-for stalk rot resistance was greater than that for half-sib family selection (20 plants per family), For a given selection intensity and effective population size, predicted gain in stalk rot resistance for mass selection with pollen control is about equal to that for S~ selection at a great reduction in the number of plants rated for disease reaction and at no increase in the required number of hand pollinations.Genetic correlations between grain yield in the absence of disease and disease reactions were all near zero and nonsignificant. All significant genetic correlations among disease reactions were positive. These results suggest that mass selection would be the most efficient method of improving disease resistance in corn populations and that such improvement would not affect yield potential of the populations if adequate effective population size is maintained.

The inheritance of flower, seed testa, and hypocotyl colour, and growth habit were studied in the F2 generation of biparental crosses between Stylosanthes guianensis accessions exhibiting contrasting phenotypes. Segregation ratios for flower colour in seven crosses and the pooled ratio supported a conclusion of single-gene inheritance, with yellow dominant to white. The data on seed colour (purple v. brown) gave inconsistent results in the two crosses evaluated. Neither red v. white hypocotyl colour nor normal v. dwarf growth habit appeared to be inherited monogenically, since a range of intermediate phenotypes was observed in the F2 populations examined. The open-pollinated progenies of 12 homozygous recessive (white-flowered) individuals within one F2 population contained yellow-flowered plants attributed to outcrossing. Overall outcrossing rate ( � s.e.) was estimated as 0.138�0.021. The proportion of yellow-flowered outcrosses in these 12 progenies was related to the number of yellow-flowered individuals adjacent to the F2 parent, indicating that pollen movement was limited within the F2 plot. Based on these findings a practical, recurrent population improvement scheme for S. guianensis is proposed.