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Evaluations of the genetic diversity of many crop breeding populations have been conducted in response to concern over their genetic vulnerability to diseases and insects. The purpose of this study was to evaluate the genetic diversity of U.S. mainland sugarcane (Saccharum L. spp.) cultivars. Eighty-eight cultivars from Florida, Louisiana, and Texas were traced back to seventeen original ancestors. Coefficients of parentage (r X 100) were calculated among cultivars and ancestors. Cytoplasmic genetic sources were also traced. Ten ancestors contributed germplasm to 90% or more of Florida cultivars, whereas only two ancestors contributed germplasm to 90% or more of Louisiana cultivars. Mean coefficients of parentage for current commercial cultivars in Florida ranged from 8.2 to 18.6. For Louisiana commercial clones, coefficients of parentage ranged from 16.3 to 25.8. Cytoplasmic sources traced to three S. officinarum L. clones. The ancestor Black Cheribon (S. officinarum) contributed the greatest amount of nuclear and cytoplasmic germplasm. In comparison with many crops, sugarcane is probably relatively well buffered genetically.

On silicon-deficient soils, fertilization with silicon (Si) has reduced disease severity and increased yield of rice (Oryza sativa L.). Breeding rice genotypes with greater Si concentration has been proposed, and some African and Asian rices have been evaluated for variability of Si concentration on upland and flooded mineral soils. This experiment investigated the variability and relation of Si concentration in rice plant tissue with disease severity and yield components of selected U.S. rice genotypes grown on flooded organic soils. Ten rice genotypes were grown at two Florida locations on Si-deficient organic Histosols. Plots were replicated five times in each of two Si treatments: Si-amended soil with silicon added at 2 Mg ha to the -1, and an unamended control. Plots were rated for disease severity at growth stage 8 to 9 (dough to mature) and sampled for determination of Si concentration in plant tissue (leaves and straw). Genotypes differed for Si concentration and disease severity at each location and for each Si treatment. Among genotypes, disease severity was negatively correlated with Si concentration in plant tissue. Increases in yield with added Si were attributable to a greater number of grains per panicle, whereas weight per 100 seed and panicles per square meter exhibited less change. Results indicated that although Si concentration varies among genotypes and is negatively correlated with disease severity, the strength of this association is mitigated by other genotypic factors which also affect response to disease.

`CP 88-1540' sugarcane (a complex hybrid of Saccharum officinarum L., S. barberi Jeswiet, S. spontaneum L., and S. sinense Roxb. Emend. Jeswiet) (Reg. no. CV-107, PI 607916) was selected from [...]

`CP 89-2143' sugarcane (a complex hybrid of Saccharum officinarum L., S. barberi Jeswiet, S. spontaneum L., and S. sinense Roxb. Emend. Jeswiet) (Reg. no. CV-109, PI 607918) was selected from [...]

Most of the sugarcane (interspecific hybrids of Saccharum sp.) production in Florida is on organic soils. Supplemental phosphorus (P) fertilizer is often applied for optimum yields, but producers are required to reduce P levels in farm drainage waters. The objectives of this study were to relate optimum leaf P tissue concentration with yield in organic soil, and to determine optimum leaf sampling dates during the summer. Eight genotypes were planted at two locations, eight additional genotypes were planted at a third location, and eight more genotypes were planted at a fourth location. Crops were grown for three years. Measurements of leaf P concentration were repeated during growth seasons and over crop years for a total of six sampling dates at each location. Three fertilizer P treatments (0, 24, and 48 kg ha -1 yr-1) were applied to all genotypes at each location. Leaf samples were partitioned into early-, mid-, and late-summer dates. Early-leaf samples had the widest range in leaf P concentrations compared with mid- and late-season leaf samples. Correlation analyses of yield vs. leaf P concentration across all treatments in early- and mid-summer were statistically significant (P < 0.05), but coefficients were low(r = 0.14 and 0.26, respectively). No consistent relationship across locations describedthe effect of leaf P tissue concentration on yield. Leaf P concentrations could not provideaccurate P fertilization rates that will give maximum sugarcane yields and prevent overfertilizationof P. The highest potential for relating leaf P concentrations with yieldappears to be from early leaf samples. [ABSTRACT FROM AUTHOR]