Effect of Temperature on Severity of Fusarium Wilt of Lettuce Caused by Fusarium oxysporum f. sp. lactucae.

The effect of temperature on Fusarium wilt of lettuce (Lactuca sativa), caused by Fusarium oxysporum f. sp. lactucae, was examined in a controlled environment. Nine lettuce cultivars planted in infested potting mix (500 or 5,000 CFU/g) were maintained under high/low diurnal temperature regimes of 26/18°C, 28/20°C, or 33/26°C. Three cultivars were resistant to Fusarium wilt under all test conditions, and thus were little affected by differences in inoculum level or temperature. The remaining cultivars were more susceptible and manifested more severe symptoms at the higher inoculum level and when maintained at higher temperatures. The tendency for the disease to be more severe under warmer conditions may be due, in part, to an effect of temperature on growth of the pathogen. Radial growth rates calculated for six isolates of F. oxysporum f. sp. lactucae were observed to increase from 10°C up to an apparent maximum near 25°C. The results of this study suggest that growers can reduce the risk of damage from Fusarium wilt by avoiding susceptible cultivars during the warmest planting periods. Further, isolates of F. oxysporum f. sp. lactucae were shown to have a distinctive colony morphology in culture, which made it possible to distinguish them from nonpathogenic strains.

Limiting Effects of Low Temperature on Growth and Spore Germination in Gibberella circinata, the Cause of Pitch Canker in Pine Species.

Pitch canker, caused by Gibberella circinata (anamorph = Fusarium circinatum), causes canopy dieback and mortality in susceptible pine species in many parts of the world. Pitch canker is most problematic in areas with a relatively warm climate, suggesting a possible limitation on disease development imposed by low temperatures. To test this hypothesis, the effect of temperature on radial growth was examined in isolates of G. circinata of diverse geographic origin. All isolates grew most rapidly at 25°C and progressively more slowly at 20, 15, and 10°C. Spore germination occurred most rapidly at 20°C and was slowest at 10°C. To determine if the time required for spore germination might influence the likelihood of infection, the duration of wound susceptibility was examined by inoculating branches of susceptible Monterey pines (Pinus radiata). In each of six field trials, branches were wounded and then inoculated immediately or at 2, 6, or 9 days after wounding. The results indicated that wounds inoculated immediately became infected at a significantly higher rate than those inoculated 2 days later. Thus, if low temperatures extend the time required for germination beyond this period, a reduced infection frequency would be expected. Such a limiting effect of temperature could help to explain the current distribution of pitch canker.

General business theory applied to the physician's practice.

In the pursuit of clinical excellence in today's competitive medical market place, practice managers--clinical or non-clinical--can loose sight of standard management and business principles that are key to success. Also, at times individuals are hesitant to identify a physician practice as a 'business,' preferring to see it as a social good. Still, it is a business--perhaps dealing with a product that is a social good, but still, a business. And, as such, benefits can be derived from a review of business management theory. This article provides a brief review of such theory and also illustrates how to apply this theory to the physician's practice. Key factors in building a successful business will be discussed and applied to the clinical practice, such as resource maximization, rate of return and product mix synergy. Some tools to assist the reader in analyzing their practice will also be provided, such as the RVU Analysis and the Ratio of Service Analysis.

Practice efficiency and physician compensation: a case study.

One of the major challenges facing today's health care executive is that of achieving maximum efficiency. The public also requires an efficient health care system. However, a problem occurs when the health care executive defines "efficiency" in a manner that is diametrically opposed to the public's definition. Maximum efficiency in the physician practice is defined by productivity equal to capacity. Maximum efficiency of the health care system is defined by lower health care costs. If the physician practice is achieving its goal of maximum efficiency, the market economy will likely force a failure in achieving the public's goal of a lower cost health care system! The following case study provides an opportunity to review this health care management conundrum and offers insights into a possible approach for some solution through attention to physician compensation.

Solving the problem of the uninsured.

During the past 12 years, the number of uninsured has continued to climb. A sign of hope occurred in 1999, however; a decline of 1.7 million people was registered. While this decrease brings optimism of a new downward trend replacing the old upward trend, the number of uninsured remains unacceptably high-42.6 million people. Additionally, a significant portion of the 1.7 million people who were able to obtain health insurance were individuals covered by employment-based insurance, leading one to believe that the decline in the uninsured that we saw in 1999 might be connected to the US economy's full employment status. Supporting this thought is the Census Bureau's finding that the 10.4 million poor who had no health insurance in 1998 did not change significantly in 1999. This article provides a profile of the uninsured and describes how health care's evolution towards a market place commodity has contributed to America's unacceptably high number of uninsured. After reviewing various programs and initiatives launched in an attempt to expand health care coverage, a summary of problems with the current program is provided. An alternative is offered.

Audit. Operations in an academic setting.

A-U-D-I-T...the very word instills fear in the hearts of many. We recently received a letter from the director of the University of Rochester's Internal Audit Department, notifying us that they had scheduled a routine operational audit of our department. What is an "operational audit"? What is meant by "routine"? Who are these internal auditors and what do they want from us? This article illustrates two actual experiences: an operational audit and the process used to develop and implement standards and practices consistent with an auditor's recommendations. Additionally, it provides information on what an auditor looks for during an audit, and lastly, provides tips on how to prepare for a "painless" audit.

Comparison of ancestral and current-generation inbreeding in an experimental strawberry breeding population.

Progenies from first-generation self, half-sib, full-sib, and cross fertilizations were generated to evaluate the magnitude of inbreeding depression for vegetative and production traits in strawberry. Tests were conducted to determine the linearity of trait mean depression with inbreeding rate (ΔF) over this range of inbreeding values, as an indication of the presence of non-additive epistasis. A control population, for which a similar range of coancestry had accumulated over several cycles of breeding and selection, was also generated to compare the consequences of ancestral and current-generation inbreeding. Trait means for crosses among current-generation half-sibs, full-sibs, and selfs were 2-17%, 3-12%, and 14-45% lower than for unrelated crosses among the same set of parents, respectively. Linear regression of progeny means on current generation ΔF was significantly negative for all traits and explained 17-44% of the variance among progeny means. Mean depression was largely linear over the range of inbreeding rates tested in this population, indicating the absence of epistasis for the traits evaluated. Conversely, (F) regressions of progeny means on pedigree inbreeding coefficients, where coancestry had accumulated over several cycles of breeding and selection, were uniformly non-significant and explained 0-10% of the variance among cross means. Further, multiple regression of progeny means for current-generation relatives on pedigree F failed to improve fit significantly over regression on current-generation ΔF alone for all traits. Together, these results suggest that pedigree inbreeding coefficients are poor predictors of changes in homozygosity when populations are developed through multiple cycles of breeding and selection. They also imply that inbreeding depression will be of minor importance for strawberry breeding populations managed with adequate population sizes and strong directional selection.

The inheritance of vegetative growth traits in strawberries (Fragaria x ananassa) grown at low temperatures and their relationship to field productivity.

The genetic relationship between vegetative growth at low temperatures and productivity was investigated for strawberries grown in controlled and field environments. Genotypes from 20 biparental crosses were grown in controlled environments with 11°, 14°, and 17 °C days, 11 °C nights, and 11-h daylength to simulate a range of winter growing conditions expected in mediterranean environments. Individual plants were scored for two initial runner traits and eight vegetative growth traits. Significant main effects of temperature and cross were detected for all growth chamber traits, and conservative estimates of the broad sense heritability (h(2)) for these traits were 0.10-0.28. None of the temperature x cross interaction effects were significant, suggesting that genetic potential for vegetative growth and vigor is expressed similarly at low and optimal growing temperatures. Highly significant genetic correlations were detected between many growth chamber trait pairs, indicating pleiotropic effects for the genes that condition these traits. Complementary field trials were established, and individual plants were scored for traits that describe yield, production pattern, and plant size. Significant negative genetic correlations were detected between traits that describe growth in the chambers and early production in the field trials, but genetic correlations between chamber growth traits and mid-season or total production were significantly positive and occasionally large. Several of the yield and field growth variables were genetically correlated to initial runner plant traits, suggesting that indirect selection using traits scored in the nursery can be used to improve yield and modify production pattern in the field.

Genetic correlations between vegetative growth traits and productivity at different within-season intervals for strawberries (Fragaria X ananassa).

Genetic and environmental relationships between vegetative growth and production traits at different intervals within a single season were investigated using unselected strawberry genotypes from 20 biparental crosses and their parents. Vegetative growth and productivity patterns differed between test locations and larger yields were detected where fall growth was greatest. Positive genetic correlations were detected between fall growth increments and mid-season production traits, but fall growth was uncorrelated or negatively correlated with late-season production. Conversely, growth during the production season was genetically uncorrelated or negatively correlated to early production traits, but was positively correlated to mid and late-season production. Together, these results suggest that the growth pattern required for early vs sustained production may represent conflicting breeding objectives. Also, although vegetative and reproductive functions compete for assimilates in strawberry, sustained productivity appears dependent on adequate vegetative growth throughout the spring and early summer. Significant correlations were detected between fall plant growth and early yield, but these were attributed to environmental rather than genetic sources. Genetic correlations between spring growth and early production traits were significantly negative and large, suggesting that vegetative during this interval may indicate limited fall inflorescence development.

Genetic parameters and selection efficiency using part-records for production traits in strawberries.

The efficiency of selection for yield and fruit size using parts of the complete-season record was evaluated using data collected for individual strawberry seedlings (Fragaria x annanasa) in four genetic tests. Part-records were generated for each trait using cumulative weekly sums, and these were compared with complete records to assess the value of extended data collection. In addition, part-records were generated using data from alternate weeks of harvest. Scoring separate sets of seedlings in alternate weeks was assumed to allow a doubling of the unselected population size, halving the selection proportion and increasing selection intensity. Heritabilities estimated for part-records were often larger for mid-season cumulative part-records than for the complete-season records. Seasonal patterns for broad-sense and narrow-sense heritabilities differed, suggesting temporal expression of genes that condition yield and fruit size. Predicted genetic gains were largest using cumulative part-records between 4 and 12 weeks of the 15-week season, depending on trait and breeding objective (breeding value versus clonal value), with 8-9 weeks as a reasonable compromise. Selection using alternate-weeks records was identified as an efficient alternative to selection using total complete-season records. Superiority of the alternate-weeks option depends on the balance between increased selection intensity and decreased individual genetic information, and will differ for specific traits and program designs.

Using clonal replicates to explore genetic variation in a perennial plant species.

An experimental design is presented for estimating genetic parameters using a family structure with clonally replicated individuals. This experimental design provides a technique to quantify genetic variation in a population, with partial separation of additive, dominance and epistatic gene action. Our method is offered as an alternative to techniques for estimating epistatic gene action that require several generations and/or inbreeding. Such methods are not particularly useful for long-lived perennials with long generation cycles. An example of the analysis is given with a forest tree species, Populus deltoides Bartr., and parameter estimates are presented for traits measured over 8 years.

Maximizing gain per effort by using clonal replicates in genetic tests.

Models for predicting cummulative genetic gain from recurrent selection applicable to predominantly outcrossing plant species are derived to include the effect of observations on clonal replicates (ramets) in addition to observations on individuals and family means. Such models are discussed with special reference to forest trees. The consequence of redistributing effort from individuals to ramets is investigated for several conditions with a fixed number of families and fixed total test size. Factors that affect the distribution of variance among sources and factors that affect individual selection intensity are the primary determinants of the optimum distribution of effort. The optimum number of ramets ranged from 1 to 6 for the conditions tested and the efficiency of redistribution (ratio of gain for the optimum distribution to the gain for the single-ramet, or non-clonal case) ranged from 1.00 to 1.20. Using clonal replicates in genetic tests usually results in increased cummulative genetic gain relative to non-clonal tests, without an increase in test effort.

Optimum number of marker loci for estimating outcrossing in plant populations.

For the measurements of outcrossing rates in plant populations, current electrophoretic procedures permit many loci to be scored per individual progeny. Given that the total experimental effort or cost is limited, the choice exists then between assaying a large number of loci on a restricted number of individuals, or assaying a large number of individuals at a few loci. Using simple models and the criterion of minimising the variance of the estimate, several factors which affect this choice are considered (levels of polymorphism, heterozygosity, linkage disequilibrium, pollen or outcrossing heterogeneity). The general conclusion is that the actual level of outcrossing is a major factor in determining experimental strategy. Maximum efficiency for estimating outcrossing in predominantly inbreeding plants comes from large samples assayed for few polymorphic loci. In contrast, in predominantly outcrossing plants, more loci should be assayed at the expense of sample size for improved statistical efficiency.

Estimation of outcrossing rates in Duglas-fir using isozyme markers.

Seeds produced under open-pollination were collected from eight natural stands and a plus-tree seed orchard of Douglas-fir. These seeds were germinated and both diploid embryos and haploid gametophytes were analyzed by starch-gel electrophoresis. Eleven variable loci were resolved for both kinds of tissue and used as genetic markers for estimating outcrossing rates. Estimates made with single-locus and multilocus methods both indicated that the proportion of viable embryos resulting from outcrossing is about 0.90 for the natural stands, and for the seed orchard. Comparison of single-locus and multilocus estimates of outcrossing rates indicated that little or no inbreeding other than selfing occurred. Estimated outcrossing rates were higher for seeds from the upper portion of the crown than for seeds from the lower crown. It was also found that some trees selfed at a much higher rate than other trees.

A multilocus estimator of mating system parameters in plant populations.

A multilocus method of estimating mating system parameters in populations is presented that recovers information from classification over multiple loci that single-locus estimators do not detect. It is shown that the multilocus estimator provides a standard of reference (null hypothesis) that can be useful in analyzing the effects of factors such as population heterogeneity and post-mating zygotic selection on the transmission of genetic information at the population level.