fulfillment of the requirements for the MS degree. The authors gratefully acknowledge the technical assistance of Velva Groover. Plant material generously provided by Yoder Green Leaf, Lancaster, Pa. Multivariate repeated measures analysis of plant growth
Sarah A. White, Holly L. Scoggins, Richard P. Marini, and Joyce G. Latimer
Richard P. Marini
Experiments with perennial crops often span several years, and a response variable may be measured on the same plant at several points in time. Such data are often analyzed as a split-plot design, taking time as the split-plot factor. In other cases, separate analyses are performed for each time. The mathematical conditions required for validity of these types of analyses might not hold because measurements repeated on the same plant are not independent. Annual trunk cross-sectional-area (TCSA) measurements from a peach tree training experiment will be used to compare two methods of analyses. The 6-year experiment was a factorial of two heading heights at planting (low vs. high) and two tree forms (central leader vs. open vase). Univariate analysis of variance (ANOVA) and a multivariate repeated measures analysis (MANOVA) was performed. Main effects and interactions were more often significant with ANOVA than with MANOVA. ANOVA performed each year inflated the probability of falsely rejecting a true null hypothesis (Type I error), and was not appropriate for this data set.
George C.J. Fernandez
Dawn M. VanLeeuwen, Rolston St. Hilaire, and Emad Y. Bsoul
Statistical analysis of data from repeated measures experiments with missing factor combinations encounters multiple complications. Data from asynchronous cyclic drought experiments incorporate unequal numbers of drought cycles for different sources and provide an example of data both with repeated measures and missing factor combinations. Repeated measures data are problematic because typical analyses with PROC GLM do not allow the researcher to compare candidate covariance structures. In contrast, PROC MIXED allows comparison of covariance structures and several options for modeling serial correlation and variance heterogeneity. When there are missing factor combinations, the cross-classified model traditionally used for synchronized trials is inappropriate. For asynchronous data, some least squares means estimates for treatment and source main effects, and treatment by source interaction effects are inestimable. The objectives of this paper were to use an asynchronous drought cycle data set to 1) model an appropriate covariance structure using mixed models, and 2) compare the cross-classified fixed effects model to drought cycle nested within source models. We used a data set of midday water potential measurements taken during a cyclic drought study of 15 half-siblings of bigtooth maples (Acer grandidentatum Nutt.) indigenous to Arizona, New Mexico, Texas, and Utah. Data were analyzed using SAS PROC MIXED software. Information criteria lead to the selection of a model incorporating separate compound symmetric covariance structures for the two irrigation treatment groups. When using nested models in the fixed portion of the model, there are no missing factors because drought cycle is not treated as a crossed experimental factor. Nested models provided meaningful F tests and estimated all the least squares means, but the cross-classified model did not. Furthermore, the nested models adequately compared the treatment effect of sources subjected to asynchronous drought events. We conclude that researchers wishing to analyze data from asynchronous drought trials must consider using mixed models with nested fixed effects.
Barrett R. Gruber, Libby R.R. Davies, and Patricia S. McManus
completed in SAS (Version 9.1.3; SAS Institute Inc., Cary, NC). Data from 2007, 2008, and 2009 were analyzed separately. A mixed model (PROC MIXED) approach to repeated measures analysis ( Littell et al., 2006 ) was used to determine differences in the mean
Natalie R. Bumgarner, Whitney S. Miller, and Matthew D. Kleinhenz
Wheeler, 1992 ; Im and Jensen, 2008 ). Destructive sampling also tends to disrupt repeated measures of experimental plants or plots through time ( Baker et al., 1996 ; Casadesus et al., 2007 ; Tucker, 1980 ). Reliable, resource-saving tools are required
Ann L. Hild, E.B. Fish, and D.L. Morgan
For multi-stemmed shrubs, especially those with fine foliage, obtaining measures of leaf area or density of foliage and twigs within the crown may be both difficult and time-consuming. However, this measure may be an indication of the ornamental quality of a species. A method of photographic analysis was developed to perform repeated measures within the crown of woody shrubs. Slides of 5 species of arid land woody shrubs were analyzed by use of a Visual Image Processor system. This digital imaging technique may be applied where comparative measures over time for individual plants is useful. Comparisons were made of slides taken in the fall of 1989 and the spring and fall of 1990. The use Of slides limited handling or removal of any portion of the plants. Initial care in slide production and continuity of photographic techniques permits consistent results between measurement dates. This computerized method al lows comparative analysis of the growth and “fullness” of plant crowns.
Robert L. Geneve and Sharon T. Kester
Early seedling growth rate can be used to estimate seed vigor for small-seeded vegetable and flower seeds. However, hand measurement of small seedlings is tedious and difficult to reproduce among analysts. Computer-aided analysis digital images of seedlings should improve accuracy and reproducibility. A flat-bed scanner fitted with base and top lighting provided high resolution images of even small-seeded species like petunia [Petunia ×hybrida `Blue Picotee' (Hort) Vilm.] and lisianthus [Eustoma grandiflorum `Mariachi Pure White' (Raf.) Shinn]. Uniform lighting was provided and images were captured and analyzed in less than 2 minutes. A clear, cellulose film was used as the germination substrate in petri dish germination assays to facilitate capturing images with a flat-bed scanner. The transparent medium permitted seedlings to be imaged without removal from the petri dish and also allowed for repeated measures of the same seedlings in order to calculate growth rate. Six species evaluated in this study included cauliflower (Brassica oleracea L., var. Botrytis), tomato (Lycopersicon esculentum Mill. `New Yorker'), pepper (Capsicum annuum L. `North Star'), impatiens [Impatiens walleriana Hook. f. `Impact Lavender'], vinca [Catharanthus roseus (L.) G. Don. `Little Bright Eye'], and marigold (Tagetes patula L. `Little Devil Flame'). For germination and early seedling growth, the cellulose film compared favorably with other standard germination media (blue blotter and germination paper) for five of the six species tested. Computer analysis of seedling length was possible for all six species and was statistically similar to hand measurements averaged for three analysts.
Isabelle Babic and Alley E. Watada
Fresh-cut spinach has been shown to have a bacteriostatic effect on Listeria monocytogenes ATCC 19111 (Babic et al., 1997). A study was undertaken to determine if this effect is noted on other species of Listeria and to determine if the spinach or the natural microorganisms on the spinach was the cause of the bacteriostatic effect. Six species of Listeria was cultivated in pure tryptic soy broth, tryptic soy broth containing freeze-dried spinach powder, or broth containing mesophilic aerobic microorganisms (MAM) isolated from spinach powder. The cultures were incubated at 10°C for 6 days and growth measured daily. Growth data were analyzed as four factor general linear repeated measures mixed model with species, treatment, and day as the fixed effects. The fixed effects showed a significant interaction between treatment × day and day × species. Results indicated that both the spinach and MAM had an inhibitory effect on Listeria as noted by the maximum population at 6 days, which was 8.8 Log10 cfu/ml in control, 6.4 in spinach powder cultures, and 7.4 in mixed cultures (P < 0.05). Of the six Listeria species, three L. monocytogenes were affected similarly whereas the remaining three, particularly L. innocua, were affected differently. In conclusion, the bacteriostatic effect of fresh-cut spinach differs with Listeria species and the native microorganisms play a major role as competitors.
M.K. Upadhyaya and N.H. Furness
Surface area of cucumbers, carrots, parsnips, and beets was determined using the following non-destructive methods: Baugerod's method, Baugerod's method with inclusion of a factor correcting for substitution of weight for volume in the formula, and a novel image analysis method. Accuracy of the methods was ascertained by comparison with a direct shrink-wrap replica method of surface area measurement. Vegetables ranged in shape from cylindrical (cucumber and carrot) to conical (parsnip and beet). No difference in accuracy among methods of surface area determination was detected for carrots or beets. Baugerod's method and the image analysis technique differed significantly from the direct shrink-wrap replica technique for surface area determination of parsnips and cucumbers, respectively. Inclusion of a correction factor in Baugerod's method did not increase the accuracy of this method for any of the vegetables. The precision and repeatability of each method was determined by repeated measures analysis. Baugerod's method lost precision and repeatability for the conically shaped vegetables. Conversely, the shrink-wrap replica method lost precision and repeatability for the cylindrically shaped vegetables. The image analysis technique was precise and highly repeatable over the range of vegetable shapes. The development of a rapid, accurate, and precise non-destructive method of surface area measurement using image analysis techniques will provide a useful tool in the physiological study of vegetable products. Applicability of such a method over a range of vegetable shapes will be of additional value.