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Yingmou Yao and Peter M.A. Tigerstedt

Genetic variation in growth rhythm, hardiness and height of 24 populations from 3 subspecies in sea buckthorn (Hippophae rhamnoides) were studied in a field test. The relative variance component of subspecies varied from 26.2% to 73.7% of total variance. Subspecies turkestanica had a growth mode of late start-late finish, ssp. rhamnoides, intermediate start-early finish and ssp. sinensis, early start-intermediate finish. Subspecies rhamnoides had a growth period of 129 days, ≈30 days shorter than the two Asian subspecies. The average height of ssp. rhamnoides was 43.7 cm, about one-third of that for ssp. tarkestanica and sinensis. Subspecies rhamizoides was more hardy than ssp. sinensis, which was still more hardy than ssp. turkestanica. The variance among populations was generally comparable with within population variance. Except for hardiness, variations for all characters were much larger in ssp. rhamnoides than in ssp. sinensis. The total genetic variance (subspecies plus population) varied from 50% to 84% of total variance for all characters, except 37% for secondbracts. Later growth cessation was correlated with longer growth period, taller plants, more severe frost and winter damage. Strong clinal variation showed that the higher the latitude, the earlier the growth cessation, the shorter the growth period and plant height, the more hardy the population. -The results indicated that population selection should bean efficient way for growth rhythm and plant height. Clinal variation provides guidelines for seed and plant transfer as well as plant introduction. With limited collection and management capacity in germplasm conservation, the recommendation is to collect fewer individuals in each population but more populations along latitude.

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Dale T. Lindgren, Kent M. Eskridge, James R. Steadman, and Daniel M. Schaaf

Severity of rust (Uromyces appendiculatus) and yield of dry edible beans (Phaseolus vulgaris L.) were recorded for 9 years in west-central Nebraska in fungicidal efficacy trials. A weighted analysis of covariance was used to estimate yield loss due to rust. The model fit the data well (R2=0.94), and the slope over all years had a 19 kg.ha−1 decrease in yield for each 1% increase in severity of rust. Yield response within years occurred only through reduction of rust for most fungicide treatments.

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Osamu Kawabata and Joseph DeFrank

A modified power function, y = (A + B·x)–C, was developed for determining the relationship between plant growth and growth retardant treatment. This function accounts for the plant response characteristics by incorporating three coefficients: A, growth level of the nontreated plants; B, the degree of growth reduction; and C, the smallest effective dose of the growth inhibitor. The function accounted for 97% of the variation in purple nutsedge (Cyperus rotundus L.) leaf length as a function of the amount of a growth retardant applied. The procedure resulted in a smaller error sum of squares than several common nonlinear functions because of its greater shape flexibility.

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J.J. Steiner and K. Opoku-Boateng

We investigated the effects of variation in ambient air temperature on seed production in the field during the reproductive development phase of `Salinas' head-type lettuce (Luctuca sativa L.) in the central San Joaquin Valley of California where daytime maxima may exceed 38C for many consecutive days during reproduction. Florets were tagged daily for 41 days and harvested seeds were sampled to determine temperature-sensitive periods during seed development. The number of seeds per inflorescence (NOS), seed mass (SM), and seedling root length (SRL) were reduced and percentage germination (GERM) increased with increasing minimum (LT) and maximum (HT) temperatures. Daily HT > 35C greatly reduced NOS. Increasing LT reduced SM and SRL, but to a lesser extent than NOS (r2 = 0.23 and 0.40; P = 0.01 and 0.001, respectively). The advantage of increasing HT on GERM (r2 = 0.20; P = 0.01) was overshadowed by the severe reduction in NOS and the vigor components SM and SRL. The periods of greatest sensitivity to high air temperature for NOS, SM, GERM, and SRL were - 1 to +1, - 4, +1, and - 4 to - 3 days from anthesis, respectively. The hours of peak sensitivity for these variables occurred during the same days at - 36, - 101, + 15, and - 83 hours from anthesis, respectively. Using Box-Jenkins time series analysis, diurnal periodicity in temperature sensitivity for the four variables was determined.

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Dennis T. Ray, Maren Elizabeth Veatch-Blohm, Valerie Hunter Teetor, and Bruce Walsh

much less heritable in Arizona ( Estilai et al., 1992 ). In a third study, when progeny and parents from single plant selections were compared when they were 2 and 3 years of age, respectively, no significant regressions were found between parents and

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Martin P.N. Gent

weights harvested at 4- to 9-d intervals, depending on the time of year, using the equation Another experiment measured the lettuce grown in similar troughs in 1996–98. The experimental conditions are described elsewhere ( Gent, 2003 ). Regressions. Values

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S.B. Sterrett, M.R. Henningre, and G.S. Lee

acknowledge the assistance of C.P. Savage, Jr. and F.W. Punk with the field studies and M. Lentner with the regression analyses. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper

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Russell Galanti, Alyssa Cho, Amjad Ahmad, and Javier Mollinedo

(version 13.1; SAS Institute, Cary, NC). Linear regressions were fitted for foliar N concentrations on SPAD values. Linear regressions were fitted for foliar Fe concentrations on SPAD values. One-way analysis of covariance with interaction simple slopes

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Timothy L. Righetti, David R. Sandrock, Bernadine Strik, and Anita Azarenko

The ratio of labeled fertilizer nitrogen (N) divided by the amount of total N is a convenient expression for evaluating the amount of N that is derived from fertilizer. The slope of the regression line for the relationship between total N and

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Yun Kong, Xiangyue Kong, and Youbin Zheng

using a linear regression model, the included variables may be different between the two species. Although quite a few studies have been performed to estimate plant biomass (especially dry biomass) from measurable morphological traits by using both