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  • Author or Editor: Randy Johnson x
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Twenty-one control-pollinated families of lilac (Syringa) were evaluated for the presence of powdery mildew (Microsphaera syringae). Because disease developed first in the lower portions of the plant and moved up, infection was scored from the lowest (1 =only on the lower quarter of the plant) to the highest quarter of the plant (4=present on all quarters of the plant). Family means for mildew score ranged from 2.3 to 3.8 and averaged 3.1, and for height ranged from 59 to 107 cm and averaged 82 cm. Narrow sense and broad sense he&abilities were estimated to be 0.08 and 0.27 respectively. Since any selections will be clonal, this relatively large proportion of non-additive variance can be fully utilized. There was a significant positive correlation between family means of height and mildew score (0.58); however, the phenotypic correlation between height and mildew score was -0.11. For this population the genetic correlation between mildew infection and height was positive (the taller families on average had mildew farther up the plant), but the environmental correlation was negative.

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A primary mission of the research unit at the U.S. National Arboretum (USNA) is to develop landscape trees and shrubs which are pest resistant and tolerant of environmental stresses. These improved trees and shrubs will ultimately enhance environmental quality. Breeding, early screening, and evaluation activities are carried out at USNA. Superior selections are further evaluated through a cooperative evaluation program of private nurseries and public institutions located throughout the U.S. If the selection is deemed “superior” by the cooperators it is named, released through the USDA, registered with the appropriate International Registration Authority, and distributed to our stock increase cooperators. These cooperators are private nurseries which produce liners for the industry. All material is provided free of charge and is not patented or trademarked. The USNA provides some marketing support in the form of publishing the releases in scientific and trade journals.

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Development of a new turfgrass cultivar requires an evaluation of numerous traits as well as an understanding of environmental factors influencing those traits. Growth or ability to fill in gaps and time of fall dormancy (fall color retention) that indicates cold hardiness are important traits for turfgrasses. This study was initiated to characterize variation in saltgrass [Distichlis spicata L. (Greene)] growth and time of fall dormancy related to climatic and geographical factors at the source location (geographical location of clone origin). Growth traits and time of fall dormancy were measured on 52 saltgrass clones collected from 41 locations and established at one location (common garden) in Fort Collins, CO. Principal component analysis on the morphological traits extracted the first principal component that explained 78% of the variability. The first principal component and time of fall dormancy were related to climatic and geographical factors at the source locations. Variation in growth traits was related to seasonal climatic variables of summer drying and fall cooling that explained ≈50% of variability in morphological traits. Variation in time of fall dormancy was related to longitude of clone origin and minimum winter temperature. These two variables explained ≈60% of the total variability in time of fall dormancy. Information obtained in this study may help breeders identify the best environments for specific traits and suggests that cold tolerance could be a problem for some clones from western sources if established too far east.

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Abstract

A computer simulation of asparagus growth is developed and used to evaluate the effects of various harvest strategies on short and long term commercial yield of asparagus (Asparagus officinalis L.). At present asparagus is harvested until the canners stop buying, usually in the 3rd or 4th week of June in southern Michigan, purchase generally being terminated by the reduction of spear diameter (whips), increase in fiber content of the spears or opening of the bracts. The simulation shows that this stragety is economically optimal for any single year; however, if the grower terminates the harvest every year on June 1, then the average yearly yields are significantly greater than those derived from the previous strategy. Skipping strategies, in which the grower skips a harvest every nth year (2nd, 3rd, or 4th), produced significantly lower 15 year average yields than either of the other 2 strageties, but produced significantly greater yields per plant.

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