Thomas M. Sjulin
Susceptible day-neutral strawberry (Fragaria ×ananassa Duch.) cultivars are readily infected by Colletotrichum acutatum J.H. Simmonds during nursery propagation. The fungus infects strawberry flowers and fruit under warm, moist conditions and spreads rapidly throughout the nursery planting during repeated cycles of infection. Plants transplanted from infected nurseries into fruit-production fields have increased plant mortality and yield loss. This paper reviews practices adopted by California strawberry nurseries that reduce or eliminate sources of fungal inoculum, reduce strawberry plant susceptibility, or reduce pathogen spread in the nursery. California nurseries are currently using a combination of these practices to produce specific pathogen-free planting stock of susceptible day-neutral cultivars.
Thomas M. Sjulin
Adam Dale and Thomas M. Sjulin
Patrick P. Moore, Jo Ann Robbins, and Thomas M. Sjulin
The field performance of micropropagated and runner-propagated subclones of `Olympus' strawberry (Fragaria × ananassa Duch.) was compared. The yield of micropropagated plants was not greater than that of runner-propagated plants. There was significant variability among micropropagated subclones, with the highest yielding subclone having 68% higher yield than the lowest yielding subclone in each of the first 2 years. However, after runner propagation for 4 years, selected subclones showed no differences in yield. Differences among subclones of `Olympus' were not stable and were most likely transient responses to the micropropagation environment. The apparent superiority of the subclones was not genetic.
Patrick P. Moore, Thomas M. Sjulin, and Carl H. Shanks Jr
Thomas M. Sjulin, J. Scott Cameron, Carl H. Shanks Jr., and Carlos E. Munoz
In January, 1990, a team of U.S. and Chilean scientists collected native and cultivated Fragaria from central and southern Chile. During the course of this expedition, 363 new accessions of Fragaria were collected. Approximately 2,500 plants of 250 clones were collected from 66 sites in 19 different areas, and 113 seedlots (estimated at over 100,000 seeds) were obtained.
Plants were collected from a wide range of habitats, and considerable variability was observed in vegetative and reproductive characteristics. Fruit were round to conical in shape, deep red to white in color, soft to moderately firm, with soluble solids ranging from 5-18%, dull to glossy skin, bland to strong flavor, low to very high aromatics, and difficult to moderately easy capping. Fruit size in situ approached 4 g, while fruit larger than 12 g were found under cultivated conditions. Strawberry aphids (Chaetosiphon fragaefolii) were found on plants in situ and under cultivation. Little or no evidence of other pests were observed on clones collected in situ.
Adam Dale, Patrick P. Moore, Ronald J. McNicol, Thomas M. Sjulin, and Leonid A. Burmistrov
Pedigrees of 137 red raspberry (Rubus idaeus L.) varieties released throughout the world since 1960 were used to calculate: 1) the genetic contribution of founding clones to these varieties; 2) genetic relatedness among them; and 3) their inbreeding coefficients. Fifty founding clones contributed to the pedigrees of these varieties with a mean genetic contribution ranging from <0.1% to 21%. Varieties were clustered according to the genetic contribution into groups strongly related to geographical origin. Varieties developed in the former USSR and derived from `Novost Kuzmina' formed a distinct cluster. The remaining varieties were clustered in groups based mainly on whether they were of North American or European origin. Varieties were clustered also on the basis of Wright's coefficient of relationship-a measure of genetic relatedness. Cluster groups were related to their geographical origin and the varieties within the groups could be traced to similar intermediate parents. Inbreeding coefficients ranged from 0.0 to 0.625 and were related, in part, to the numbers of generations of controlled hybridization from common ancestors. The British group, with the largest number of generations of breeding, had a low mean inbreeding coefficient, indicating that inbreeding can be minimized with attention to the mating system. Strategies are suggested for maintaining and increasing the genetic diversity in the world's red raspberry breeding populations.