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Royce S. Bringhurst

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Victor Voth and Royce S. Bringhurst

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Hamid Ahmadi and Royce S. Bringhurst

Two groups of Fragaria decaploid (2n = 70, x = 7) breeding populations were studied. The first was derived from pentaploid (2n = 35) and hexaploid (2n = 42) natural or synethetic interspecific hybrids between octoploid (2n = 56) F. chiloensis (L.) Duch. or F. virginiana Duch. both from California, and various Fragaria diploids (2n = 14). Their chromosome number was doubled with colchicine or through the naturally generated unreduced gametes. They were selfed repetitively, intercrossed, and open pollinated. Gametic viability of the hermaphroditic and female decaploid hybrids exceeded 50%. The hybrids exhibited heterosis for runner production and vegetative vigor. Fragaria chiloensis bred for large fruit and desirable fruit qualities, and, in combination with diploids F. vesca L. and F. viridis Duch., resulted in hybrids that produced a single early spring crop and prolific runner production throughout the summer. Fragaria virginiana L. derivatives were characterized by high pollen fertility, and by day neutrality (photo-insensitivity). Together, they may contribute genes for adaptation to various regions and climates of the world and for pest and disease resistance. The second and most important group of decaploids involved here were those derived from hybrids between day-neutral octoploid cultivars (F. ×ananassa) crossed to F. vesca or F. viridis. This group of decaploids combined the genomes of the best octoploid cultivars with those of the above diploid species: facilitating the incorporation of genes responsible for high yield, day neutrality, and excellent fruit quality into the decaploid strawberries.

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Royce S. Bringhurst, Victor Voth and Douglas Shaw

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Royce S. Bringhurst and Jose Godoy F

There is a great deal of interest in the possibility of developing suitable materials or procedures for use in strawberries and other crops in place of methylbromide as a soil fumigant. One such has been soil heating resulting from the bed application of transparent polyethylene. This requires high mid-summer soil temperatures with relatively high soil humidity. We present the results of a solarization experiment. Bed soil temperature were measured regularly at a depth of 12 cm through the 9 weeks of differential treatments. The soil temperature differences were highly significant, averaging ≈7°C higher than the non-solarized treatments. Weed control is one of the results of high interest. The number of weeds were counted twice. The number in the solar plots were not significantly different from the number counted for the methyl-bromide-fumigated plots. Vegetative vigor (asexual response) was also an important measurement. This was measured in two ways: first, the number of runners, and second, the measurement of plant size. The results were identical. The solarized plots and fumigated plots were identical in plant size and identical in runner production, and both were significantly different from the non-solarized and non-fumigated plots. Similar results were obtained for the sexual responses, yield, and fruit size. Solarization should be tested sufficiently in detail as a possible procedure to replace some methyl-bromide fumigation.

The biggest problem may be difficulty getting the temperature high enough to be adequately effective.

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Hamid Ahmadi, Royce S. Bringhurst and Victor Voth

Genetic analysis of day-neutral (photo-insensitive) cultivars and their derivatives hybridized to standard short-day clones of octoploid strawberries [Fragaria × ananassa Duchn., F. chiloensis (L.) Duchn., and F. virginiana glauca Staudt., x = 7, 2n = 56] revealed that photo-insensitivity is controlled by a single dominant allele of a Mendelian gene. The dominant genetic trait is expressed in hybrids with other Fragaria spp. Intergeneric hybrids of day-neutral Fragaria and short-day Potentilla glandulosa L. and P. fruticosa L. also express photo-insensitivity. The day-neutral genes in European perpetual flowering (photo-insensitive) diploid `Alpine' F. vesca (2N = 14) apparently have evolved independently, since photo-insensitivity is recessive to photo-sensitivity. Native California diploid F. vesca have diverged considerably from European F. vesca. No photo-insensitive diploids have been found among them. Photo-sensitivity in native California F. vesca is controlled by three dominant genes. The origins of day-neutral cultivars of F. × ananassa and the classification of day-neutrality are discussed.

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Sandra L. Uratsu, Hamid Ahmadi, Royce S. Bringhurst and Abhaya M. Dandekar

Several strains of Agrobacterium tumefaciens and A. rhizogenes were shown to form tumors on runners of the diploid strawberry species Fragaria vesca L. Tumors, weighing from 0.1 to 8.3 mg, appeared from 2 to 4.5 weeks after infection. The majority of tumors tested for opine synthesis by high-voltage paper electrophoresis analysis showed positive results. These results demonstrate that diploid strawberry plants are susceptible to infection with Agrobacterium and that there are differences in the relative virulence of Agrobacterium strains.