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- Author or Editor: Carl H. Shanks Jr. x
Abstract
Segregation for resistance to the strawberry aphids, Chaetosiphon fragaefolii (Cockerell) and C. thomasi (Hille Ris Lambers), occurred in the first backcross from the resistant ‘Del Norte’ clone of Fragaria chiloensis (L.). Aphid populations on ‘Del Norte’ were 4 and 7% of those found on the susceptible cultivar ‘Totem’ in greenhouse and field evaluations respectively. Resistance of the most resistant backcross seedlings was comparable to that of the F1 parent but slightly less than ‘Del Norte’. Greenhouse and field evaluations gave generally similar results although field evaluations have greater practical significance.
Abstract
The ‘Del Norte’ and ‘Yaquina’ clones of Fragaria chiloensis (L.) Duchesne exhibited a high degree of resistance to the strawberry aphid, Chaetosiphon fragaefolii (Cockerell), but a third clone, ‘OR-US 3162’, was very susceptible. Resistance of ‘Del Norte’ was transmitted to progeny when crossed with commercial strawberry cultivars, Fragaria × ananassa Duch. None of 30 commercial strawberry cultivars and advanced selections tested showed resistance to this aphid.
Abstract
Thirty clones of the beach strawberry, Fragaria chiloensis (L.) Duch., that were known to be resistant to strawberry aphid, Chaetosiphon fragaefolii (Cockerell), were evaluated for resistance to twospotted spider mite, Tetranychus urticae Koch. AH clones had fewer mites per leaf than the cultivar ‘Totem’. Two clones, BSP-14 and LCM-19, had totals of only 6 and 82 mites, respectively, on 4 dates compared to 1741 mites on ‘Totem’. The ‘Del Norte’ clone of F. chiloensis, previously used as a source of aphid resistance in breeding, was more susceptible than BSP-14 and LCM-19 to the mite.
Abstract
Mite resistance of strawberry, Fragaria ☓ ananassa Duch, based on the ability to support low populations of the twospotted spider mite, Tetranychus urticae Koch, was assessed in the progeny of 15 crosses at two locations. The best parents were Washington State University selections 72–83M, 75-7-5 and 75-57-3 and the poorest parents were the susceptible cultivars ‘Totem’ and ‘Rainier’. General combining ability estimates for mite resistance were higher than specific combining ability estimates. Heritability estimates, based on parent/offspring regression, were high and ranged from 0.62 to 0.92. These observations suggest that additive genetic factors play a major role in the inheritance of mite resistance.
More than 170 clones of Fragari ×ananassa Duch., F. chiloensis (L.) Duch., and F. virginiana Duch. were tested for resistance to the twospotted spider mite (Tetranychus urticae Koch). Twenty-seven clones had >75% fewer mites than did F. ×ananassa `Totem', a susceptible clone. About two-thirds of the clones also were tested for resistance to the strawberry aphid [Chaetosiphon fragaefolii (Cockerell)]. Survival and reproduction was significantly lower on two clones each of F. ×ananassa and F. virginiana than on `Totem'.
`Totem' strawberries (Fragaria ×ananassa Duch.) were planted with clean-cultivated inter-rows or inter-rows planted with permanent cover crops of white clover (Trifolium repens L.) or `Manhattan' perennial ryegrass (Lolium perenne L.). There were no significant differences between treatments in the number of twospotted spider mites (Tetranychus urticae Koch), strawberry aphids [Chaetosiphon fragaefolii (Cockerell)], or Pratylenchus sp. or Xiphinema sp. nematodes on strawberry plants. The cover crops reduced strawberry yields relative to cultivation, although fruit size was significantly larger the second year. Root weight did not differ significantly in either year. Weight of above-ground vegetation was significantly higher in cultivated plots the first year, but not the second year.
Abstract
Nine commercial strawberry cultivars (Fragaria X ananassa Duch.) and 557 clones of wild F. chiloensis (L.) Duch. from the Pacific coast of the United States were tested in the field for resistance to strawberry aphids (Chaetosiphon spp.). No cultivar was highly resistant but ‘Benton’ consistently supported fewer aphids than the other cultivars. In the first evaluation year, 29 clones of F. chiloensis had fewer aphids than the highly resistant ‘Del Norte’ clone of F. chiloensis on 5 sampling dates, although the differences were not statistically significant but in the second year, only 1 clone, RCP-37, had fewer aphids than ‘Del Norte’.
Eleven clones of Fragaria spp. were tested for resistance to the twospotted spider mite, Tetranychus urticae Koch, at Dover, Fla.; Watsonville, Calif.; and Vancouver, Wash. Ten clones, which had been selected previously as being mite-resistant, had generally the same relative resistance when compared to susceptible `Totem' at all three of the widely separated locations. It appears that Fragaria clones selected for resistance to spider mites at one location likely will be resistant elsewhere, in spite of environmental differences.
At two-week intervals from 17 June to 15 July, three groups of `Meeker' red raspberry plants were infested with two-spotted spider mites (Tetranychus urticae) in a greenhouse. While populations on individual plants were allowed to develop freely, control plants were kept free of mites with a chemical miticide. Gas exchange measurements were made on 27 July prior to visible mite damage, and on 7 October after injury was apparent. The relationships between mite populations and leaf gas exchange and chlorophyll characteristics were described using a logarithmic function.
Physiological responses to mite feeding were observed prior to visible leaf injury. On both dates, CO2 assimilation rates decreased (p ≤ 0.001) with increasing mite numbers per leaflet. On 27 June, a significant relationship (R2 = 0.61***) was found between mite number and mesophyll conductance (gm). On 7 October, significant relationships (p ≤ 0.001) were also observed with gm, stomatal conductance (gs), and transpiration (E). Total chlorophyll content of leaves decreased with increasing mite populations, but chlorophyll a/b ratio and dry weight per leaf unit area were unchanged.