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  • Author or Editor: John L. Maas x
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Nineteen strawberry (Fragaria × ananassa Duch.) cultivars in nursery rows were sprayed in the fall with methyl 1-(butylcarbamoyl)-2-benzimidazolecarba-mate (benomyl), dug 1 month later and cold-stored for 8 months. Plants of ‘Catskill’, ‘Dixieland’, ‘Earlibelle’, ‘Earlidawn’, ‘Empire’, ‘Fletcher’, ‘Fulton’, ‘Jerseybelle’, ‘Marlate’, ‘Midway’, ‘Raritan’, and ‘Redglow’ sprayed with benomyl were in significantly better condition after storage than nonsprayed plants. ‘Dunlap’, ‘Ozark Beauty’, and ‘Redchief plants were in only slightly better condition due to treatment, but showed significantly higher percentage field survival or first-year fruit yields compared to nontreated plants. ‘Midland’, ‘Ogalla’, and ‘Redstar’ plants showed no difference due to treatment Results indicate that plants of cultivars most difficult to maintain in cold storage benefit the most from preharvest benomyl application.

Open Access
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Scanning electron microscopy studies were made on pollen samples from several small fruit crops: 3 selections of blueberry (Vaccinium), 4 Vitis spp. (V. vinifera L., V. cinerea Engelm., V. rupestris Scheele, and V. amurensis Rupr.), 2 cultivars of raspberry (Rubus), 5 cultivars of blackberry (Rubus), and several species and ploidy levels of strawberry (Fragaria) including 54 cultivars of F. × ananassa Duch., as well as pollen of Duchesnea and Potentilla.

Pollen size and exine characteristics were similar for 4 grape species examined. Polyploid blueberry selections were separable from the diploid selection by pollen grain size. Raspberry and blackberry pollen differed in size, exine ridging or reticulation, and presence of borderless or collared pores. Strawberry pollen is characterized by exine ridging and absence of pores. Cultivars of Fragaria × ananassa could be categorized into 4 groups according to exine ridge patterns. Cultivars exhibited broad longitudinal ridges or were characterized by less prominant to indistinct ridges. One cultivar was unique in that anastomosing ridges were present between adjacent ridges.

Pollen grains of diploid F. vesca L., F. vesca fma. semperflorens Duch., and F. nubicola Lindl, ex Lacaita; a tetraploid clone of F. vesca; the hexaploid F. moschata Duch.; and octoploid F. × ananassa, F. chiloensis (L.) Duch., and F. virginiana Duch. are broadly elliptical, tricolporate and moderately to prominently ridged. Size of pollen and prominance of exine ridges appeared to correspond with ploidy level. Pollen of F. nipponica Mak. differed in that grains are subprolate to sphaeroidal and exine is ornamented with minute, rounded to subconical verrucae arranged in rows. Pollen of the related genera Duchesnea and Potentilla were very similar morphologically to those of octoploid Fragaria spp., except that pollen of D. indica (Andr.) Focke are larger and the exine of P. recta L. exhibits an extremely minute pore structure.

Open Access
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The interrelationships among red stele infection (Phytophthora fragariae Hickman races A-2 and A-5), symptom development (in susceptible ‘Blakemore’ strawberry (Fragaria × ananassa Duch.) runner plants and ‘Midland’ × ‘Midland’ and ‘Sequoia’ × ‘Earlibelle’ seedlings), and soil pH were examined in two experiments. Percent of plants infected and disease symptom severity ratings were high when plants were grown in soil infested with P. fragariae race A-2 and soil pH 5.4 to 8.0. The length of incubation period had a greater effect on infection and disease development by race A-2 than did either soil pH or type of plant (runner plant or seedling). Symptom severity ratings among ‘Blakemore’ runner plants and ‘Sequoia’ × ‘Earlibelle’ seedlings grown in soil infested with race A-5 was highest at low to intermediate pH levels and decreased as soil pH increased. No direct relationship between soil pH and plant infection was found. Interactions among soil pH, pathogen race, and runner plant or seedling populations were significant.

Open Access

Nuclear magnetic resonance (NMR) can be used to examine tissue structure and developmental changes during growth and maturation of plant organs nondestructively. Spin-lattice, relaxation time (T1)-weighted, inversion recovery, spin-echo images of strawberry (Fragaria×ananassa Duch.) flower buds were acquired at 3 and 1 day before anthesis and receptacles at 4, 10, 15, and 25 days after anthesis (DAA). The central pith and ovules of flower buds imaged intensely with inversion echo times between 0.1 and 0.5 seconds. Achenes and the vascular cylinder, composed of vascular bundles surrounding the pith, were prominent in receptacles at 4 and 10 DAA. Vascular bundles leading to achene positions, cortex and pith tissues, and the vascular cylinder were evident in receptacles at all developmental stages. A general trend to homogeneity of structure was observed in images of receptacles nearing full maturity (25 DAA). Inversion recovery, spin-echo NMR microimaging may be useful for studying internal physicochemical changes in flower buds and fruit of strawberry and of other fruit crops.

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We report the use of nuclear magnetic resonance (NMR) imaging to detect differences in invasion and colonization of fruit by pathogens (Botrytis cinerea, Colletotrichum acutatum, and Phytophthora cactorum), and bruise wounds are sharply distinguishable from healthy fruit tissue by their T1 times. Digitized images from T1 images clearly show two or more zones of pathogen activity in fruit tissue. The innermost zone corresponds to the area of greatest invasive activity at the leading margin of the infection. A second zone corresponds to the area of tissue that has been killed and is being degraded by the pathogen. Sometimes, a third zone is present at the outer border of the lesion and this correspond to where aerial sporulation may occur. Images of bruises, however, are uniform with no apparent gradations in T1 characteristics. Detection of fruit deterioration and decay is important in understanding and controlling postharvest loss of fruit crops. The nondestructive nature of MRI provides a means to quantify the process of decay development and control measures applied to fruits.

Free access

Bacterial angular leafspot disease (BALD) of strawberry, caused by Xanthomonas fragariae, a slow-growing and often difficult pathogen to isolate from infected plants, is most commonly manifested as small discrete, angular, translucent lesions on leaves and sepals. As the bacteria infect systemically, plants may wilt and die. BALD has become increasingly important in North America and other strawberry-growing areas of the world. The systemic nature of the pathogen also is cause for concern with international shipment of strawberry plants, especially because there is no practical method for determining the presence of the bacteria in symptomless, infected plants, nor is there a practical method of chemical control. All cultivars of Fragaria × ananassa (8×) are susceptible to BALD, although a range of susceptibility is often apparent in plantings. Resistant genotypes have been reported among clones of F. virginiana (8×), F. moschata (6×), and F. vesca (2×). A program has been initiated to evaluate native octoploid and diploid strawberry germplasm for resistance to BALD.

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Abstract

The effects of supplemental light provided by high- and low-pressure sodium (HPS and LPS), metal halide (MH), and incandescent filament (INC) lamps were determined on the photomorphogenic responses of strawberry (Fragaria × ananassa Duch.) plants. Supplemental light was provided in the greenhouse under normal winter conditions of 9–12 hr of daylight in Beltsville, Md. Growth responses of representative Junebearer (‘Badgerbelle’), everbearer (‘Our Own’), and day-neutral (‘Tribute’) plants propagated by tissue culture (TC) and conventional means (RP) were recorded under supplemental lighting compared to natural day length (ND) conditions and with long days simulated by ND supplemented with a daily 4-hr night interruption (NI) with 0.9 W·m–2 (400–850 nm) INC exposure (ND and NI) at 2200–0200 hr. Vegetative and reproductive responses to supplemental lighting varied with the photoperiod class of the cultivar and with its mode of propagation. Vegetative growth (stolon and daughter plant development) of Junebearer RP and both Junebearer and everbearer TC plants was promoted by all supplemental light treatments. Supplemental light did not promote growth of everbearer RP plants or day-neutral TC or RP plants. Crown branching of day-neutral TC plants was promoted by several treatments, but the number of crowns on RP plants was increased only under LPS at 12 W·m–2 for 24 hr. Flower truss initiation of Junebearer plants was not stimulated by supplemental light treatments compared to ND. Everbearer RP plants produced more flower trusses under supplemental light treatments compared to ND, but TC plants were stimulated only by LPS at 12 and 24 W·m-2 for 24 hr. Day-neutral RP plants produced more flowers per truss under most treatments compared to ND, but TC plants produced the greatest number of flowers per truss under MH at 12 W·m-2 for 24 hr.

Open Access
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Abstract

Strawberry (Fragaria × ananarsa Duch.) plants treated with methyl 1-(butylcar bam oyl) 2-benzimidazolecarbamate (benomyl) before removal from the field were in better condition after 7 months of storage, survived better in the field after planting, and produced higher yields than those not treated with fungicide. Fungicide application dates ranged over 6 weeks in the fall. The time of application made no significant difference in the condition of the plants during storage, however, fruit yield data in some cultivars indicated that late treatment was more beneficial than early treatment for maintaining overall plant quality. Treated plants stored at 1°C for 7 months were of very good quality, while those at 3° were mediocre to poor. Poor quality and high mortality characterized all nontreated plants regardless of storage temperature.

Open Access

Plugs are rapidly replacing fresh-dug bare-root and cold-stored frigo plants as transplants for strawberry (Fragaria × ananassa) production worldwide. Plugs have many advantages over these other types of propagules. They are grown in controlled environments (greenhouses, tunnels) in less time than field produced bare-root transplants, and are not exposed to soilborne pathogens. Plugs afford greater grower control of transplanting dates, provide mechanical transplanting opportunities and allow improved water management for transplant establishment relative to fresh bare-root plants. New uses for plugs have been identified in recent years; for example, photoperiod and temperature conditioned plugs flower and fruit earlier than traditional transplants and plugs have been used for programmed greenhouse production. Tray plants have superior cold storage characteristics relative to bare-root, waiting-bed transplants. Both fresh and frozen plugs are used in a number of indoor and outdoor growing conditions and cultural systems.

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Ellagic acid in tissue extracts of green and red-ripe strawberries (Fragaria × ananassa Duch.) was detected and quantified by HPLC. Ellagic acid content of green fruit pulp ranged from 1.32 to 8.43 mg·g-1 of tissue dry weight (mean 3.36 mg·g-l) and in achenes of green fruit from 1.32 to 20.73 mg·g-1 (mean 7.24). Ellagic acid content of red fruit pulp at one location for 35 cultivars and selections ranged from 0.43 to 4.64 mg·g-1 of dry weight (mean 1.55) and from 0.43 to 3.47 mg·g-l (mean 1.45) for 15 clones at another location. Achenes from red-ripe fruit ranged from 1.37 to 21.65 mg·g-1 (mean 8.46) for 34 clones at one location and from 2.81 to 18.37 mg·g-1 (mean 8.93) for 15 clones at another location. Leaf ellagic acid content ranged from 8.08 to 32.30 mg·g-1 of dry weight (mean 14.71) for 13 clones examined. Large differences in ellagic acid content were found among cultivars, but tissue values were not consistent within cultivars. Values from one tissue type did not correlate consistently with values of the other tissues. Sufficient variation was found among cultivars to suggest that increased ellagic acid levels may be achieved in progeny from crosses with selected parental material.

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