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- Author or Editor: John L. Maas x
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.
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.
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.
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.
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.
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.
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.
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.
Fruit quality of 24 selected strawberry cultivars and selections were evaluated. There were great variations in the contents of soluble solids, titratable acidity, carbohydrates, organic acids, and ascorbic acid among different cultivars, reflecting primary genetic differences. Fructose, glucose, and sucrose were found to be the three major sugars, comprising >65% of the total soluble solids in strawberry. Fruit contained lower sucrose compared to fructose and glucose, whereas leaves contained comparable amounts of fructose, glucose, and sucrose. Citric acid was the major organic acid in strawberries. Strawberries were also rich in ascorbic acid. Leaves were much higher in ascorbic acid than fruit. There appeared to be no correlation between fruit and leaves on carbohydrate, organic acid, and ascorbic acid contents.
We have determined in tests conducted both at Beltsville and Poplarville that several strawberry isolates of Colletotrichum acutatum, C. gloeosporioides and C. fragariae produce toxin-like compounds in culture. Crude culture filtrates (CFI elicited general and specific responses in tomato and strawberry plants. Tomato plants initially were used because they are highly responsive to toxins in general, whereas the reaction of strawberry plants apparently is greatly affected by environmental and nutritional growing conditions of the test plant. Toxin symptoms included leaf chlorosis and wilting, leaf midvein darkening, and plant death when CF was applied to leaves or if seedlings or petioles were immersed into CF. Juvenile tissues appear to be more susceptible to the effects of the toxins than mature tissue. No differences in response to culture filtrates were apparent among those from the Colletotrichum isolates. The putative toxins appear to act differentially with susceptible or resistant strawberry germplasm.