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G.J. Galletta and J.L. Maas

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John L. Maas and M.J. Line

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.

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John L. Maas and Michael J. Line

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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John L. Maas and Gene J. Galletta

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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G.J. Galletta, J.M. Enns and J.L. Maas

The cultivars Allstar, Honeoye, Kent, and Jewel yielded the most successful summer and subsequent spring crops when planted in mid-July from dormant, cold-stored, multiple-crowned, nursery mother plants. Summer fruit sizing during very high temperatures was a problem; fruit number and quality was not. In a second hot year, the same cultivars did not give satisfactory summer crops when planted after late July. The return spring crop was most successful following planting in July rather than August or September, though there was a significant cultivar × planting date interaction for a number of characters. Nursery mother plants were more productive than first daughter plants. `Tristar' outyielded `Seascape' on black poly-mulched beds but not on killed vetch sod beds. `Allstar' runnered freely and produced good crops on three types of raised bed killed sod mulches and on red, blue, and silver-painted black poly raised bed mulches. Compared to the summer-planted, black, poly-mulched standard, `Mohawk' had increased but later yields, when the poly was painted blue, red, or silver, and much later yields, when mulched with recycled paper or wood fiber. The silver and paper treatments depressed fruit size. The wood fiber mulch seems promising for deliberately delaying ripening by lowering soil temperatures under the mulch. Seedling and selection plantings have generally responded favorably to summer planting from potted or “plug” plant stocks on unfumigated soil, thus, shortening the selection and evaluation cycles, with accompanying savings in land, water, fertilizer, and pesticide use.

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John L. Maas, Gene J. Galletta and Barbara J. Smith

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.

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John L. Maas, Gene J. Galletta and Gary D. Stoner

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John L. Maas, Shiow Y. Wang and Gene J. Galletta

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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L.E. Francois, T.J. Donovan and E.V. Maas

Globe artichokes (Cynara scolymus L.) were grown for 2 years in artificially salinized field plots in the irrigated desert area near Brawley, Calif. Saline treatments were imposed by irrigation with waters that contained equal weights of NaCl and CaCl,. Increased incidence and severity of Ca deficiency in the inner bracts of artichoke buds were directly related to increased levels of salinity. The Ca-deficient bracts were subject to infection by species of Botrytis and Erwinia. The number of marketable artichokes was reduced 20% or more when irrigation water salinity exceeded 2.0 dS·m–1, and up to 50% at 10 dS·m–1. Calcium deficiency in the artichoke bud is believed to be the result of disparate Ca distribution among the tissues, which is caused by high transpiration rates in the desert environment and the reduction in root pressure by soil salinity. Elemental analysis of leaf tissues can not be used to predict Ca deficiency within the artichoke buds.

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Shiow Y. Wana, John L. Maas and Gene J. Galletta

Ellagic acid, a putative anticarcinogenic compound, was detected in plants of mayhaw (Crataegus spp.), false strawberry (Duchesnea indica), strawberry (Fragaria spp.), black currant (Ribes nigrum), thornless blackberry (Rubus subgenus Eubatus), red raspberry (Rubus subgenus Idaeobatus), and cranberry (Vaccinium macrocarpon). Large differences in ellagic acid contents have been found among species and cultivars and also among tissues. Ellagic acid content in plant tissues is also affected by environmental factors and shows a seasonal variation in strawberry leaves. A decrease in ellagic acid content of leaves was associated with seasonal decreases in photoperiod and temperature from September to December. Ellagic acid content in the leaves of red raspberry infected with orange rust showed more than a 3-fold increase compared to healthy leaves.