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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.
Proton Density and T2 maps were created throughout the dormant season in `Anna' and Northern Spy′ apple cultlvars. The percentige of oixels with 15-25 ms T2 time increased from 30% in both cultlvars at the beginning of dormancy to 80 and 72% respectively, by the end of dormancy. The conversion in `Anna' was rapid and in `Northern spy was slow. Growth occured only when conversion of bound to free water reached 70% of the total number of pixels. Buds entered into a transitional phase when conversion of water reached 50%. Buds in the transitional phase are willing to respond to treatments aimed to end dormancy. Thus dormancy can be divided into two major part based on the boundness of freeness of water in the bud.
Magnetic resonance imaging estimates unreasonably high T2 times when creating T2 images in woody plants when tissues contain a limited amount of water. We developed a system to correct such images. Tissue distribution of proton density and states of water were determined by creating images of proton density and T2 relaxation times in summerdormant (paradormant) apple (Malus domestica Borkh.) buds. These images reveal that the proton density and water states obviously are not distributed uniformly in the bud and stem; but, the distribution of water depends greatly on the tissue type (bark, xylem, or meristem of the stem), and there are differences in the states of water even within the same tissue. At low proton density T2, calculated relaxation times were unreasonably high in tissues, with the exception of meristem of the shoot. In buds that were induced to grow and in which proton density was higher, T2 times appeared as expected. Variance of T2 times in tissues containing little water was 50 times higher than in those with a higher water content. Data with such high variance were excluded from the images; thus, the image was “corrected.” Corrected images of T2 times fit the distribution of water indicated by the proton density images well.
Dormant and chilled highbush blueberry (Vaccinium corymbosum L.) flower buds were examined by magnetic resonance imaging (MRI). T2 relaxation times of water molecules were too short to create images from flowers within buds that were dormant and had received no chilling, but they were sufficiently long to create images from buds that had their chilling requirement satisfied. To explain the change in relaxation times, we concluded that water is present in a motionally restricted form in flowers of dormant blueberry buds and in a freer form in flowers of buds after the chilling requirement has been satisfied. T2 values for chilled blueberry buds indicated that one population of water molecules with a detectable T2 time was present in flowers of chilled buds with a relaxation time of ≈8 to 15 ms.
Strawberry fruit were non-destructively examined by spin-echo nuclear magnetic resonance imaging (NMRI) to determine internal structure, proton (water) density and T2 proton relaxation times of healthy fruit in order to determine physical and water density and water binding changes due to injury and fungal infection. Detached strawberry flower buds prior to anthesis, anthesis, developing receptacles, and fruit from green, white, to red-ripe stages were examined to determine variations in normal fruit. Fruit rots caused by Botrytis cinerea, Hainesia lythri, and Colletotrichum acutatum were compared. B. cinerea causes a watery rot that occurs as a uniform gradient from infected to healthy tissue, whereas C. acutatum causes a dry rot with an indistinct border between healthy and infected tissue. H. lythri, on the other hand, causes a rot that forms a distinct and disparate boundary between the advancing infection and healthy tissue; the infected portion of the fruit may be extracted as a mass of hyphae and fruit tissue that retains its shape. NMRI may be a useful tool for identifying enzyme systems of pathogens involved in fruit decay.
Magnetic resonance imaging was used to determine water states in paradormant apple (Malus domestica Borkh.) buds and during early events when buds resumed growth. Proton density and states of water were determined by creating image maps of proton density and relaxation times (T2). Summer-dormant (paradormant) buds had T2 relaxation times up to 30 ms. This water in bud tissues is considered relatively free compared to water that had T2 relaxation times of <1 ms in other parts of the stem and bark. Buds were forced to grow either by pruning off the terminal bud or by starting the bud with thidiazuron (TDZ). Both treatments gave essentially the same results. After treatment, buds started to grow immediately and water moved into the stem and into the bud. As there was more free water in the bud, T2 values ranged up to 50 ms. There appeared to be an inhibitory gradient down on the shoot, which was removed temporarily by excising the top bud. However, between the 2nd and 10th day after removal of the top bud this dominance was reinstated by the highest bud on the stem, which eventually formed a shoot. TDZ treatment overcame this inhibitory gradient effect. There was also a growth potential gradient coinciding with the inhibitory gradient. The growth of lower buds was much slower than that of the upper buds. The growth potential gradient was not overcome by TDZ treatments.