Roger H. Lawson

Chrysanthemum stunt: A viroid disease

Abstract Infectious material in crude extracts from chrysanthemum stunt-affected cineraria or chrysanthemum leaves sediments heterogeneously, some pelleting during low-speed centrifugation, some during high-speed centrifugation. High-speed supernatants, however, always contain appreciable amounts of infectious material. Treatment of crude extracts with chloroform-butanol, phenol, or ethanol does not reduce infectivity. The infectious agent is sensitive to treatment with ribonuclease, but not to treatment with deoxyribonuclease. The agent can be concentrated by ethanol precipitation and resuspension in a smaller buffer volume. Partial purification of the infectious agent by methods developed for the purification of potato spindle tuber viroid (PSTV), followed by analysis in linear-log sucrose density gradients and by electrophoresis in 20% polyacrylamide gels demonstrated that the stunt agent is a low molecular weight RNA. Its electrophoretic mobility is somewhat greater than that of PSTV. Thus, the causative agent of the chrysanthemum stunt disease is a viroid similar to, but distinct from, PSTV.

The establishment of cell suspension cultures ofGladiolus that regenerate plants

SummaryInflorencence stalks from greenhouse-grownGladiolus plants of the cultivars ‘Blue Isle’ and ‘Hunting Song’ cultured on a Murashige and Skoog basal salts medium supplemented with 53.6 μM 1-napthaleneacetic acid formed a compact, not friable type of callus that regenerated plantlets. Cormel slices and intact plantlets of three cultivars (‘Peter Pears’, ‘Rosa Supreme’, ‘Jenny Lee’) propagated through tissue culture formed a friable type of callus when cultured on Murashige and Skoog basal salts medium supplemented with 2,4-dichlorophenoxyacetic acid. This friable callus readily formed a cell suspension when the callus was placed in a liquid medium. Plants were regenerated from two-month-old suspension cell cultures of the commercial cultivar ‘Peter Pears’ after the suspension cells had been cultured on solid medium.

Development of pinwheel inclusions associated with sweet potato russet crack virus

Abstract Developmental changes associated with pinwheel inclusions induced by sweet potato russet crack virus in Ipomoea setosa were studied over a time course. Bundle inclusions, closely associated with plasmodesmata, were first observed apposed to the cell wall in inoculated leaves after 5 days. Pinwheel configurations appearing in the cytoplasm could be traced to the cell wall in serial section. The centers of the pinwheels were observed directly over the plasmodesmatol openings. Cytoplasmic strands with viruslike particles between the membranes were present at 5 days. Seven days after inoculation may bundles were perpendicular to the wall, but some were separated from the wall. Endoplasmic reticulum was present at the base of the bundles. Rows of filamentous particles separated by a dark-staining matrix were present in some cells. Loops and arcs were occasionally present. After 10 days many bundle inclusions were completely dissociated from the plasmalemma, and bundles were randomly oriented in the cytoplasm. Loops and circles resulting from dissociated pinwheel septa were common, and intact pinwheels were absent in some cells. The sequence of pinwheel development and maturation in systemically infected tissue was similar to the sequence of development in the inoculated leaf. Crystalline inclusions in plants sampled after 2 months were present in lower leaves. Strandlike particles, possibly virus particles, were associated with membranes in plants infected 2 and 3 months. We conclude that pinwheel inclusions induced by russet crack virus change in form and position; and a sequence of inclusion development can be observed when inoculated and systemically infected tissues are sampled at several intervals.

1-aminocyclopropane-1-carboxylic-acid-dependent ethylene production during re-formation of vacuoles in evacuolated protoplasts of Petunia hybrida

SummaryEthylene formation from 1-aminocycloprane-1-carboxylic acid (ACC) was studied in whole protoplasts, evaluolated protoplasts and isolated vacuoles from mesophyll cells of Petunia hybrida L. cv. Pink Magic. The re-formation of the large, central vacuole in evacuolated protoplasts and morphological characteristics of both types of protoplasts were examined by electron microscopy. Both the normal, whole protoplasts and vacuoles isolated from them produced ethylene from ACC at similar rates. Freshly-prepared evacuolated protoplasts had lost the capacity to produce ethylene. Re-formation of the central vacuole in these evacuolated protoplasts occurred between 14 to 17 h of incubation in the recovery medium and was followed by the development of ethyleneforming activity. Both these processes were inhibited by cycloheximide, indicating a requirement for new protein synthesis. Light stimulated the conversion of ACC to ethylene in both the regenerating, whole protoplasts and the evacuolated protoplasts that had re-formed the central vacuole.

Evaluation of Curcuma as potted plants and cut flowers

Summary Sixteen accessions of Curcuma germplasm that included C. alismatifolia ‘Chiang Mai Pink’, and ‘Lady Di’ and C. thorelii ‘Chiang Mai Snow’ and C. alismatifolia ‘Pink’, C. parviflora ‘White Angel’, and C. sp. ‘CMU Pride’ were evaluated for use as potted plants or as cut flowers. All cultivars of C. alismatifolia and C. thorelii ‘Chiang Mai Snow’ were considered suitable for cut-flower and pot-plant use, respectively. C. parviflora ‘White Angel’ also proved to be a suitable cultivar for potted plant production. Optimum storage temperatures for rhizomes in relation to greenhouse forcing and ethanol-soluble glucose, fructose and sucrose concentrations were determined. Storing rhizomes at 25° – 30°C for 2 – 3 months after harvest is recommended to break dormancy. Plants of C. parviflora ‘White Angel’ flowered 50 – 89 d after potting and can be used as potted plants. Plants of C. alismatifolia flowered 96 – 133 d after potting, with floral stem-lengths suitable as cut flowers. High levels of boron or manganese were correlated with burn symptoms at the margins of the leaves [‘leaf-margin burn’ (‘LMB’)] and were observed in old leaves of ‘CMU Pride’ at flowering. Levels of ethanol-soluble fructose, glucose and sucrose in the tuberous roots of Curcuma were higher than the levels in rhizomes, and increased as storage temperatures increased. Accelerated leaf emergence from rhizomes stored at 30°C took 16 d and was associated with increases in glucose and fructose contents. Very similar morphological characters between C. thorelii ‘Chiang Mai Snow’ and C. parviflora ‘White Angel’ emphasised that identification of Curcuma accessions using DNA-markers is required for future studies.

Propagation and Transplant Production Technology of New Floral Crops

In 1982 the new crops research program was initiated in the Florist and Nursery Crops Laboratory to increase the diversity of florist crop germplasm in the United States. Anigozanthos, Chamelaucium, Correa, a dwarf form of Eustoma grandiflorum ‘Little Blue Belle’, Chamelaucium, Cupressus, and other crops have been introduced to the industry with information that describes propagation, culture, and controlled flowering. Rooting of cutting or in vitro tissue culture propagation of new crops had included Achimenantha, Chamelaucium uncinatum, ‘Purple Pride’, and Eustoma grandiflorum, ‘Little Belle Blue’, Ornithogalum dubium, Lachenalia aloides, and Lilium. In addition, a new production technology using bulbils as propagules was developed for Lilium elegans, Asiatic hybrid lily. This production technology is discussed.

Pathogen Detection and Elimination

Detection of a pathogen is an essential step in plant disease diagnosis. Diagnosis of biotic pathogens requires a knowledge of biotic pathogens and factors in the environment that are involved in disease development. Disease diagnosis is often an art based on experience with a particular crop that allows a series of observations of the plant in both a diseased and healthy state and from knowing the often subtle differences in symptoms and their variability over-time (13). It is also essential to observe and interpret the significance and implications of changing patterns of disease distribution that occur over time.

Source of Boron in Curcuma for Burn Symptoms at Leaf Margins

ABSTRACT This study was initiated to investigate the source of boron (B) accumulated in margins of old leaves of Curcuma ‘Chiangmai University Pride’ (‘CMU Pride’). Nutrient elements were analyzed from different parts of the rhizome before potting and from whole rhizomes at harvest, and different leaf locations of young and old leaves during forcing in coarse sand medium. Plants were fertilized with solutions lacking B during the forcing period. Leaf-margin burn symptoms in old leaves of ‘CMU Pride’ could result from the combination of high levels of B and low total N levels. High levels of manganese (Mn) may not be involved in leaf margin-burn symptoms. Boron accumulated in the outer region of the old leaves could result from following evaporation of gutatted water droplets containing dissolved B. High levels of B in the edge of the old leaves may not be transported from the rhizomes.