Peter H. Lovell

Anatomical changes during adventitious root formation

Organization is one of the most characteristic traits of living organisms. It is especially conspicuous in the orderly growth that every organism undergoes and which produces the specific forms so characteristic of a particular species [1]. The evidence for biological organization is manifested in studies in which the normal processes of growth and development are modified experimentally, e.g. by removing parts of the growing body. Thus, a ‘cutting’ removed from a plant, under appropriate conditions, may produce a new root system and finally an entire individual with a balanced ratio of root to shoot. These regeneration processes are present in a great range of plants. Roots that originate in locations other than from the embryo or as branches of the primary root are termed adventitious [2, 3]. They may arise spontaneously on intact plants, especially at nodes of prostrate stems and on rhizomes, or stolons or they may develop only as a response to damage when part of the plant has been deliberately or accidentally severed from the existing root system. This involves various anatomical changes associated with wound responses in addition to those involved in root formation itself. Adventitious roots are produced vigorously and rapidly in some species under appropriate conditions, but much less readily in others, and plants can be grouped according to their ease of rooting (Fig. 1).

Environmental factors controlling germination of Leptospermum scoparium (manuka)

Abstract Laboratory studies using seed of Leptospermum seoparium J. R. et G. Forst. collected from tagged trees in the Waitakere Ranges near Auckland showed that there was a low overall germination percentage but substantial variation in germination from tree to tree. Germination rate but not final percentage was affected by temperature and by alternating periods of dehydration WIth periods of adequate availability of water. Only a very low total incident radiation was necessary for germination but germination was reduced 10 the dark. It is probable that the low germination percentage is a result of a high proportion of non-VIable seed. There was no evidence of dormancy and, in the Auckland region, it is likely that the major ‘seed bank’is present in the unshed capsules rather than on the ground surface.

The effects of light and cotyledon age on growth and root formation in excised cotyledons of Sinapis alba L.

SummaryRoot formation on excised mustard cotyledons was found to be determined by cotyledon age at excision and by light. Light treatment after excision enhanced root production in cotyledons excised 6 hours to 6 days after the start of imbibition and was essential for root production in cotyledons older than 6 days at excision. Three or more 12 hour light periods after excision were sufficient to induce root production in almost 100% of 7 day old cotyledons. The interposition of up to 5 days of darkness between excision and subsequent culture in the light did not reduce the final rooting percentage but delayed the onset of rooting by a time equivalent to the length of the dark period. The dry weight values of the cotyledons were directly related to the total light energy received after excision.The age and light effects on rooting may be mediated by their effects on the rate of breakdown and on the total levels of available reserves present in the cotyledons.

Seasonal variation in seedfall and germination of Leptospermum scoparium (manuka)

Abstract Field studies on the seedfall and germination of Leptospermum scoparium J. R. et G. Forst showed that viable seed is shed throughout the year. It was found that there is a significant seasonal pattern to both seedfall and germination. Peak seed fall occurred in October and January, although capsule-borne seeds made an important contribution to the October peak. Germination was found to be highest in mid-winter and early spring. Analysis is described of the possible role of climatic factors in controlling seed fall and germination. No simple model could be found to account for the observed pattern of seed fall. However, a highly significantmodel (involving temperature and moisture regime) could account for the observed pattern of germination. The significance of these relationships is discussed in the context of the ecology of the species.

Flower senescence in monocotyledons: A taxonomic survey

Abstract Flower senescence was observed in representatives of 102 genera from 33 monocotyledon families. This is the first comparative study to cover such a wide range of monocotyledons. All of the species studied are of horticultural importance as ornamentals or cut flowers. Observations were made on attached flowers (i.e., still on the plant) on plants growing under cultured conditions, and on detached flowers held in water. Emasculation and style removal was also performed on some of the flowers to prevent pollination occurring. Abscission of unpollinated flowers, and flowers that are persistent regardless of pollination, were both widespread. In contrast, abscission of floral parts (perianth, style, stamens) was much less common, occurring predominantly in the Liliales. This database will form the starting point for more detailed studies of senescence and variation between cultivars.

Variation in cypsela morphology in Soliva valdiviana and S. pterosperma (Anthemideae, Asteraceae) in a local population at Auckland, New Zealand

Abstract Soliva valdiviana and Soliva pterosperma are annual species of Composites, native to South America. They were first recorded in New Zealand about 100 years ago. Soliva taxonomy relies heavily on cypsela shape, although leaf shape has also been used. The shapes of cypselas of S. valdiviana and S. pterosperma are very distinctive and quite different from each other. Collections of cypselas from Old Government House grounds, Auckland showed that, in addition to S. valdiviana and S. pterosperma, a continuum of intermediate-shaped cypselas between the two species was present. Sometimes a wide range of cypsela shapes could be collected from an area as small as 100 cm2. The variation was not due to differences in cypsela maturity, nor to packaging effects within a capitulum. There were only very minor differences in cypsela shape between capitula on the same plant and plants bred true for cypsela shape. Observations on flower and capitulum structures suggest that pollen from the central, tubular flowers...

Value of morphological characters for cultivar identification in strawberry (Fragaria x ananassa)

Abstract Strawberry (Fragaria × ananassa Duch.), like many other crops, has large numbers of cultivars both in breeding programmes and in commercial production. Problems with the accurate identification of cultivars have arisen. These difficulties are exacerbated by the need for unequivocal identification by vegetative characters alone when plants are clonally propagated from elite stocks before transplanting for fruit production. Thus, accurate identification at all stages of plant growth is essential if costly errors are to be avoided. In New Zealand, the varieties are characterised solely by morphological characters. An analysis of 17 strawberry cultivars in Auckland showed that there is substantial intra‐cultivar variability for many of the characters. This, when coupled with poor discrimination between cultivars for many of the characters, leads to difficulty in their use for identification purposes. Additionally, it was often found that our profile for a cultivar differed from that in the New Zealand Plant Variety Rights (PVR) description. Furthermore, there were often differences in the rating of the morphological characters between the New Zealand PVR description and the United States Patent for the same cultivar. However, a cluster of 14 vegetative, flower, and fruit characters could be used to identify the 17 cultivars used in this study. A significant problem of identification still remains for the plant breeder/propagator who deals almost exclusively with vegetative plants because vegetative characters alone are not sufficient for accurate identification.

Architecture of a clonal population of Muehlenbeckia astonii Petrie (Polygonaceae), a divaricating shrub endemic to New Zealand

Abstract Muehlenbeckia astonii Petrie is a compact, divaricating shrub. It produces both orthotopic and plagiotropic shoots but after a period of time the orthotopic shoots revert to a plagiotropic form. Orthotropic shoots differ from plagiotropic ones in that the internodes are longer, the shoots more erect and much straighter for the first 10-15 intemodes. A clonal population of two-year-old cuttings, taken from a female plant, was grown outdoors in pots. Those cuttings supplied with a balanced nutrient solution were more vigorous and produced more second-order orthotropic shoots than those not provided with nutrient. However, nutrient level did not affect the ultimate divaricating nature of the shoots. The vigour of the shoots varied. Generally, a shoot grew vigorously for the first season producing many other shoots of higher orders; then extension of the second-order axis ceased and further growth was restricted to the higher-order laterals. Most of the growth was carried out by shoots initiated in t...

In vitro abscission of kauri (Agathis australis) branches

Abstract When nodal explants from tips of horizontal branches of seedling Agathis australis (Araucariaceae) are cultured in vitro, the distal 3 mm of internode progresses through a series of morphological and anatomical changes, and ultimately detaches. Changes include: desiccation; regional chlorosis; internode swelling associated with proliferation and radial expansion of cortical parenchyma; interruption of vascular contiguity by invading vascular parenchyma; necrosis and separation. Explains from material older than one growth flush, and those from orthotropic axes, do not exhibit this syndrome. Second‐generation explants show internode abscission, regardless of age of parent material. The technique may be a useful experimental system for studying branch cladoptosis in woody species.

Bands of root hairs are produced in tomato (Lycopersicon esculentum) in response to specific combinations of thermoperiods and photoperiods

Abstract Tomato (Lycopersicon esculentum) seedlings were grown in non‐aerated culture solution in a controlled environment under 10 different combinations of photoperiod and thermoperiod. It was found that the pattern of distribution of root hairs was controlled by the photoperiod and thermoperiod. Under a diurnal rhythm consisting of a 16/8 h photoperiod, at temperatures of 25°C/15°C, regions of the root had bands of hairs that were separated by hairless regions. After 5 days under these conditions, four bands of hairs were most commonly found. Other combinations of light and temperature also gave rise to bands of root hairs, but the bands were fewer and less defined. A lower night temperature, together with 8 h of darkness, switched off root‐hair production. These findings are consistent with the hypothesis that all epidermal cells in tomato are “switched on” for hair production, but that this state can be altered by specific environmental conditions.