Tree Growth Habit Research Articles

‘Shamrock’ Apple

Abstract ‘Shamrock’ apple (Malus domestica Borkh.) is a green apple nearly identical in appearance, texture, and taste to ‘Granny Smith.’ It differs from ‘Granny Smith’ by maturing 6 weeks earlier and by having a more favorable tree growth habit. It develops full maturity and good quality in northern tree fruit production areas where ‘Granny Smith’ does not mature before cold weather slows growth. ‘Shamrock’ is introduced to allow growers in northern areas to compete with ‘Granny Smith’ imported from production areas with long growing seasons. It also may extend the season for ‘Granny Smith’-type apples where ‘Granny Smith’ is presently grown.

‘Biloxi’, ‘Miami’, and ‘Wichita’ Lagerstroemia

Abstract ‘Biloxi’, ‘Miami’, and ‘Wichita’ are the first introduced tree growth habit Lager-stroemia indica L. × L. fauriei Koehne cultivars that combine mildew resistance, dark trunk bark coloration, and a range of flower colors. Lagerstroemia, commonly referred to as crape-myrtle, is the primary southern summer-flowering small tree, traditionally associated with the colonial era as was the lilac (Syringa vulgaris L.) in the northern frontiers. Crape-myrtle no longer is just a summer-flowering tree, but is a year-round landscape plant with magnificent trunk bark coloration. ‘Natchez’ and ‘Muskogee’ (4), the first U.S. National Arboretum L. indica × L. fauriei hybrids, have become leading nursery production and landscape plants as much for spectacular trunk bark coloration as the flowers. On the other hand, ‘Tuscarora’ (5) and ‘Tuskegee’ (6), both of similar parentage, lack intense bark coloration but are noteworthy cultivars because of the unique coral to dark pink flowers. More recently, the growth habit diversity was extended by the release of ‘Acoma’, ‘Hopi’, ‘Pecos’, and ‘Zuni’ with semi-dwarf growth habits (7). ‘Biloxi’, ‘Miami’, and ‘Wichita’ bring to 17 the U.S. National Arboretum Lagerstroemia cultivar introductions (2, 3).

Assessment of citrus diversity in Ghana

Citrus is among the plant germplasm conserved at the CSIR - Plant Genetic Resources Research Institute (CSIR - PGRRI), Bunso in Ghana; however, due to lack of information on the specific traits of this germplasm at the Institute, the potential diversity within the collection is not yet fully exploited. The objective of this study was to evaluate the morphological diversity among the citrus accessions under conservation at the field genebank of the CSIR - PGRRI, Bunso, Eastern region of Ghana. The various accessions were raised on rough lemon rootstocks, planted using the augmented design. The citrus accessions evaluated include different citrus types suitable for different purposes, such as Flying Dragon for rootstock, Sweet Lime for medicine and Mediterranean Sweet for fruit drink. Late Valencia and Mediterranean Sweet were used as checks. Planting was done at 8 m by 8 m. Apart from watering immediately after planting, the plants grew under natural condition without irrigation. Variability was revealed by all the traits studied, including scion trunk surface, tree shape, tree growth habit and branch angle, based on IPGRI descriptors for citrus. The resulting phylogenic tree clustered the citrus accessions mainly based on known genetic relationships, using the clustering away of citrons from mandarins as an example. Although the morphological traits used in the characterisation were not sophisticated, they were useful in discriminating among the accessions. Based on this study, the citrus genebank at CSIR - PGRRI, Bunso, Eastern region of Ghana contains 44 morphologically distinct accessions. The information generated in this study is important for guiding conservation and utilisation decisions geared towards the improvement of the citrus sub-sector in the country.

The radiosensitivity of gymnosperms II. On the nature of radiation injury and cause of death of Pinus Rigida and P. Strobus after chronic gamma irradiation

Various measurements of and observations on the effects of chronic gamma irradiation of Pinus rigida and P. strobus were made and analyzed. Pinus rigida was exposed for a period of 17–18 years and P. strobus for 7 years. Both species show severe inhibition of growth leading to ultimate death of some trees at daily exposure rates of 6 R/day and lower. At the end of the exposure periods, average length of mature needles of trees receiving the higher exposure rates was less than one-half that of needle lengths of unirradiated trees. The reduced growth of branches and needles and premature shedding of needles yielded a greatly reduced amount of photosynthetic tissue, resulting in small sparse crowns. Such trees had a characteristic appearance similar to that in non-irradiated trees growing under highly unfavorable conditions. In ten-year-old P. strobus trees exposed to about 6 R/day for 7 years, the dry weight of needles on surviving trees was reduced by 75 per cent over controls. In P. strobus exposure rates of 1–2 R/day resulted in a statistically significant (at the 5 per cent level) increase in tree height and mature needle length. Needle dry weight also showed an increase at low exposures though these data were not subjected to statistical analysis. The growth habit and aging process of unirradiated trees competing for raw materials and space within a forest community were compared to the syndrome of chronically irradiated P. rigida and P. strobus trees. The authors propose that the slow decline and eventual death of chronically irradiated trees as well as unirradiated ones growing under other conditions of stress probably result from slow starvation, brought about by a critical reduction in the amount of photosynthetic tissue.

EFFECTS OF EXFLORATION ON PLANT METABOLISM

The practical importance of the proper balance between the vegetative and reproductive processes in fruit crops has stimulated many horticultural investigations seeking to improve our practical control of these functions. Owing to the slow growth, large stature, and perennial habit of fruit trees as well as their delayed response to experimental manipulation, it has been difficult to secure comprehensive data directly. Consequently considerable work has been done on short-lived annuals, like tomatoes, the development of which is known to be comparable to that of fruit trees.