A survey of Japanese pear trees growing in the highlands of northern Thailand revealed that erratic budbreak and flowering are the major problems attributable to the lack of winter chilling and high temperature during the growing season. To analyze the process of flower differentiation under these conditions, experiments were conducted to observe the flowering habit of Japanese pear (Pyrus pyrifolia Nakai cv. Kosui) trees. To simulate tropical conditions, trees were grown in a heated greenhouse made of plastic materials (plastic house) . Flower buds were found to differentiate in the axillary buds of elongating shoot in May, more than one month earlier than shoots on trees grown in open field. Longer shoots produced a larger number of flower buds than shorter shoots. Abscisic acid (ABA) and paclobutrazol treatments depressed the vegetative growth in the plastic house and open field. Paclobutrazol promoted flower set in the plastic house more than in the open field, whereas the reverse was true for ABA. Possible use of growth regulators to stimulate flowering of pear trees in Thailand is discussed.

View full abstract

This report deals with the slash and burn system applies for developing rice fields in the Santa Cruz district of Bolivia. When a field was subjected to slash and burn, weeds started to grow, hindering rice production.
In the first year of the study, broad-leaved weeds and grassy weeds proliferated. However, as both types of weeds died during the winter season trees with roots underground started to grow.
It is generally recognized that in the slash and burn system weeds can be well controlled naturally in the first year. In this report, however, the authors suggest that the weeds must be controlled by using chemicals from the beginning of the first year to increase rice production.
The authors evaluated the effect of herbicides used for the control of tropical weeds and concluded that Stanpyr emulsifiable concentrate was the most effective chemical for the prevention of weed growth.

View full abstract

Light, deep and medium skiffings of branches are applied as pruning techniques for the rejuvenation of tea plants. Although root plowing is considered to be useful to improve soil productivity, it often causes a depression of the vigor of tea plants due to unexpected root cutting.
In this study, we described the effect of pruning of top and root parts on the rejuvenation of old tea plants to develop a practical pruning method.
1. The pruning of top parts of the tea plants improved the growth and yield. Although the pruning of the root parts depressed the vigor of the plants in the first year, the vigor recovered three years after the treatment.
2. Pruning of both top and root parts improved the leaf size and thickness.
3. When only top parts were pruned, the plucking surface tended to be rough due to the increase in the emergence of new sucker shoots and withered branches.
4. Pruning of both top and root parts of old tea plants resulted in an early recovery of yield and improvement of the quality of tea leaves.

View full abstract

In order to improve the devices enabling year-round propagation of cuttings in arid lands, a device equipped with mist nozzles in a tunnel enclosed by a non-woven fabric was developed on an experimental basis for preserving the cuttings. Changes in the air temperature and relative humidity, and rooting conditions of the cuttings subjected to this treatment were compared with other enclosure devices and a control.
The results were as follows :
1. The use of enclosure and enclosure-mist devices was effective for the preservation of cuttings in arid lands.
2. When the inner part of the enclosure was maintained under high humidity conditions, the cuttings were able to survive at a high temperature (35-40°C) for a long period of time.
3. Although the cuttings were exposed to a wide range of temperature and humidity conditions in the day time, when a high humidity was maintained during the night, the survival and rooting percentage of the cuttings were not affected.
4. Temperature decreased by more than 5°C by mist spraying for 1 min and was maintained for about 40 min.
It was concluded that enclosure-mist devices are suitable for the propagation of cuttings in mid summer in arid lands. However, further studies should be carried out on the effect of the structure and thickness of the nonwoven fabric, size of mist particles, and frequency of mist spraying on the maintenance of stable temperature and himidity conditions in the enclosure-mist devices.

View full abstract

Seed growth of the castor-oil plant, cultivar Shanghai, was investigated in order to know the process of determination of the one-seed-weight, which is one of the yield components, using the seeds of flowers whose anthesis dates were recorded. The seed length, width and thickness, increased immediately after flower anthesis. The seed fresh weight markedly increased with the size increment. As the increase in the seed dry weight was minimal during this stage and most of the increase was attributed to the development of the seed coat, the endosperm seemed to be filled with water. After the increase of the seed size was completed, the seed dry weight increased markedly. Most of the dry weight increase was due to the increase of the endosperm weight during this stage. The higher the air temperature during the seed growth, the higher the growth rate of seeds. However, the seed at the full ripe stage became small and light under high air temperature conditions, due to the shortened ripening period. In this experiment, the seed size increased during the 10 to 20 day period after anthesis. The dry weight of seed and endosperm increased during the 15 to 25 day period after the seed size was almost fixed. It appears that the difference in the anthesis dates in the same inflorescence as well as the processes mentioned above should be considered in order to know the process of determination of the one-seed-weight in an inflorescence.

View full abstract

Brown leaf spot disease of kapok, Ceiba pentandra GAERTN, was found in East Java, Indonesia. It was recorded to be prevalent on the seedlings and young trees of kapok. The causal fungus was identified as Pseudocercospora italica (CURZI) DEIGHTON, through the etiological and mycological studies. It grew on PDA at 13 to 30°C with optimum temperature between 20 and 24°C. Employment to product conidia artificially on agar media was unsuccessful. Incubation period was confirmed as 4 weeks through the inoculation experiment.

View full abstract

This investigation was, therefore, carried out for the purpose of developing a new bioassay method, using in vitro microtuber of yam (Dioscorea alata L., cv. Solo Yam), detecting the activity of the endogenous growth substances considered to induce the growth and enlargement of tubers.
The effects of four kinds of media, mineral composition, sucrose concentration (0, 2, 4, 6, 8, 10%), photoperiod (0, 8, 12, 16, 24h) and growth regulators (NAA, IAA, ZR, JA-Me, ABA) on the development of microtubers, roots and shoots in nodal stem segment cultures of D. alata L. (cv. Solo Yam) were evaluated.
Microtuberization in nodal stem segment occurred on all of the media supplemented with growth regulator and sucrose. Among basic media, 1/2 MS medium was the best on microtuber induction. NAA was most effective among the growth regulators. Optimum NAA concentration was 1mg/l. The microtuberization was the highest at the concentration of sucrose 6%.
When the nodal stem segment cultures were held under 0-h photoperiods (total darkness), the tuberization was incredsed markedly compared to those under light condition. It was also noticeable that the culture in medium with NAA produced only microtubers and roots, but no shoots in nodal segments.
In this study, the optimal medium composition for microtuberization in nodal stem segment was found to be 1/2-sterngth MS medium supplemented with 1mg/l NAA and 6% sucrose held under dark condition at 25°C. And it was reasonably cosidered that the microtubers produced could be used for the bioassay detecting the activity of the endogenous growth substances.

View full abstract

Due to the high productivity L. leucocephala is important plant resource in tropical region. The leaves and the culm of L. leucocephala are widely used as feedstuffs and fertilizers because of their high protein and calcium contents but the seeds have not been used effectively. The effect of galactomannan extracted from the seeds of L. leucocephala on serum, liver cholesterol concentration and digestive organ were investigated. The results obtained as follows. Total serum cholesterol and total liver cholesterol concentrations were significantly lower in rats fed L. leucocephala seed galactomannan or guar gum than those fed the fiber free diet + cholesterol. Serum triglyceride, serum phospholipid, and serum high density lipoprotein (HDL) levels were not significantly different among them, but serum very low density lipoprotein (VLDL) + low-density lipoprotein (LDL) cholesterol was markedly decreased. Relative liver weight was significantly lower in rats fed the diets containing water-soluble polysaccharides. The length and weight of the small intestine plus the large intestine were higher in rats fed water-soluble polysaccharide. The length of the small intestine was larger in rats fed the diets containing polysaccharide, the diet containing 5% L. leucocephala seed galactomannan was the most effective.

View full abstract

Cassava (Manihot esculenta CRANTZ) had seldom been a target of organized research due to its image as a crop produced on poor soils by small farmers and consumed by poor people. The crop has been largely unknown to the research community in the developed countries because no production took place in the temperate areas. There have been steady production increases in recent years, in Africa for human consumption and in Asia for processing. In the beginning of the 1970s, an international germplasm development program with a global mandate was established at CIAT, Colombia, South America, where the crop originated and diversified, and another at IITA, Nigeria for African cassava. Since then, national cassava breeding programs have been established and strengthened in many tropical countries. For Asian cassava, the CIAT Asian program has been developing advanced breeding materials in close collaboration with the Thai national cassava research program. Through the network involving national breeding programs in major cassava producing countries and CIAT, many cultivars have been officially released and some of these are now being planted in rapidly expanding areas. The capacity of national breeding programs has much improved simultaneously. I have participated in most of this network development and herein intend to convey these experiences to those younger generation agronomists/breeders, who will hopefully participate in tropical crop breeding in the future.
In this first paper of the series, I introduce the organization of the CIAT/Colombia and CIAT/Thailand breeding programs and report on the collection, maintenance, evaluation and utilization of basic cassava germplasm.

View full abstract