A-Shiang Hwang

Associate Researcher Horticulturist of

Department of Horticulture

Chia-Yi Agricultural Experiment Station

Taiwan Agricultural Research Institute

Phone :886-5-2771341ext 560

Fax:886-5-2773630

Education

B. S. (1978) in Horticulture, National Chung-Hsing University

M. S. (1987) in Horticulture, National Taiwan University

Area of Research Interest

Citrus breeding

Citrus cultural practice

Fruit crop physiology

Publication

Journal papers

1.Hwang, A. S. and C. C. Lin. 1986. Identification of sexual embryo by genetic marker in polyembryony citrus. J. Chinses Soc. Hort. Sci. 32(2):103-108.

Calamondin (C. madurenis) was pollinated with two varieties of pummelo (C. grandis (Linn.) Osbeck), 'Mi-youh' and 'Wan-pai-youh'. Xenia phenomenon was found in hybrid seeds, and zygotic embryos were identified by its color. In nine months old, all the seedlings germinated from cream embryos, which have large leaves are zygotic, and nucellar seedlings germinated from yellow green embryos. Among the five survived seedlings germinated from pale yellow green embryos, four of them are zygotic and the other one is nucellar.

2.Hwang, A. S. 1987 Embryos development of 'Shueh-ken' orange at different growing stages. Jour. Agric. Res. China, 36(4):367-371.

'Shueh-ken' orange (C. sinensis Osbeck) was pollinated with 'Valencia', 'Pineapple' and trifoliate oranges. Fruits were harvested 80, 120, and 140 days after pollination, numbers of embryos were counted with dissecting microscope, and the embryos of hybrid seeds crossed by trifoliate orange were cultured on MS medium supplemented with 7.5g/1 agar and 20g/1 sucrose.

Average number of embryos increased slightly throughout the growing stages and that of the smallest embryos (stage l) decreased significantly from 80 to 100 days after pollination. These implied that most embryos began to develop at the same time. The percentage of zygotic seedling crossed by trifoliate increased as seeds were more mature, so it was recommended that seeds about to mature were preferred if embryos were induced to germinate with the help of embryo culture.

3.Hwang, A. S. 1991 The polyembryony and identification of zygotic seedlings of lemon. Jour. Agric. Res. China 40(2):225-232.

The number of embryos of 'Eureka' and 'Lisbon' lemon was investigated during the development of the fruits. Open-pollinated fruits were harvested on June 5 and June 21, and hybrid fruits were harvested in early August. All the mean numbers of embryo per seeds were less then 2. 0, and 40 % to 68 % monoembryo seeds of hybrid fruits were found. These indicated that lemon contain low degree of polyembryony. Zygotic seedlings of hybrid seeds were identified by leaf morphology, and 73% zygotic seedlings of Eureka lemon crossed by trifoliate orange and 38% to 56% zygotic seedlings of lemon crossed by sweet orange were obtained. This variation might be influenced by the difference of leaf morphology among the pollen parents. The color of growing shoot of these zygotic seedlings was observed from February to March in 1990. Eighty-nine to seventy percent of the zygotic seedlings were green, and the others were purplish as the seed parent. The results showed that both the leaf morphology and the color of young shoot could be used to distinguish the zygotic from nucellar seedlings of lemon crossed by other citrus species.

4.Hwang, A. S. 1993 Effect of bagging on fruit growth and quality of 'Wentan' pummelo (Citrus grandis (L.) Osbeck) and the temperature inside the bag. J. Chinese Soc. Hort. Sci. 39(4):199-208.

To investigate the effect of bagging on fruit growth and quality of 'Wentan' pummelo, the fruits were bagged with white or brown paper bags on 24 May, 26th June and 25th July . Fruit size was measured on each day of bagging and on September 11 after the fruits were harvested. Temperatures inside the bags in different positions of the canopy were recorded from middle to late August.

The results showed that fruit character including size, weight, specific gravity, fruit shape, rind thickness, rind texture, sugar content and flavor were not significantly different among the treatments. In daytime the temperature differences inside and outside the bags can be as high as 9 ⁰C. The differences of relative humidity were 5 to 10%. The temperatures increased inside the bags were related to the intensity of solar radiation. The growth rate of fruits which bagged earliest was lowest, but that was not significantly different among the treatments.The color of fruit peel was analyzed on one day and one week after harvesting. L values of the fruits bagged with white bag were higher than those of the fruits bagged with brown bag or without bagging, but the a and b values were not significantly different among the treatments. These results explained that the fruits without bagging were a little dark greener than the other treatments, but the difference was not much that it can not be visually distinguished.

5.Hwang, A. S. and K. Y. Ho. 1994 Relationship between growth vigor of citrus trees and damage by white-spotted longicorn beetles. Chinese J. Entomol. 14:271-275.

The damage to citrus species by white-spotted longicorn beetles (Anoplophhora maculata Thomson) was correlated with the growth vigor of the trees, and declined trees tend to be damaged by the insects. In early May, 40.64% Furadan ( F. P. diluted with 100-fold water ) was sprayed on the trunks, and larvae of the beetles in the trunks were investigated from mid to late July. The decision coefficients (R ) between the fraction of injured tree and the rating of growth vigor were between 0.944 and 0.623 for various species of citrus.

6.Hwang, A. S. and H. T. Hsu. 1994 Alternate bearing and chemical thinning of 'Ponkan' mandarin .Jour. Agric. Res. China 43(3):320-329.

To adjust the alternate bearing of 'Ponkan' mandarin (Citrus reticulata Blanco), experiments were conducted in two commercial orchards located in Chia-yi and Tong-shih (planted in 1979 and 1983 respectively). Five single-tree replicates were sprayed with NAA at rate 0, 200, 300, 400 and 500 ppm in early May (50 day after full bloom), and fruit drop, yield and fruit quality were investigated. The fraction of fruit thinned correlated significantly with the concentration of NAA. Fruit weight and the percentage of larger fruit sampled from the outer skirt of canopy varied insignificantly for various treatments. The alternate bearing intensity (ABI) of successive years correlated with the yield, fruit weight and number of fruit of the pervious year. The yield to diminish alternate bearing (ABI=0) was calculated by regression analysis of ABI and the number of fruit of the previous year, which was 648 fruits for 1991 ,531 fruits for 1992 and 609 fruits for the three years. The result showed that optimum yield to alleviate alternate bearing may be estimated by this model.

Conference papers

1.Hwang, A. S. and C. S. Yeuh 1989 Studies on polyembryony and improvement of breeding efficiency of oranges. Proceeding of symposium on the researches and development of citrus in Taiwan. Taiwan agricultural Research Institute special publication No. 27 p28-38.

In order to improve the breeding efficiency in oranges (Citrus sinensis), the polyembryony and ratio of zygotic progenies were studied. 'Lin-cheng' (C. sinennsis) and Tankan (C. tankan) were polyembryonic, their open-pollinated fruits were picked at different growing stages, and number of embryos were counted with dissecting microscope. Among these species, 'Liu-cheng' had higher number of embryos, but Tankan contained lower degree of polyembryony. The mean number of embryos of 'Liu-cheng' orange changed greatly during the development of seeds, it increased from mid June to early August, the number of embryos might excess 20, then the number of distinguishable embryos decreased to about 10 in early October. Mean number of embryos produced per seed of Tankan was mostly less than 5 during the development of seeds.

'Liu-cheng' orange and Tankan pollinated with trifoliate, the percentageof fruit set and seeds per fruit were generally lower in comparing with those pollinated with pummelos or sweet oranges . Percentage of zygotic seedlings of 'Liu-cheng' crossed by pummelos and trifoliate were 6.6% and 0%, respectively.

The percentage of monoembryo seeds of Tankan crossed by sweet oranges changed greatly at different years. In 1985, all the 1599 hybrid seeds were polyembryo, but 40 % monoembryo seeds were found in 3326 hybrid seeds in the following year. Crosses were made within Citrus sinensis, the percentage of zygotic seedlings which can be distinguished from leaf morphology varied from 2.7% to 10.7%.

2.Hwang, A. S ., C. Y. Cheng and P. Lin 1989 Effect of water control on concentrations of carbohydrates and flower formation of citrus. Proceeding of symposium on the Researches and Development of Citrus in Taiwan. Taiwan agricultural research institute special publication No.27, p.84-97.

Two experiments were conducted to investigate the effect of drought oncarbohydrate content and flower formation of citrus. (I) Six months old Rough lemon seedlings were subjected to a water-stressed period of 28 days till 32% RWC (Relative water content) of newly full expended leaves. (2) Liu-cheng orange buddlings of nine months old were water-controlled for 2 months.

When Rough lemon seedlings were water stressed, alcohol soluble sugar increased slightly, and starch decreased before the mature leaaves wilted. After rewatering there was a lag period of growth, and starch accumualated, its concentration reached 13 % to 17 % of dry weight.

Because dry weight of leaf (g/m2) of water-stressed seedlings and DW/FW ratio of rewatered seedlings changed in accordance with the content of tolal carbohydrate, it should be noticed that nutrient concentration may be influenced if dry weight is used as a basis.

A significant effect of water control on flower bud formation wasobserved when container-grown Liu-cheng orange young trees were irrigated 150 ml/week for each tree. We found water-controlled trees producde 45.8 flowers per tree comparing with 20.0 flowers of well-irrigated trees after the treatment of 2 months. Soluble sugar content in water-controlled trees was 2.7 times hightt than of well-irrigated trees.

3.Hwang , A. S. and H. T. Hsu 1995 Citrus breeding-ldentification, cultre and priliminray selection of hybrid . Proceeding of symposium research and development of citrus in taiwan. Taiwan Agricultural Research Institute special publication No.51, p.43-52.

To develop citrus cultivars, 'Tankan' (Citrus tankan), 'Wentan' (C. grandis), Kiyomi and 'Fortune' were used as major seed parents and pollinated with sweet oranges and mandarins. The polyembryony of some cultivars were investigated for choosing suitable seed parents. 'Liu-cheng' had higher number of embryos, but 'Tankan', Calamondin and lemon contained low degree of polyembryony and produced certain ratio of zygotic seedlings. ln the past years, 24,000 seedlings were raised and zygotic seedlings of polyembryonic seed parents were identifid from the nucellar by leaf morphology, embryo color and color of young shoot . A total of 5,960 zygotic seedlings were planted in field in high-density planting and single-trunk trained. Flowering rate of seedlings of the major combinations in 5 years varied from 60.7% ('Fortune' x 'Chandler') to 17.5% ('Wentan' x sweet oranges). The period of juvenile phase seems to be inherented essentially by seed parent. Seedlings were more resistant to citrus canker as they were aging. Ten promising hybrids with the characters of few seeds, early maturity, high quality or resistant to citrus canker were selected and propagated for further test in different area.

4.Hwang, A. S. and H. T . Hsu 1995 Chemical thinning and estimation of optimum yield in 'Ponkan' mandarin. Research and development of citrus in taiwan. Taiwan agricultural research institute special publication No.51, p.59-70.

To adjust the alternate bearing of 'Ponkan' mandarin (Citrus reticulata Blanco), experiments were conducted in two commercial orchards located in Chia-yi and Tong-shih. Five singe-tree replicates were sprayed with NAA at 0, 200 ,300,400 and 500 ppm in early May, and fruit drop, yield and quality were investigated. The fraction of fruit thinned was significantly correlated with the concentration of NAA. Fruit weight and the percentage of larger fruit increased in treated trees, but sugar and acid content of the fruit sampled from the outer skirt of canopy varied insignificantly for various treatments. The alternate bearing intensity (ABI) of succesive years was correlated with the yield, fruit weight and number of fruit of the pervious year. The yield to diminish alternate bearing (ABI=0) was calculated by regression analysis of ABI and the number of fruit of the previous year. The result showed that optimum yield to alleviate alternate bearing may be eastimated by this model.

5.Ho, K. Y., K. C. Lo., C. Y. Lee., A.S . Hwang 1995 Ecology and control of the white-spotted longicorn breetle on citrus. Proceeding of Research and development of citrus in Taiwan. Taiwan agricultural research institute special publication No.51 P.263-278.

The white-spotted longicorn beetle, Anoplophora macularia (Thomson) is the most destructive insect pest of citrus tree trunks. It injuries more than 50 host plants. There is only one generation per year in Taiwan and the adult often emergences from early April through October with a peak on June. The adult needs to feed on the new leaves and twigs,and after a few days it begins to do copulation and oviposition. Mostly, the female bites an incision with her mouthpart and deposits an egg inside at the base part of tree. The eggs hatched within 7-10 days and the young larvae fed on the bark first, and then bored into the solid wood after the third instar that might cause the plant to die. The control methods include the white-brushing (with Lime and Sulfur), chemical spraying (on tree base or canopy to avoid egg depositing or to kill the adult), mechanical method (hand picking, wire net and iron wire), biological control (egg and larval parasitic wasps and fungus Beauveria spp.) and cultural practice (sanitation on tree base, irrigation, fertilization, tree vigor and tolerance variety), etc.

Other publications

1. Hwang, A. S. 1987 Effect of drought on the physiology of Citrus - Growth, nutritional status and change of MACC and ACC contents. MS thesis of Taiwan University.