Tae-Myung Yoon

Biological Characterization of Marssonina coronaria Associated with Apple Blotch Disease

Abstract Marssonina coronaria associated with apple blotch disease causes severe premature defoliation, and is widely distributed in Korea. Thirteen isolates were collected from orchards located in Gyeongbuk Province from 2005~2007. All isolates displayed over 99.6% and 99.2% sequence similarity to each other in internal transcribed spacer regions and partial sequences of 28S rDNA, respectively. The isolates were phylogenetically closely related to Chinese isolates. Selected isolates did not differ in their pathogenicity. The optimum conditions for fungal growth were 20°C and pH 6 on peptone potato dextrose agar (PPDA). Peptone and mannose were the best nitrogen and carbon source, respectively. Fungal growth was better on PPDA than on common potato dextrose agar. This study provides valuable information for integrated disease management program and facilitates the routine culturing of M. coronaria.

Impacts of Urban High Temperature Events on Physiology of Apple Trees: A Case Study of `Fuji`/M.9 Apple Trees in Daegu, Korea

In this study, we examined the effect of high temperature of urban area on the physiological response of apple tree including the photosynthesis, shoot growth, and fruit quality of ‘Fuji’/M.9 apple trees planted at Daegu urban area (DUA) and Gunwi rural area (GRA) for 2 years (2009-2010). During the apple growing season (April-October), the average air temperature of DUA was about 3.0 o C higher than that of GRA and the total rainfall of DUA was 130 mm more than that of GRA. During fruit enlargement stage (June-August), the number of days that recorded daily mean temperature of over 30 o C were ten on DUA in 2010, but there was no day when such temperature was experienced in 2009. Average air temperature of DUA during the maturation stage (September-October) was 19.8 o C, which was 4.0 o C higher than that of GRA. The higher temperature of over 30 o C during fruit enlargement stage decreased the photosynthetic rate, shoot growth, fruit weight, and soluble solid content of ‘Fuji’/M.9 apple tree. The moderate temperature of about 20 o C during maturation stage increased the photosynthetic rate and soluble solid content of ‘Fuji’/M.9 apple tree, but decreased fruit red color. In regional comparison with GRA, photosynthetic rate of DUA was changed from lower before rainy season to higher after rainy season. Fruit weight was higher in DUA than that of GRA. However, fruit weight between DUA and GRA did not show the difference when accumulated days that recorded daily maximum temperature over 35 o C of DUA was increased. Compared to the GRA, soluble solid content of DUA was higher, but fruit red color of DUA was less. These results indicate that the poor red coloring is the most problematic in ‘Fuji’/M.9 apple tree by global warming and urbanization.

Morphological Differences between Larvae of the Oriental Fruit Moth (Grapholita molesta Busck) and the Peach Fruit Moth (Carposina sasakii Matsumura) in Korea

The oriental fruit moth (Grapholita molesta Busck) and the peach fruit moth (Carposina sasakii Matsumura) are the most severe insect pests affecting apple orchards in Korea. To prevent an outbreak of these two species and to control these agricultural insect pests, it is important to identify them accurately. However, it is hard to classify them when they were in the larval stage since they tunnel into the apple fruit. In this study, surface structures of the two species of larvae were observed using stereo microscope and scanning electron microscope. Distinct differences between the two species of larvae were found. The prothorax spiracles of oriental fruit moth larvae were approximately twice as large as those of peach fruit moth larvae. The arrangements of subventral setae, located around the proleg, were different between oriental fruit moth and peach fruit moth larvae. Furthermore, subdorsal setae of oriental fruit moth were located next to the spiracle on the 8th abdominal segment, while that of peach fruit moth was located above the spiracle. The identification of the two species of larvae observed in this study was confirmed using polymerase chain reaction-restriction fragment length polymorphism method. Surface structural differences are intrinsic characteristics for each species of larvae and can easily be identified using stereo microscope. These specificities will be helpful where a large number of field-collected larvae need to be identified routinely in pest control research.

The Influence of Materials for Surface Mulching on Soil Temperature and Vegetative Growth of Apple Nursery Trees

This study was conducted to investigate the influence of different polyethylene film (P.E. film) for mulching on the changes in soil temperature and the production of good feathered apple nursery trees. M.9 rootstocks with stem diameter of 9.1~11.0 mm were planted in plots covered with different P.E. film (i.e., transparent P.E. film, black P.E. film, and bare soil as control). Three weeks after planting, the rootstocks were veneer grafted with `Sinano Sweet` apple cultivar. In the middle of June, BA was sprayed to nursery for inducing feathering during the growing season. The soil temperature of the control was higher than air temperature by about from mid April to early October, and that of P.E. film mulching was about higher than that of the control. The soil temperature under transparent P.E. film was about higher than that under black P.E. film. The diurnal range of soil temperature under the black P. E. film was lowest among all treatments. The P.E. film mulching induced better tree growth and feathering than bare soil. Percentage of good feathering apple nursery of black P.E. film was highest among all treatments because the soil temperature unuder black P.E. film in the early growing season was higher than that of the control and the number of days when the maximum soil temperature was over in the summer was lower than that under the transparent P.E. film.

Influence of Low Temperature and Chilling Time on Freezing Hardness of Apple Dwarf-rootstocks and Main Cultivars in Korea

This study was conducted to find out the freezing hardness of apple tree as influenced by dwarfrootstocks, cultivars, and low temperature treatments. The dwarf-rootstocks used were M.9 and M.26, and three cultivars used were early-maturing `Tsugaru`, mid-maturing `Hongro`, and late-maturing `Fuji`. Chilling temperatures were applied from to . Checking points of apple tree for freezing hardness were rootstock, trunk, feather, floral bud and foliar bud. Investigations were evaluated by the measure of water loss, electrolyte leaching, and sprouting. The results did not show the differences in water loss, electrolyte leaching, and sprouting by dwarf-rootstocks. Water loss of `Fuji` was lower than that of `Tsugaru` and `Hongro`, but sprouting ratio of `Fuji` was higher than that of `Tsugaru` and `Hongro`. Water loss and electrolyte leaching increased as treated by lower temperature, while sprouting ratio decreased. In treatment, sprouting of rootstock and trunk part were higher than that of feather, while sprouting of floral bud was lower than that of foliar bud. Sprouting of bourse shoot at the accumulated low temperature in terms of per day was 100% in the 28 days, and sharply decreased about 50% in the 35 days. In conclusion, there were no differences in freezing hardness between M.9 and M.26, but freezing hardness of late-maturing cultivar was tended to stronger than that of early-maturing and mid-maturing cultivars. Freezing hardness of floral bud was extremely weak .

Summer pruning and reflective film enhance fruit quality in excessively tall spindle apple trees

Tall spindle planting systems achieve high-quality fruit from plants that flower early and sustain a high yield. While some growers in Korea let apple trees grow up to 4 m or higher in high-density planting systems with M.9 rootstock to produce more fruits, such practices lead to very tall trees with low-quality fruit that develop in the lower canopy. To minimize this effect, we used the ‘Hongro’ cultivar to examine the effect summer pruning and installation of reflective film had on fruit size and quality in the lower canopy. We measured light distribution, diameter of flower buds, fruit quality, and leaf physiological characteristics at different parts of the canopy of trees that were treated with summer pruning (SP) and the installation of reflective film (RF), compared to those allowed to maintain their dense canopies (unpruned control; UC). The SP + RF treatment improved the overall light availability throughout the canopy and increased the amount of light by approximately 25% in the lower parts of the canopy compared to that in the UC group. The SP + RF treatment increased size, color, and soluble solids content in fruits from the lower parts of the canopy. Moreover, this treatment increased leaf photosynthetic activity, specific leaf weight, and flower bud diameter. Therefore, summer pruning and the installation of reflective film helps light penetration in excessively tall spindle trees and improves fruit quality in a high-density apple production system.

Applications of Organic Fungicides Reduce Photosynthesis and Fruit Quality of Apple Trees

Two different pest control programs were applied on 8-year-old ‘Ryoka’/M.26 apple trees (Malus domestica Borkh.). Lime sulfur or Bordeaux mixture with emulsified oil were applied 12 times from late March to mid-September as organic treatment, and synthetic chemicals were 7 times applied as control treatment. Over the entire apple-growing season, photosynthesis rates of apple trees were significantly lower in the organic treatment than in the control, and this photosynthetic differences were larger in July and August. Photosynthesis-related parameters such as stomatal conductance and transpiration behaved similarly to photosynthesis. The leaf area in the organic treatment was significantly smaller (24.7 ㎠) than that in the control treatment (30.7 ㎠). Organic leaves contained significantly less Chl. a (15.5 ㎎·g -1 ) than did control leaves (17.6 ㎎·g -1 ). Fruit yield per tree was significantly lower in the organic treatment (18.8 ㎏) than in the control (24.5 ㎏), because organic fruits experienced a higher rate of disease infection such as white rot (Botryosphaeria dothidae ) and bitter rot (Glomerella cingulata ) than did control fruits. Organic fruits had high flesh firmness but less color development (lower Hunter’s a values). In this experiment, the pest control program with frequent applications of organic fungicides showed negative effects on photosynthesis and disease infection on leaves and fruits, and thus reduce the fruit quality and yield in ‘Ryoka’/M.26 apple trees.

Influence of Water Stress through Root Pruning on Tree Growth and Fruit Quality in 'Fuji'/M.9 Apple Tree at Full Bloom

This study was conducted to find out the influence of water stress from May to June on photosynthesis, shoot growth and fruit quality of apple trees. Fuji’/M.9 apple trees were root pruned at full bloom (30th April), parallel to the row of 30 cm or 60 cm from the trunk, to one side or both sides of trunk. The average value of afternoon leaf water potential from May to June of the no root pruning was maintained over –1.80 MPa, but that of root-pruning treatments was maintained under –1.80 MPa. In the comparison of average value of leaf water potential from May to June by root-pruning degree, the root pruning both sides at 30 cm from trunk was lowest (–2.06 MPa), followed by the root pruning both sides at 60 cm (–2.02 MPa) and the root pruning one side at 30 cm (–1.91 MPa). Root pruning one side at 30 cm or both sides at 60 cm reduced photosynthetic rate from May to June by 80% or 65%, respectively, compared with no root pruning. So, the degree of decreasing total shoot length or average fruit weight compare to the no root pruning of the root pruning one side at 30 cm was 25% or 11%, respectively, and those of the root pruning both sides at 30 cm was 45% or 15%, respectively. However, the soluble solid content and fruit color of the root pruning was higher than those of the no root pruning, and those of the root pruning both sides was higher than root pruning one side. These results indicate that the fruit enlargement was decreased when the average value of average leaf water potential from May to June was under –1.80 MPa, and the shoot growth was decreased when that was under –2.00 MPa.