• Research in Plant Disease
• /
• v.25 no.2
• /
• pp.71-78
• /
• 2019

In 2018, severe diebacks have occurred on yuzu trees cultivated in Goheung, Jeonnam Province. On-farm surveys at 18 randomly selected orchards revealed the dieback incidence ranged from 7.5% to 100% with an average of 43.6%, and 56.6% of the affected yuzu trees were eventually killed. In order to find the reason for this sudden epidemic, we investigated the weather conditions that are exclusively distinct from previous years, hypothesizing that certain weather extremes might have caused the dieback epidemic on yuzu trees. Since different temperatures can cause freeze damage to plants depending on their dormancy stages, we investigated both periods when yuzu becomes hardy under deep dormancy (January-February) and when yuzu loses its cold hardiness (March-April). First, we found that daily minimum air temperatures below $-10^{\circ}C$ were recorded for 7 days in Goheung for January and February in 2018, while no occasions in 2017. In particular, there were two extreme temperature drops ($-12.6^{\circ}C$ and $-11.5^{\circ}C$) beyond the yuzu cold hardiness limit in 2018. In addition, another occasion of two sudden temperature drops to nearly $0^{\circ}C$ were occurred right after abnormally-warm-temperature-rises to $13^{\circ}C$ of daily minimum air temperatures in mid-March and early April. In conclusion, we estimated that the possible damages by several extreme freeze events during the winter of 2018 could be a major cause of severe diebacks and subsequently killed the severely affected yuzu trees.

• Proceedings of the Plant Resources Society of Korea Conference
• /
• 2018.10a
• /
• pp.32-32
• /
• 2018

Flora investigations in Korea have been conducted by many researchers for diverse purposes. Accumulated flora investigation data has not been utilized efficiently because there is no accessible database for comparison. To overcome this shortcoming, we constructed web-based database of flora investigation, named as the Integrated Korean Flora Database (IKFD; http://www.floradb.net/intro.php). Until now, 284 flora references (263 papers, 14 reports and books, and 7 unpublished papers written in between 1962 and 2017) were digitalized into the database. From 134,711 records, 4,301 species belonging to 228 families and 1,079 genera were identified via mapping with two major Korean plant species lists. Polygon areas originated from references were used for distribution of plant species, identifying precise distribution area. It will be a better index to show plant ecological characteristics. Collected micro-climate data provided by Korea Meteorology Administration were also integrated in IFKD for understanding correlation between distribution of plants and micro-climate. Cold hardiness zone which has been utilized for classifying climate zones. 12 out of 26 zones identified based on micro-climate data in Korea were mapped with distribution of plants. More than half species were appeared in zone 6a, 6b, 7a, and 7b. Taken together with these results, IKFD will be a fundamental platform for understanding plants in Korea flora investigation as well as a new standard for classifying distribution of plants. Moreover, Biodiversity Observation Database (BODB; http://www.biodiversitydb.info/intro.php) which integrates plant distribution data was also integrated for further studies.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.50 no.2
• /
• pp.67-72
• /
• 2005

Overwintering capacity, closely related to winter hardiness, of Chinese milk vetch planted with different sowing times and sowing practices was investigated to improve the incorporation into cropping system in Korea. The tolerance to low temperature was evaluated with $LT_50$ using leaf disc leaching method. Dry weight of CMV was reduced remarkably with delayed planting from Sep. 5 to Oct. 20. The differences in tolerance to freezing temperature were not conspicuous among CMV genotypes, however, the differences between genotype (collections at different regions) were due to the plant architecture, mainly to the leaf angle. The crouching genotype collected at central region of Korean peninsula, which showed excellent freezing tolerant, has planophile leaves. The feature of internal constituents of CMV genotypes did not show any noticeable differences with respect to the freezing tolerance which evaluated by leaf disc leaching experiment. To overcome the poor overwintering capacity, tolerant genotype should be developed by selection with considering the plant architecture. The reduction of CMV growth during overwintering period was ameliorated with furrow-sowing under late-sown condition, therefore, when the CMV is inevitably sown late after recommended time, the seeds should be sown on furrow to overcome the cold stress.

• Weed & Turfgrass Science
• /
• v.4 no.4
• /
• pp.383-389
• /
• 2015

The use of zoysiagrass (Zoysia japonica Steud.) in the transition zone is limited because of a lack of cold hardiness although zoysiagrass has many advantages compared to other warm-season and cool-season grasses. Late-fall N fertilization is often applied for darker green color of turfgrass in early spring and more extensive root growth without rapid top growth. The objective of the study was to evaluate the effects of late fall N application and turf cover for zoysiagrass spring green-up. Clear polyvinyl chloride (PVC) film was used for turf cover. The amount of N applied were 5 and $10g\;N\;m^{-2}$ for the low and high N rate treatments, respectively. Covered zoysiagrass had greater turfgrass color and quality in early spring than non-covered zoysiagrass. The high N rate had 0.6 to 2.3 greater turfgrass quality than the low N rate on 7 of 9 rating dates. Slow-release N as late fall fertilization is more effective for turfgrass color and quality than fast-release N in spring. Turf cover could reduce the period of yellow zoysiagrass, and the earlier time of spring green-up could be advanced by increasing turfgrass quality and growth of zoysiagrass.

• Korean Journal of Agricultural and Forest Meteorology
• /
• v.14 no.3
• /
• pp.124-131
• /
• 2012

This study was carried out to evaluate a possible change in freeze risk for 'Changhowon Hwangdo' peach buds in three major peach growing areas under the future climate projected by RCP8.5 emission scenario. Mean values of the monthly temperature data for the present decade (2000s) and the future decades (2020s, 2050s, 2080s) were extracted for farm lands in Icheon, Chungju, and Yeongcheon-Gyeongsan region at 1km resolution and 30 sets of daily temperature data were generated randomly by a stochastic process for each decade. The daily data were used to calculate a thermal time-based dormancy depth index which is closely related to the cold tolerance of peach buds. Combined with daily minimum temperature, dormancy depth can be used to estimate the potential risk of freezing damage on peach buds. When the freeze risk was calculated daily for the winter period (from 1 November to 15 March) in the present decade, Icheon and Chungju regions had high values across the whole period, but Yeongcheon-Gyeongsan regions had low values from mid-December to the end of January. In the future decades, the frequency of freezing damage would be reduced in all 3 regions and the reduction rate could be as high as 75 to 90% by 2080's. However, the severe class risk (over 80% damage) will not disappear in the future and most occurrences will be limited to December to early January according to the calculation. This phenomenon might be explained by shortened cold hardiness period caused by winter warming as well as sudden cold waves resulting from the higher inter-annual climate variability projected by the RCP8.5 scenario.

• Journal of Bio-Environment Control
• /
• v.26 no.2
• /
• pp.64-71
• /
• 2017

The study was performed on the effects of crop load of pear (Pyrus pyrifolia Nakai) trees on shoot growth, reserved nutrients, and fruit production for two years, as well as regrowth of cuttings treated with various cold temperatures in 2012 and 2013. Crop load adjustments included three levels of fruiting; 54 (60%), 90 (100%), and 126 fruits per tree (140%). As increasing crop load from 60% to 140%, water sprout growth decreased, and one-year old shoot resulted in declined concentrations of total carbon, macro-nutrients, and free sugar. The 140% of crop load greatly increased fruit yield of approximately 35 tons per ha in both 2011 and 2012 but slightly reduced weight, size, and soluble solid contents in fruit. However, 140% of crop load increased annual production income to approximately over 10 million won compared to the 60% and 100% of crop load. Germination rates in the cuttings did not rapidly decrease up to $-20^{\circ}C$ in a growth chamber condition. The 140% of crop load decreased germination rates less than 70% of cuttings grown under $-30^{\circ}C$. Amounts of electrolyte leakage in the cuttings under various cold temperatures were not significantly different among the adjustment of crop load.

• Journal of The Korean Society of Grassland and Forage Science
• /
• v.27 no.4
• /
• pp.249-256
• /
• 2007

This experiment was conducted to compare the agronomic characteristics and productivity in introduced hairy vetch cultivars and developed new Korean Hairy vetch cultivars in two areas of the experimental field of Grassland and Forage Crops Division, National Institute of Animal Science from 2005 to 2006. The experiment was arranged in randomized complete block design with three replications. A total of 11 hairy vetch cultivars used in this study including 9 introduced cultivars (Penn-02, Sander, Latigo, Welta, Ostsaat, VV4712, Minnie, Barlosa and Capello) and 2 Korean cultivars (Cold green and Cheong pa). The early flowering varieties of Minnie, Barlosa, Capello and Cold green were grown as early maturity cultivars, while the late flowering varieties of Penn-02, Sander, Latigo, Welta, Ostsaat, VV4712 and Cheong pa were grown as medium and late maturity. The winter hardiness of hairy vetch was good except for Minnie, Barlosa and Capello of early maturity cultivars. In this study, dry matter yield of VV4712 was the highest of 11 hairy vetch cultivars. And dry matter yield of medium and late maturity vetch increased in the middle region while that of early maturity increased in the south. The new Korean cultivar, Cheong pa, as a medium and late maturity hairy vetch was not bad compared to introduced cultivars and Cold green as an early maturity hairy vetch was an excellent cultivar compared to introduced cultivars in both regions. Latigo in NDF (neutral detergent fiber) and Welta in ADF (acid detergent fiber) were lower than other cultivars, while Sander in IVDMD (in vitro dry matter digestibility) and CP (crude protein) content were higher than other cultivars. The results of this experiment indicated that the productivity of hairy vetch cultivars was highest in VV4712, and Cheong pa and Cold green of new Korean cultivar were the promising cultivars of hairy vetch in Korea.

• Korean journal of applied entomology
• /
• v.61 no.3
• /
• pp.409-422
• /
• 2022

Two dominant thrips in hot pepper (Capsicum annuum) cultivating in greenhouses are Frankliniella occidentalis and F. intonsa in Korea. This study investigated their overwintering physiology. These two thrips were freeze-susceptible and suppressed the body freezing temperature by lowering supercooling point (SCP) down to -15~-27℃. However, these SCPs varied among species and developmental stages. SCPs of F. occidentalis were -25.7±0.5℃ for adults, -17.2±0.3℃ for pupae, and -15.0±0.4℃ for larvae. SCPs of F. intonsa were -24.0±1.0℃ for adults, -27.0±0.5℃ for pupae, -17.2±0.8℃ for larvae. Cold injuries of both species occurred at low temperature treatments above SCPs. Thrips mortality increased as the treatment temperature decreased and its exposure period increased. F. occidentalis exhibited higher cold tolerance than F. intonsa. In both species, adults were more cold-tolerant than larvae. Two thrips species exhibited a rapid cold hardening because a pre-exposure to 0℃ for 2 h significantly enhanced the cold tolerance to a lethal cold temperature treatment at -10℃ for 2 h. In addition, a sequential exposure of the thrips to decreasing temperatures made them to be acclimated to low temperatures. To investigate the overwintering sites of the two species, winter monitoring of the thrips was performed at the greenhouses. During winter season (November~February), adults of the two species were not captured in outside of the greenhouses. However, F. occidentalis adults were captured to the traps and observed in weeds within the greenhouses. F. occidentalis adults were also emerged from soil samples obtained from the greenhouses during the winter season. F. intonsa adults did not come out from the soil samples at November and December, but emerged from the soil samples obtained after January. To determine the adult emergence due to diapause development, two thrips species were reared under different photoperiods. Adult development occurred in all photoperiod treatments in F. occidentalis, but did not in F. intonsa especially under short periods. Tomato spotted wilt virus, which is transmitted by these two species, was detected in the weeds infested by the thrips during the winter season. These results suggest that F. occidentalis develops on weeds in the greenhouses while F. intonsa undergoes a diapause in the soil during winter.

• Korean journal of applied entomology
• /
• v.53 no.4
• /
• pp.355-365
• /
• 2014

It has been unclear whether the diamondback moth, Plutella xylostella can overwinter in Korean field conditions. This study determined overwintering conditions of P. xylostella by conducting field exposure tests based on its cold tolerance and monitoring overwintering populations by direct examination of overwintering larval habitats and capturing adults with sex pheromone traps. In addition, the overwintering populations were analyzed using polymorphic genetic markers to trace their sources. When all immature stages of P. xylostella were exposed to $-5^{\circ}C$, which was the temperature much above their supercooling points, they significantly suffered with direct cold injuries, where larval stage was most tolerant to the cold injury. However, the exposure to $5^{\circ}C$ for a long period (4 weeks) did not give any significant cold injury to nonfeeding stages, while this treatment gave lethality to larval stage without diet. When all developmental stages of P. xylostella were exposed to open field conditions during winter, they exhibited significant decreases of survival rates. However, some protected and indoor conditions reduced the cold injuries and the diet provision significantly increased larval survival rates. Adult monitoring with sex pheromone during winter period indicated that the first captures were observed at similar periods at different locations (${\approx}260$ Km apart). The overwintering adults were captured until early April. Genetic variation of these overwintering populations was analyzed with polymorphic molecular markers, indicating significant genetic divergences among the overwintering populations. This study indicates that P. xylostella can overwinter in southern Korean fields or some protected greenhouses with host plants.

• The Plant Pathology Journal
• /
• v.31 no.3
• /
• pp.290-298
• /
• 2015

Starting in 2012, severe diebacks usually accompanied by abundant gum exudation have occurred on yuzu trees in Goheung-gun, Jeonnam Province, where severely affected trees were occasionally killed. On-farm surveys were conducted at 30 randomly-selected orchards located at Pungyang-myeon, Goheung-gun, and the resulting disease incidences were 18.5% and 39.6% for dieback and gumming symptoms, respectively. Black spots on branches and leaves also appeared on infected trees showing a typical dieback symptom. Morphological and molecular identifications of the isolated fungal organisms from lesions on the symptomatic leaves and branches revealed that they are identical to Phomopsis citri, known to cause gummosis. In order to find the reason for this sudden epidemic, we investigated the weather conditions that are exclusively distinct from previous years, hypothesizing that certain weather extremes might have caused the severe induction of pre-existing disease for yuzu. There were two extreme temperature drops beyond the yuzu's cold hardiness limit right after an abnormally-warm-temperature-rise during the winter of 2011-12, which could cause severe frost damage resulting in mechanical injuries and physiological weakness to the affected trees. Furthermore, there was an increased frequency of strong wind events, seven times in 2012 compared to only a few times in the previous years, that could also lead to extensive injuries on branches. In conclusion, we estimated that the possible damages by severe frost and frequent strong wind events during 2012 could cause the yuzu trees to be vulnerable to subsequent fungal infection by providing physical entries and increasing plant susceptibility to infections.