D-PSA-K: A Model for Estimating the Accumulated Potential Damage on Kiwifruit Canes Caused by Bacterial Canker during the Growing and Overwintering Seasons

We developed a model, termed D-PSA-K, to estimate the accumulated potential damage on kiwifruit canes caused by bacterial canker during the growing and overwintering seasons. The model consisted of three parts including estimation of the amount of necrotic lesion in a non-frozen environment, the rate of necrosis increase in a freezing environment during the overwintering season, and the amount of necrotic lesion on kiwifruit canes caused by bacterial canker during the overwintering and growing seasons. We evaluated the model’s accuracy by comparing the observed maximum disease incidence on kiwifruit canes against the damage estimated using weather and disease data collected at Wando during 1994–1997 and at Seogwipo during 2014–2015. For the Hayward cultivar, D-PSA-K estimated the accumulated damage as approximately nine times the observed maximum disease incidence. For the Hort16A cultivar, the accumulated damage estimated by D-PSA-K was high when the observed disease incidence was high. D-PSA-K could assist kiwifruit growers in selecting optimal sites for kiwifruit cultivation and establishing improved production plans by predicting the loss in kiwifruit production due to bacterial canker, using past weather or future climate change data

Occurrence of stem and shoot cankers caused by Phomopsis fukushii on mango

In July 2014, an outbreak of stem and shoot cankers was observed in mango experimental plots in Jeju, Korea. Initial disease symptoms were dark or reddish brown stem and shoot cankers on branches and leaves. Dieback symptoms followed in the areas above the lesions, progressing to development of numerous small white-brown pycnidia. The causative agent was initially identified as Phomopsis fukushii based on morphological characteristics, colony appearance, and shape of alpha and beta conidia of isolates recovered from cankers. Further confirmation was obtained by assessment of DNA sequences of internal transcribed spacer regions and translation elongation factor and actin genes

Temperature and CO₂ Level Influence Potato leafroll virus Infection in Solanum tuberosum

We determined the effects of atmospheric temperature (10–30 ± 2°C in 5°C increments) and carbon dioxide (CO₂) levels (400 ± 50 ppm, 540 ± 50 ppm, and 940 ± 50 ppm) on the infection of Solanum tuberosum cv. Chubaek by Potato leafroll virus (PLRV). Below CO₂ levels of 400 ± 50 ppm, the PLRV infection rate and RNA content in plant tissues increased as the temperature increased to 20 ± 2°C, but declined at higher temperatures. At high CO₂ levels (940 ± 50 ppm), more plants were infected by PLRV at 30 ± 2°C than at 20 or 25 ± 2°C, whereas PLRV RNA content was unchanged in the 20–30 ± 2°C temperature range. The effects of atmospheric CO₂ concentration on the acquisition of PLRV by Myzus persicae and accumulation of PLRV RNA in plant tissues were investigated using a growth chamber at 20 ± 2°C. The M. persicae PLRV RNA content slightly increased at elevated CO₂ levels (940 ± 50 ppm), but this increase was not statistically significant. Transmission rates of PLRV by Physalis floridana increased as CO₂ concentration increased. More PLRV RNA accumulated in potato plants maintained at 540 or 940 ± 50 ppm CO₂, than in plants maintained at 400 ± 50 ppm. This is the first evidence of greater PLRV RNA accumulation and larger numbers of S. tuberosum plants infected by PLRV under conditions of combined high CO₂ levels (940 ± 50 ppm) and high temperature (30 ± 2°C)

HR-Mediated Defense Response is Overcome at High Temperatures in Capsicum Species

Resistance to Tomato spotted wilt virus isolated from paprika (TSWV-Pap) was overcome at high temperatures (30 ± 2°C) in both accessions of Capsicum annuum S3669 (Hana Seed Company) and C. chinense PI15225 (AVRDC Vegetable Genetic Resources). S3669 and PI15225, which carrying the Tsw gene, were mechanically inoculated with TSWV-Pap, and then maintained in growth chambers at temperatures ranging from 15 ± 2°C to 30 ± 2°C (in 5°C increments). Seven days post inoculation (dpi), a hypersensitivity reaction (HR) was induced in inoculated leaves of PI152225 and S3669 plants maintained at 25°C ± 2°C. Meanwhile, necrotic spots were formed in upper leaves of 33% of PI15225 plants maintained at 30 ± 2°C, while systemic mottle symptoms developed in 50% of S3669 plants inoculated. By 15 dpi, 25% of S3669 plants had recovered from systemic mottling induced at 30 ± 2°C. These results demonstrated that resistance to TSWV-Pap can be overcome at higher temperatures in both C. chinense and C. annuum. This is the first study reporting the determination of temperatures at which TSWV resistance is overcome in a C. annuum genetic resource expressing the Tsw gene. Our results indicated that TSWV resistance shown from pepper plants possess the Tsw gene could be overcome at high temperature. Thus, breeders should conduct evaluation of TSWV resistance in pepper cultivars at higher temperature than 30°C (constant temperature)

Impact of Cold Stress on Physiological Responses and Fruit Quality of Shiranuhi Mandarin in Response to Cold Conditions

We identified the minimum temperature limits to ensure Shiranuhi mandarin growth and fruit quality and provided overwintering temperature management guidelines. Expanded polystyrene panels with air conditioners were exposed to −1, −3, and −5 °C in the greenhouse for 15 h to determine the overwintering temperature. Leaves and fruits were analyzed at intervals for physiological response, fruit quality, and aromatic components. The low temperature treatment groups showed 1.3 to 1.4 times increased malondialdehyde content in leaves and 1.1 to 1.3-fold higher electrolyte linkage rates in the −5 °C treatment group alone. The sugar/acidity ratio was 1.1 to 1.3 times higher in the −5 °C treatment than in the control due to rapid acid reduction. The fruit firmness and citrus color index decreased notably after 21–28 days of treatment. Ascorbic acid content significantly decreased 17.3%–41.1% at −5 °C. Among the aromatic compounds, decanal levels notably increased with −5 °C treatment; −5 °C cold treatment notably affected oxidative stress in leaves and the sugar/acid ratio, ascorbic acid content, and aromatic compounds in fruits. If prolonged exposure to temperatures 0 °C during fruit growth and >−3 °C after harvest as the minimum temperature to preserve fruit set and quality

Effects of Temperature on Systemic Infection and Symptom Expression of Turnip mosaic virus in Chinese cabbage (Brassica campestris)

Using the Chinese cabbage (Brassica campestris) cultivar ‘Chun-goang’ as a host and turnip mosaic virus (TuMV) as a pathogen, we studied the effects of ambient temperature (13°C, 18°C, 23°C, 28°C and 33°C) on disease intensity and the speed of systemic infection. The optimal temperature for symptom expression of TuMV was 18–28°C. However, symptoms of viral infection were initiated at 23–28°C and 6 days post infection (dpi). Plants maintained at 33°C were systemically infected as early as 6 dpi and remained symptomless until 12 or 22 dpi, depending on growth stage at the time of inoculation. It took 45 days for infection of plants grown at 13°C. Quantitative real-time polymerase chain reaction (q-PCR) results showed that the accumulation of virus coat protein was greater in plants grown at 23–28°C. The speed of systemic infection increased linearly with rising ambient temperature, up to 23°C. The zero-infection temperature was 10.1°C. To study the effects of abruptly elevated temperatures on systemic infection, plants inoculated with TuMV were maintained at 10°C for 20 d; transferred to a growth chamber at temperatures of 13°C, 18°C, 23°C, 28°C, or 33°C for 1, 2, or 3 d; and then moved back to 10°C. The numbers of plants infected increased as duration of exposure to higher temperatures and dpi increased

Occurrence of Stolbur Phytoplasma Disease in Spreading Type Petunia hybrida Cultivars in Korea

In January 2012, spreading type petunia cv. Wave Pink plants showing an abnormal growth habit of sprouting unusual multiple plantlets from the lateral buds were collected from a greenhouse in Gwacheon, Gyeonggi Province, Korea. The presence of phytoplasma was investigated using PCR with the primer pairs P1/P6, and R16F1/R1 for nested-PCR. In the nested PCR, 1,096 bp PCR products were obtained, and through sequencing 12 Pet-Stol isolates were identified. Comparison of the nucleotide sequences of 16S rRNA gene of the 12 Pet-Stol isolates with other phytoplasmas belonging to aster yellows or Stolbur showed that Pet-Stol isolates were members of Stolbur. The presence of phytoplasma in petunia was also confirmed by microscopic observation of the pathogens. In this study, Stolbur phytoplasma was identified from spreading type petunia cultivars by sequence analysis of 16S rRNA gene of phytoplasma and microscopic observation of phytoplasma bodies. This is the first report of Stolbur phytoplasma in commercial Petunia hybrida cultivars