Bacterial Leaf Blight (BLB) Disease Incidence and Severity in Basmati and Non-Basmati Rice Growing Areas of Punjab, Pakistan

Bacterial leaf blight (BLB) is one of the most damaging diseases of rice in Asia and annually incurring significant yield loss to rice production in Pakistan. Management of disease required the information of BLB incidence and severity in basmati and non-basmati rice areas. The current study presented the observation of BLB disease incidence and severity in 19 major rice growing districts of Punjab. In this study, 9 Basmati growing and 10 non-basmati rice growing districts were surveyed from September to October in 2009, 2010, 2012, and 2013. Rice fields near to roadside, research stations and adjoining farmer fields were preferred for the survey. Each halt was after 10 km on the route depending upon the crop intensity. The general appearance of the field was observed for the absence or presence of BLB disease symptoms. The incidence of BLB was recorded as a percentage of plants infected in a field on a visual basis. For each field, 4 plants were observed at 5 points/hill along the diagonal transect for disease symptoms. The data of severity was recorded as the percentage of leaf area infected out of the total leaf area. Among the districts with basmati rice, the mean incidence of BLB was maximum in Gujranwala, Sheikhupura and Hafizabad followed by Mandi Bahauddin and Gujrat. A similar pattern of disease severity was observed in the basmati rice belt with maximum BLB mean severity in Gujranwala, Sheikhupura and Hafizabad having most of the field with a severity scale of 9. Overall, the disease trend showed that both the incidence and the severity were higher in 2010, 2012 and 2013 in the basmati rice belt. The ten districts, comprising of mostly non-basmati rice varieties showed relatively less BLB incidence and severity compared to basmati rice districts. The maximum mean incidence of 20-25% was observed in Faisalabad, Chiniot and Sahiwal in at least one year of the rice season. None of the field with BLB disease symptoms was observed in districts Okara, Khanewal and Bahawalpur during the 2012 and 2013 rice season. Maximum disease severity of mean value 3 was observed in Sahiwal during 2009 while the rest of the districts showed less than 2 mean severity during all rice growing season. Overall, in non-basmati rice districts, no specific trend of disease incidence and severity was apparent, however, the disease was present in very low magnitude or absent during the surveyed years. The information from this study is helpful in the selection of variety for basmati and non-basmati districts of Punjab and the adoption of appropriate disease management strategies.

Download Full-text

Assessing Taro (Colocasia esculenta (L.) Schott) Leaf Blight Incidence, Severity, and Farmers’ Knowledge of the Disease in Fako Division of Cameroon

International Journal of Pathogen Research ◽

10.9734/ijpr/2020/v5i230128 ◽

2020 ◽

pp. 17-29

Author(s):

Mandah Cicelia Takor ◽

Ekwa Yawa Monono ◽

Ojong Agbor Ntane ◽

Jemimah Evenye Ngale ◽

Lum A. Fontem

Keyword(s):

Disease Severity ◽

Disease Incidence ◽

Management Strategies ◽

Leaf Blight ◽

Cultural Methods ◽

Randomized Design ◽

High Prevalence ◽

Severity Of The Disease ◽

Blight Disease ◽

Taro Leaf Blight

Taro leaf blight (TLB), a major disease of taro plant caused by Phytophthora colocasiae, a pseudo-fungus, that occurs in many taro producing areas, especially in the South West of Cameroon. A Survey was conducted to assess farmers’ knowledge, as well as to determine the incidence and the severity of the disease in taro fields. Structured questionnaires were administered in selected locations (Bokova, Ekona, Muea, Mile 16, Mutengene, and Likomba) of taro production. Two farms were selected with two quadrats of 64 m2 each were carved to assess disease incidence and severity on taro. The number of plants infected with taro leaf blight were counted and the area of the affected leaves measured was used to evaluate the disease incidence and disease severity. Data collected were subjected to ANOVA for complete randomized design and the means were compared using Tukey test at 0.05 probability levels. The results revealed that most of the farmers could identify the disease while practicing cultural methods in controlling the disease. The results also revealed significant differences (p = 0.001) in disease incidence and disease severity in all the localities, with Mile 16 showing the highest percentage mean of 96.53% and 85.59%, respectively. The severity scored showed high infection range of 3 – 3.95 in all locations except in Likomba (2.60). It could be concluded from the results that there were high prevalence of taro leaf blight disease in Fako Division. Good management strategies are therefore required to control Taro leaf blight and improve taro production in the area.

Download Full-text

Disease Incidence, Yield and Quality Comparisons among Rice Varieties with Different Resistance to Bacterial Leaf Blight

Research in Plant Disease ◽

10.5423/rpd.2008.14.3.171 ◽

2008 ◽

Vol 14 (3) ◽

pp. 171-175

Author(s):

Tae-Hwan Noh ◽

Ki-Young Kim ◽

Du-Ku Lee ◽

Hyeong-Kwon Shim ◽

Mi-Hyung Kang ◽

...

Keyword(s):

Disease Incidence ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Rice Varieties ◽

Yield And Quality

Download Full-text

Leaf Blight Disease caused by Pseudomonas syringae pv. syringae in the Nurseries of Litchi (Litchi chinensis Sonn.) and its Management

The Agriculturists ◽

10.3329/agric.v15i1.33424 ◽

2017 ◽

Vol 15 (1) ◽

pp. 10-18

Author(s):

MAH Khan ◽

I Hossain ◽

MU Ahmad ◽

MSM Chowdhury

Keyword(s):

Disease Severity ◽

Pseudomonas Syringae ◽

Copper Sulphate ◽

Disease Incidence ◽

Foliar Spray ◽

Antibiotic Sensitivity ◽

Weather Conditions ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Blight Disease

Leaf blight of seven varieties of litchi caused by Pseudomonas syringae pv. syringae was surveyed in the nurseries of major litchi growing areas in Bangladesh viz. Rajshahi, Dinajpur, Rangpur, Mymensingh and Khagrachari. The mean level of incidence and severity were 8.58 and 7.88% in Rajshahi, 9.88 and 8.88% in Dinajpur, 8.44 and 7.76% in Rangpur, 6.50 and 6.18% in Mymensingh and 9.00 and 7.98% in Khagrachari. Incidence and severity of bacterial leaf blight disease of litchi varied significantly depending on weather conditions. Correlation studies revealed that bacterial leaf blight disease of litchi seedlings were positively correlated with temperature, rainfall and relative humidity, where temperature and rainfall was the major factor to the variations of both incidence and severity. Antibiotic sensitivity test revealed that among fifteen isolates, most of the isolates of P. syringae pv. syringae collected from litchi were sensitive to Gentamycin and Erythromycin. Under net house condition, six different treatments (i) Gentamycin @ 0.05%, (ii) Erythromycin @ 0.05%, (iii) Doxycycline @ 0.05%,(iv) Copper sulphate @ 0.05%, (v) BAU-Biofungicide @ 2% and (vi) Control were used for controlling bacterial leaf blight of litchi (Variety: China-3). BAU-Biofungicide was found to be superior in controlling bacterial leaf blight of litchi that reduced 33.64% disease incidence and 60.77 % disease severity in 2010-11 and 63.76% disease incidence and 61.40 % disease severity in 2011-12 over control when applied as foliar spray @ 2% followed by Copper sulphate (0.05%) and Erythromycin (0.05%).The Agriculturists 2017; 15(1) 10-18

Download Full-text

Ginger Essential Oils-Loaded Nanoemulsions: Potential Strategy to Manage Bacterial Leaf Blight Disease and Enhanced Rice Yield

Molecules ◽

10.3390/molecules26133902 ◽

2021 ◽

Vol 26 (13) ◽

pp. 3902

Author(s):

Abdullahi Adamu ◽

Khairulmazmi Ahmad ◽

Yasmeen Siddiqui ◽

Intan Safinar Ismail ◽

Norhayu Asib ◽

...

Keyword(s):

Antibacterial Activity ◽

Electron Microscope ◽

Essential Oils ◽

Disease Severity ◽

Rice Yield ◽

Cell Structure ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Control Treatment ◽

Promising Alternative

The bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious rice diseases, causing huge yield losses worldwide. Several technologies and approaches have been opted to reduce the damage; however, these have had limited success. Recently, scientists have been focusing their efforts on developing efficient and environmentally friendly nanobactericides for controlling bacterial diseases in rice fields. In the present study, a scanning electron microscope (SEM), transmission electron microscope (TEM), and a confocal laser scanning microscope (CLSM) were utilized to investigate the mode of actions of ginger EOs on the cell structure of Xoo. The ginger EOs caused the cells to grow abnormally, resulting in an irregular form with hollow layers, whereas the dimethylsulfoxide (DMSO) treatment showed a typical rod shape for the Xoo cell. Ginger EOs restricted the growth and production of biofilms by reducing the number of biofilms generated as indicated by CLSM. Due to the instability, poor solubility, and durability of ginger EOs, a nanoemulsions approach was used, and a glasshouse trial was performed to assess their efficacy on BLB disease control. The in vitro antibacterial activity of the developed nanobactericides was promising at different concentration (50–125 µL/mL) tested. The efficacy was concentration-dependent. There was significant antibacterial activity recorded at higher concentrations. A glasshouse trial revealed that developed nanobactericides managed to suppress BLB disease severity effectively. Treatment at a concentration of 125 μL/mL was the best based on the suppression of disease severity index, AUDPC value, disease reduction (DR), and protection index (PI). Furthermore, findings on plant growth, physiological features, and yield parameters were significantly enhanced compared to the positive control treatment. In conclusion, the results indicated that ginger essential oils loaded-nanoemulsions are a promising alternative to synthetic antibiotics in suppressing Xoo growth, regulating the BLB disease, and enhancing rice yield under a glasshouse trial.

Download Full-text

Komposisi dan Sebaran Patotipe Xanthomonas oryzae pv. oryzae, Penyakit pada Padi di Nusa Tenggara Barat

Jurnal Penelitian Pertanian Tanaman Pangan ◽

10.21082/jpptp.v34n2.2015.p113-120 ◽

2015 ◽

Vol 34 (2) ◽

pp. 113

Author(s):

Sudir Sudir ◽

Dini Yuliani ◽

Lalu Wirajaswadi

Keyword(s):

Disease Severity ◽

Xanthomonas Oryzae ◽

Rice Crop ◽

Bacterial Leaf Blight ◽

Rice Varieties ◽

Rice Leaf ◽

Rice Leaves ◽

Differential Varieties ◽

Planting Season ◽

Screen House

A study was carried out to identify the composition and distribution of Xanthomonas oryzae pv. oryzae (Xoo) pathotypes on rice crop in West Nusa Tenggara, during the 2012 planting season. Three activities were conducted, namely collection of rice leaf samples from the fields, isolation of Xoo from the leaf samples at the laboratory, and testing pathotypes of Xoo at the screen house. Rice leaves showing typical bacterial leaf blight (BLB) symptom were collected from various farmers’ fields. The samples were detached and put into paper envelopes, and were taken to the laboratory for isolation of Xoo, at the Laboratory of Pythopathology of Indonesian Center for Rice Research (ICRR), Sukamandi. Pathotype testing was done in the ICRR screen house by inoculating the leaves of five differential rice varieties using inocula of the Xoo isolates. Resistance of the rice differential varieties was determined based on the BLB disease severity. Inoculated plant with disease severity ≤11% was considered resistant (R) and disease severity >11% was susceptible (S). From the 240 samples of rice leaf infected with BLB collected from West Nusa Tenggara, 232 Xoo isolates were obtained. The Xoo pathotype identification showed that pathotype IV was the most dominant in West Nusa Tenggara during the 2012 planting season, numbering 118 isolates or 51.0% out of the total isolates, followed by pathotype VIII (67 isolates or 29.0%), and pathotype III (47 isolates or 20.0%).

Download Full-text

Field efficacy of formulation of fungal bioagents against bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae (Uyeda and Ishiyama) Dowson

Journal of Applied and Natural Science ◽

10.31018/jans.v5i2.346 ◽

2013 ◽

Vol 5 (2) ◽

pp. 423-426 ◽

Cited By ~ 2

Author(s):

Gokil Prasad Gangwar

Keyword(s):

Grain Yield ◽

Disease Severity ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Comparative Efficacy ◽

Trichoderma Spp ◽

Maximum Increase ◽

Kharif Season ◽

Field Efficacy ◽

Different Sources

In the present study, Trichoderma harzianum, T. hamatum, T. virens and three isolates of Trichoderma spp. were evaluated for their comparative efficacy against bacterial leaf blight of rice, under field conditions. All the bioagent formulations were significantly effective in reducing disease severity over check during Kharif season 2006 and 2007. T. harzianum was found to be most effective and resulted 48.26 and 59.22 % reduction in disease severity during Kharif season 2006 and 2007, respectively. Maximum increase in grain yield (16.21%) was recorded with T. harzianum followed by isolate 40 (14.58%), during Kharif season 2006. Whereas during Kharif season 2007, maximum increase in grain yield (18.95%) was recorded with T. harzianum which is followed by T. virens (14.65%) and isolate 40 (12.57 %). Present study revealed that T. harzianum (isolated from rice phylloplane) was found to be most effective in reducing disease severity and increasing grain yield as compared to other isolates obtained from different sources.

Download Full-text

GENETIC VARIABILITIES OF AGRONOMIC TRAITS AND BACTERIAL LEAF BLIGHT RESISTANCE OF HIGH YIELDING RICE VARIETIES

Indonesian Journal of Agricultural Science ◽

10.21082/ijas.v20n2.2019.p43-54 ◽

2020 ◽

Vol 20 (2) ◽

pp. 43

Author(s):

Nafisah Nafisah ◽

Celvia Roza ◽

Nani Yunani ◽

Aris Hairmansis ◽

Tita Rostiati ◽

...

Keyword(s):

Agronomic Traits ◽

Genetic Resistance ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Yield Potential ◽

Blight Resistance ◽

Wet Season ◽

Rice Varieties ◽

Superior Genotypes ◽

Productive Tiller

Hundred of high yielding and bacterial leaf blight (Xanthomonas oryzae pv. oryzae, Xoo) resistant rice varieties released since the 1960s are important sources of genetic materials for exploring superior genotypes. The study aimed to evaluate the genetic resistance of 177 rice varieties to Xoo and their agronomic traits. The evaluations were conducted at the Indonesian Center for Rice Research Experimental Station during the wet season (December 2015-March 2016). The bacterial leaf blight resistance was evaluated for Xoo pathotypes III, IV, and VIII using the clipping method. The genetic variation among genotypes was categorized as low (0–10%), medium (10–20%), and high (>20%), whereas the heritability was categorized as low (0-30%), medium (30-60%), and high (>60%). The variability of resistance to Xoo pathotypes, grain yield, and spikelet fertility was low, while the variability of plant height, productive tiller number, filled grain, and total spikelet was medium, and the variability of unfilled grain number was high. The 29 varieties were categorized as superior based on their agronomic traits or resistance to Xoo pathotypes. In conclusion, Batutegi and Fatmawati were superior in the total spikelet number, while Rojolele and Inpari 2 were supreme in the thousand-grain weight. Dodokan had a very short maturity, and Inpari 24, Conde, Kalimas, Angke, Inpari 17, and Inpara 8 had the highest resistance to Xoo pathotypes. The study implies that the identified rice superior genotypes could be used as genetic materials to design cross combinations for higher yield potential and BLB resistance varietal improvement.

Download Full-text

First Report of New Bacterial Leaf Blight of Rice Caused by Pantoea ananatis in Southeast China

Plant Disease ◽

10.1094/pdis-05-21-0988-pdn ◽

2021 ◽

Author(s):

Lin Yu ◽

Changdeng Yang ◽

Zhijuan Ji ◽

Yuxiang Zeng ◽

Yan Liang ◽

...

Keyword(s):

Oryza Sativa L ◽

Sequence Similarity ◽

Disease Incidence ◽

Leaf Blight ◽

Bacterial Leaf Blight ◽

Bacterial Suspension ◽

Rrna Gene ◽

Pantoea Ananatis ◽

Southeast China ◽

First Report

In autumn 2020, leaf blight was observed on rice (Oryza sativa L., variety Zhongzao39, Yongyou9, Yongyou12, Yongyou15, Yongyou18, Yongyou1540, Zhongzheyou8, Jiafengyou2, Xiangliangyou900 and Jiyou351) in the fields of 17 towns in Zhejiang and Jiangxi Provinces, China. The disease incidence was 45%-60%. Initially, water-soaked, linear, light brown lesions emerged in the upper blades of the leaves, and then spread down to leaf margins, which ultimately caused leaf curling and blight during the booting-harvest stage (Fig. S1). The disease symptoms were assumed to be caused by Xanthomonas oryzae pv. oryzae (Xoo), the pathogen of rice bacterial blight. 63 isolates were obtained from the collected diseased leaves as previously described (Hou et al. 2020). All isolates showed circular, smooth-margined, yellow colonies when cultured on peptone sugar agar (PSA) medium for 24h at 28℃. The cells were all gram-negative and rod-shaped with three to six peritrichous flagella; positive for catalase, indole, glucose fermentation and citrate utilization, while negative for oxidase, alkaline, phenylalanine deaminase, urease, and nitrate reductase reactions. 16S rRNA gene sequence analysis from the 6 isolates (FY43, JH31, JH99, TZ20, TZ39 and TZ68) revealed that the amplified fragments shared 98% similarity with Pantoea ananatis type strain LMG 2665T (GenBank JFZU01) (Table S3). To further verify P. ananatis identity of these isolates, fragments of three housekeeping genes including gyrB, leuS and rpoB from the 6 isolates were amplified and sequenced, which showed highest homology to LMG 2665T with a sequence similarity of 95%-100% (Table S3). Primers (Brady et al. 2008) and GenBank accession numbers of gene sequences from the 6 isolates are listed in Table S1 and Table S2. Phylogenetic analysis of gyrB, leuS and rpoB concatenated sequences indicated that the 6 isolates were clustered in a stable branch with P. ananatis (Fig. S2). Based on the above morphological, physiological, biochemical and molecular data, the isolates are identified as P. ananatis. For pathogenicity tests, bacterial suspension at 108 CFU/mL was inoculated into flag leaves of rice (cv. Zhongzao39) at the late booting stage using clipping method. Water was used as a negative control. The clipped leaves displayed water-soaked lesions at 3 to 5 days after inoculation (DAI); then the lesion spread downward and turned light brown. At about 14 DAI, blight was shown with similar symptoms to those samples collected from the rice field of Zhejiang and Jiangxi provinces (Fig. S1). In contrast, the control plants remained healthy and symptomless. The same P. ananatis was re-isolated in the inoculated rice plants, fulfilling Koch’s postulates. In the past decade, P. ananatis has been reported to cause grain discoloration in Hangzhou, China (Yan et al. 2010) and induce leaf blight as a companion of Enterobacter asburiae in Sichuan province, China (Xue et al. 2020). Nevertheless, to the best of our knowledge, this is the first report of P. ananatis as the causative agent of rice leaf blight in southeast China. This study raises the alarm that the emerging rice bacterial leaf blight in southeast China might be caused by a new pathogen P. ananatis, instead of Xoo as traditionally assumed. Further, the differences of occurrence, spread and control between two rice bacterial leaf blight diseases caused by P. ananatis and Xoo, respectively need to be determined in the future.

Download Full-text

PEMANFAATAN PIRAMIDA GEN KETAHANAN TERHADAP PENYAKIT HAWAR DAUN BAKTERI DALAM MENDUKUNG PERAKITAN VARIETAS UNGGUL PADI Application of Gene Pyramiding For Resistance to Bacterial Leaf Blight to Develop New Rice Variety

Jurnal Penelitian dan Pengembangan Pertanian ◽

10.21082/jp3.v39n1.2020.p11-20 ◽

2020 ◽

Vol 39 (1) ◽

pp. 11

Author(s):

Fatimah Fatimah ◽

Joko Prasetiyono

Keyword(s):

Molecular Marker ◽

Rice Variety ◽

Gene Pyramiding ◽

Leaf Blight ◽

Rice Production ◽

Xanthomonas Oryzae ◽

Bacterial Leaf Blight ◽

Yield Potential ◽

Rice Varieties ◽

Marker Assisted Backcrossing

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv oryzae (Xoo) is an important bacterial disease and very destructive to rice plant. BLB decreased rice production from 20%-30% up to 80%. Host-plant resistance is a cost-effective and environmentally safe approach to reduce yield loss. However the development of new rice variety by conventional selection would take several years. The genetic improvement in rice production considered as a vital program in order to ensure national food security. The availability of corresponding molecular marker makes it more precision and efficient by reducing the time required for selection. This present article highlights the molecular approach in breeding for BLB disease resistant rice varieties. In detail, it will be discussed the application of molecular marker assisted backcrossing and pyramiding gene resistance offered breeders to accelerate the rice breeding program for resistance to BLB. The pyramiding of three resistance BLB genes (xa5, Xa7, and Xa21and one gene (Xa4) as a background into two elite indica rice varieties, Ciherang and Inpari 13, was introduced successfully. The combining of conventional breeding, marker assisted backcrossing, disease evaluation, agronomic performance and yield has led the significant resistance of pyramid lines to Xoo Race III, IV and VIII in vegetative and generative phase while their yield potential was maintained (6-7 ton/ha). The current status of Ciherang-HDB and Inpari 13-HDB pyramid lines is the production of nucleoseeds and breeder seeds. This broad spectrum and durable resistance characteristic may help in controlling BLB disease in different region of Indonesia and it will facilitate the rice self-sustainability program.Keywords: Rice, gene pyramiding, plant breeding, molecular marker. AbstrakPenyakit hawar daun bakteri (HDB) yang disebabkan oleh Xanthomonas oryzae pv oryzae (Xoo) merupakan penyakit penting pada tanaman padi karena dapat menurunkan produksi padi rata-rata 20-30% bahkan dapat mencapai 80%. Penggunaan varietas tahan merupakan cara pengendalian yang paling efektif, ramah lingkungan, dan mudah dilakukan. Namun pengembangan varietas unggul baru melalui seleksi konvensional memerlukan waktu lebih lama. Perbaikan varietas padi perlu terus dikembangkan dalam mendukung ketahanan pangan dan kemandirian pangan nasional. Tersedianya marka molekuler membantu proses pemuliaan tanaman menjadi lebih presisi dan lebih efisien sehingga mengurangi waktu seleksi pada tanaman progeni. Tulisan ini memfokuskan pendekatan molekuler dalam pemuliaan varietas tahan penyakit HDB melalui piramida gen ketahanan untuk mempercepat progam pemuliaan padi tahan penyakit HDB. Kegiatan menggabungkan tiga gen ketahanan (xa5, Xa7, dan Xa21) dan satu gen (Xa4) sebagai background ke dalam padi varietas Ciherang dan Inpari-13 telah berhasil dilakukan. Melalui penggabungan beberapa pendekatan yaitu pemuliaan konvensional dan silang balik berbantu marka, evaluasi penyakit dan keragaan agronomi serta komponen hasil telah menunjukkan peningkatan ketahanan yang nyata pada galur-galur piramida Ciherang HDB dan Inpari-13 HDB pada tiga ras Xoo (Ras III, IV, dan VIII), baik pada fase vegetatif maupun generatif dengan potensi hasil tidak berbeda nyata dengan tetuanya (6-7 t/ha). Saat ini sudah diproduksi benih inti (NS) dan benih penjenis (BS) galur-galur piramida Ciherang HDB dan Inpari-13 HDB. Dengan demikian, galur-galur piramida memiliki spektrum yang luas dan mampu bertahan dalam jangka waktu lama sehingga dapat mengontrol penyakit HDB di berbagai wilayah Indonesia dan mendukung target pemerintah untuk mempertahankan swasembada beras secara berkelanjutan.Kata kunci: Padi, piramida gen, pemuliaan tanaman, marka molekuler.

Download Full-text

Susceptibility of Deciduous Azalea Cultivars to Powdery Mildew Disease

HortScience ◽

10.21273/hortsci.39.4.773a ◽

2004 ◽

Vol 39 (4) ◽

pp. 773A-773

Author(s):

Michael C. Long* ◽

Stephen L. Krebs ◽

Stan C. Hokanson

Keyword(s):

Powdery Mildew ◽

Leaf Area ◽

Disease Severity ◽

Host Resistance ◽

Resistance Mechanism ◽

Disease Symptoms ◽

Leaf Surfaces ◽

The Mean ◽

Commercial Sources ◽

Symptom Rating

Forty deciduous azalea (Rhododendron sp.) cultivars from commercial sources were evaluated for powdery mildew (Microsphaera sp.) resistance. Plants were established in two duplicate field plantings in Ohio and Minnesota and evaluated in 2002 and 2003. Plants were scored using a disease symptom rating based on the percent of leaf area infected, evaluating both ab- and adaxial leaf surfaces. Highly significant differences were found for cultivar, location, year, cultivar × location and cultivar × year for disease severity. Calendulaceum × speciosum, `Fragrant Star', `Garden Party', `Late Lady', `Millennium', `Parade', and `Popsicle' showed no powdery mildew symptoms in both locations. Another group of plants with only minimal symptoms (<25% leaf area affected) included `Jane Abbott', `Magic', `Northern Hi-Lights' and `Snowbird'. The symptom-free cultivars exhibited glaucous foliage, suggesting a potential, common resistance mechanism. The mean scores for the abaxial and adaxial leaf surfaces were 2.34 and 1.64, respectively, although four cultivars had more disease symptoms on the adaxial surface. `Arneson Gem' showed nearly a two-point difference between abaxial and adaxial scores. Evaluations of azalea powdery mildew susceptibility should consider both leaf surfaces and use the highest score as the best estimate of host resistance.

Download Full-text