scholarly journals Cercosporin From Pseudocercosporella capsellae and its Critical Role in White Leaf Spot Development

Plant Disease ◽  
2016 ◽  
Vol 100 (8) ◽  
pp. 1521-1531 ◽  
Author(s):  
Niroshini Gunasinghe ◽  
Ming Pei You ◽  
Gregory R. Cawthray ◽  
Martin J. Barbetti
Keyword(s):  
Host Species ◽  
Leaf Spot ◽  
Critical Role ◽  
Chemical Extraction ◽  
Leaf Spot Disease ◽  
Raphanus Raphanistrum ◽  
Spot Disease ◽  
White Leaf ◽  
Pink Pigment

Pseudocercosporella capsellae, the causative agent of white leaf spot disease in Brassicaceae, can produce a purple-pink pigment on artificial media resembling, but not previously confirmed as, the toxin cercosporin. Chemical extraction with ethyl acetate from growing hyphae followed by quantitative (thin-layer chromatography [TLC] and high-performance liquid chromatography [HPLC]) and qualitative methods showed an identical absorption spectrum, with similar retardation factor (Rf) values on TLC papers and an identical peak with the same retention time in HPLC as for a standard for cercosporin. We believe this is the first report to confirm that the purple-pink pigment produced by P. capsellae is cercosporin. Confocal microscopy detected green autofluorescence of cercosporin-producing hyphae, confirming the presence of cercosporin inside hyphae. The highly virulent UWA Wlra-7 isolate of P. capsellae produced the greatest quantity of cercosporin (10.69 mg g−1). The phytotoxicity and role of cercosporin in disease initiation across each of three Brassicaceae host species (Brassica juncea, B. napus, and Raphanus raphanistrum) was also studied. Culture filtrates containing cercosporin were phytotoxic to all three host plant species, producing large, white lesions on highly sensitive B. juncea, only water-soaked areas on least sensitive R. raphanistrum, and intermediate lesions on B. napus. It is noteworthy that sensitivity to cercosporin of these three host species was analogous to their susceptibility to the pathogen, viz., B. juncea the most susceptible, R. raphanistrum the least susceptible, and B. napus intermediate. The presence of cercosporin in the inoculum significantly increased disease severity on the highly cercosporin-sensitive B. juncea. We believe that this is the first study to demonstrate that P. capsellae produces cercosporin in liquid culture rather than agar media. Finally, this study highlights an important role of cercosporin as a pathogenicity factor in white leaf spot disease on Brassicaceae as evidenced by the ability of the cercosporin-rich culture filtrate to reproduce white leaf spot lesions on host plants and by the enhanced virulence of P. capsellae in the presence of cercosporin.

Canola Growth Stage at Time of Infection Determines Magnitude of White Leaf Spot (Neopseudocercosporella capsellae) Impact

Plant Disease ◽  
2020 ◽  
Author(s):  
Tamsal Murtza ◽  
Ming Pei You ◽  
Martin John BARBETTI
Keyword(s):  
Plant Growth ◽  
Seed Yield ◽  
Leaf Spot ◽  
Growth Stage ◽  
Disease Incidence ◽  
Leaf Spot Disease ◽  
Leaf Stage ◽  
Spot Disease ◽  
White Leaf ◽  
Field Plots

White leaf spot (Neopseudocercosporella capsellae) is a persistent and increasingly important foliar disease for canola (Brassica napus) across southern Australia. To define the role of plant growth stage on development of the disease epidemic, we first investigated the response of different canola cultivars (Scoop and Charlton) at five Sylvester-Bradley growth stages against N. capsellae. White leaf spot disease incidence and severity was dependent upon plant growth stage and cultivar (both P < 0.001), with plants being most susceptible at plant growth stage 1,00 (cotyledon stage) followed by plant growth stage 1,04 (4th leaf stage). Then, second, to quantify the impact of this disease on canola yield, we investigated the in-field relationship of white leaf spot disease incidence and severity with seed yield loss following artificial inoculation commencing at growth stage 1.04 (4th leaf stage). White leaf spot significantly (P < 0.001) reduced seed yield by 24% in N. capsellae inoculated field plots compared with non-inoculated field plots. We believe that this is the first time that serious seed yield losses from this disease have been quantified in-field. The current study demonstrates that N. capsellae disease incidence and severity on canola is determined by host growth stage at which pathogen infestation occurs. Emerging seedling cotyledons were highly susceptible, followed by less susceptibility in first true leaves to emerge but then increasing susceptibility as plants subsequently age towards the 4th leaf stage. This explains field observances where white leaf spot readily establishes on emerging seedlings and subsequently becomes more prevalent and severe as plants age.

Outstanding host resistance will resolve the threat from white leaf spot disease (Pseudocercosporella capsellae) to oilseed and vegetable Brassica spp.crops

2017 ◽  
Vol 46 (2) ◽  
pp. 137-146 ◽  
Author(s):  
Niroshini Gunasinghe ◽  
Ming Pei You ◽  
Surinder S. Banga ◽  
Shashi K. Banga ◽  
Martin J. Barbetti
Keyword(s):  
Host Resistance ◽  
Leaf Spot ◽  
Leaf Spot Disease ◽  
Spot Disease ◽  
White Leaf ◽  
Vegetable Brassica

scholarly journals Temperature Drives Contrasting Alternaria Leaf Spot Epidemic Development in Canola and Mustard Rape from Alternaria japonica and A. brassicae

Plant Disease ◽  
2020 ◽  
Vol 104 (6) ◽  
pp. 1668-1674
Author(s):  
Hebba F. D. Al-lami ◽  
Ming Pei You ◽  
Martin J. Barbetti
Keyword(s):  
Host Species ◽  
Leaf Spot ◽  
Critical Role ◽  
Disease Index ◽  
Leaf Spot Disease ◽  
Alternaria Leaf Spot ◽  
Different Temperatures ◽  
Percent Disease Index ◽  
Epidemic Development ◽  
Lower Temperature

Recent surveys of canola (Brassica napus) crops across southern Australia highlighted that Alternaria leaf spot on canola is not solely caused by Alternaria brassicae but that other Alternaria spp. are also involved, including A. japonica. Studies were undertaken into the effects of different temperatures (14 and 10°C [day and night] or 22 and 17°C [day and night]) on development of Alternaria leaf spot caused by A. japonica as compared with A. brassicae in cotyledons (embryonic leaves) and true leaves (first leaves) of canola (B. napus ‘Thunder TT’) and mustard rape (B. juncea ‘Dune’). Both pathogens expressed less disease at lower temperatures of 14 and 10°C with percent disease index (%DI) of 19.1 for A. japonica and 41.8 for A. brassicae, but expressed significantly more disease at higher temperatures of 22 and 17°C with %DI of 80.8 and 88.2 for the same pathogens, respectively. At 14 and 10°C, mustard rape cotyledons showed less disease (percent cotyledons disease index [%CDI] = 18.1) from A. japonica but showed more disease (%CDI = 75.0) from A. brassicae. However, at 22 and 17°C, cotyledons and true leaves of both canola and mustard rape showed significantly more disease and varied in expressing the disease severity to the two pathogens; true leaves of mustard rape showed less disease (percent true leaf disease index [%TDI] = 48.4) from A. japonica but showed more disease (%TDI = 92.0) from A. brassicae. At 22 and 17°C, cotyledons of canola expressed more disease from A. japonica (%CDI = 99.1) than from A. brassicae (%CDI = 70.7). At the lower temperature, both host species showed the least disease, with mean %DI of 27.3 and 33.5 for canola and mustard rape, respectively, as compared with the higher temperatures, where there was a greater DI, with %DI values of 87.9 and 81.2 for these same host species, respectively. We believe that these are the first studies to highlight the critical role played by temperature for A. japonica as compared with A. brassicae in Alternaria leaf spot disease development and severity. These findings explain how temperature affects Alternaria leaf spot severity caused by A. japonica as compared with A. brassicae on different foliage components of canola and mustard rape.

TWO NEW SEVERE LEAF SPOT DISEASE ON FOREST TREES OF JALGAON (MAHARASTRA) INDIA

2017 ◽  
Vol 23 (2) ◽  
Author(s):  
S. A. FIRDOUSI
Keyword(s):  
Leaf Spot ◽  
Fungal Disease ◽  
Leaf Spot Disease ◽  
Forest Trees ◽  
First Report ◽  
Spot Disease ◽  
Severe Leaf

During the survey of the forest fungal disease, of Jalgaon district, two severe leaf spot diseases on Lannae coromandelica and ( Ougenia dalbergioides (Papilionaceae) were observed in Jalgaon, forest during July to September 2016-17. The casual organism was identified as Stigmina lanneae and Phomopsis sp. respectively1-4,7. These are first report from Jalgaon and Maharashtra state.

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