Cleistothecia and Flag Shoots: Sources of Primary Inoculum for Grape Powdery Mildew in the Western Cape Province, South Africa

Halleen, F.; Holz, G.

doi:10.21548/21-2-2212

Cited by 10 publications

(8 citation statements)

References 16 publications

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“…Chasmothecia were formed on 38.7% of leaves in average, and they occurred in small number on leaves (1.1 / leaf), and most of them were immature. These results are in according with those of Halleen and Holz [15] who showed that the number of chasmothecia formed on leaves were 1-10 per leaf. No ascospores were trapped by the spore traps, nor found on the bark in spring at the beginning of the season, although they have been observed on the leaves in fall.…”

Section: Discussionsupporting

confidence: 91%

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Initiation and development of Erysiphe necator chasmothecia and their role in the epidemiology of grapevine powdery mildew in southern Syria

2016

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Powdery mildew caused by Erysiphe necator is the most important fungal disease of grapevine in southern Syria. The purpose of this study was to determine the development of chasmothecia and their role as a primary inoculum in spring. Leaves and/or branches were examined by a stereo binocular from July to December 2014 and 2015. The number of chasmothecia was estimated on both surfaces of the leaves, and their viability was estimated by microscopic examination. During 2 years of survey chasmothecia were detected in 45.5% of vineyards. The initial development of chasmothecia on infected leaves was observed in the second half of July. Their numbers increased from July to October, and the sudden reduction at the beginning of November was noted. Chasmothecia were formed on 38.7% of infected leaves, with 12.5%, 18.4%, and 7.5% on the upper, under and on both surfaces of infected leaves respectively. Chasmothecia were more frequent on the leaf under side (0.6 / leaf) than on the leaf upper side (0.4 / leaf), but their occurrence on both sides together was relatively low (0.2 / leaf), and their numbers were highly variable between vineyards and years. Microscopic examination showed that chasmothecia contained 1-5 (usually three) asci with 1-4 (usually three) ascospores in each asci, and 65.6% of chasmothecia were empty. Their viability decreased between December and February, with an average viability of 1.2% and 0.2% in March and April, respectively. Chasmothecia were not detected on bark and ascospores were not trapped at the beginning of the season. These results indicate that the ascospores have no or little role in the initiation of spring infection. To the best of our knowledge, this is the first report of E. necator chasmothecia development and their role in the initiating infection on grapevine in Syria.

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Section: Discussionsupporting

confidence: 91%

“…In contrast, in Australia chasmothecia are formed during late April and early May [14]. In South Africa, chasmothecia were also observed during April to May on severely infected leaves [15]. Chasmothecia were formed on 38.7% of leaves in average, and they occurred in small number on leaves (1.1 / leaf), and most of them were immature.…”

Section: Discussionmentioning

confidence: 99%

Initiation and development of Erysiphe necator chasmothecia and their role in the epidemiology of grapevine powdery mildew in southern Syria

2016

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“…The data coincide with the publications of Gadoury et al (2012) [38], Halleen and Holz (2000) [34] developing the hypothesis that these are spots caused by the ascospores of the pathogen. The studies on the oidium in Bulgaria show that these symptoms can be seen in the years, when during the last vegetation period, the fungus cleistothecia were massively formed.…”

Section: The Status Of the Grapevine Powdery Mildew Issue In Bulgariasupporting

confidence: 91%

“…In certain regions of California [23] the fungus is stated to survive as micelia and cleistothecia. In South Africa the sources of the initial infection are the micelium in the infected buds and the cleistothecia [34]. Gee et al (2000) [35] conclude that the cleistothecia are the source of the additional inoculum in Australia.…”

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confidence: 99%

Grapevine powdery mildew (Uncinula necator (Schw.) Burr.) – a permanent issue concerning the health status of grapes cenosis in Bulgaria

2017

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Grapes powdery mildew appeared permanently in the grapes growing regions of Bulgaria. The disease was reported in our country by Kostov in 1900. More than a century the powdery mildew disease has been causing less or greater yield losses depending on the climate. In the past when the vineyards were small and scattered, the disease was not an economic problem. Later, during the second half of the 20 th century, the grapes growing areas consolidated and enlarged, and the concentration and intensification of production took place. The pathogen spread permanently to epidemic in the vineyards and the disease became destructive and economically important. During that period commercial varieties were grown susceptible to the causal agent of the powdery mildew, and organic fungicides were applied in the disease control system. Mistakes in the grapes growing technology are observed and the disease management strategies applied are not always scientifically proved. The statements that in Bulgaria there exist conditions suitable for the appearance and development of grapes powdery mildew only in the Black sea region are disproved. A new research is necessary to be done to answer the questions about: the sources of primary inoculum, the influence of the ecological conditions on the appearance and spread of the powdery mildew, and the timing for the disease control. In the survey the overwintering of the pathogen, the appearance of the first symptoms and the dynamics of the disease spread have been discussed. As for the ecological conditions in Bulgaria, it is considered that the fungus mainly survives as mycelia in the buds and on the shoots of the vines serving as a source of a permanent infection background. The studies carried through during 1994-2002 proved that the pathogen influenced by the ecological conditions could also form cleistothecia and they could be the source of the initial infection. The effect of the leaves removal around the clusters on the spread of the grapes powdery mildew and the field resistance of some varieties were studied. Critical stages of the disease appearance and spread are defined based on the research data. Management strategies are proposed including alternative approach practices.

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“…In fact, the dominance of either sexual or asexual overwintering forms of E. necator have been investigated in several grapevine growing regions of the world (Steinkellner 1998;Grove et al 1999;Halleen and Holz 2000;Grove 2004;Miladinovic et al 2007). Th ese results are in line with many previous studies (Gemmrich and Seidel 1996;Halleen and Holz 2001;Hajjeh et al 2008).…”

Section: Chasmothecia Formationmentioning

confidence: 99%

Overwintering form of Erysiphe necator, the causal agent of grapevine powdery mildew in southern Syria

Alimad¹,

Naffaa²,

Azmeh³

2017

Journal of Plant Protection Research

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Th e main aims of this study were to determine the overwintering form and the primary inoculum of Erysiphe necator, the causal agent of grapevine powdery mildew in southern Syria. Eleven vineyards located at fi ve diff erent geographical sites were visited every week from March to November in 2014 and 2015. Th e results of fi eld and histopathological studies showed that E. necator survived as mycelium in dormant grapevine buds during the winter season. Th e fi rst fl ag shoots were observed shortly aft er bud break in spring. Th e number of fl ag shoots varied greatly according to vineyards, cultivars and years, being present on 27.4 to 61.9% of the grapevines in 2014, and on 5.2 to 40% of the grapevines in 2015. Th e percentage of fl ag shoots on the same grapevine also varied according to the year, cultivar and location. It was between 4.3 to 9.4% in 2014, and 2.1 to 3.6% in 2015. Th e disease was observed only on Balady and Black cultivars. Conidia were released from the second week of May to early September. Th e fi rst conidia were trapped around mid-May, and the fi rst secondary symptoms were observed on leaves from mid-May to early June according to the site. Chasmothecia were observed on leaves in 45.5% of the studied vineyards. Th e fi rst observation of chasmothecia on leaves was in July, and their numbers varied greatly between vineyards and years. Chasmothecia were not detected on bark, nor were ascospores trapped at the beginning of the season. Th ese results confi rmed that the ascospores did not have any role in the initiation of spring infection. To the best of our knowledge, this is the fi rst report of the overwintering form of E. necator in Syria.

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Cleistothecia and Flag Shoots: Sources of Primary Inoculum for Grape Powdery Mildew in the Western Cape Province, South Africa

Cited by 10 publications

References 16 publications

Initiation and development of Erysiphe necator chasmothecia and their role in the epidemiology of grapevine powdery mildew in southern Syria

Initiation and development of Erysiphe necator chasmothecia and their role in the epidemiology of grapevine powdery mildew in southern Syria

Grapevine powdery mildew (Uncinula necator (Schw.) Burr.) – a permanent issue concerning the health status of grapes cenosis in Bulgaria

Overwintering form of Erysiphe necator, the causal agent of grapevine powdery mildew in southern Syria

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