A standardised method for the quantitative analysis of resistance to grapevine powdery mildew

Abstract

Powdery mildew caused by Erysiphe necator is one of the most important diseases affecting grapevine (Vitis vinifera, L.). Control of this pathogen is based on the use of fungicides, which cause environmental damage and increase production costs. A costeffective and environmentally friendly alternative to control the disease relies on using resistant varieties. While most V. vinifera cultivars are susceptible to powdery mildew, several species belonging to the Vitaceae have been described as resistant. Several loci for resistance to grapevine powdery mildew have been identified through genetic analysis of segregating populations derived from different resistance sources. Identifying quantitative trait loci (QTL) with minor effects on the resistance may prove valuable in a strategy of pyramiding, which aims at increasing the durability of the resistance. However, current methods for evaluation of resistance either do not take into account quantitative variations, or, if they do, are not adapted to large sample sets. Here we develop a method for the analysis of quantitative resistance to grapevine powdery mildew in large populations. We devised a semi-quantitative resistance scale and confirmed the usefulness of a cell counter to quantify sporulation. We compared three inoculation methods and identified dry inoculation using a settling tower as the one giving the best infection. Finally, we confirmed the value of the method by applying it to a set of plants segregating for resistance to E. necator. Using the method described here for the quantitative analysis of the resistance to powdery mildew will prove valuable for breeding for durable resistance.

Screening for resistance of grape varieties to powdery mildew (Erysiphenecator) disease

“…These can be crossed to varieties such as Chancellor to produce hybrids which will have combined traits of disease resistance, high yielding and excellent flavour quality. This is in agreement with previous studies which reported that susceptible varieties of Vitis vinifera cultivars can be introgressed to varieties with resistant traits to produce hybrid varieties which on top of excellent attributes they have hybrid [25,20,6,3,1]. Producing new varieties with several disease resistance including powdery mildew helps to keep plant health and maintain its sugar content in fruits and avoids damages from other pests thus maintain original quality [5,28].…”

“…These results are complementary with other authors who have been documented that, when using these two methods of screening grapevine samples against resistance to powdery mildew, suspension E. necatorinoculum has shown high disease severity than dry inoculation method, [18,19] reported the similar results by comparing the differences in the effectiveness of these two inoculation methods of which suspension method responded positively. However, [1] on his study, dry inoculation showed more efficient compared to wet and drop inoculation methods used. The infection efficiency may be important component of rate reducing resistance; suspension inoculation method has been reported to be more efficiency on sporulation of inoculum where, the earlier of the first symptoms of the pathogen appeared, the more severe powdery mildew infection was observed on the leaves and clusters [3].…”

“…Powdery mildew is a disease caused by a fungal, Erysiphe necator, which is an obligate parasite of most grapevine(Vitis vinifera L.) varieties [1]. The grape powdery mildew was first reported in North America in 1834 [2], China in the 1950's and in Africa in 1880 [3].…”

“…In addition, continuous use of fungicides is not only costly but affects the environment. Therefore, development of grapevine varieties which are resistant to powdery mildew is the only cost-effective and environmentally friendly approach towards management of the disease [1].This study therefore, aims to screen grape varieties for resistance to powdery mildew in order to introduce appropriate traits which may be useful for the development of grapevine resistant varieties.…”

Quantitative Resistance to Biotrophic Filamentous Plant Pathogens: Concepts, Misconceptions, and Mechanisms

“…Phenotypic screens in seedlings may reveal effects of so-called adult plant resistance genes if seedlings are submitted to low temperature and to very homogeneous administration of inoculum, e.g., Lr34 (106), and if very detailed observations are performed. Successful phenotyping for minor differences in QR depends on precise inoculation methods, such as settling towers (18,33,79,110), and on appropriate observation criteria in monocyclic tests. To detect differences in LP and infection frequency (Video 1), careful and laborious observations are required in order to map QTLs with small-sized to medium-sized effects.…”