Cultivar Susceptibility and Environmental Parameters Affecting Symptom Expression of Red Leaf Blotch of Almond in Spain

Abstract

Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and Middle East regions. In recent years, the incidence of this disease has increased in Spain corresponding to increases in the area of newly-planted orchards and the use of susceptible cultivars. In 2009, an experimental orchard including 21 almond cultivars was planted at Les Borges Blanques, Lleida, NE Spain. No fungicide treatments were applied during the 10-year experimental period (2009-2018) in order to allow natural disease development. Cultivar susceptibility to RLB was assessed each year, from 2011 to 2018, through visual observations of symptoms in naturally-infected trees. The experimental results led us to classify the cultivars into five susceptibility groups. The most susceptible were 'Tarraco', 'Guara', 'Tuono', 'Marinada', 'Desmayo Largueta', and 'Soleta', whereas 'Mardía' was the most tolerant. The annual incidence of disease was positively correlated with accumulated rainfall in spring, and especially in April, while it was negatively correlated with high spring and summer temperatures, especially in May. These findings could be used to improve disease management strategies by identifying the most susceptible cultivars and improving the timing of fungicide application.

Susceptibility of Almond (Prunus dulcis) Cultivars to Twig Canker and Shoot Blight Caused byDiaporthe amygdali

“…Tul.) (Miarnau et al 2021;Ollero-Lara et al 2019;Teviotdale et al 2002), as well as by the reemergence of old ones such as anthracnose (Colletotrichum acutatum J.H. Simmonds) (López-Moral et al 2019), and the new branch canker and dieback diseases caused by trunk pathogens (Gramaje et al 2012;Holland et al 2021;Olmo et al 2016).…”

“…In Spain, Egea et al (1984) carried out an evaluation of the susceptibility to red leaf blotch with 81 almond cultivars. In California, Gradziel and Wang (1994) carpophilus (Miarnau et al 2021;Ollero-Lara et al 2019).…”

Airborne inoculum dynamics of Polystigma amygdalinum and progression of almond red leaf blotch disease in Catalonia, NE Spain

“…A Hirst 7-day recording volumetric spore trap (Burkard Manufacturing Co. Ltd., Rickmansworth, Hertfordshire, England) was placed in a central position in each orchard, under 'Tarraco' trees, a highly susceptible cultivar to RLB (Miarnau et al, 2021). Spore traps operated with an airflow of 10 L min À1 from mid-February (weeks 7-8) to mid-September (weeks 36-37) 2019-2021.…”

“…On each tree, 50 fully expanded leaves were arbitrarily selected from new shoots, at different heights and orientations on the outer canopy, and visually assessed. Disease incidence and severity were evaluated according to procedures described by Miarnau et al (2021). RLB incidence was recorded as the percentage of leaves showing at least one identifiable RLB lesion regardless of its size, whereas RLB severity was estimated from the mean percentage of affected leaf surface, by classifying leaves into the following category classes: class 0 (0% affected leaf surface), 1 (1%-10%), 2 (11%-20%), 3 (21%-50%), and 4 (>50%).…”

“…Thus, the main objectives of this study were: (i) to describe the dynamics of P. amygdalinum airborne ascospores over a 3-year period in NE Spain using spore traps coupled with qPCR-based methods, (ii) to explore the correlations between ascospore catches and weather variables, (iii) to model the RLB disease progress over time, and (iv) to explore the correlations of disease progress with weather variables and ascospore catches. (Vargas et al, 2008), grafted onto 'INRA GF 677' rootstock, planted in 2007, pruned as openvase, and with a tree spacing of 7 m  6 m. In both orchards, RLB disease occurs naturally (Miarnau et al, 2021). Orchards were drip irrigated, and pruning, soil management, and fertilization were based on the Spanish Integrated Production Management practices (BOE, 2002).…”