Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Abstract

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures >30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.

Geographic location and year determine virulence, and year determines genetic change, in populations of Neopseudocercosporella capsellae

“…Manning & Tiedemann, ; Rosenzweig et al , ). Other Australian studies on rapeseed have demonstrated more severe disease under warmer rather than cooler temperatures, including for H. brassicae (Mohammed et al , ), Erysiphe cruciferarum (Uloth et al , ) and L. maculans (Barbetti, ; Li et al , ). The present study with isolates collected in 2016 across three states of Australia highlights distinct overall differences in terms of virulence between the states.…”

Molecular characterization of disease resistance in Brassica juncea – The current status and the way forward

“…Such impacts include changes of temperature, rainfall, and humidity, the main drivers of plant disease severity. For example, the expression of some Brassica resistance genes against pathogens are temperature dependent, including blackleg (Li et al, 2006b), TuMV (Nyalugwe et al, 2014), Sclerotinia (Uloth et al, 2015c), powdery mildew (Uloth et al, 2018), and downy mildew epidemics in B. juncea and B. napus (Mohammed et al, 2018a). Li et al (2006a) argued that resistance against sclerotinia stem rot may not be currently necessary for B. juncea due to its optimal cultivation in low rainfall regions, where the conditions are less favourable for this disease.…”

“…Such impacts include changes of temperature, rainfall, and humidity, the main drivers of plant disease severity. For example, the expression of some Brassica resistance genes against pathogens are temperature dependent, including blackleg (Li et al, 2006b), TuMV (Nyalugwe et al, 2014), Sclerotinia (Uloth et al, 2015c), powdery mildew (Uloth et al, 2018), and downy mildew epidemics in B . juncea and B .…”

“…In Australia, blackleg and sclerotinia have been identified as the most destructive diseases for oilseed-and vegetable-type mustards (Murray and Brennan, 2012;Uloth et al, 2013Uloth et al, , 2014Uloth et al, , 2015aUloth et al, , 2015bVan de Wouw et al, 2016). However, there are several other diseases also identified as important in Australia, including TYV, downy mildew, white leaf spot, alternaria blight, bacterial leaf blight, and powdery mildew (Li et al, 2006a(Li et al, , 2007(Li et al, , 2008a(Li et al, , 2009bEshraghi et al, 2007;Murray and Brennan, 2012;Gunasinghe et al, 2014;Van de Wouw et al, 2016;Mohammed et al, 2017Mohammed et al, , 2018aMohammed et al, , 2018bMohammed et al, , 2019Al-lami et al, 2019aAl-lami et al, , 2019bAl-lami et al, , 2019cGuerret et al, 2017;Uloth et al, 2016Uloth et al, , 2018Murtza et al, 2019).…”

“…napus , epidemics are favoured by warmer seasonal conditions such as occur in late winter/early spring that coincide with more susceptible and more mature plants, and it is likely the same applies for B . juncea (Uloth et al, 2018).…”