The role of precipitation, and petal and leaf infections in Sclerotinia stem rot of spring oilseed Brassica crops in Norway

Abstract

Sclerotinia stem rot (SSR) is the most important disease of oilseed Brassica crops in Norway. Fungicide applications should be aligned with the actual need for control, but the SSR prediction models used lack accuracy. We have studied the importance of precipitation, and the role of petal and leaf infection for SSR incidence by using data from Norwegian field and trap plant trials over several years. In the trials, SSR incidence ranged from 0 to 65%. Given an infection threshold of 25% SSR, regression and Receiver Operating Characteristics (ROC) analysis were used to evaluate different precipitation thresholds. The sum of precipitation two weeks before and during flowering appeared to be a poor predictor for SSR infection in our field and trap plant trials (P = 0.24, P = 0.11, respectively). Leaves from three levels (leaf one, three, five), and petals were collected at three to four different times during flowering from nine field sites over two years and tested for SSR infection with real-time PCR. Percentage total leaf and petal infection explained 57 and 45% of variation in SSR incidence, respectively. Examining the different leaves and petals separately, infection of leaf three sampled at full flowering showed the highest explanation of variation in later SSR incidence (R 2 = 65%, P < 0.001). ROC analysis showed that given an infection threshold of 45%, both petal and leaf infection recommended spraying when spraying was actually needed. Combining information on petal and leaf infection during flowering with relevant microclimate factors in the canopy, instead of the sum of precipitation might improve prediction accuracy for SSR.

Modeling first order additive × additive epistasis improves accuracy of genomic prediction for sclerotinia stem rot resistance in canola

“…Ideally, in a plant breeding context, plants would be screened under the environment in which they are to be cultivated. However, this may be difficult for sclerotinia stem rot resistance because of the very sporadic nature of the disease (Ficke et al., 2018). Since a controlled screen is an abstraction from such a field environment anyway, it may be better in this case to attempt to mitigate as much environmental variability as possible by using a controlled environment instead of a glasshouse in future.…”

“…The fungus Sclerotinia sclerotiorum infects several hundred plant species in diverse dicotyledonous families (Boland & Hall, 1994). Many of its hosts are important crops, in which it may substantially reduce yield in conditions conducive to infection (Ficke et al., 2018). One of the most economically important oilseed crops infected by S. sclerotiorum is canola ( Brassica napus L. subsp.…”

Predicting field diseases caused by Sclerotinia sclerotiorum: A review

“… a 1, Kurle et al (2001); 2, Holley and Nelson (1986); 3, Schwartz and Steadman (1978); 4, Fall, Willbur, et al (2018); 5, McCartney and Lacey (1991); 6, Willbur, Fall, Bloomingdale, et al (2018); 7, Jones et al (2012); 8, Bom and Boland (2000); 9, Boland and Hall (1988b); 10, Boland and Hall (1988c); 11, Gugel and Morrall (1986); 12, Gracia‐Garza et al (2002); 13, Morrall and Dueck (1982); 14, Qandah and del Río Mendoza (2012); 15, Reich et al (2017); 16, Kader et al (2018); 17, Turkington & Morrall (1993); 18, Makowski et al (2005); 19, Ficke et al (2018); 20, Wallenhammer et al (2007). …”

“…Petal infection has been consistently positively correlated with disease in the field, with most studies showing a moderate to strong positive correlation between the two. Nevertheless, the degree of association may be influenced by sampling time of day (Turkington et al, 1991), stage of the crop (Ficke et al, 2018; Turkington & Morrall, 1993) and location of flowers within canopy (Ficke et al, 2018). Subsequent disease development is moderated by the environment and, as a result, it can be difficult to generalize findings across studies.…”

Baseline Sensitivity and Control Efficacy of Various Group of Fungicides against Sclerotinia sclerotiorum in Oilseed Rape Cultivation

“…The pathogen can infect oilseed rape crops in two different ways, either basal infection in autumn from myceliogenically germinated sclerotia (happens seldom) or in spring through ascospores that come from carpogenic germination of sclerotia (main way of infection). Flower petals of oilseed rape supply as an energy source to help ascospore infection of healthy plants [2]. Once disease is established, it can expand to stem, leaves, and pods.…”