The importance of the type and time of inoculation and assessment in the determination of resistance in Brassia napus and B. juncea to Sclerotinia sclerotiorum

Abstract

Sclerotinia stem rot (SSR) is a significant agricultural problem worldwide. Finding sources of resistance is crucial to the ongoing search for better management of this disease. Brassica germplasm from Australia, China and India was screened for resistance to SSR under Western Australian field conditions following stem inoculation, application of a spray of mycelial suspension, or as a consequence of myceliogenic germination originating from sclerotia resident in soil. Significant differences in response were observed among 53 genotypes using each of the three screening methods. There was a variable impact of the time of inoculation on the disease level depending upon time of assessment post-stem inoculation. However, this impact could be reduced to an insignificant level provided the assessment after stem inoculation was delayed until 3 weeks post-inoculation. The results of these studies indicate that the use of appropriate inoculation and assessment methods could significantly reduce variability in the responses commonly observed in screening for resistance in crop plants against Sclerotinia sclerotiorum.

New sources of resistance to Sclerotinia sclerotiorum for crucifer crops

“…For instance, B. napus Mystic ranked second in the study of Garg et al (2010b) and again in our study. Similarly, B. napus ZY006, which was the most resistant variety in the study of Li et al (2007), performed well again, ranking 14 out of 120 selections in our study. Selections with moderate levels of resistance such as B. juncea JM06006 (ranked 106 out of 120) and B. napus Charlton (ranked 73 out of 120) were less consistent across different screening studies.…”

“…While the expression of stem resistance in commercial field situations is generally reflected by intact field stem tests (Buchwaldt et al, 2005;Li et al, 2006Li et al, , 2007Li et al, , 2009aGe et al, 2012), and while occasionally there is correlation between detached leaf and stem in terms of expression of resistance across small and less diverse genotype sets (e.g., Bradley et al, 2006), there still remains a need to clearly determine the relevance, or otherwise, of detached leaf and detached stem assays to in-field situations. This is a critical issue, as to date, when we have evaluated published detached leaf or detached petiole with severed leaf inoculation methods across more diverse germplasm sets, there is little or no correlation between infection from such studies with either field artificial stem inoculations or natural field infections (C.X.…”

Pathogenicity of morphologically different isolates of Sclerotinia sclerotiorum with Brassica napus and B. juncea genotypes

“…This further illustrates the advantage of screening Brassica genotypes with a range of S. sclerotiorum isolates so that the reaction of different host genotypes can be precisely identified. Where such a spectrum of isolates is not readily available, it is best to use a highly pathogenic isolate such as MBRS-1, as used by Li et al (2006Li et al ( , 2007.…”

Identification of resistant sources against Sclerotinia sclerotiorum in Brassica species with emphasis on B. oleracea

“…Several researchers tried to improve resistance through traditional breeding programs (Wang et al 2004;Yu et al 2010), but practical benefits from such programs were low due to lack of germplasm with high level of resistance in rapeseed gene pool (Li et al 2007;Zhao et al 2004).…”