Quantitative trait loci (QTL) analysis for Sclerotinia stem rot resistance was carried out in five doubled haploid (DH) populations of Brassica napus. Sclerotinia stem rot is caused by the necrotrophic fungus Sclerotinia sclerotiorum (Lib.) de Bary. Sclerotinia stem rot has worldwide occurrence and causes significant yield losses in many crop species. Several screening methods have been recommended in the literature to evaluate plant resistance to Sclerotinia stem rot. Four controlled environment based screening methods: 1) excised leaf assay, 2) cotyledon assay, 3) mycelial stem inoculation technique and 4) petiole inoculation technique compared for their ability to differentiate between plant susceptibility/resistance, their reliability and suitability for large scale screening using eight B. napus cultivars/lines of varying reaction to S. sclerotiorum. The petiole inoculation technique and the mycelium stem inoculation technique were identified as reliable methods in this study. Previously developed, five B. napus DH populations (H1, H2, H3, DH179 and DH180) segregating for resistance to Sclerotinia stem rot were used in this study. The petiole inoculation technique was used to evaluate resistance to Sclerotinia stem rot. Data on days to wilting was recorded for a two week period. Twelve plants per line were screened in each evaluation and each population was evaluated three times. Two to three day-old mycelial cultures of S. sclerotiorum isolate Canada 77 was used. QTL analyses were carried out using a LOD threshold value of 2.5 on each individual replicate and on the average of all the replicates. In the H1 population, the number of QTL detected ranged from four to six in each analysis. In the H2 population, there were three to six QTL in each analysis. There were two to six QTL in each analysis of the H3 population. In the DH179 population, the number of QTL detected ranged from three to five in each analysis. In DH180 population, the number of QTL identified varied from three to six in each analysis. A number of common QTL were found between the replicates of each population. Five common QTL were identified between these populations. The markers linked to these QTL are now available for marker assisted selection.

Quantitative trait loci (QTL) analysis for Sclerotinia stem rot resistance was carried out in five doubled haploid (DH) populations of Brassica napus. Sclerotinia stem rot is caused by the necrotrophic fungus Sclerotinia sclerotiorum (Lib.) de Bary. Sclerotinia stem rot has worldwide occurrence and causes significant yield losses in many crop species. Several screening methods have been recommended in the literature to evaluate plant resistance to Sclerotinia stem rot. Four controlled environment based screening methods: 1) excised leaf assay, 2) cotyledon assay, 3) mycelial stem inoculation technique and 4) petiole inoculation technique compared for their ability to differentiate between plant susceptibility/resistance, their reliability and suitability for large scale screening using eight B. napus cultivars/lines of varying reaction to S. sclerotiorum. The petiole inoculation technique and the mycelium stem inoculation technique were identified as reliable methods in this study. Previously developed, five B. napus DH populations (H1, H2, H3, DH179 and DH180) segregating for resistance to Sclerotinia stem rot were used in this study. The petiole inoculation technique was used to evaluate resistance to Sclerotinia stem rot. Data on days to wilting was recorded for a two week period. Twelve plants per line were screened in each evaluation and each population was evaluated three times. Two to three day-old mycelial cultures of S. sclerotiorum isolate Canada 77 was used. QTL analyses were carried out using a LOD threshold value of 2.5 on each individual replicate and on the average of all the replicates. In the H1 population, the number of QTL detected ranged from four to six in each analysis. In the H2 population, there were three to six QTL in each analysis. There were two to six QTL in each analysis of the H3 population. In the DH179 population, the number of QTL detected ranged from three to five in each analysis. In DH180 population, the number of QTL identified varied from three to six in each analysis. A number of common QTL were found between the replicates of each population. Five common QTL were identified between these populations. The markers linked to these QTL are now available for marker assisted selection.

Canola/rapeseed (Brassica napus L.) is a major oilseed crop worldwide. However, its production is largely affected by the fungal disease Sclerotinia stem rot as well as seed glucosinolates. So far the genetic mechanisms controlling these two traits have been poorly understood. In the present study, three bi-parental doubled haploid B. napus populations M730, M692 and ZT were grown in either natural or artificial environments and genotyped using the Brassica 60K Infinium® SNPs and/or sequence related amplified polymorphisms. Three genetic linkage maps covered 2,597.7 cM, 2,474.1 cM and 1,731.6 cM in 19 chromosomes for M730, M692 and ZT, respectively. Plants were inoculated with Sclerotinia sclerotiorum mycelia on stems at the reproductive stage to evaluate their resistivity. Four aliphatic glucosinolates and one indolic glucosinolate were detected in the seeds using high-performance liquid chromatography. 4-hydroxy-3-indolylmethyl predominated over aliphatic glucosinolates in canola, but inversely constituted a small portion of total glucosinolate content in semi-winter rapeseed. In rapeseed, 2-hydroxy-3-butenyl predominated in 4C aliphatic glucosinolates, which in turn predominated in total aliphatic glucosinolates, which likewise predominated in total glucosinolate content. QTLs regulating major glucosinolates were located on chromosome A9 for high glucosinolate content populations M730 and ZT, and on chromosome C7 for low glucosinolate content population M692. Major QTLs for Sclerotinia stem rot resistance were located on chromosomes A7 and C6 in M730, on chromosomes A3 and A7 in ZT, while no major QTLs were found in M692. Additive genetic effect was the major factor explaining phenotypic variations of the two traits. No direct genetic relationship was observed between Sclerotinia stem rot resistance in adult plants and seed glucosinolates in B. napus. The findings in the studies could be used to formulate breeding and research strategies in B. napus and the major QTLs controlling the two traits and their closely linked SNP markers could be validated over wide germplasm and used in marker assisted selection. / October 2016

<p>  </p> <p><em>Sclerotinia sclerotiorum </em>is a soilborne pathogen of soybean that causes Sclerotinia stem rot, alternatively called white mold. Sclerotinia stem rot can cause significant yield losses under cool and wet environmental conditions. Two biofungicides, <em>Coniothyrium minitans </em>and <em>Bacillus amyloliquefaciens, </em>are currently available and labeled to limit or suppress <em>S. sclerotiorum</em> in soybean. These biofungicides can be applied in place of synthetic foliar fungicides to provide an alternative mode of action for the control of Sclerotinia stem rot. However, limited information is available regarding the efficacy of <em>C. minitans </em>and <em>B. amyloliquefaciens </em>as biocontrol agents of <em>S. sclerotiorum </em>in soybean and the sensitivity of the biofungicides biological activity on <em>S. sclerotiorum </em>to pesticides commonly used in soybean production systems. This research aims to provide management recommendations for <em>S. sclerotiorum </em>in soybean using <em>C. minitans </em>and <em>B. amyloliquefaciens </em>and to develop guidelines for how to incorporate the biofungicides into an established soybean pest management program. To assess the effectiveness of <em>C. minitans </em>and <em>B. amyloliquefaciens </em>as biocontrol agents of <em>S. sclerotiorum </em>dual culture, amended media, and soil plate assays were conducted along with experiments in the growth chamber and field. The presence of a distinct inhibition zone surrounding the <em>B. amyloliquefaciens </em>colony in the dual culture assay and the absence of mycelial growth on the media plates amended with <em>B. amyloliquefaciens </em>confirmed that the bacteria can control the mycelial growth of <em>S. sclerotiorum </em>through antibiosis. The absence of an inhibition zone surrounding the <em>C. minitans </em>isolate in the dual culture assay along with the degradation of sclerotia following treatment with <em>C. minitans </em>in the soil plate assay indicates an inability to limit the mycelial growth of <em>S. sclerotiorum </em>and confirms that the primary mode of action is mycoparasitism. In the growth chamber, <em>B. amyloliquefaciens</em> at 14.03 L/ha applied using the dip method significantly reduced Sclerotinia stem rot lesion length when compared to the non-treated control and resulted in the lowest lesion area under the disease progress curve (lAUDPC). When <em>B. amyloliquefaciens </em>and <em>C. minitans </em>were applied in the field, no differences were observed between treatments for soybean moisture, test weight, or yield. To evaluate the sensitivity of <em>B. amyloliquefaciens </em>and <em>C. minitans</em> biological activity on <em>S. sclerotiorum </em>to pesticides commonly used in soybean production systems a poison plate assay as well as soil plate, growth chamber, and field experiments were conducted. In the poison plate assay <em>C. minitans </em>was most sensitive to the preemergence herbicide flumioxazin and the synthetic fungicides boscalid and fluazinam, while <em>B. amyloliquefaciens </em>was sensitive only to the synthetic fungicide fluazinam. In the soil plate assay the mycoparasitic activity of <em>C. minitans </em>on sclerotia of <em>S. sclerotiorum </em>was sensitive to flumioxazin, metribuzin, glyphosate, picoxystrobin, and boscalid. In the controlled environment experiments, none of the pesticides tested decreased the efficacy of <em>B. amyloliquefaciens</em>. There were no significant interactions between <em>C. minitans </em>and <em>B. amyloliquefaciens </em>with preemergence herbicides, postemergence herbicides, and synthetic fungicides for soybean moisture, test weight, and yield. This research demonstrates that <em>B. amyloliquefaciens </em>and <em>C. minitans </em>are effective biocontrol agents of <em>S. sclerotiorum </em>in soybean. However, antagonistic relationships exist between the biofungicides and certain preemergence, postemergence, and synthetic fungicides used in soybean production systems.</p>