Reaction ofBrassica junceato Australian isolates ofLeptosphaeria maculansandLeptosphaeria biglobosa‘canadensis’

Abstract

Blackleg (causal agents Leptosphaeria maculans and L. biglobosa) is the most significant disease of canola (Brassica napus) worldwide. This was the first survey of Leptosphaeria isolates recovered from Brassica juncea stubble in Australia. Sixty-four L. maculans isolates and 88 L. biglobosa 'canadensis' isolates were collected from B. juncea stubble over two years (2005)(2006). These isolates were screened over three canola quality B. juncea and three B. napus differentials. As expected, L. biglobosa 'canadensis' isolates caused lower disease severity than the L. maculans isolates. However, 13 L. biglobosa 'canadensis' isolates were capable of causing ≥50% mean internal infection on at least one of the six differentials. Although these isolates were recovered from B. juncea stubble, disease severity was low when canola quality B. juncea differentials were inoculated. The same differential lines were also screened over two field sites by placing pots containing each of the differential lines onto B. napus and B. juncea stubble from commercial fields. At one site, inoculum in B. napus stubble caused higher internal infection severity than the B. juncea stubble in all differentials except B. napus differential 'ATR-Beacon'. At the other site, however, inoculum from B. juncea stubble produced more internal infection in one B. juncea differential in 2007 and in four differentials in 2008. This investigation suggests that when B. juncea is widely grown, increased blackleg symptoms could occur and that L. biglobosa 'canadensis' isolates can contribute to disease severity.Résumé: La jambe noire, causée par Leptosphaeria maculans et L. biglobosa, est la plus importante maladie du canola (Brassica napus) à l'échelle de la planète. Cette étude est la première concernant des isolats de Leptosphaeria provenant de chaume de Brassica juncea australien. Au cours de deux années (2005)(2006), 64 isolats de L. maculans et 88 de L. biglobosa 'canadensis' ont été collectés sur du chaume de B. juncea. Ces isolats ont été criblés sur trois variétés de B. juncea de qualité comparable à celle du canola et sur trois variétés différentielles de B. napus. Comme il était prévu, la gravité de la maladie causée par les isolats de L. biglobosa 'canadensis' était moindre que celle causée par les isolats de L. maculans. Toutefois, 13 isolats de L. biglobosa 'canadensis' ont causé de l'infection interne dans au moins une des six lignées différentielles, et ce, dans une proportion moyenne de ≥50 %. Bien que ces isolats aient été collectés sur du chaume de B. juncea, la gravité de la maladie était faible lorsque des lignées différentielles de B. juncea de qualité comparable à celle du canola étaient inoculées. Les mêmes lignées différentielles ont été criblées sur deux sites en champ en plaçant des pots contenant chacune des lignées différentielles sur le chaume de cultures commerciales de B. napus et de B. juncea. À un site, l'inoculum du chaume de B. napus a causé une plus haute gravité d'infection interne que le chaume de B. juncea dans toutes ...

Impact of a resistance gene against a fungal pathogen on the plant host residue microbiome: The case of the Leptosphaeria maculans–Brassica napus pathosystem

“…Alpaga, which is sus- Leptosphaeria and Plenodomus. This should be also connected to the results of field studies from Australia whereby P. biglobosus has been shown to colonize the stems of Brassica juncea plants, a species resistant to most L. maculans isolates (Van de Wouw et al, 2008;Elliott et al, 2011).…”

“…The hypothesis that P. biglobosus colonizes the stem base niche in the absence of L. maculans or in the presence of low‐level L. maculans colonization is consistent with the results of ENA, which detected no direct interactions between Leptosphaeria and Plenodomus . This should be also connected to the results of field studies from Australia whereby P. biglobosus has been shown to colonize the stems of Brassica juncea plants, a species resistant to most L. maculans isolates (Van de Wouw et al, 2008; Elliott et al ., 2011).…”

Identification of candidate genes for blackleg resistance in the new Brassica juncea canola

“…juncea, an allotetraploid plant species with AABB genome, is produced by natural interspecific hybridisation between the diploid species B. nigra (BB) and B. rapa (AA) (U 1935;Yang et al, 2016). It is widely planted worldwide, as it is known to contain many good agronomic traits compared to B. napus, such as increased heat and drought tolerance, high blackleg and shatter resistance and early vigour (Bhardwaj et al, 2015;Chèvre et al, 1997;Elliott et al, 2011;Oram et al, 2005;Potter 2011;Van de Wouw et al, 2014a). Moreover, the B. juncea reference genome, about 922 Mb, is currently available (Yang et al, 2016).…”