Quantitative resistance against an isolate of Leptosphaeria maculans (blackleg) in selected Canadian canola cultivars remains effective under increased temperatures

Abstract

Blackleg disease, caused by Leptosphaeria maculans, is a serious threat to canola production in western Canada. While specific major resistance (R) genes can be effective, they can also be eroded rapidly by a shift in pathogen race composition. Quantitative resistance (QR) has the potential to provide more durable, if less complete, protection. However, the effectiveness of QR may vary widely in the field. It has long been suspected that elevated temperatures may limit the expression of QR. To test this hypothesis, the infection development of blackleg was assessed on three common Canadian canola cultivars (74‐44 BL, PV 530 G and 45H29) showing QR, with and without a heat treatment of 7 h daily exposure to 32 °C for 1 week during rosette to early flowering under controlled environment conditions. The impact of elevated temperature on the susceptibility to blackleg was compared with that of a moderate temperature with a 22 °C daytime high. A susceptible cultivar, Westar, was used as a control. When data from both temperatures were pooled, all three QR cultivars showed lower blackleg severity relative to Westar. Elevated temperatures increased blackleg severity in Westar only (in terms of the stem‐lesion length from the inoculation of the first true‐leaf petiole in trials involving Westar and 74‐44 BL) and in pooled data for disease severity index in trials involving Westar, PV 530 G and 45H29. These findings suggest that the QR traits in 74‐44 BL, PV 530 G and 45H29 are useful for blackleg management in western Canada, especially under warmer growing conditions when plants are at the rosette to early flowering stages.

Exploring Mechanisms of Quantitative Resistance to Leptosphaeria maculans (Blackleg) in the Cotyledons of Canola (Brassica napus) Based on Transcriptomic and Microscopic Analyses

“…Specifically, more restricted host tissue colonization and lesion development were observed on 74-44 BL, relative to Westar. Earlier studies [12,32] also found consistent QR with 74-44 BL in stems, as well as in cotyledons, against multiple Lm races, confirming the race-nonspecific nature of resistance. This study also found that the Lm hyphal growth often extended beyond the borders of visible lesions in Westar, while the growth was consistently restricted within the lesion in 74-44 BL.…”

“…However, the enrichment analysis did not uncover any GO terms related to PCD (Supplementary Tables S6 and S7). Furthermore, the upregulation of BnaC09g20030D, with sequence similarity to a Bax inhibitor-1, might negate the effect of BnaCnng58090D by inhibiting PCD [32]. The hypersensitivity that DCD would otherwise be induced in response to infection might be prevented by the upregulation of BnaC09g20030D in Westar.…”

“…The differential reaction of the 74-44 BL cotyledons to Lm isolates with and without AvrLm1 and AvrLm3 (Supplementary Figure S1) confirmed the presence of Rlm1/LepR3 and Rlm3. 74-44 BL also carries a level of QR against multiple Lm races in cotyledons [12], with lower lesion scores [32], more restricted Lm colonization [12], as well as QR displayed in adult plants in the absence of major-gene interactions [32].…”

Fine mapping of Brassica napus blackleg resistance gene Rlm1 through bulked segregant RNA sequencing

“…Although recent data showed lower presence of AvrLm1 in L . maculans populations 28,29 due to use of Rlm1 in canola cultivars extensively 30 , Rlm1 could still be valuable for effective control of blackleg disease in Canada as a strategy through rotation of R genes that has been recently implemented.…”

Effect of Elevated CO2 Concentration on the Disease Severity of Compatible and Incompatible Interactions of Brassica napus–Leptosphaeria maculans Pathosystem

“…have been identified [29,30,31,32,33]. Apart from the qualitative resistance (major gene resistance), the effect of quantitative resistance against an isolate of L. maculans in selected Canadian canola cultivars under increased temperature was investigated [34]. Very few studies have reported on the effects of environmental changes, especially the CO 2 concentration, on the interactions of the B. napus–L.…”