Abstract
BackgroundRice blast caused by Magnaporthe oryzae (M. oryzae) is one of the most destructive diseases in rice production. Development of resistant varieties through pyramiding of resistant (R) genes is considered as an effective strategy to cope with the disease. However, is it really essential to pyramid more R genes in a specific ecological regions? To answer this question, a set of rice improved lines were developed in this study. Afterwards, the blast disease resistance and agronomic traits of the recurrent parent (RP), donor parents (DPs) and improved lines were investigated.ResultsWe developed seven improved lines, comprising three monogenic lines, three two-gene pyramids and one three-gene pyramid, by introgression of R gene(s) into a common genetic background using marker-assisted backcross breeding (MABB). Based on 302 SSR markers, the recurrent genome of the seven improved lines reached a range of 89.1 to 95.5%, with the average genome recovery of 92.9%. The pathogenicity assays inoculated with 32 different blast isolates under artificial conditions showed that the resistance spectrum of all the improved lines was significantly broadened. The assays further showed that the two-gene pyramids and the three-gene pyramid exhibited wider resistance spectrum than the monogenic lines. At natural nurseries, the three monogenic lines still showed high ratios of infected panicles, whereas the two-gene pyramids and the three-gene pyramid showed high level of panicle blast resistance. However, the two-gene pyramid R504 reached the similar resistance effect of the three-gene pyramid R507 considering resistance spectrum under artificial conditions and panicle blast resistance under field conditions. Generally, the improved lines showed comparable agronomic traits compared with the recurrent parent (RP), but the three-gene pyramid showed reduced grain yield per plant.ConclusionsAll the improved lines conferred wider resistance spectrum compared with the RP. Yet, the three monogenic lines did not work under field conditions of the two nurseries. Given the similar performances on the main agronomic traits as the RP, the two-gene pyramids have achieved the breeding goals of broad resistance spectrum and effective panicle blast resistance. Whereas, the three-gene pyramid harboring Pi2, Pi46 and Pita seems superfluous considering its reduced yield, although it also showed displayed high level of blast resistance. Thus, rational use of R genes rather than stacking more R genes is recommended to control the disease.
Highlights
Rice blast caused by Magnaporthe oryzae (M. oryzae) is one of the most destructive diseases in rice production
Some broad-spectrum resistant varieties were identified to harbor multiple R genes, including Tetep (Barman et al 2004), IR64 (Sallaud et al 2003), Sanhuangzhan 2 (Liu et al 2004), Digu (Chen et al 2004; Shang et al 2009) and Gumei2 (Wu et al 2005). These findings suggest that the combination of multiple race-specific R genes is an effective strategy to develop cultivars with broadspectrum resistance to blast disease (Hittalmani et al 2000, Tacconi et al 2010, Khanna et al 2015, Xiao et al 2016)
We developed three-gene pyramid harboring Pi2, Pi46 and Pita, two-gene pyramids harboring either two of Pi2, Pi46 and Pita and monogenic lines harboring either Pi2, Pi46 or Pita by introgression of R gene(s) into a common genetic background using marker-assisted backcross breeding (MABB)
Summary
Rice blast caused by Magnaporthe oryzae (M. oryzae) is one of the most destructive diseases in rice production. Development of resistant varieties through pyramiding of resistant (R) genes is considered as an effective strategy to cope with the disease. Afterwards, the blast disease resistance and agronomic traits of the recurrent parent (RP), donor parents (DPs) and improved lines were investigated. Rice production encounters several constraints including biotic stresses, among which rice blast caused by the ascomycete M. oryzae is the most destructive. It was reported that more than 1500 ha of rice was damaged by panicle blast disease in Leizhou City of Guangdong province, China in 2008, of which over 250 ha were completely yieldless (http://seed.aweb.com.cn/2 008/1208/155631350.shtml). Nearly 10,000 ha of rice in Guangdong province, China was affected negatively by blast disease in 2016, with about 900 ha being damaged severely (http://kb.southcn.com/content/201605/06/content_147276723.htm). Though effective fungicide was used, fungicide application is not a sustainable, viable and bio-safe option for managing the disease
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