Characterization of New Races of Xanthomonas oryzae pv. oryzae in Mali Informs Resistance Gene Deployment

Abstract

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae represents a severe threat to rice cultivation in Mali. Characterizing the pathotypic diversity of bacterial populations is key to the management of pathogen-resistant varieties. Forty-one X. oryzae pv. oryzae isolates were collected between 2010 and 2013 in the major rice growing regions in Mali. All isolates were virulent on the susceptible rice variety Azucena; evaluation of the isolates on 12 near isogenic rice lines, each carrying a single resistance gene, identified six new races (A4 to A9) and confirmed race A3 that was previously reported in Mali. Races A5 and A6, isolated in Office du Niger and Sélingué, were the most prevalent races in Mali. Race A9 was the most virulent, circumventing all of the resistance genes tested. Xa3 controlled six of seven races (i.e., 89% of the isolates tested). The expansion of race A9 represents a major risk to rice cultivation and highlights the urgent need to identify a local source of resistance. We selected 14 isolates of X. oryzae pv. oryzae representative of the most prevalent races to evaluate 29 rice varieties grown by farmers in Mali. Six isolates showed a high level of resistance to X. oryzae pv. oryzae and were then screened with a larger collection of isolates. Based on the interactions among the six varieties and the X. oryzae pv. oryzae isolates, we characterized eight different pathotypes (P1 to P8). Two rice varieties, SK20-28 and Gigante, effectively controlled all of the isolates tested. The low association observed among races and pathotypes of X. oryzae pv. oryzae suggests that the resistance observed in the local rice varieties does not simply rely on single known Xa genes. X. oryzae pv. oryzae is pathogenically and geographically diverse. Both the races of X. oryzae pv. oryzae characterized in this study and the identification of sources of resistance in local rice varieties provide useful information to inform the design of effective breeding programs for resistance to bacterial leaf blight in Mali.

Pathotype profiling, distribution and virulence analysis of Xanthomonas oryzae pv. oryzae causing bacterial blight disease of rice in Bangladesh

“…The variability of Xoo isolates has been reported from many countries including Bangladesh (Alam et al, 2016;Islam et al, 2016;Noer et al, 2018;Tekete et al, 2020). But no one yet uses the Xa23 gene for the identification of pathotypic variations in Xoo.…”

“…Xoo can be further classified into races based on the ability to infect different rice cultivars. To date, over 30 races of Xoo have been discovered all over the world (Mishra et al., 2013; Reddy, 1979; Tekete et al., 2020) and Xoo can cause up to 70% yield loss under favourable condition (Reddy, 1979). All growth stages of rice are susceptible to BB albeit the amount of yield loss depends on crop stage, degree of susceptibility and environmental conditions (Mew, 1993; Ou, 1984).…”

Intra‐regional diversity of rice bacterial blight pathogen,Xanthomonas oryzaepv.oryzae, in the Andaman Islands, India: revelation by pathotyping and multilocus sequence typing

“…2008; Tekete et al . 2020) and selection of appropriate host genetic backgrounds for resistance transfer (Sakthivel et al . 2017) are highly recommended.…”

Assessment of potentiality of known bacterial blight resistant genes against Xanthomonas oryzae pv. oryzae pathotypes exist in Bangladesh

“…Around 2 -5 resistance genes from 16 gene pyramids derived in 10 NILs (near isogenic lines) and IRBB lines were detected against 61 isolates that Xa21 and Xa13 genes accorded resistance to more than average Xoo isolates in Pakistan (Khan et al, 2012). A combination of three R-genes Xa1, Xa3, and Xa4 in promising lines could lead to a significant outcome controlling BLB in suitable areas of Mali reported by Tekete et al (2020) Pyramiding line bearing Xa2, Xa4, Xa5 would be the highest fruitful genotype for developing Korean cultivars against BB resistance (Jeung et al 2006) as similar to our findings. IRBB63 showed resistance to around 75% of total pathotypes followed by IRBB57, IRBB58, IRBB64 (62.50% each) and IRBB65, IRBB52 (50.00% each), while IRBB61 showed susceptibility to all of the pathotypes followed by IRBB60, IRBB53, IRBB54.…”