Sources and Origin of Resistance toXanthomonas campestrispv.campestrisinBrassicaGenomes

Abstract

Two hundred and seventy-six accessions of mainly Brassica spp. were screened for resistance to Xanthomonas campestris pv. campestris races. In Brassica oleracea (C genome), the majority of accessions were susceptible to all races, but 43% showed resistance to one or more of the rare races (2, 3, 5, and 6) and a single accession showed partial resistance to races 1, 3, 5, and 6. Further searches for resistance to races 1 and 4, currently the most important races worldwide, and race 6, the race with the widest host range, were made in accessions representing the A and B genomes. Strong resistance to race 4 was frequent in B. rapa (A genome) and B. napus (AC genome), indicating an A genome origin. Resistance to races 1 and 4 was present in a high proportion of B. nigra (B genome) and B. carinata (BC genome) accessions, indicating a B genome origin. B. juncea (AB genome) was the most resistant species, showing either strong resistance to races 1 and 4 or quantitative resistance to all races. Potentially race-nonspecific resistance was also found, but at a lower frequency, in B. rapa, B. nigra, and B. carinata. The combination of race-specific and race-nonspecific resistance could provide durable control of black rot of crucifers.

Comparison of Positions of QTLs Conferring Resistance to <i>Xanthomonas campestris</i> pv. <i>campestris</i> in <i>Brassica oleracea</i>

“…Nine races of Xcc have been identified to date from pathogenicity tests based on the interaction between differential cultivars and races [5][6][7][8][9]. [7] reported that the appearance of race 1 and 4 was predominant worldwide and other races, 2, 3, 5 and 6, were rare.…”

“…Screening for Xcc resistance was performed in Brassica species and related species [11][12][13][14] and extensive screening using more than 100 genotypes was done by [8]. As a result, resistance to Xcc has been identified in genotypes of B. rapa (A genome), B. nigra (B), B. oleracea (C), B. carinata (BC), B. juncea (AB), and B. napus (AC).…”

Characterization of isolates that cause black rot of crucifers in East Africa

“…The predominance of races 1 and 4 can be attributed to wide cultivation of B. oleracea cultivars that are susceptible to these races. This is also supported by the lack of observation of symptoms on B. carinata which has been reported to display resistance to races 1 and 4 (Taylor et al, 2002). The limited observation of race 1 in Tanzania and absence in Uganda could be attributed to the small sampling population.…”

“…Management of this disease is mainly based on using pathogen-free planting material (seeds or transplants) and eliminating potential sources of inoculum especially crop debris and cruciferous weeds (Taylor et al, 2002). However, Xcc is a seed-borne pathogen that is difficult to eliminate from seeds (Roberts et al, 1999) and therefore pathogen-free planting material is not always available.…”

“…Resistance to these races has not been reported in B. oleracea (C genome) but in B. rapa (A), Brassica nigra (B) and Brassica carinata (BC) (Taylor et al, 2002). Studies on the nature of resistance to race 1 and 4 in B. rapa ssp.…”