Broad-spectrum resistance in lettuce germplasm to the soil-borne pathogens Berkeleyomyces basicola and B. rouxiae

One of the emerging biotic problems of the lettuce (Lactuca sativa) crop in Brazil is the black root rot caused by two Berkeleyomyces species, B. basicola and B. rouxiae. Although sources of resistance have already been reported for B. basicola, there is still no information about the response of distinct lettuce accessions to B. rouxiae. Herein, we evaluated a diversified germplasm collection, composed of accessions from different L. sativa morphotypes, searching for sources of genetic resistance effective against isolates of both causal agents of the black root rot disease complex. Sixty-eight L. sativa accessions were initially screened for resistance to one B. basicola isolate. Thirty-three accessions (with the highest levels of resistance) were inoculated again with two B. basicola and two B. rouxiae isolates. Similar levels of resistance were observed for the isolates of B. basicola and B. rouxiae. The lettuce morphotypes ‘Romaine’, ‘Batavian’, and ‘Crispy loose-leaf’ displayed higher frequency of accessions with resistance to both fungi. Broad-spectrum resistance against both pathogens detected in distinct lettuce morphotypes opens the opportunity for breeding programs to incorporate these genetic factors in a wide range of commercial cultivars.