Inheritance of Resistance to Leptosphaeria maculans in Brassica juncea

Abstract

The inheritance of resistance to Leptosphaeria maculans, the causal agent of black leg of crucifers, was studied in Brassica juncea. Three resistant accessions (UM3021, UM3043, and UM3323) and one susceptible accession (UM3132) of B. juncea were crossed in a complete diallel. Parents, F(1), and F(2) progenies were evaluated for all crosses using both cotyledon and stem inoculation. Cotyledon reaction was evaluated with two isolates of L. maculans, but stem reaction was evaluated with one isolate. Disease reactions observed for individual plants were the same for both inoculation methods and for both isolates of the pathogen for cotyledon reaction. No segregation was observed for the crosses between resistant accessions (UM3043 x UM3323 and UM3021 x UM3323), but a few susceptible plants were observed in the F(2) progeny of crosses between resistant parents (UM3021 x UM3043). This was probably due to heterozygosity in some parental plants of UM3021. For crosses be tween the susceptible parent and resistant parents, F(1) plants for two crosses were all resistant. For cross UM3132 x UM3021, some susceptible plants occurred, which was also suggestive of heterozygosity in UM3021. Although resistance in F(1) was dominant, for F(2) populations, segregation fit either 13:3, 3:1, or 1:3 ratios, indicating that resistance can be either adominant or recessive trait. F(3) families derived from some susceptible F(2) plants from crosses UM3021 x UM3132 and UM3043 x UM3132 were evaluated using the cotyledon inoculation method only. Segregation of F(2) plants and F(3) families in crosses involving resistant and susceptible parents indicated that the resistance to L. maculans in B. juncea is controlled by two nuclear genes with dominant recessive epistatic gene action.

Identification of a Brassica juncea‐derived recessive gene conferring resistance to Leptosphaeria maculans in oilseed rape

“…Through RFLP analysis Dixelius and Wahlberg (1999) identified three conserved regions in the B genome that contain genes for both seedling and adult leaf resistance. In B. juncea, resistance to L. maculans (in the seedling and adult plant) appears to be controlled by two genes with dominantrecessive epistatic interaction (Keri et al 1997) which could be identical to genes found in the B genome introgressions. From the results compiled by these researchers, one might conclude that oligogenic control of resistance exists in both the seedling and adult (stem, leaf) tissues.…”

Major Gene and Polygenic Resistance to Leptosphaeria maculans in Oilseed Rape (Brassica napus)

“…Based on cotyledon and stem resistance ratings, Keri et al (1997) suggested that resistance in B. juncea is mediated by two genes. This is consistent with genetic data obtained with L. maculans, which showed that the interaction was governed by two avirulence genes termed AvrLm5 and AvrLm6 (Balesdent et al, 2002).…”

Resistance genes toLeptosphaeria maculansinBrassica napus

“…Screening of cultivated accessions of Brassica oleracea L. and B. rapa (A genome) has not identified many accessions with resistance to L. maculans. Keri et al (1997) studied resistance in three accessions of B. juncea crossed with a susceptible accession (UM3132) to two isolates (PG2) of L. maculans and demonstrated that resistance was controlled by one dominant and one recessive gene. A similar two gene dominant-recessive interaction was found using a cross with a resistant cultivar, 'AC Vulcan', and the same susceptible line, UM3132.…”