Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2008
Publication Date: 6/1/2008
Citation: Njambere, E.N., Chen, W., Frate, C., Wu, B., Temple, S.R., Muehlbauer, F.J. 2008. Stem and Crown Rot of Chickpea in California Caused by Sclerotinia trifoliorum. Plant Disease.92:917-922.
Interpretive Summary: Chickpea white mold can be caused by three Sclerotinia spp. S. minor, S. sclerotiorum, and S. trifoliorum. S. sclerotiorum is the common cause of chickpea white mold world wide. In North America, both S. minor and S. trifoliorum are reported to cause white mold of chickpea. S. trifoliorum along with S. sclerotiorum is reported to occur on chickpea only in Australia. During investigation of Sclerotinia white mold of chickpea in central California, isolates showed obvious different characteristics that indicate different species are involved. This research was conducted to determine the species identities of Sclerotinia isolates obtained from chickpea plants showing stem and crown rot, using cultural characteristics, ascospore morphology, variations in group I introns and ITS sequences. Results correlated a number of cultural characters and molecular markers with the definitive morphological character of ascospore dimorphism, and conclusively showed for the first time in North America that S. trifoliorum causes crown and stem rot of chickpea. The results impact on management of the disease in choosing rotational crops and selecting production fields.
Technical Abstract: The identities of Sclerotinia isolates obtained from chickpea (Cicer arietinum L.) plants showing stem and crown rot were determined using cultural characteristics, ascospore morphology, variations in group I introns and ITS sequences. Isolates could be separated into two groups based on growth rates at 25°C on PDA, fast growing (attained 40 mm colony diameter in 24 hours) vs. slow growing (attained 20 mm colony diameter in 24 hours). All fast growing isolates produced acid that induced strong color change of a pH-indicating medium, whereas all slow growing isolates did not induce color change or induced only slight color change of the pH-indicating medium. The slow growing isolates contained at least one group I intron in the nuclear small subunit rDNA, whereas all fast growing isolates lacked group I introns in the same DNA region. ITS sequences of the slow growing isolates were identical to previously deposited sequences of Sclerotinia trifoliorum. ITS sequences of the fast growing isolates were identical to deposited sequences of S. sclerotiorum. There are two single nucleotide differences in ITS sequences between the fast growing and the slow growing isolates. Finally, the slow growing isolates showed ascospore dimorphism, a definitive character of S. trifoliorum, whereas the fast growing isolates showed no ascospore dimorphism. Isolates of both the slow growing and the fast growing are pathogenic on chickpea and caused symptoms similar to those observed in the field. This study not only correlated the differences between S. sclerotiorum and S. trifoliorum in growth rates, group I introns, ITS sequences and ascospore morphology, but also represented the first report that S. trifoliorum causes stem and crown rot of chickpea in North America.