Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2007
Publication Date: 10/24/2007
Citation: Liu, B., Wasilwa, L.A., Guerber, J.C., Morelock, T.E., Oneill, N.R., Correll, J.C. 2007. Comparison of Colletotrichum orbiculare and several allied Colletotrichum species for mtDNA RFLPs, intron RFLP and sequence variation, vegetative compatibility, and host specificity. Phytopathology. 97:1305-1314 Interpretive Summary: The fungus called Colletotrichum consists of a large number of species, each one causing a different disease on different plants. These fungi attack the foliage and stems of economically important crops worldwide. One of the most devistating diseases is on alfalfa, caused by the fungus Colletotrichum trifolii. Other economically important diseases occur on bean and cucurbit crops are and are caused by different Colletotrichum species. It is really hard to tell these fungi apart, even with the aid of a microscope. Four species are so similar that their distinction is based only on the plant that they attack. Since it is not possible to tell them apart, you can't figure out how to treat the disease. Basic information about the specific cause of a disease is important to scientists and breeders so that they will be able to control the diseases. We used molecular and biology tools to come up with a way to tell them apart. We demonstrated that the four organisms can be distinguished by definable characteristics and that they should be recognized as four distinct species. The research will be used by breeders, seed companies, APHIS, and research scientists concerned with controlling diseases caused by fungi in the genus Colletotrichum.
Technical Abstract: Based on spore morphology, appressorium development, sequence similarities of the rDNA and similarities in amplified restriction fragment length polymorphism (AFLPs), others have concluded that C. orbiculare, C. trifolii, C. lindemuthianum, and C. malvarum represent a single phylogenetic species. In this study, 72 isolates of C. orbiculare from cucurbit or weed hosts, C. trifolii from alfalfa, C. lindemuthianum from green bean, and C. malvarum from prickly sida were examined for mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs), RFLPs and sequence variation of a 900 bp intron of the glutamine synthetase gene and a 200 bp intron of the glyceraldehyde-3-phosphate dehydrogenase gene, and vegetative compatibility. In addition, host specificity was examined in foliar inoculations on cucurbit, bean, and alfalfa hosts. Inoculations also were conducted on cucumber fruit. Isolates of C. orbiculare, C. trifolii, and C. malvarum had an identical mtDNA haplotype (haplotype A) when examined with each of three restriction enzymes. Isolates of C. lindemuthianum had very similar mtDNA haplotype to haplotype A, with a single polymorphism detected with the enzyme HaeIII. The four species represent a monophyletic group and, although phylogenetically closely related based on intron sequence analysis, distinct RFLPs in the 900 bp intron were consistently associated with each species and could be used to qualitatively distinguish each species. Furthermore, each of the species showed a distinct host specificity with isolates of C. orbiculare (from cucurbits), C. lindemuthianum, and C. trifolii only being pathogenic on cucurbits, green beans, and alfalfa, respectively. Consequently, it is proposed that distinct and fixed genotypic (intron sequences and RFLPs) and phenotypic characteristics (host specificity) can be used to distinguish C. oribulare, C. lindemuthianum, and C. trifolii from one another and that they should be recognized as distinct species.