Biological Diversity Of Alternaria Spp. Isolated From Diseased And Healthy Leaves Of An Invasive Plant Eupatorium Adenophorum

The invasion of exotic plant Eupatorium adenophorum causes serious ecological and society problems, as well as great losses of economy in Southwest of China. Currently it is very necessary to elucidate the invasive mechanisms of E. adenophorum and further to control its spread. In recent years, several reports provide evidence that Alternaria can destroy seriously the leaves of E. adenophorum by production of toxin, and therefore has great potential for biocontrolling E. adenophorum spread. However, both Alternaria with pathogeneity and with symptomless infection are very common in a variety of native plants. Alternaria cannot be applied as biocontrol agent of E. adenophorum till the genetic relationships between these strains are characterized.In this case, 279 Alternaria strains were isolated from diseased and healthy leaves of E. adenophorum, and leaf spot of several native plants living around of E. adenophorum, as well as atmosphere of E. adenophorum habitat. Restriction fragment length polymorphism (RFLP) of their ITS rRNA genes were performed by three restrictive enzymes, Haeâ…¢, RsaI and Hin fâ… . Then 274 Alternaria strains with the same RFLP pattern of ITS rRNA gene were carried out analysis of genetic variation based on Alt gene sequences and randomly amplified microsatelites (RAMs). Furthermore, pathogeneity, morphology and sporulation patterns of these strains were also determined. Some conclusions were made:1. Alternaria isolated from diseased and healthy leaves of E. adenophorum are rich in genetic diversity. The resulted 190 strains were divided into 19 haplotypes based on their Alt gene sequences. These haplotypes were phylogenetically close to Alternaria alternate, A. arborescens, A. tenuissima, A. dumosa, A. limoniasperae, A. longipes and A. solani.2. Among obtained 23 haplotypes, haplotype 9 is numberically dominant, including 161 strains from four isolation resources. Although most of strains isolated from E. adenophorum belonged to haplotype 9, strains belonged to other 18 haplotypes were also observed. Therefore, Alternaria strains living in leaves of E. adenophorum are not genetically distinct from other isolation resources of Alternaria.3. Alt gene sequences and randomly amplified microsatelites (RAMs) were carried out analysis of molecular variance (AMOVA). No genetic differentiation was found among Alternaria populations obtained neither from different regions, from different invaded history, nor from different isolation resources.4. Because the same Alt gene haplotype contains many strains from different species of Alternaria and a variety of Alternaria species belonged to the same Alt gene haplotype, it is suggested that some species of Alternaria are possibly named by mistakes.5. The pathogeneity of Alternaria to E. adenphorum varied from genetic background, morphology and isolation resources. Strains with sporulation pattern 3 cause the strongest damage to leaves of E. adenophorum. Meanwhile, strains with bigger size of spores have more damage to leaves of E. adenophorum. In addition, strains from haplotype 7 are the most toxic to leaves of E. adenophorum, in contrast, those from haplotype 12 have little adverse effects on leaves of E. adenophorum. In total, strains only isolated from leaf spot displayed stronger damage than those only from healthy leaves of E. adenophorum.