Genetic diversity within and between sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides in Japan

Abstract

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides, six sulfonylurea-resistant (SU-R) and eight sulfonylurea-susceptible (SU-S) populations were analysed using 40 polymorphic inter-simple sequence repeat loci. The plants were collected from three widely separated regions: the Tohoku, Kanto and Kyushu districts of Japan. Genetic diversity values (Nei's gene diversity, h) within each SU-S population ranged from h = 0.125 to h = 0.235. The average genetic diversity within the SU-S populations was H S = 0.161, and the total genetic diversity was H T = 0.271. Although the H S of the SU-R populations (0.051) was lower than that of the SU-S populations, the H T of the SU-R populations (0.202) was comparable with that of the SU-S populations. Most of the genetic variation was found within the region for both the SU-S and SU-R populations (88% of the genetic variation respectively). Two of the SU-R populations showed relatively high genetic diversity (h = 0.117 and 0.161), which were comparable with those of the SU-S populations. In contrast, the genetic diversity within four SU-R populations was much lower (from h = 0 to 0.018) than in the SU-S populations. The results suggest that selection by sulfonylurea herbicides has decreased genetic diversity within some SU-R populations of S. juncoides. The different level of genetic diversity in the SU-R populations is most likely due to different levels of inbreeding in the populations.

Microsatellite variability of sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides (Cyperaceae) in Kinki, Japan

“…The result of the present study is inconsistent with that of ISSR analysis of Japanese S. juncoides populations (Imaizumi et al ., ), in that the latter detected lower levels of genetic diversity in SU‐R populations than in SU‐S populations. The reason of the difference between the results is largely unknown.…”

“…In this study, microsatellite analysis revealed a high value of genetic differentiation among populations ( G ST = 0.617 for a total of 21 populations). This value is comparable with those estimated with ISSR data ( G ST = 0.403 for SU‐S populations and G ST = 0.746 for SU‐R populations) (Imaizumi et al ., ). Compared with other weed species, S. juncoides seems to have a higher level of differentiation.…”

“…Genetic diversity is expected to be lower in populations characterised by herbicide resistance, because of the bottleneck effect on the whole genome throughout the process of resistance selection, especially in predominantly self‐fertilising populations (Imaizumi et al ., , ). In the present study, SU‐R populations and populations with mixed SU‐R and SU‐S individuals showed slightly lower values for average gene diversity, compared with that observed in SU‐S populations.…”

“…No significant difference was observed in genetic diversity between SU‐R and SU‐S populations after anova , and no significant correlation was found between population values of H S and the frequency of resistant individuals. This result is mostly inconsistent with previous studies that have indicated a lower level of genetic diversity in herbicide‐resistant populations than that in susceptible populations of S. juncoides (Imaizumi et al ., ) and other species (Warwick & Black, ; Mengistu et al ., ; Imaizumi et al ., ; Aper et al ., ). Although our results about the frequencies of SU‐R individuals within populations must be considered with caution because of small number of samples and large variances of the estimates, the lack of relationship between the level of genetic diversity and the degree of resistance at population level indicate that positive selection for the SU‐R phenotype in the presence of herbicide does not necessarily accompany genome‐wide reduction in genetic variation.…”

“…Imaizumi et al . () studied genetic relationships among Japanese S. juncoides populations distantly located to each other. In the present study, sampling of SU‐S and SU‐R individuals from spatially adjacent populations, combined with the use of highly sensitive microsatellite markers, allows us to infer a contribution of gene flow to dispersal of herbicide resistance among populations.…”