Molecular evolution of shattering loci in U.S. weedy rice

Cultivated rice fields worldwide are plagued with weedy rice, a conspecific weed of cultivated rice (Oryza sativa L.). The persistence of weedy rice has been attributed, in part, to its ability to shatter (disperse) seed prior to crop harvesting. In the United States, separately evolved weedy rice groups have been shown to share genomic identity with exotic domesticated cultivars. Here, we investigate the shattering phenotype in a collection of U.S. weedy rice accessions, as well as wild and cultivated relatives. We find that all U.S. weedy rice groups shatter seeds easily, despite multiple origins, and in contrast to a decrease in shattering ability seen in cultivated groups. We assessed allelic identity and diversity at the major shattering locus, sh4, in weedy rice; we find that all cultivated and weedy rice, regardless of population, share similar haplotypes at sh4, and all contain a single derived mutation associated with decreased seed shattering. Our data constitute the strongest evidence to date of an evolution of weeds from domesticated backgrounds. The combination of a shared cultivar sh4 allele and a highly shattering phenotype, suggests that U.S. weedy rice have re‐acquired the shattering trait after divergence from their progenitors through alternative genetic mechanisms.     

Zearalenone production in barley

A plot of barley cv. Golden Promise was sprayed with an isolate of Fusarium culmorum known to produce zearalenone, an oestrogenic toxin. The grain was harvested and stored under conditions that were known to induce toxin production in sterilized grain inoculated with the same strain. Toxin was not found in the harvested grain but appeared 20 wk after storage. A plot of unsprayed barley was harvested at the same time as the sprayed plot. F. culmorum was isolated from the grain at the time of harvesting but there was no toxin detectable. This appeared at the same time as toxin in the sprayed plot. Higher concentrations of zearalenone were produced in the control suggesting that the F. culmorum isolated was either a different strain from that used to inoculate the sprayed plot or that the microbial flora of the grain affected toxin production.