Final germination of stratified (solid lines and symbols) and nonstratified (dashed, open symbols) seeds of herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> populations across a range of oxygen levels.

<p>Seeds were germinated at 25°C and 0 MPa, following three months of chilling at 3°C in water (stratified) or under dry conditions (nonstratified). Symbols represent averages of observations ±SE based on six replicate sets of 35 seeds; lines are linear regressions. The LSD_0.05 for the interaction between population and stratification treatment was  = 7% with 192 d.f.</p

Germination rates (GR, calculated by replicate as the inverse of median time to germination (<i>1/t₅₀</i>) using Equation 5) following 24 days of stratification at three temperatures <<i>T_b</i> for germination.

<p>Herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> seeds were germinated at 14/26°C night/day, 0 MPa and 21% oxygen. Values are averages ±SE of 3 replicate sets of 50 seeds.</p

Herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> germination in response to stratification duration and water potential.

<p>Seeds were immersed in PEG solutions of 0, −0.4, −0.8 and −1.6 MPa at a constant 5°C for 3, 4, 7, 10, 14, 17, 23, 30, 57 and 92 days prior to germination at 21°C and 0 MPa. Final germination for all treatments was ≥95%. Germination rates were calculated by replicate as the inverse of median time to germination (<i>1/t₅₀</i>), which was determined from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071457#pone.0071457.e005" target="_blank">Equation 5</a>. Seeds were germinated at 17/24°C night/day temperatures, 0 MPa and 21% oxygen. Symbols are averages of two replicates of 50 seeds per treatment. Peak GR was attained at 30, 23, 30, 23, 23 and 17 days of stratification in 0 MPa for AL, CR, HR, KS, RD and SW, respectively. The LSD_0.05 for the interaction between population, stratification duration and stratification <i>Ψ</i> was 0.06; d.f.  = 478.</p

Average observed (symbols) and predicted (lines) germination among herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> populations across a gradient of for stratified (solid) and nonstratified (open/dashed) seeds.

<p>Seeds were germinated following three months of chilling at 3°C in water (stratified) or under dry conditions (nonstratified). Hydrotime germination models were fit by replicate with the equation<i> probit(g)</i>  =  [<i>Ψ</i> – <i>θ_H</i>/<i>t_g</i>–<i>Ψ_b</i>(50)]/σ<i>_Ψb</i>, where <i>Ψ</i> is experimental water potential, <i>θ_H</i> is the hydrotime constant to germination, <i>t_g</i> is time to germination of fraction <i>g</i> of the seed population, <i>Ψ_b</i>(50) is median base water potential and σ<i>_Ψb</i> is the standard deviation in <i>Ψ_b</i> among seeds in a population. Average stratified and nonstratified root mean squared errors (RMSE) ±SE were: 0.079±0.009 and 0.082±0.009 for CR, 0.065±0.006 and 0.107±0.003 for HR, 0.082±0.005 and 0.116±0.014 for KS, and 0.077±0.006 and 0.126±0.007 for SW, respectively. Symbols represent averages of observations and bars represent SE based on six replicate sets of 35 seeds.</p

Effects of alternating temperatures on final germination (G) and germination rates (GR, calculated by replicate as the inverse of median time to germination (<i>1/t₅₀</i>) using Equation 5) of herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i>.

<p>Nonstratified seeds were germinated at 0 MPa and 21% oxygen, with temperatures either held constant at 20°C or set to 14/26°C day/night regime. Values are averages ±SE of four replicate sets of 50 seeds.</p

Parameters of the hydrotime model (Equation 2) characterizing the responses of herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> populations germinated at 25°C, 21% oxygen and <i>Ψ</i> of 0, −0.2, −0.4 or −0.7 MPa, after being stratified [16] or not for three months at 3°C; <i>θ_H</i> is the hydrotime constant; <i>Ψ_b</i>(50) is median base water potential, and<i>σ_Ψb</i> is the standard deviation in <i>Ψ_b</i> among seeds around <i>Ψ_b</i>(50).

<p>Models were fit for each of six replicates; values are parameter averages ±SE.</p

Maximum germination rates (GR, calculated by replicate as the inverse of median time to germination (<i>1/t₅₀</i>) using Equation 5) after stratification at 5°C under various water potentials.

<p>GR was assessed for each herbicide-resistant (R) and –susceptible (S) <i>E. oryzicola</i> population after 0, 3, 4, 7, 10, 14, 17, 28, 35, 57 and 92 days of stratification and values are averages ±SE of the maximum GR for each replicate.</p>a.<p>To meet ANOVA assumptions, a Box-Cox transformation (λ  =  −1.8) was applied.</p

Final germination of stratified (solid lines and symbols) and nonstratified (dashed lines, open symbols) seeds of herbicide-resistant (R) populations (KS and SW) and –susceptible (S) <i>E. oryzicola</i> populations (CR and HR) across a range of water potentials.

<p>Seeds were germinated for 14 days at 25°C and 21% oxygen following three months of chilling at 3°C. Symbols represent averages of 6 observations ±SE; the LSD_0.05 for the interaction between population and stratification treatment was 7% with 192 d.f.; lines are polynomial regressions.</p

Escape to Ferality: The Endoferal Origin of Weedy Rice from Crop Rice through De-Domestication

<div><p>Domestication is the hallmark of evolution and civilization and harnesses biodiversity through selection for specific traits. In regions where domesticated lines are grown near wild relatives, congeneric sources of aggressive weedy genotypes cause major economic losses. Thus, the origins of weedy genotypes where no congeneric species occur raise questions regarding management effectiveness and evolutionary mechanisms responsible for weedy population success. Since eradication in the 1970s, California growers avoided weedy rice through continuous flood culture and zero-tolerance guidelines, preventing the import, presence, and movement of weedy seeds. In 2003, after decades of no reported presence in California, a weedy rice population was confirmed in dry-seeded fields. Our objectives were to identify the origins and establishment of this population and pinpoint possible phenotypes involved. We show that California weedy rice is derived from a different genetic source among a broad range of AA genome <i>Oryzas</i> and is most recently diverged from <i>O</i>. <i>sativa</i> temperate <i>japonica</i> cultivated in California. In contrast, other weedy rice ecotypes in North America (Southern US) originate from weedy genotypes from China near wild <i>Oryza</i>, and are derived through existing crop-wild relative crosses. Analyses of morphological data show that California weedy rice subgroups have phenotypes like medium-grain or gourmet cultivars, but have colored pericarp, seed shattering, and awns like wild relatives, suggesting that reversion to non-domestic or wild-like traits can occur following domestication, despite apparent fixation of domestication alleles. Additionally, these results indicate that preventive methods focused on incoming weed sources through contamination may miss burgeoning weedy genotypes that rapidly adapt, establish, and proliferate. Investigating the common and unique evolutionary mechanisms underlying global weed origins and subsequent interactions with crop relatives sheds light on how weeds evolve and addresses broader questions regarding the stability of selection during domestication and crop improvement.</p></div

Average population differentiation estimates (<i>Ф</i>_<i>ST</i>) between California weedy rice and other rice groups.

<p>Average population differentiation estimates (<i>Ф</i>_<i>ST</i>) between California weedy rice and other rice groups.</p