1 
Supporting information1
DataS1 Eqn1inHooftmanetal.2005 2
no.ofcapitula = 50·6 (no.ofbranches)+ 177 (no.ofshoots)− 5·3 3
(Regression analysis:R2= 0.51, P < 0·001, n = 315 plants)4
 5
Table S1 Weather conditions in Sijbekarspel (SB) and Wageningen (WG) during the period of the6
experiment (May—October). InSijbekarspel,weusedadataloggertorecordtemperatureand7
humidity levels.Daily temperatureand rainfall in Wageningen waselectronically available from the8
Haarwegweatherstation(www.met.wau.nl) thatwas located aboutone km from the site.9
 Sijbekarspel Wageningen
Averagetemperature(°C ) 15.5 14.8 
Relativehumidity(%) 85.2 79.5 
Highestaveragemaximum dailytemperature(°C ) 27.4 27.9 
Lowestaverageminimum dailytemperature(°C ) 5.0 4.3 
 10
Table S2 Positions of quantitative trait loci (QTL) for seeds produced per seed sown (SPSS) in a11
recombinantinbred lines population from a Lactucasativa cv.Salinas×Lactucaserriola(UC96US23) 12
crossusing composite intervalmapping. Other RIL QTL results are described in detailin Hartman et13
al.(2012).A positiveadditiveeffectindicatesthatcropgenomicbackground(L.sativa) causes higher 14
trait values, whereas a negative additive effect indicates that the wild genomic background (L.serriola) 15
causeshighervalues.QTL on the same line have peak valueswithin 5 cM.PVE = PercentageVariation 16
Explained;AbbreviationsarelistedinTable1.  17
LG 
 
Trait Position one-LOD 
interval
Additive
effect
PVE LOD Position one-LOD 
interval
Additive
effect
PVE LOD 
 Sijbekarspel Wageningen
3 SPSS      40.8 40.3–41.0 –21.57 12.5 4.8 
 SPSS      75.5 72.7–77.5 21.93 13.5 4.3 
5 SPSS 148.0 147.2–150.2 14.61 10.0 4.0 148.0 146.6–150.6 20.40 11.4 4.8 
7 SPSS 18.5 18.4–21.5 –19.36 17.9 7.2 19.9 19.4–22.2 –28.02 21.3 8.3 
 SPSS 76.7 75.1–77.3 –29.84 16.1 6.5      
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