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Core accretion and disk instability have traditionally been regarded as thetwo competing possible paths of planet formation. In recent years, evidencehave accumulated in favor of core accretion as the dominant mode, at least forclose-in planets. However, it might be hypothesized that a significantpopulation of wide planets formed by disk instabilities could exist at largeseparations, forming an invisible majority. In previous work, we addressed thisissue through a direct imaging survey of B2--A0-type stars, and concluded that<30% of such stars form and retain planets and brown dwarfs through diskinstability, leaving core accretion as the likely dominant mechanism. In thispaper, we extend this analysis to FGKM-type stars by applying a similaranalysis to the Gemini Deep Planet Survey (GDPS) sample. The results strengthenthe conclusion that substellar companions formed and retained around theirparent stars by disk instabilities are rare. Specifically, we find that thefrequency of such companions is <8% for FGKM-type stars under our mostconservative assumptions, for an outer disk radius of 300 AU, at 99%confidence. Furthermore, we find that the frequency is always <10% at 99%confidence independently of outer disk radius, for any radius from 5 to 500 AU.We also simulate migration at a wide range of rates, and find that theconclusions hold even if the companions move substantially after formation.Hence, core accretion remains the likely dominant formation mechanism for thetotal planet population, for every type of star from M-type through B-type.

How do Most Planets Form? -- Constraints on Disk Instability from Direct Imaging