There is no definitive answer to this question as it depends on a number of factors, such as what you consider to be rare, and what your definition of a tractor is. However, we can narrow it down to a few contenders for the title of rarest tractor in the world.
One possibility is the Lamborghini Orione, which was produced in very limited numbers between 1974 and 1976. Only about 60 of these tractors were ever made, making them extremely rare and sought-after by collectors. Another contender is the Ferrari F130, which was also produced in very limited numbers (between 30 and 40). These tractors are incredibly valuable due to their rarity and association with luxury brands; an Orione sold for $110,000 at auction in 2014 while a F130 sold for $200,000 in 2015.
Other contenders for the title of rarest tractor include antique or vintage models that are no longer in production. For example, the John Deere Model D was only produced between 1918 and 1924; fewer than 10,000 were made during that time period and they are now highly prized by collectors. Similarly, the Allis-Chalmers WD45 was only manufactured between 1953 and 1957; fewer than 40,000 were ever made so they too are quite rare today.
So there you have it â€“ some possible contenders for the title of rarest tractor in the world!