Can a pilot rated in one category solo in another category without a current flight review? Scenario:


A pilot is rated to fly gliders in the United States.  
The pilot allows his glider flight review to lapse.
That pilot now decides he wants to get a type rating for the airplane category, single engine land.  


Question:


Does the pilot have to be flight review current in order to solo in a powered airplane?
(Secondary question, as long as we are at it) Does the pilot have to be flight review current in order to take the FAA practical (check ride) in a powered airplane?


Note: I'm most interested in the answer under US FAA regulations, though the answer in other countries would be of interest as well.

I have spent some time looking over the FARs, specifically 14 CFR 61.56 and I cannot find anything conclusive either way. 

I should mention that I suspect the answer to this question to be no, though I am not prepared to offer evidence to back this up.

I've already seen this related question asking whether a biennial flight review is valid for any airplane category, but I don't believe it's a duplicate because that only covers the situation where the pilot is rated in both catagories. This question refers to the situation where the pilot is rated in one category, but not the other.
You do require a flight review, per the Beard (2013) interpretation:


  Finally, you have also asked whether a person operating in solo flight
  under a § 61.31(d) endorsement must comply with the flight review
  requirements in § 61.56(c). With a few listed exceptions, no person
  make act as pilot in command of an aircraft unless within the previous
  24 calendar months that person completed a flight review with an
  authorized  instructor. 14 C.F.R. § 61.56(c). Section 61.56(g)
  provides an exception for student pilots provided the student pilot is
  undergoing training for a certificate and has a current solo flight
  endorsement as required under § 61.87. Because this exception applies
  to student pilots, a pilot who holds a higher level pilot certificate
  and has an endorsement for solo flight under § 61.31(d) must comply
  with the flight review requirements in § 61.56 before acting as pilot
  in command of any aircraft.


Regarding the student pilot exception, others have suggested in comments that you are in fact a student pilot because you're new to the category/class. However, the interpretation says you are not:


  Section 61.81 states that subpart C "prescribes the requirements for
  the issuance of student pilot certificates, the conditions under which
  those certificates are necessary, and the general operating rules and
  limitations for the holders of those certificates." As such, by its
  express language, subpart C to part 61 applies only to those persons
  who are seeking or hold a student pilot certificate.


So, since you will be acting as PIC and none of the exceptions in 61.56 apply, you need a flight review. As for a checkride, the person taking the checkride is acting as PIC (61.47(b)) so again, you would need a valid flight review.