The food reserve in Albugo usually is

The correct option is Glycogen.

Explanation:
Albugo is a genus of plant-parasitic oomycetes (commonly referred to as white rusts). Though historically classified under fungi due to their filamentous growth habit and absorptive nutrition, they are phylogenetically distinct and belong to the group of oomycetes (kingdom Stramenopila).
Like true fungi, Albugo and other oomycetes store their surplus food reserves in the form of glycogen and oil/fat droplets. Glycogen acts as a primary energy reserve that can be quickly metabolized by the organism during growth and reproduction.
Therefore, the major food reserve in Albugo is glycogen.