Minimum 1 (the same allele exists on each chromosome set of both species - most likely scenario for conservative genes, most unlikely for high-mutating sequences such as microsatellites), maximum 4 (e.g. differrent alleles in 2n gamete of one parent, the third allele in n gamete of the other parent, and forth allele in F2 generation after backcrossing of infertile 3n hybrid with the second parent -> fertile allotetraploid).

Allele , means the alternative sequence for the wild sequence of the gene found in a locus in chromosome . in diploid organisms like humans we have three alleles for ABO types, but individual can have only two of them in his genotype , in polyploid , if I understand your question the genotype can have four different alleles ( if it found really in the population ) or may be four similar allele .

Good Luck

The answers to your question are depending at what level you are investigating the number of alleles in a particular locus.

If it is at an individual level, then:

(1) Diploid organism (2n=2x): Minimum is probably 1 and maximum are probably 2

(2) Autotetraploid organism (2n=4x): Minimum 1 and maximum 4

(3) Allo-tetraploid organism (2n=2A+2B): minimum1 and maximum 2 for loci in the chromosomal regions in A are the same as in B; and maximum 4 for loci in the chromosomal regions in A are not the same as in B.

If it is at the population level, then:

the allele numbers existed in the population are the sum of all allele diversity existed in the individual members of the population (i.e. the minimum it can be 1 and the maximum may be more than 4)

Good luck...

For an organism with 2n=4x=36 .. looks like and amphidiploid like Brassica species. Minimum copies of a gene expected is one although maximum is expected to be 6 (given the mesoploid nature of the diplod base genomes). However, due to genome rearrangements the expected copies vary a lot. 

Please refer to Cheng et al. 2012 for more details on polyploid genome structures..

Good Luck!!