Can i say cell fusion instead of zygote?

No

Explanation:

because cel fusion is when the male and female cell fuse together while the zygote is an already fused male and female cell

In fungi,The sexual fusion of haploid cells is called karyogamy

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs