With reference to self-incompatibility, consider the following statements
1. Sporophytic system of self-incompatibility is governed by a single gene with multiple alleles.
2. The incompatibility reaction of pollen is governed by the genotype of the plant on which pollen is produced.
3. The 's' alleles are responsible for sporophytic incompatibility
4. Failure of pollen germination on stigma, slow pollen tube growth after pollination are some of the reasons for this self-incompatibility.
Which of the statements given above are correct?

Concerning self-incompatibility, all four statements are correct.
Self-incompatibility is a widespread mechanism in flowering plants that prevents inbreeding and promotes outcrossing.
The sporophytic system of self-incompatibility is governed by a single gene with multiple alleles. The incompatibility reaction of pollen is governed by the genotype of the plant on which pollen is produced.
The 's' alleles are responsible for sporophytic incompatibility.
Failure of pollen germination on stigma, and slow pollen tube growth after pollination are some of the reasons for this self-incompatibility.