Disease Resistance and Molecular Variations in Irradiation Induced Mutants of Two Pea Cultivars

Induced mutation is useful for improving the disease resistance of various crops. Fusarium wilt and powdery mildew are two important diseases which severely influence pea production worldwide. In this study, we first evaluated Fusarium wilt and powdery mildew resistance of mutants derived from two elite vegetable pea cultivars, Shijiadacaiwan 1 (SJ1) and Chengwan 8 (CW8), respectively. Nine SJ1 and five CW8 M₃ mutants showed resistant variations in Fusarium wilt, and the same five CW8 mutants in powdery mildew. These resistant variations were confirmed in M₄ and M₅ mutants as well. Then, we investigated the genetic variations and relationships of mutant lines using simple sequence repeat (SSR) markers. Among the nine effective SSR markers, the genetic diversity index and polymorphism information content (PIC) values were averaged at 0.55 and 0.46, which revealed considerable genetic variations in the mutants. The phylogenetic tree and population structure analyses divided the M₃ mutants into two major groups at 0.62 genetic similarity (K = 2), which clearly separated the mutants of the two cultivars and indicated that a great genetic difference existed between the two mutant populations. Further, the two genetic groups were divided into five subgroups at 0.86 genetic similarity (K = 5) and each subgroup associated with resistant phenotypes of the mutants. Finally, the homologous PsMLO1 cDNA of five CW8 mutants that gained resistance to powdery mildew was amplified and cloned. A 129 bp fragment deletion was found in the PsMLO1 gene, which was in accord with er1-2. The findings provide important information on disease resistant and molecular variations of pea mutants, which is useful for pea production, new cultivar breeding, and the identification of resistance genes.