Identification of resistance to root rot and preliminary establishment of its SSR markers in castor bean

Abstract

Castor bean root rot is a root disease caused by Fusarium solani, which seriously threatens the production of castor bean. Due to the lack of resistance genes, the breeding for root rot resistance in castor bean is seriously restricted. In order to mine resistant resources and establish resistant molecular markers, the phenotypic and molecular marker identification was performed on the disease resistance of 252 castor bean accessions in this study. The results were as follows: (1) Irrigating roots with the conidia suspension of 1×106 spores·mL-1 was an effective inoculation method. The 5-grade evaluation method based on the days of wilt after inoculation could be used as the criteria to evaluate the resistant level of accessions objectively. (2) According to the criteria, the resistance of 252 accessions were divided into five grades from high to low, among which Grade 1 was high resistance and Grade 2 was moderate resistance. The number of accessions with different grades from 1 to 5 were 105, 25, 33, 31 and 58, respectively, accounting for 42%, 10%, 13%, 12% and 23%, respectively. A total of 130 resistant accessions were identified, of which 105 were high resistance and 25 were moderate resistance. (3) The proportion of resistant accessions in wild accessions (66%) was much higher than that in cultivated accessions (35%). Among wild accessions from South China, 69% were resistant accessions, and 60% were high resistance accessions. It is strongly suggested that the research and utilization of wild accessions, especially the wild accessions in South China, should be an important direction of resistance breeding in the future. (4) Eight SSR markers associated with the resistance were preliminarily established. Although different resistant accessions carried different markers or marker combinations, most of them carried three to four of the above markers, therefore, they can be used as resistant molecular markers for assisted selection. The results of this study provide an effective method and evaluation criteria for root rot resistance identification, screen out a number of resistance genetic resources urgently needed in breeding, and preliminarily establish the SSR markers available for assisted selection, which lay an important foundation for resistance breeding of castor bean root rot.

Keywords

• castor bean
• root rot
• resistance identification
• fusarium solani
• conidia suspension
• ssr