S02 - Session O6 - Screening of soybean genotypes for resistance to Colletotrichum truncatum at seedling stage

Authors: Zong-ming Sheu *, Yu-Shin Chiu, Yu-yu Huang, Song-Bin Chang

Soybean ( Glycine max ) is the most crucial cash crop worldwide to supply protein sources to human nutrition and animal feed. Anthracnose, mainly caused by Colletotrichum truncatum , is an important disease and results in significant economic losses. To date, no resistant cultivar has been developed for commercial production, although a few resistance sources have been identified. This study aims to identify more diverse resistance sources to this disease in the soybean collection from WorldVeg for further utilization. A total of 126 soybean genotypes, comprising 100 accessions, 25 breeding lines and 1 cultivar were screened in twice preliminary trials. The seedling plants at V2 to V3 stage were inoculated by spraying the conidial suspension (ca. 5x10 7 spores per plant) of C. truncatum Coll-1508. The inoculated plants were incubated at 25 ℃, 99-100%RH in the dark for the first 24 hr, and then switched to 95-98% RH with a 14 hr/day photoperiod for disease development. The disease severity rating (DSR) was conducted based on a 6-point scale (0-5) at 10 days after inoculation. Most tested soybean genotypes were susceptible, and no immune genotype was identified. To confirm the resistance, nine accessions with DSR < 2.5 were re-evaluated along with cv. Kaohsiung No. 9 and Mandarin 507 as susceptible and resistant checks, respectively. The study identified 5 accessions (VI017590, VI063762, VI027011, VI026746, and VI014587) with consistent resistance to be potential resistance sources. In addition, molecular assays by using 100 SSR markers derived from 20 chromosomes of cv. William 82 were explored to identify markers associated with anthracnose resistance. However, the result of either phenotyping or genotyping indicated significant segregations in the tested accessions. More research, such as developing homozygote or pure lines from these candidate genotypes, is needed to further develop molecular marker as well as resistance breeding.