Brown Spot Severity and Yield of Soybeans Regenerated from Calli Resistant to a Host-Specific Pathotoxin Produced bySeptoria glycines

Abstract

Regenerated soybean lines from the R 3 to R 7 generations were field-evaluated for their reactions to Septoria glycines, the brown spot pathogen, from 1991 to 1994. The regenerated lines from cvs. BSR201, Fayette, and L86P-1615 were selected from calli resistant to a host-specific pathotoxin produced by S. glycines. Selected resistant plants to the pathogen from the R 3 generation produced R4 progeny that were resistant, intermediate and susceptible in their reaction to S. glycines in 1991. In 1992, 1993, and 1994 among the R 3 to R 7 generations, brown spot reaction was only intermediate and susceptible. F 3 families obtained from a cross between R 3 regenerants and BSR201 had low heritability (23%) for resistance to S. glycines. Lines in the R 5 or R 6 generation, obtained originally from plants regenerated from calli of BSR201 that had intermediate and susceptible reactions to S. glycines in 1992, and five commercial soybean cultivars were evaluated for brown spot resistance, maturity, and yield in 1993 and 1994. Area-under the disease progress curve (AUDPC), maturity, and yield varied among entries. The 10 lines selected with an intermediate reaction had lower AUDPC, matured later, and had higher yields than the nine susceptible lines. Three regenerated lines, 2728, 2733, and 2734, had significantly (P = 0.05) lower AUDPC, later maturity, and higher yields than the other regenerated lines. AUDPC was significantly (P = 0.01) negatively correlated to yield (r = -0.29), to plant height (r = -0.74) and number of nodes (r = -0.39) ; but positively correlated to pods having 0 seed (r = 0.44) and two seeds (r = 0.49).