Host range of Septoria glycines, quantification of partial resistance, and brown spot evaluation of soybeans regenerated from calli

Septoria glycines Hemmi causes brown spot of soybeans. Brown spot is a foliar disease distributed throughout the world. The host range of S. glycines, partial resistance to brown spot in soybean, and brown spot and yield evaluation of soybeans regenerated from calli resistant to a pathotoxin produced by S. glycines were studied.Thirteen genera representing 30 legume species, two weed species (Abutilon theophrastii and Cynanchum leave), and five cultivars of soybean were inoculated with Septoria glycines in the field and greenhouse. Of these, 29 legume species and A. theophrastii had leaf symptoms. Only Cicer arietinum and C. leave were symptomless. Leaf symptoms were separated into three types. Two isolates of Septoria spp. obtained from leaf lesions on A. theophrastii and C. leave were similar in conidia and pycnidia sizes when compared to an isolate from soybean. In cross inoculation studies, soybeans and A. theophrastii developed brown spot lesions. The fungus was reisolated from both hosts.Eleven soybean genotypes in four maturity groups were evaluated for partial resistance to S. glycines in the field and greenhouse. In the field, the area under disease progress curve (AUDPC), the area under defoliation progress curve (AUFPC), and lesion and pycnidia counts were useful parameters for evaluating partial resistance. Plant introductions 347814A and 347556 were considered to have the highest level of partial resistance and susceptibility, respectively, based on AUDPC, AUFPC, incubation period, and number of lesions and pycnidia. In the greenhouse, parameters for measuring partial resistance were not differentiated on the genotypes except for the number of pycnidia. Disease parameters measured in the greenhouse and field were generally not correlated.Regenerated soybean lines were evaluated from the $\rm R\sb3$ to $\rm R\sb7$ generations for resistance to Septoria glycines in the field from 1991 to 1994. These regenerated lines were derived from calli of cvs. BSR201, Fayette, and L86P-1615 which were selected based on resistance to a pathotoxin produced by S. glycines. Selected resistant plants from the $\rm R\sb3$ generation produced $\rm R\sb4$ progeny that were both susceptible and resistant in 1991. Brown spot resistance was intermediate and susceptible among the $\rm R\sb3$ to $\rm R\sb7$ generations in 1992, 1993, and in 1994. Regenerated $\rm F\sb3$ families obtained from a cross between $\rm R\sb3$ regenerants and cv. BSR201 had low heritability (23.1%) for resistance to S. glycines. Ten and nine lines from calli of cv. BSR201 with an intermediate and susceptible reaction, respectively, to S. glycines in 1992 of either $\rm R\sb5$ or $\rm R\sb6$ generations, and five commercial cultivars were evaluated for brown spot resistance, the number of days to maturity, and yield in 1993 and 1994. AUDPC, days to 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. Regenerated lines, R91-3773, R92-2654, and R92-2657, were screened for resistance to Phialophora gregata and to Heterodera glycines race 3 and race 4. All lines and cv. BSR201 had brown stem rot resistance and were susceptible to soybean cyst nematode.U of I OnlyETDs are only available to UIUC Users without author permissio