An analysis of progress in breeding Sclerotinia blight resistant runner-type peanut

Abstract

Evaluating segregating (runner x spanish) peanut populations for physiological resistance to Sclerotinia blight is complicated by the situation that the disease reaction can be affected by canopy density and vine form. Three field screening tests were conducted in 1991, 1992, and 1993 to identify Sclerotinia blight resistant runner type peanuts. Selections were made from three populations, 'backcross to runner', 'backcross to Tamspan 90', and'singlecross'. The parents were chosen for agronomic qualities and resistance to other pathogens. Resistant (spanish) parents used were Tamspan 90 and TxAG-5 gerrnplasm. Families within populations were planted as single row plots 3m long with .9m alleys. Repeated plant by plant inspections (PBPI) were made for assessment of sequence of infection and subsequent calculation of a weighted average disease estimate. Effect of vine form on disease reaction was investigated, but had no significant effect on total number of diseased plants per plot. The backcross to Tamspan 90 population consistently had a disease reaction close to or lower than Tamspan 90, the most resistant check, but retained the most undesirable plant forms (i.e., upright). By 1993, the. backcross to runner population had the highest percentage of runner - type families (88%), and a mean disease reaction close to Tamspan 90. A visual field screening method less meticulous than PBPI was compared for effectiveness on a segregating population containing a mixture of 298 F4:7 singlecross and F2:5 backcross entries. The visual system used a scale of 0= no visible plot infection to 5 = 80 - 100% plot destruction. Both visual and PBPI evaluations were made seven times during the 1993 epidemic. Correlation between area under disease progress curve values of both systems was high (>.85) from inspections four to seven. Remnant seed of selections screened for resistance using a greenhouse in vivo technique were compared under field situations. Chi - square test for independence indicated a significant relationship between greenhouse and field. Data suggests that the greenhouse could be useful in supplementing field studies by eliminating susceptible families before field testing.