Physiological Characterization Of Partial Resistance In Soybean To Sclerotinia Sclerotiorum (Lib.) De Bary.

The genetic or physiological bases of the partial resistance of soybean to Sclerotinia stem rot need to be characterized before it can be incorporated effectively into new soybean cultivars. This disease is caused by Sclerotinia sclerotiorum. The objective of this research is to describe physiological and anatomical responses in susceptible and partially resistant soybean cultivars infected by Sclerotinia sclerotiorum. Variations in host-pathogen interactions have been examined comparing the response of soybean cultivars, OAC Salem (partially resistant) and OAC Shire (susceptible) to S. sclerotiorum, isolate #1980.  Evaluations on starch grain accumulation, penetration sites and structures of the pathogen were studied. Measurements of area under canker progress curve (AUCPC), number of days for visible disease related symptoms, stomatal conductance (g_s), dry and fresh matter were analyzed for both cultivars for a period up to 12 days after inoculation. After day 2 susceptible plants presented significantly greater starch accumulation than tolerant plants. Infection of host tissue through direct penetration of the cuticle and through the base of trichomes was observed on susceptible plants; however, only direct penetration of the cuticle was present for tolerant plants.  No significant differences were found between the cultivars for AUCPC and fresh matter. A significant increase in g_s was observed in the susceptible plants only. Disease related symptoms, such as severity of wilting and number of days to plant death were significantly lower in the susceptible cultivar. Physiological characterization of soybean - S. sclerotiorum pathosystem would allow for the development of novel strategies to incorporate partial resistance to white mold into commercial soybean cultivars varieties and may help the development of breeding strategies for other host crop as well.