Environmental Sensitivity of Soybean Cultivar Response to Sclerotinia sclerotiorum

Abstract

The sporadic occurrence of Sclerotinia stem rot in soybeans often is attributed to the sensitivity of Sclerotinia sclerotiorum to environmental factors. Environmental sensitivity in soybean response to the pathogen also could contribute to the unpredictable nature of this disease. We used stability analysis to determine whether soybean cultivar response to S. sclerotiorum was sensitive to light and temperature. Five greenhouse experiments examined the response of seven cultivars to limited-term inoculation with S. sclerotiorum. The cultivars, selected at random from Pennsylvania variety trials, represented maturity groups grown in Pennsylvania and other states sharing that latitude. Photon flux density of photosynthetically active radiation (PAR) and temperature were recorded hourly and varied among experiments. Environmental sensitivity was detected in the response of five cultivars to S. sclerotiorum when individual cultivar disease ratings (assessed 6 days after inoculation) were regressed against the mean disease rating of each experiment. Stability analysis with temperature during the 48-h inoculation period as the environmental index found that all cultivars responded similarly to the number of hours that temperatures were <19 degrees C, 19 to 22 degrees C, or >22 degrees C. In contrast, cultivars separated into PAR-sensitive and PAR-insensitive groups when the environmental index was moles of PAR at a photon flux density >/=475 mumol m(-2) s(-1) during the inoculation period. The photon flux density of PAR on a cloudy day in the field is </=200 mumol m(-2) s(-1). The two cultivar groups were identical to those identified as environmentally sensitive and insensitive in the initial analysis. The PAR-sensitive cultivars had homogeneous negative regression coefficients different (P = 0.001) from zero. As the accumulated moles of PAR during the inoculation period increased, the disease ratings of the PAR-sensitive cultivars decreased; the disease ratings of the PAR-insensitive cultivars remained stable. The photon flux density of PAR during the 48-h inoculation period explained the environmental sensitivity of soybean cultivar response to S. sclerotiorum in these experiments.

Tillage, Crop Sequence, and Cultivar Effects on Sclerotinia Stem Rot Incidence and Yield in Soybean

“…Before the early 1990s, SSR occurred sporadically in soybean in this area (Grau, 1988). Since then outbreaks of SSR have become more frequent and more severe (Doupnik, 1993; Yang et al, 1999; Pennypacker and Risius, 1999). Management practices—including narrow row spacing, increased plant populations, early planting dates, and high soil fertility—that are intended to increase soybean yields, create favorable conditions for SSR development within the crop canopy (Pennypacker and Risius, 1999).…”

“…Since then outbreaks of SSR have become more frequent and more severe (Doupnik, 1993; Yang et al, 1999; Pennypacker and Risius, 1999). Management practices—including narrow row spacing, increased plant populations, early planting dates, and high soil fertility—that are intended to increase soybean yields, create favorable conditions for SSR development within the crop canopy (Pennypacker and Risius, 1999). Shortened crop sequences, frequently limited to corn and soybean, reduced tillage, or rotation with susceptible crops such as sunflower ( Helianthus annuus L.), canola ( Brassica rapa L.), or dry bean ( Phaeseolus vulgaris L.) increase soil inoculum density (Schwartz and Steadman, 1978).…”

“…As a result, strategies for controlling SSR in soybean emphasize cultivar selection and management practices that reduce canopy density (Hall and Nasser, 1996). Complete resistance to SSR has not been reported (Boland and Hall, 1987; Grau et al, 1982; Kim et al, 1999; Pennypacker and Risius, 1999; Yang et al, 1999). Planting in wide row spacings or at lower plant populations, by delaying canopy closure and reducing canopy density, causes less favorable humidity and temperature conditions for fungal development within the crop canopy (Blad et al, 1978; Buzzell et al, 1993; Grau and Radke, 1984; Steadman, 1979).…”

Incidence and severity of white mold for soybean under different cultural practices and local meteorological conditions

“…Based on such combined biotic and abiotic factors, it has been determined that the most susceptible phenological stage of soybean plants to the occurrence of white mold is flowering and the beginning of grain filling. GROGAN, 1979;HALL, 1988;PENNYPACKER;RISIUS, 1999;DEL RÍO, 2006). Moreover, during this period of time temperatures neither reached values lower than 10 o C nor higher than 30 o C; levels of temperature that could affect the development of the fungus and cease the progress of the disease in soybean production fields (ABAWI; GROGAN, 1979GROGAN, , 1975WEISS et al, 1980;HANNUSCH;BOLAND, 1996).…”

“…In short, regimes of air temperature between 5 o C and 30 o C, high levels of relative air humidity and high water vapor concentration at the surface of the plants (recurring between 12 and 16 hours in order to produce a leaf wetness duration of 42 to 72 hours), along with the occurrence of precipitations throughout the Incidence and severity BERUSKI, G. C. et al flowering stage of the growing season of the crop are the main factors in the development of white mold (STEADMAN, 1983). Microclimatic conditions inside the canopy of the crop can be modified, depending on the management practices adopted in compliance with different sowing dates, reductions in row spacing, rises in plant populations, the use of genotypes with a greater height, and usage of irrigation systems (PENNYPACKER;RISIUS, 1999). Different management practices can interfere both with the disease control measures and its intensification in production fields (WORKNEH;YANG, 2000;MILA et al, 2003;DEL RIO, 2008).…”