Compatibility of Rhizobium japonicum with Chemical Seed Protectants¹

Abstract

The literature on the compatibility of Rhizobium sp. with seed protectant chemicals is controversial because of variation in methods and the lack of quantitative data. The present study was planned to develop a reliable quantitative method of measuring compatibility of Rhizobium japonicum with seed‐applied fungicides. The effect of four seed protectant chemicals on survival of R. japonicum on soybean (Glycine max L. Merr. cv. ‘Hark’) seed was studied in laboratory growth chamber experiments. The chemicals tested and levels used were tetramethyl‐thiuram‐disulfide (thiram), 0.6 g/kg seed; N‐trichloromethylthio‐4‐cyclohexene‐l,2‐dicarboximide (captan), 0.8 g/kg seed; 5,6‐Dihydro‐2‐methyl‐l,4‐oxathiin‐3‐carboxanilide (carboxin), 1.1 g/kg seed; and pentachloronitrobenzene (PCNB), 0.9 g/kg seed. Quantitative measurements for compatibility included plate counts for survival of R. japonicum on inoculated chemically treated seed and counts of taproot nodules on plants at 2 weeks age. R. japonicum were compatible with Thiram and Carboxin but not with PCNB and Captan. PCNB reduced Rhizobium survival on seed and decreased taproot nodulation. Captan was less toxic to rhizobia than was PCNB, but taproot nodulation of plants was greatly reduced by captan. Carboxin had little effect on viable rhizobia or taproot nodulation when seeds were planted within 4 hours of inoculation. Nodulation was poor when these seeds were planted 24 hours after inoculation despite the presence of what would normally be considered adequate viable rhizobia. Thiram had no adverse effect on viable rhizobia or taproot nodulation even when seeds were held 24 hours before planting. The results also indicate that compatibility must be measured quantitatively in relation to time and that nodulating ability of the surviving bacteria is the prime factor in determining compatibility.

Rhizobium inoculant and seed-applied fungicide effects on field pea production

“…The observations in this experiment indicated that the fungicide treatments had no effect on the assessed field pea parameters in most cases, caused negative effects in a few cases and had few positive effects. The lack of effect of Thiram on field pea nodulation and seed yield agrees with results on field pea (Dunfield et al 2000), chickpea (Kyei-Boahen et al 2001) and soybean (Wrobel 1963;Mikaly and Vincent 1969;Curley and Burton 1975), but not with the observations of reduced nodulation in field pea (Rennie et al 1985) and soybean (Tu 1980). Wrobel (1963) and Dunfield et al (2000) observed that fungicides containing Thiram did not affect nodulation and yield.…”

“…It also appeared to be relatively non-lethal to seed-applied bacterial inoculant in a study by Mikaly and Vincent (1969), and out of the pesticides tested it possessed the lowest toxicity toward rhizobia. Similarly, seed treatment with Thiram had no effect on rhizobial numbers on the seed or nodule numbers on the roots (Curley and Burton 1975).…”

“…They observed variation in root rot severity among sites and years, but recommended seed treatments with systemic fungicides where spring conditions favor disease development or when inoculum levels were high. The effect of fungicides on rhizobia establishment, nodulation and crop yield appears to vary from one study to another (Curley and Burton 1975;Tu 1980;Graham et al 1980;Kyei-Boahen et al 2001). Consequently, knowledge of the effect of fungicides on rhizobia under given soil and climatic conditions is pertinent for optimum crop production.…”

Symbiotic effectiveness and ecological characterization of indigenous Rhizobium loti populations in Uruguay

“…Bromfield et al (1986) and Vance & Graham (1995) emphasize the importance of understanding the ecology and characteristics of indigenous rhizobia populations as a prerequisite for inoculant establishment and persistence. Characteristics such as: antibiotic resistance (Mueller et al, 1988), fungicide resistance (Curley & Burton, 1975), low pH tolerance (Munns & Keyser, 1981;Wood et al, 1988), drought and high temperatures tolerance (Munevar & Wollum II, 1981;Graham, 1992), bacteriocin production (Schwinghamer & Brockwell, 1978) are considered in the selection of rhizobial strains with high adaptability in regions with adverse conditions. These properties could explain their saprophytic persistence (Frioni, 1990(Frioni, , 1999.…”

SELECTION FOR CAPTAN TOLERANCE IN THE Rhizobium phaseoli-Phaseolus vulgaris L. N2-FIXING SYMBIOSIS

“…Unfortunately, the use of fungicides has been shown to be incompatible with successful nodulation and N, fixation by seed-applied rhizobia (Curley and Burton 1975;Graham et al 1980), particularly in Canadian soils containing no indigenous rhizobia (see Rennie and Dubetz (1984), Rennie et al (1985) The '5N content of the plant material was de-termined by LiOBr conversion of NHo* to N, (Ross and Manin 1970;Porter and O'Deen 1977) followed by analysis of r5N''4N ratios on a VG Micromass 602D isotope ratio mass spectrometer. All isotope terminology was according to Rennie et al (1978).…”