Abstract: The effect of sewage sludge application to a desert soil on nodulation, nitrogen fixation and plant growth of faba bean (Vicia faba cv. Giza 1), soyabeans (Glycine max cv. Clark) and lupin (Lupinus albus cv. Marita) was investigated in a pot experiment under greenhouse conditions. Nodulation, nitrogenase activity and plant growth of faba bean, soyabeans and lupin were significantly increased by moderate application rates of sewage sludge (20 and 30%, w/w). The decisive effect caused by application of sewage sludge on legume growth was the promotion of nodulation and subsequent nitrogen fixation. At an application level of 30% (w/w), nodulation was increased by 55%, 96%, and 171% for faba bean, soyabeans and lupin, respectively, compared with controls. Conversely, at high application rates (40 and 50%) sewage sludge significantly inhibited nodulation, nitrogen fixation, dry matter accumulation and nitrogen yields of faba bean and soyabeans. Again, inhibition of nodulation by high amounts of sludge was the decisive process responsible for low nitrogen fixation and dry matter production of legume plants. At 50% application rate, sewage sludge decreased nodulation by 62%, 79% and 29% for faba bean, soyabeans and lupin, respectively, compared with controls. Plant analysis indicated that the inhibitory effect of sewage sludge at high application rates was most probably due to a toxic (noxious) effect of heavy metals (Cu and Zn) on the microsymbiont rather than on host plants. It is concluded that sewage sludge at low application rates may significantly improve legume growth on desert soils.

Twenty-oneRhizobium andBradyrhizobium strains were testedin vitro against the mycelial growth of three pathogenic fungi on solid and liquid media. All tested rhizobia and bradyrhizobia significantly suppressed the growth of the three soil-borne root-infecting fungi (Fusarium solani, Macrophominia phasolina andRhizoctonia solani) either in the absence or presence of iron. This indicates that the siderophore played a minor role in the biocontrol potential ofRhizobium andBradyrhizobium against pathogenic fungi. Pot experiments revealed that the numbers of propagules causing disease after 4 weeks of planting varied with species and host plant. The three most activeRhizobium andBradyrhizobium strains (R. leguminosarum bv.phaseoli TAL 182,B. japonicum TAL 377 andBradyrhizobium sp. (lupin) WPBS 3211 D) tested under greenhouse conditions for their ability to protect one leguminous (soybean) and two non-leguminous (sunflower and okra) seedlings from root rot caused byFusarium solani, Macrophominia phaseolina andRhizoctonia solani provided significant suppression of disease severity compared with nonbacterized control in both leguminous and non-leguminous seedlings.Bradyrhizobium sp. (lupin) WPBS 3211 D provided the lowest degree of resistance against all the tested pathogens with all host plants.

The effect of six Bradyrhizobium sp. (lupin) strains (WPBS 3201D, WPBS 3211D, USDA 3040, USDA 3041, USDA 3042 and CB 2272) and Fe supply on nodulation, N2-fixation and growth of three lupin species (Lupinus termis, L. albus and L. triticale) grown under Fe deficiency in an alkaline soil, were examined in sterilized and non-sterilized pot experiments. When inoculated with USDA 3040, 3041, 3042 and CB2272 without Fe addition, the three lupin species had a very low nodule number and mass, low shoot and root dry matter accumulation and lower N yield. However, inoculation with WPBS 3201D and 3211D without Fe treatments increased all these parameters substantially. The ability of WPBS 3201D and 3211D to form nodules on the three lupin species under conditions of Fe stress could be attributed to their ability to scavenge Fe from Fe-deficient environments through their siderophore production. Addition of Fe to the other four strains significantly increased nodulation and N2-fixation of the three lupin species, indicating that the poorer nodulation and N2-fixation of these strains in the absence of Fe, resulted from a low ability to obtain Fe from alkaline soils. Bradyrhizobium strains WPBS 3201D and 3211D were superior to the other four strains in terms of promoting greater nodulation, N2-fixation, plant growth and N accumulation of L. termis and L. albus. However, the other four strains were more efficient in symbiotic association with L. triticale. The greater variations in nodule efficiencies (specific nitrogenase activity) under different levels of Fe supply could be attributed to the quantities of bacteroid protein and leghaemoglobin in the nodules. The results suggested that Bradyrhizobium (lupin) strains differ greatly in their ability to obtain Fe from alkaline soils, and that the selection of bradyrhizobial strains which are tolerant of Fe deficient soils could complement plant breeding for the selection of legume crops for Fe-deficient soils.

Faba bean cultivar Giza 3 inoculated with Rhizobium leguminosarum RCR 1001 was grown in a pot experiment and irrigated with saline water (mixture of NaCl and CaCl sub(2) 0.25 Ca:Na on molar basis). Salinity levels of 5.8, 8.8, 11.6 and 14.6 dSm super(-1) (equivalent to 50, 75, 100 and 125 mM NaCl) significantly decreased nodule number, nodule fresh weight and total nitrogenase activity. Salinity inhibited specific nitrogenase activity, protein, leghaemoglobin and carbohydrate content of the nodules at 11.6 and 14.6 dSm super(-1) (100 and 125 mM NaCl). Salinity levels of 8.8, 11.6 and 14.6 dSm super(-1) (75, 100 and 125 mM NaCl) caused a significant reduction in dry weights of roots, stems, leaves and total plant nitrogen.

Identification of commonality of nodulation control among legumes will facilitate progress in improving symbiotic N2 fixation in agricultural systems. Interspecies grafts between soybean [Glycine max (L.) Merr] and mung bean (Vigna radiata L.), or soybean and hyacinth bean (Lablab purpureus L.), were made to evaluate whether a common translocatable signal controls expression of hypernodulation among legume species. Grafting of a ‘NOD1-3’ (hypernodulating soybean) shoot to roots of mung bean or hyacinth bean resulted in hypernodulation, a 4.1-fold increase in nodule number for mung bean, and a 2.7- to 5.5-fold increase (depending on bacterial strain) in nodule number for hyacinth bean, relative to self-grafted mung bean or hyacinth bean, respectively. ‘Williams 82’ shoots doubled nodule number when grafted to mung bean roots, but had no effect on nodulation when grafted to hyacinth bean roots. Symbiotic Nz fixation (as measured by nitrogen accumulation in the plant) by nodulated mung bean roots was enhanced by 67% when grafted to Williams 82 and by 78% when grafted to NOD1-3 soybean shoots, compared with self-grafted mung bean plants. Grafting soybean shoots to hyacinth bean roots positively affected symbiotic N2 fixation (9–40% depending on bacterial strain), but the magnitude was less than observed when mung bean roots were grafted to soybean shoots. It was concluded that control of hypernodulation expression by a shoot-transmissible factor is common among soybean, mung bean, and hyacinth bean. Seed were obtained from reciprocal grafts between soybean and mung bean to test for bacterial specificity for infection and nodule development. Seedling progeny from the reciprocal mung bean-soybean grafts were not altered in terms of bacterial specificity for nodulatiou.

Abstract Effects of the pesticides Afugan, Brominal, Gramoxone, Selecron and Sumi Oil on growth, nodulation and root colonisation by arbuscular mycrrhizal (AM) fungi of the legumes cowpea (Vigna sinensis L.), common bean (Phaseolus vulgaris L.) and Lupin (Lupinus albus L.) were determined. The growth of all plants was inhibited by pesticide application, but this effect varied with the pesticide and plant species. Nodule formation was significantly inhibited in cowpea after 20 days of planting by all pesticides tested. Following the initial decrease, there was recovery from the inhibitory effects at 40 and 60 days after planting. Although the number of nodules on common bean and lupin did not differ from control at 20 days after planting, differences were evident during the later stages of plant growth. The pesticides significantly inhibited AM root colonisation and the number of spores in all legumes, but on the other hand, spore formation was stimulated in pesticide-treated cowpea 60 days after planting. The accumulation of N, P and K in pesticide-treated plants was lower than in control plants. Growth and nutrient status of the legumes varied with nodulation and AM colonisation. The results suggest that pesticides affect plant growth, Rhizobium/Bradyrhizobium and AM fungi at different stages of plant growth and effects varied with pesticide and plant species.

Rhizobium leguminosarum biovar viceae strain TAL 1236 growing on different organic phosphorus compounds as sources of phosphate exhibited phosphatase activities. The strain was able to produce both acid and alkaline phosphatases. However, its ability to produce alkaline phosphatase was much higher. When cellular phosphate fell to 0.115% of cell protein, cellular and extracellular phosphatase activities were promoted. Mg2+, Co2+ and Ca2+ enhanced slightly the activity of alkaline phosphatase more than acid phosphatase. However, Mn2 + and Fe2+ activated acid phosphatase rather than alkaline phosphatase. It may be concluded that Rh. leguminosarum plays an important role in the release of phosphorus from its organic compounds through the action of phosphatases which can be slightly activated by a range of cations.

Soil salinity is a major limitation to legume production. We evaluated specific soybean [Glycine max (L.) Merr.] genotypes to identify a salt-tolerant soybean-Bradyrhizobium system, and to determine by grafting experiments if the scion or the root was responsible for salt tolerance. The effects of three levels of salinity (0, 30, and 60 mM NaCl) on nitrogenase activity (acetylene reduction), nodule number, nodule dry matter, and growth of four soybean genotypes (Williams 82, PI 416937, DR-1 [an Egyptian cultivar], and NOD1-3 [a hypernodulating mutant selected from Williams]) were investigated in hydroponic cultures and growth chamber environments. Salt stress significantly inhibited nitrogenase activity, nodule number, and dry matter accumulation per plant of all four cultivars. The detrimental effects of salinity on nodulation parameters and dry matter accumulation were most pronounced for NOD1-3 and Williams 82, intermediate for DR-l, and less marked for PI 416937. Self-grafted NOD1-3 plants showed 50 to 62% inhibition in nodulation responses (activity, number, mass) while grafting of P1416937 scions to NOD1-3 roots resulted in less than 7% inhibition by salt. Nodule number on PI 416937 roots was greater when grafted to NOD1-3 scions (relative to self-grafted PI 416937 plants), confirming a shoot role in autoregulation of nodule number. Conclusions are that shoot factors are of primary importance in determining salt-tolerance of the PI 416937 genotype and that hypernodulation expression in the mutant is negatively affected by salt treatment.