Responses of sugarcane, maize, and soybean to phosphorus and vesicular-arbuscular mycorrhizal fungi

The presence of vesicular-arbuscular mycorrhizal (VAM) fungi in long-term cane-growing fields associated with yield decline led to the supposition that VAM fungi may be responsible for the poor yields. A glasshouse trial was established to test the effectiveness of a species of VAM fungi, Glomus clarum, extracted from one of these North Queensland fields on the growth of sugarcane (Saccharum interspecific hybrid), maize (Zea mays), and soybean (Glycine max) for 6 phosphorus (P) rates (0, 2.7, 8.2, 25, 74, 222 mg/kg). For maize and soybean plants that received VAM (+ VAM), root colonisation was associated with enhanced P uptake, improved dry weight (DW) production, and higher index tissue-P concentrations than those without VAM (-VAM). By comparing DW responses of maize and soybean for different P rates, savings in fertiliser P of up to 160 and 213 kg/ha, respectively, were realised. Sugarcane plants were generally less responsive. Apart from a 30% DW increase with VAM when 2.7 mg P/kg was added, DW of +VAM plants was equivalent to, or worse than in the case of 222 mg P/kg, DW of -VAM plants. For all 3 host species, colonisation was least at the highest P application, presumably from excessive P within the plant tissue. Critical P concentrations for the 3 host species were below those reported elsewhere, and for soybean and sugarcane, the critical concentration for +VAM plants was lower than that of -VAM plants. There are 3 implications that arise from this study. First, VAM fungi present in cane-growing soils can promote the growth of maize and soybean, which are potential rotation crops, over a range of P levels. Second, the mycorrhizal strain taken from this site did not generally contribute to a yield decline in sugarcane plants. Third, application of P fertiliser is not necessary for sugarcane when acid-extractable P is

DAF yields a cloned marker linked to the soybean (Glycine max) supernodulation nts-1 locus

We report a further characterization of the genomic region containing the soybean supernodulation gene NTS-1. We performed a search for new markers linked to NTS-1 by combining DNA amplification fingerprinting (DAF) and bulked segregant analysis (BSA). The search resulted in one cloned polymorphism (B44-456) linked in trans, 8.5cM from the locus. Southern hybridization showed duplication of the B44-456 sequence in the soybean genome. Additionally, a DNA database search revealed one Arabidopsis thaliana genomic clone from chromosome I possessing 62% homology to the B44-456 marker. A relatively low number of polymorphisms were identified by several PCR marker technologies for this soybean genomic region, providing an additional support for its highly conserved and/or duplicated organization.

Factors affecting the establishment and dispersal of nymphs of Pristhesancus plagipennis Walker (Hemiptera : Reduviidae) when released onto soybean, cotton and sunflower crops

A problem with augmenting predatory bugs through mass release is the logistical difficulty of delivering nymphs onto the foliage of field crops. In this paper we examine postrelease establishment and dispersal of the nymphs of the predatory bug Pristhesancus plagipennis on soybean, cotton and sunflower in an effort to devise an appropriate strategy for field release. The effects of predator stadia and release rates on field establishment and within-crop-canopy dispersal after hand release were recorded in soybean, cotton and sunflower. Field establishment improved with the release of more-developed nymphs, with third instars providing the most appropriate compromise between field hardiness and rearing cost. Increased nymphal density at the point of release had little effect on nymphal dispersal throughout the crop canopy. The patterns of nymphal dispersal observed on the three crops suggest that crop-canopy architecture may have an effect on the ability of nymphs to spread out postrelease, as nymphs dispersed poorly in cotton and sunflower compared to soybean. To overcome poor dispersal of nymphs after release, a mechanical release method, where nymphs were mixed with vermiculite and delivered onto a target crop through a spinning disk fertiliser spreader, was tested, and provided similar nymph establishment rates and dispersal patterns as releasing nymphs individually by hand. The implications of nymph dispersal and field hardiness in regard to inundative field release techniques are discussed.

Fast neutron mutagenesis of soybean (Glycine soja L.) produces a supernodulating mutant containing a large deletion in linkage group H

We describe for the first time the application of fast neutron mutagenesis to the genetic dissection of root nodulation in legumes. We demonstrate the utility of chromosomal deletion mutations through production of a soybean supernodulation mutant FN37 that lacks the internal autoregulation of nodulation mechanism. After inoculation with microsymbiont Bradyrhizobium japonicum, FN37 forms at least 10 times more nodules than the wild type G. soja parent and has a phenotype identical to that of chemically induced allelic mutants nts382 and nts1007 (NTS-1 locus). Reciprocal grafting of shoots and roots confirmed systemic shoot control of the FN37 nodulation phenotype. RFLP/PCR marker pUTG132a and AFLP marker UQC-IS1 which are tightly linked to NTS-1 allowed the isolation of BAC contigs delineating both ends of the deletion. The genetic/physical distance ratio in the NTS-1 region is 279 kb/cM. The deletion is estimated to be about 460 kb based on the absence of markers and bacterial artificial chromosomes (BAC) ends as well as genetic and physical mapping. Deletion break points were determined physically and placed within flanking BAC contigs.

Quantitative trait loci for agronomic and seed quality traits in an F-2 and F-4 : 6 soybean population

Molecular breeding is becoming more practical as better technology emerges. The use of molecular markers in plant breeding for indirect selection of important traits can favorably impact breeding efficiency. The purpose of this research is to identify quantitative trait loci (QTL) on molecular linkage groups (MLG) which are associated with seed protein concentration, seed oil concentration, seed size, plant height, lodging, and maturity, in a population from a cross between the soybean cultivars 'Essex' and 'Williams.' DNA was extracted from F-2 generation soybean leaves and amplified via polymerase chain reaction (PCR) using simple sequence repeat (SSR) markers. Markers that were polymorphic between the parents were analyzed against phenotypic trait data from the F-2 and F-4:6 generation. For the F-2 population, significant additive QTL were Satt540 (MLG M, maturity, r(2)=0.11; height, r(2)=0.04, seed size, r(2)=0.061, Satt373 (MLG L, seed size, r(2)=0.04; height, r(2)=0.14), Satt50 (MLG A1, maturity r(2)=0.07), Satt14 (MLG D2, oil, r(2)=0.05), and Satt251 (protein r(2)=0.03, oil, r(2)=0.04). Significant dominant QTL for the F-2 population were Satt540 (MLG M, height, r(2)=0.04; seed size, r(2)=0.06) and Satt14 (MLG D2, oil, r(2)=0.05). In the F-4:6 generation significant additive QTL were Satt239 (MLG I, height, r(2)=0.02 at Knoxville, TN and r(2)=0.03 at Springfield, TN), Satt14 (MLG D2, seed size, r(2)=0.14 at Knoxville, TN), Satt373 (MLG L, protein, r(2)=0.04 at Knoxville, TN) and Satt251 (MLG B I, lodging r(2)=0.04 at Springfield, TN). Averaged over both environments in the F-4:6 generation, significant additive QTL were identified as Satt251 (MLG B 1, protein, r(2)=0.03), and Satt239 (MLG 1, height, r(2)=0.03). The results found in this study indicate that selections based solely on these QTL would produce limited gains (based on low r(2) values). Few QTL were detected to be stable across environments. Further research to identify stable QTL over environments is needed to make marker-assisted approaches more widely adopted by soybean breeders.

Effects of heat treatment on the nutritional value of raw soybean selected for low trypsin inhibitor activity

1. Two broiler experiments and a layer experiments were conducted on Kunitz trypsin inhibitor (Kti) soybeans (SB) of low trypsin inhibitor (TI) activity to determine their nutritive value when included as mash in least-cost poultry diets. 2. Experiment 1 compared chick performance on the Kti or raw SB using a commercial full-fat SB meal (FFSBM) and a solvent extracted SB meal (SBM) as controls during a 20 d experimental period. Broiler experiment 2 compared Kti and raw SB, non-steamed, or steam-pelleted with and without DL-methionine supplementation added to every treatment containing 170 g SB/kg. For each broiler experiment the levels of each SB were 70, 120 and 170 g/kg with the control birds fed only 170 g SB/kg. 3. The layer experiment, compared steam-pelleted Kti and raw SB against a non-steamed Kti and raw SB each fed at two levels (70 and 110 g/kg) x 30 replicates from 29 weeks of age for 19 weeks in a completely randomised design. Production parameters were measured when diets were formulated to contain minimum required specifications and calculated apparent metabolisable energy (AME). At the completion of each trial, 2 broiler birds from each cage and 5 layer birds per treatment were killed, weighed, and their liver and pancreas weighed. 4. Both broiler experiments indicated that production parameters on the Kti SB treatments were significantly lower (P < 0.05) than on the two commercial control SB treatments. However, the Kti treatments were superior to the raw SB treatments. 5. Pancreas weight increased with increasing inclusion of both raw and Kti SB, suggesting that a TI was causing the depression in performance. The AME of the Kti SB was similar to that of commercial FFSB meal. After steam conditioning, the raw SB meal AME value of 9.5 MJ/kg dry matter (DM) was improved to 14.1 MJ/kg DM by reduced TI activity, but this AME improvement with TI activity reduction, plus the supplementation with DL-methionine on birds fed the raw SB had no effect (P > 0.05) on any parameter evaluated in experiment 2. 6. The layer experiment showed that hens on the Kti SB treatments had significantly greater live weight gain (LWG), egg weight and daily egg mass than birds given raw SB. A reduced food intake (FI) was observed in the Kti treatments but egg mass was generally similar to that on the FFSB control diet, indicating that Kti SB supported excellent egg production at an inclusion of 110 g/kg. The depressed performance observed for broiler chicks suggest that younger birds are more susceptible to the effects of SB TI.

Tissue-specific gene expression in soybean (Glycine max) detected by cDNA microarray analysis

We have constructed cDNA microarrays for soybean (Glycine max L. Merrill), containing approximately 4,100 Unigene ESTs derived from axenic roots, to evaluate their application and utility for functional genomics of organ differentiation in legumes. We assessed microarray technology by conducting studies to evaluate the accuracy of microarray data and have found them to be both reliable and reproducible in repeat hybridisations. Several ESTs showed high levels (>50 fold) of differential expression in either root or shoot tissue of soybean. A small number of physiologically interesting, and differentially expressed sequences found by microarray analysis were verified by both quantitative real-time RT-PCR and Northern blot analysis. There was a linear correlation (r(2) = 0.99, over 5 orders of magnitude) between microarray and quantitative real-time RT-PCR data. Microarray analysis of soybean has enormous potential not only for the discovery of new genes involved in tissue differentiation and function, but also to study the expression of previously characterised genes, gene networks and gene interactions in wild-type, mutant or transgenic; plants.

Spider fauna of soybean crops in south-east Queensland and their potential as predators of Helicoverpa spp. (Lepidoptera: Noctuidae)

Spiders are among the most abundant predators recorded in grain crops in Australia. They are voracious predators, and combined with their high abundance, may play an important role in the reduction of pest populations. The significance of spider assemblages as biological control agents of key pests such as Helicoverpa spp. in Australian agroecosystems is largely unknown. A thorough inventory was made of the spider fauna inhabiting unsprayed soybean fields at Gatton, south-east Queensland. One-hundred-and-two morphospecies from 28 families were collected using vacuum sampling and pitfall traps across two summer seasons (2000-01, 2001-02). No-choice feeding tests in the laboratory, using eggs and larvae of Helicoverpa armigera (Hubner) as prey, were used to ascertain the predatory potential of each spider group. The field-collected spider assemblage ate on average 2.4 (+/-0.7 standard error) to 5.0 (+/-0.8) eggs per 24 h per spider (10-25% of those available), depending on level of starvation. Clubionidae were the only spiders to readily consume eggs in the laboratory (mean of 18.4 +/- 1.5 eggs per starved spider and 8.2 +/- 3.9 per non-starved spider after 24 h). Starved spiders consumed 9.4 (+/- 0.1) first-instar larvae per 24 h per spider (90% of those available). This information was combined with field observations and literature from Australian and overseas studies to assess the potential of spider groups as predators of Helicoverpa spp. Lycosidae, Clubionidae, Oxyopidae, Salticidae and Thomisidae have the capacity to contribute to control of Helicoverpa spp.

Effect of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 to soybean

Screenhouse studies were conducted to investigate the effects of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 on soybean and the influence of the nematode on wilt incidence and growth of soybean. The interaction of each fungus with the nematode resulted in reduced shoot and root growth. Final nematode population was also reduced with concomitant inoculation of nematode and fungus or inoculation of fungus before nematode. While M. incognita suppressed wilt incidence in two nematode-susceptible cultivars of soybean (TGX 1485-2D and TGX 1440-IE), it had limited effect on wilt incidence in the nematode resistant cultivar of soybean (TGX 1448-2E). When F. oxysporum was inoculated with the nematode, the mean number of nematodes that penetrated soybean roots decreased by 75% in TGX 1448-2E, 68% in TGX 1485-1D and 65% in TGX 1440-1E. Similarly when the soil was treated with S. rolfsii, the number decreased by 78% in TGX 1448-2E, 77% in TGX 1485-1D and 68% in TGX 1440-1E. The nematode did not develop beyond second-stage juvenile in TGX-1448-2E.

Spider ballooning in soybean and non-crop areas of southeast Queensland

Ballooning is a form of aerial movement practiced by most miniature and some adult spiders. Very few studies have investigated the composition and rate of spider ballooning in Australian agroecosystems. Water traps were used to compare ballooning rates in irrigated soybean crops and nearby non-crop areas in southeast Queensland over two summer seasons. The highest ballooning rate (14.8 spiders/m(2) per day) was recorded in a soybean field, non-crop areas (7.0 spiders/m(2) per day) and a dry land mungbean field (6.8 spiders/m(2) per day) having similar rates. Spider ballooning in soybean increased throughout the season and showed three peaks and intervening troughs. A similar pattern in ballooning peaks was observed in non-crop areas however the numbers were lower. Peaks in ballooning activity where synchronised across habitat types and some spider groups. Composition of the ballooning fauna was different from that of the ground-dwelling fauna, some families being present in both. Ballooning is an important behaviour in terms of population dynamics for a number of spider groups in soybean and the implications for pest control are discussed. (C) 2004 Elsevier BN. All rights reserved.

Lack of mycorrhizal autoregulation and phytohormonal changes in the supernodulating soybean mutant nts1007

Autoregulatory mechanisms have been reported in the rhizobial and the mycorrhizal symbiosis. Autoregulation means that already existing nodules or an existing root colonization by an arbuscular mycorrhizal fungus systemically suppress subsequent nodule formation/root colonization in other parts of the root system. Mutants of some legumes lost their ability to autoregulate the nodule number and thus display a supernodulating phenotype. On studying the effect of pre-inoculation of one side of a split-root system with an arbuscular mycorrhizal fungus on subsequent mycorrhization in the second side of the split-root system of a wild-type soybean (Glycine max L.) cv. Bragg and its supernodulating mutant nts1007, we observed a clear suppressional effect in the wild-type, whereas further root colonization in the split-root system of the mutant nts1007 was not suppressed. These data strongly indicate that the mechanisms involved in supernodulation also affect mycorrhization and support the hypothesis that the autoregulation in the rhizobial and the mycorrhizal symbiosis is controlled in a similar manner. The accumulation patterns of the plant hormones IAA, ABA and Jasmonic acid (JA) in non-inoculated control plants and split-root systems of inoculated plants with one mycorrhizal side of the split-root system and one non-mycorrhizal side, indicate an involvement of IAA in the autoregulation of mycorrhization. Mycorrhizal colonization of soybeans also resulted in a strong induction of ABA and JA levels, but on the basis of our data the role of these two phytohormones in mycorrhizal autoregulation is questionable.