Green manures and crop sequences influence alfalfa root rot and pathogen inhibitory activity among soil-borne streptomycetes

A two-year trial was conducted to determine the effects of green manures and crop sequences on plant disease, streptomycete and bacterial densities, and inhibitory activity of indigenous streptomycetes against four target pathogens. Green manure treatments, buckwheat (Fagopyrum esculentum L.), canola (Brassica napus L.), sorghum-sudangrass (Sorghum bicolor) (L.) Moench × Sorghum sudanense (Piper) Stapf.), and fallow control were tested in conjunction with three crop sequences in a Phytophthora-infested soil placed in containers. Alfalfa (Medicago sativa L.), potato (Solanum tubersoum L.), or corn (Zea mays L.) was grown in the first year, and alfalfa was grown in all containers in the second year. Compared to fallow controls, alfalfa grown in sorghum-sudangrass- or buckwheat-treated soil had significantly greater stand counts and total biomass, respectively. In addition, alfalfa grown in fallow-treated soils had the greatest Phytophthora root rot as a function of stand count. Crop rotation also had a significant effect on alfalfa root rot and yield. Potato scab disease intensity was greatest on tubers grown in fallow-treated soils, while tubers grown in canola-treated soils had the highest yields (total tuber weight). Green-manure-treated soils tended to have greater streptomycete and bacterial densities than fallow-treated soils. In addition, buckwheat- or sorghum-sudangrass-treated soils had greater proportions of streptomycetes that were antagonistic against the target pathogens than fallow-treated soils. The proportion of antagonists in soil was negatively correlated with alfalfa root rot, and positively correlated with alfalfa stand counts. Inhibitory activity of the streptomycetes was also negatively correlated with potato scab and positively correlated with potato yield. These data suggest that green manures may provide a strategy for increasing pathogen inhibitory activity within the streptomycete community in soil, and, in conjunction with crop rotation, may contribute to the control of a diverse collection of soil-borne plant pathogens on multiple crop species.     

Inactivation of indicators and pathogens in cattle feedlot manures and compost as determined by molecular and culture assays

Accurate and conservative information about pathogen inactivation rates is needed as the basis for safe manure management on beef cattle feedlots. The survival of indicators and pathogens in faecal pen manure, stockpiled manure and manure compost was measured with autochthonous indicator bacteria (Escherichia coli, Clostridium perfringens, enterococci, total coliforms) and pathogens (Listeria monocytogenes, Campylobacter jejuni) using culture and/or real-time quantitative PCR (qPCR) methods. Additionally, the manures were incubated at 20, 37, 50 and 60 °C in microcosms to quantify the persistence of autochthonous microorganisms and selected process performance surrogates (Clostridium sporogenes, green fluorescent protein-labelled E. coli and L. monocytogenes). Estimated qPCR cell counts indicated that up to four orders of magnitude more target cells were present compared with the culturable counts. Corresponding T(90) estimates were up to sixfold higher. This study demonstrates the benefits of nucleic acid-based quantification of pathogen inactivation in cattle manures and concludes that the concurrent analysis of microorganisms by molecular and culture methods provides complementary value.     

Green manures of oat,rape and sweet corn for reducing common root rot in pea (Pisum sativum) caused by Aphanomyces euteiches

Green manure crops of sweet corn, soybean, alfalfa, snap bean, rape, pea and of the two oat cultivars Dane and Troy were incorporated into the same soil and containers in which the crop had grown for five weeks. The soil was then evaluated for suppression of common root rot (Aphanomyces euteiches) of pea grown in infested pasteurized and non-pasteurized soils in the greenhouse. Pea biomass reduction and a plant bioassay for A. euteiches were used to measure the green manure suppression of disease. Green manures of sweet corn cv.Jubilee, oat cv.Troy, and rape cv.Humus significantly reduced pea biomass losses over the non-amended control soil treatments. Oat cv.Troyand sweet corn cv.Jubilee green manures significantly reduced inoculum density of A. euteiches over the corresponding fallow controls in inoculated pasteurized soil by 87% and 76%, respectively, and in inoculated non-pasteurized soil by 67% and 66%, respectively. Only the green manure of oat cv. Troy reduced inoculum density significantly below fallow.     

Management of soil microbial communities to enhance populations of Fusarium graminearum-antagonists in soil

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe is one of the most devastating diseases of wheat. Primary inoculum generated on crop residue is the driving force of FHB epidemics. Fusarium survival on crop residues is affected by soil microbial antagonists. The incorporation of green manures has been shown to increase the density and diversity of microbes in soils, particularly the density and the pathogen-inhibitory activity of specific bacteria and fungi. Evidence of increased streptomycete populations in soil as a response to green manure incorporation, and their negative effect on the survival of Fusarium oxysporum Schlechtendahl in soil, suggests their potential use to reduce the survival of related pathogens. There is, however, no precedent for the use of green manures to promote indigenous streptomycete populations to control FHB. This study investigated the use of green manures (sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench–S. bicolor (L.) Moench var. sudanense (Piper)] and common buckwheat [Fagopyrum esculentum (Moench)]) for reducing F. graminearum survival in association with wheat residues. Soil bacterial density, streptomycete density and the density and inhibitory activity of F. graminearum-antagonists were monitored from planting until 3 and 6 months following the incorporation of green manures in greenhouse and field experiments, respectively. The decomposition of wheat residues and survival of Fusarium in residues was also assessed. The use of green manures did not statistically impact the survival of F. graminearum in wheat residue. However, green manures promoted the development of higher densities and antagonistic abilities of F. graminearum-antagonists in soils. Additionally, streptomycete densities and F. graminearum-antagonist densities were significantly and positively correlated with reduced survival of Fusarium. The results of our study suggest that the use of green manures can enhance populations of indigenous soil microorganisms antagonistic to the survival of F. graminearum in wheat residue.     

Changing fitness of a necrotrophic plant pathogen under increasing temperature

Warmer temperatures associated with climate change are expected to have a direct impact on plant pathogens, challenging crops and altering plant disease profiles in the future. In this study, we have investigated the effect of increasing temperature on the pathogenic fitness of Fusarium pseudograminearum, an important necrotrophic plant pathogen associated with crown rot disease of wheat in Australia. Eleven wheat lines with different levels of crown rot resistance were artificially inoculated with F. pseudograminearum and maintained at four diurnal temperatures 15/15°C, 20/15°C, 25/15°C and 28/15°C in a controlled glasshouse. To quantify the success of F. pseudograminearum three fitness measures, these being disease severity, pathogen biomass in stem base and flag leaf node, and deoxynivalenol (DON) in stem base and flag leaf node of mature plants were used. F. pseudograminearum showed superior overall fitness at 15/15°C, and this was reduced with increasing temperature. Pathogen fitness was significantly influenced by the level of crown rot resistance of wheat lines, but the influence of line declined with increasing temperature. Lines that exhibited superior crown rot resistance in the field were generally associated with reduced overall pathogen fitness. However, the relative performance of the wheat lines was dependent on the measure of pathogen fitness, and lines that were associated with one reduced measure of pathogen fitness did not always reduce another. There was a strong correlation between DON in stem base tissue and disease severity, but length of browning was not a good predictor of Fusarium biomass in the stem base. We report that a combination of host resistance and rising temperature will reduce pathogen fitness under increasing temperature, but further studies combining the effect of rising CO₂ are essential for more realistic assessments.     

Minimizing the time and cost of production of transgenic alfalfa libraries using the highly efficient completely sequenced vector pPZP200BAR

Alfalfa is the most important forage legume worldwide. However, similar to other minor forage crops, it is usually harvested along with weeds, which decrease its nutrient quality and thus reduce its high value in the market. In addition, weeds reduce alfalfa yield by about 50 %. Although weeds are the limiting factor for alfalfa production, little progress has been made in the incorporation of herbicide-tolerant traits into commercial alfalfa. This is partially due to the high times and costs needed for the production of vast numbers of transgenic alfalfa events as an empirical approach to bypass the random transgenic silencing and for the identification of an event with optimal transgene expression. In this focus article, we report the complete sequence of pPZP200BAR and the extremely high efficiency of this binary vector in alfalfa transformation, opening the way for rapid and inexpensive production of transgenic events for alfalfa improvement public programs.     

Investigating the response of soil and vegetable crops to poultry and cow manure using ground and satellite data

Based on the massive production of cow and poultry manures, farmers in Saudi Arabia are moving towards the application of organic fertilizers in their farms. Therefore, the present work was conducted to study the response of soil and selected vegetable crops to poultry and cow manures, using ground data and Landsat-8 and Hyperion images. The studied vegetable crops are cabbage, cauliflower, broccoli, and lettuce. A total of 100 t ha^?1 organic manures were applied as a pre-planting treatment. A 12.5 ha field in Tawdeehiya Farms, 200 km southeast of Riyadh, was earmarked for this study. The field was divided into sectors cultivated with the above-mentioned vegetable crops. Soil characteristics, including the soil pH, the electric conductivity (EC), the nitrogen (N), the phosphorus (P) and the potassium (K), were examined before the application of manures and 25 days after the transplanting process. Observations on crops chlorophyll content, number of leaves, the diameter of merchantable products and yield were also investigated. Furthermore, the relationship between the crop performance and yield was investigated through the satellite images generated vegetation indices (VIs). This study revealed the better performance of poultry manure compared to cow manure in terms of development and production parameters of the experimental crops. Dynamics of the chlorophyll content across the crop growth period revealed that all the tested crops responded significantly (R² = 0.69; P = 0.001) to the poultry manure treatments. Among the tested crops, the chlorophyll content, curd or head sizes and crop yields were quite better in poultry manure applied plots. The investigation of crop yield was significant with poultry manure (R² = 0.64; P = 0.001) than cow manure (R² = 0.57; P = 0.001) using the OSAVI and mNDVI, respectively.     

Barley response to nitrogen and non-nutritional benefits of legume green manure

Green manure application may benefit subsequent crops not only by improving nitrogen (N) fertility but also via non-nutritional mechanisms. The quantification of the latter effect, however, is complicated by the confounding effect of N fertility. Two experiments were conducted in controlled environments to partition the yield response of barley to green manure between N and non-nutritional effects. Each experiment included a factorial of fertilizer N application rates and green manure application rates. The fertilizer was labelled with ¹⁵N to facilitate discrimination between N sources. Approximately 24% of the N applied in green manure was assimilated by barley after 45 days (Experiment 1) and 32% was recovered by barley grown to maturity (Experiment 2). Apparent recovery of green manure-N by barley was not appreciably affected by fertilizer application. Regression analysis of the relationship between dry matter yield and plant N uptake demonstrated that yield responses to green manure application were not entirely attributable to improved N fertility. For a given amount of N assimilated by the crop, yields were higher in green manure-amended treatments than in those receiving no green manure. In barley grown to maturity, barley response to N and non-nutritional effects were estimated to be 5.3 and 2.2g pot⁻¹, respectively. The relationship between dry matter yield and N uptake is suggested as a method for distinguishing nutritional and non-nutritional yield responses. This approach assumes that no other nutrient is limiting growth. The presence of non-nutritional benefits observed in this study demonstrates that the agronomic value of green manure is not limited to N release and casts doubt on the assumptions inherent to calculation of fertilizer equivalents. Contribution 3879132 Contribution 3879132     

Green manure technology: Potential,usage, and limitations. A case study for lowland rice

The growing concern about the sustainability of tropical agricultural systems stands in striking contrast to a world-wide decline in the use of soil-improving legumes. It is timely to assess the future role that soil-improving legumes may play in agricultural systems. This paper reviews recent progress, potential, and limitations of green manure technology, using lowland rice cropping systems as the example.Only a few legume species are currently used as green manures in lowland rice. Sesbania cannabina is the most widely used pre-rice green manure for rice in the humid tropics of Africa and Asia. Astragalus sinicus is the prototype post-rice green manure species for the cool tropics. Stem-nodulating S. rostrata has been most prominent in recent research. Many green manure legumes show a high N accumulation (80–100 kg N ha^-1 in 45–60 days of growth) of which the major portion (about 80%) is derived from biological N₂ fixation. The average amounts of N accumulated by green manures can entirely substitute for mineral fertilizer N at current average application rates. With similar N use efficiencies, green manure N is less prone to loss mechanisms than mineral N fertilizers and may therefore contribute to long-term residual effects on soil productivity.Despite a high N₂-fixing potential and positive effects on soil physical and chemical parameters, the use of green manure legumes for lowland rice production has declined dramatically world-wide over the last 30 years. Land scarcity due to increasing demographic pressure and a relatively low price of urea N are probably the main determining factors for the long-term reduction in pre-rice green manure use. Post-rice green manures were largely substituted for by high-yielding early-maturing grain legumes. Unreliability of green manure performance, non-availability of seeds, and labor intensive operations are the major agronomic constraints. The recognition and extrapolation of niches where green manures have a comparative advantage may improve an often unfavorable economic comparison of green manure with cash crop or fertilizer N. Socio-economic factors like the cost of land, labor, and mineral N fertilizer are seen to determine the cost-effectiveness and thereby farmers' adoption of sustainable pre-rice green manure technology. Hydrology and soil texture determine the agronomic competitiveness of a green manure with N fertilizers and with alternative cash crops. In general, the niches for pre-rice green manure are characterized by a relatively short time span available for green manure growth and a soil moisture regime that is unfavorable for cash crops (flood-prone rainfed lowlands with coarse-textured soils).Given the numerous agronomic and socio-economic constraints, green manure use is not seen to become a relevant feature of favourable rice-growing environments in the foreseeable future. However, in environments where soil properties and hydrology are marginal for food crop production, but which farmers may be compelled to cultivate in order to meet their subsistence food requirements, green manures may have a realistic and applicable potential.     

Effect of combination of bio-agents and mineral nutrients for the management of alfalfa wilt pathogen Fusarium oxysporum f. sp. medicaginis

Abstract

Biological and nutrient management of soil borne disease is increasingly gaining stature as a possible practical and safe approach. Inhibitory effects of fungal and bacterial antagonists were tested under in vitro conditions against the wilt pathogen of alfalfa Fusarium oxysporum f. sp. medicaginis. Trichoderma harzianum and Pseudomonas fluorescens (PI 5) were found to be effective against the alfalfa wilt pathogen. Manganese sulphate at 500 and 750 ppm inhibited the mycelial growth of F. oxysporumf. sp. medicaginis under in vitro conditions. In pot culture studies, manganese sulphate at 12.5 mg/kg reduced the wilt incidence (23.33%). Combined application of manganese sulphate 12.5 mg/kg + T. harzianum 1.25 mg/kg of soil significantly reduced the wilt incidence accompanied by improved plant growth and yield in pot culture. The mixture of manganese sulphate (25 kg/ha) + T. harzianum (2.5 kg/ha) significantly reduced the wilt incidence when applied as a basal dose in the field conditions. The average mean of disease reduction was 62.42% over control.     

Effect of incorporated green manure crops on subsequent oat production in an acid,infertile silt loam

A field-size experiment was initiated in 1982 on an acid, low fertility Springhill silt loam to determine the effect of five unfertilized green manure crops (alsike clover, sweet clover, single- and double-cut red clover, and buckwheat) on subsequent oat production and soil fertility. The field was limed in 1982 and green manures were seeded (without fertilizer) in spring, 1983 in 1400 m² strips randomly assigned within three treatment blocks. Plant tissue samples were taken from different locations in each plot in the fall of 1983 and all crops were incorporated. In 1984 the field was separated into an upper and lower section and each section received three rates of NPK fertilizer (0; 30-36-36; 60-72-72 kg ha^-1) spread across the previous strips. Gary oats were seeded and at harvest were divided into grain and straw. The results indicated significant effects of field sample location, green manure type and fertilizer level on oat yields. Buckwheat significantly reduced oat production compared to the four clovers, while the highest fertilizer rate improved oat yields compared with the other levels of fertilizers. Elemental analysis of the green manure crops and soil fertility was compared with data of the same crops grown in more fertile, neutral soils.     

Experimental quantification of improvement during circadian wheel running in the Indian field mouse,Mus terricolor: theoretical uses

We quantified motor learning during voluntary wheel-running activity in the Indian pygmy field mouse, Mus terricolor. Wheel running in naive adults was monitored using the Clocklab system. A group of mice having 15 days prior wheel-running experience served as the control. The daily maximum wheel activity for the naive group increased from 21?±?7 counts/min to 62?±?4 counts/min in 15 days. The experienced group exhibited 62?±?1 counts/min throughout the experiment. A significant correlation between days of wheel running and natural log of the highest count/min existed in the experimental group, but not in the experienced group. Thus, improvement in wheel running follows a logarithmic learning curve. Several research applications for this quantification have been discussed. The most important outcome of this quantification is that it primes the mice for a study in which the retention period for this motor learning, i.e. the time taken to “forget” motor learning during wheel running will be elucidated.     

Molecular Detection and Pathogenicity Assay of Plasmodiophora brassicae in Chicken Manure

To determine the relationship between animal excreta and the occurrence of clubroot disease of cruciferous crops caused by Plasmodiophora brassicae, chickens were fed with resting spores of the pathogen. Their faeces were collected and used to inoculate crucifers. This study proved that both fresh and composted manures could induce clubroot and the presence of the pathogen in the manure was confirmed by PCR amplification. However, composting had detrimental effects on the virulence of the resting spores in the manure. When the temperature was over 32°C, the incidence and severity of clubroot declined with the increase in the exposure time of resting spores to high temperature and the pathogenicity was completely lost when the spores were kept at 48°C for 6 h. The control measures for the clubroot disease were discussed.     

绿肥在我国旱地农业生态系统中的服务功能及其应用

旱地农业分布面积广、增产潜力大,在保障我国粮食安全方面占有重要地位,但也面临着水资源短缺、土壤贫瘠、水土流失严重和不可再生资源利用效率低等问题。绿肥不仅具有提高土壤质量、调节土壤养分和增强土壤水分蓄纳能力,从而改善作物生长环境,促进作物持续高产稳产的作用,而且在增加农田生态系统生物多样性、提高地表覆盖度、减少养分向环境中的无效损失、增强农田系统气体调节功能、提高病虫草害的生物防控等方面也具有显著的生态效益。在全球气候变化加剧、生态环境恶化和农产品需求改变等新形势下,以肥用为主要目的的传统绿肥种植应用技术已不能满足当前农业发展的需求,需要加强旱地绿肥种质资源的选育工作,通过研制新的适应新形势的全国绿肥区划,构建适应不同区域的绿肥种植模式,优化和研发适应现代化生产水平的耕作栽培技术,探究绿肥综合效益评价体系,为旱地农业区改善生态环境、提高经济效益,构建资源节约、生态保育型的绿肥应用模式,充分挖掘绿肥效益提供科学依据和技术支撑。     

Nitrogen contribution of cowpea green manure and residue to upland rice

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to acid upland soil and can be grown for seed, green manure, and fodder production. A 2-yr field experiment was conducted on an Aeric Tropaqualf in the Philippines to determine the effect of cowpea management practice on the response of a subsequent upland rice crop to applied urea. Cowpea was grown to flowering and incorporated as a green manure or grown to maturity with either grain and pods removed or all aboveground vegetation removed before sowing rice. Cowpea green manure accumulated on average 68 kg N ha⁻¹, and aboveground residue after harvest of dry pods contained on average 46 kg N ha⁻¹. Compared with a pre-rice fallow, cowpea green manure and residue increased grain yield of upland rice by 0.7 Mg ha⁻¹ when no urea was applied to rice. Green manure and residue substituted for 66 and 70 kg urea-N ha⁻¹ on upland rice, respectively. In the absence of urea, green manure and residue increased total aboveground N in mature rice by 12 and 14 kg N ha⁻¹, respectively. These increases corresponded to plant recoveries of 13% for applied green manure N and 24% for applied residue N. At 15 d after sowing rice (DAS), 33% of the added green manure N and 16% of the added residue N was recovered as soil (nitrate + ammonium)-N. At 30 DAS, the corresponding recoveries were 20 and 37% for green manure N and residue N, respectively. Cowpea cropping with removal of all aboveground cowpea vegetation slightly increased (p<0.05) soil (nitrate + ammonium)-N at 15 DAS as compared with the pre-rice fallow, but it did not increase rice yield. Cowpea residue remaining after harvest of dry pods can be an effective N source for a subsequent upland rice crop.     

Comparative proteomic analysis of alfalfa revealed new salt and drought stress-related factors involved in seed germination

Salinity and drought are two major environmental factors that limit the growth and yield of many forage crops in semi-arid and arid regions. Alfalfa (Medicago sativa L.) is one of the most important forage crops in many countries. We aim to investigate the molecular mechanisms of alfalfa in response to salt and drought stresses in this study. Physiological and proteomic analyses were applied to examine the Zhongmu NO.3 alfalfa seed germination stage with 200 mM NaCl and 180 g·L^?1 polyethylene glycol (PEG) treatments. The germination ability of the seed and the accumulation of osmotic solutes were quite different between the NaCl and PEG treatments. More than 800 protein spots were detected by proteomics technology on two-dimensional electrophoresis (2-DE) gels. The abundance of twenty-eight proteins were decreased or increased after salt and drought stress. Seventeen of these proteins were identified and classified into six functional categories through mass spectrometry (MS). The six groups involved in salt- and PEG-mediated stress included defense response, energy metabolism, protein synthesis and degradation, oxidative stress, carbohydrate metabolism-associated proteins, and unknown proteins. We discovered that some proteins related to carbohydrate metabolism and energy production increased in abundance under salt- and PEG-mediated drought stress. This demonstrates a common mechanism of energy consumption during abiotic stresses. Further study of these proteins with unknown function will provide insights into the molecular mechanisms of abiotic stress and the discovery of new candidate markers.     

Utilization and management of organic wastes in Chinese agriculture: Past, present and perspectives

Recycling and composting of organic materials such as animal waste, crop residues and green manures has a long tradition in China. In the past, the application of organic manures guaranteed a high return of organic materials and plant mineral nutrients and thus maintained soil fertility and crop yield. As a result of rapid economic development coupled with the increasing urbanization and labour costs, the recycling rate of organic materials in Chinese agriculture has dramatically declined during the last two decades, in particular in the more developed eastern and southeastern provinces of China. Improper handling and storage of the organic wastes is causing severe air and water pollution. Because farmers are using increasing amounts of mineral fertilizer, only 47% of the cropland is still receiving organic manure, which accounted for 18% of N, 28% of P and 75% of K in the total nutrient input in 2000. Nowadays, the average proportion of nutrients (N+P+K) supplemented by organic manure in Chinese cropland is only 35% of the total amount of nutrients from both inorganic and organic sources. In China, one of the major causes is the increasing de-coupling of animal and plant production. This is occurring at a time when "re-coupling" is partly being considered in Western countries as a means to improve soil fertility and reduce pollution from animal husbandry. Re-coupling of modern animal and plant production is urgently needed in China. A comprehensive plan to develop intensive animal husbandry while taking into account the environmental impact of liquid and gaseous emissions and the nutrient requirements of the crops as well as the organic carbon requirements of the soil are absolutely necessary. As a consequence of a stronger consideration of ecological aspects in agriculture, a range of environmental standards has been issued and various legal initiatives are being taken in China. Their enforcement should be strictly monitored.     

Macrophomina phaseolina alters the biochemical pathway in Vigna radiata chastened by Zn2+ and FYM to improve plant growth

Mung bean [Vigna radiata (L.) Wilczek] is an important cash pulse crop extensively cultivated in the arid region of Pakistan, which encounters intimidating charcoal rot disease caused by Macrophomina phaseolina (Tassi) Goid. The current research was conducted to check the potential of Zn (1.25, 2.44 and 5?mg?kg^?1) and FYM [farmyard manure (1% and 2%)] in mono-, bi- and trilateral interaction in managing disease and improving yield. Suppression of plant immunity by M. phaseolina was indicated by the change in activities of antioxidant enzymes (CAT and SOD) and cell wall strengthening enzymes (POX and PAL) that revealed inability of the protein receptor to identify the pathogen elicitor. FYM improved soil physicochemical properties and beneficial microbes activity, which released antimicrobial protein- and plant defense-stimulating protein and in response to ROS (reactive oxygen species) signaling molecules plant susceptibility was reduced. However, Zn as a co-factor chastened the ROS in stressed cells by upregulation of antioxidant enzymes in favor of the plant. The complex interaction of FYM and Zn potentially hijacked the further multiplication of pathogen. Finally, soil amendment improved biological attributes and grain yield to profitable farming in terms of harvest index percentage and benefit–cost ratio.     

Impact of Bemisia whiteflies (Homoptera: Aleyrodidae) on alfalfa growth, forage yield, and quality

A 3-yr project was initiated in 1993 to examine the effects of insecticides and sustained whitefly, Bemisia argentifolii Bellows & Perring [aka. B tabaci Gennadius (Strain B)], feeding on alfalfa plant growth and vigor in greenhouse cage studies, and to determine the impact of natural Bemisia whitefly populations on alfalfa forage yields and quality in a large-plot field experiment. Alfalfa plant growth and vigor after exposure to imidacloprid and a mixture of fenpropathrin and acephate insecticides did not differ from untreated plants in the greenhouse. Consequently, foliar and soil applied insecticides were used to manipulate whitefly densities on alfalfa plants to measure whitefly feeding effects on plant growth and forage yield. Heavy whitefly densities on untreated alfalfa plants in the greenhouse resulted in significant reductions in relative growth rates and net assimilation rates as compared with imidacloprid-treated plants that were maintained relatively whitefly-free. Reductions in alfalfa plant growth measured between infested and treated plants were proportional to whitefly densities. Field plot results derived from three crop seasons were relatively consistent with our greenhouse trials. Both experimental approaches clearly showed that alfalfa plants exposed to high densities of whitefly immatures and adults grew at a significantly slower rate and produced less foliage. As a result of reduced growth rates, alfalfa maturity in the naturally infested plots was estimated to be approximately 7-10 d behind managed plots. Delays in maturity resulted in significant reductions in forage yields of 13-18% during August-September harvests when whitefly populations reached peak abundance. Whitefly feeding stresses also effected hay quality through the reduction of crude protein content and contamination of foliage with honeydew and sooty mold. The status of the Bemisia whiteflies as an economic pest to alfalfa is clearly evident from these studies, but the damage potential of whiteflies in the southwestern United States appears to be restricted to one or two harvest periods during the summer coinciding with peak adult populations and their dispersal from alternate host crops.     

The potential for protein production from green plants

Data on protein yields show that forage crops, particularly alfalfa, produce several times more protein per acre than do seed crops. Amino acid analyses and estimations of biological values by enzymatic hydrolysis and feeding trials indicate that protein concentrates from green plants have high nutritive value. The protein concentrates from 10 plant species had a similar amino acid composition and biological value which indicates that good protein might be obtained from many plant species. It is suggested that the use of the fibrous residue as a feed for ruminants and the use of the protein concentrate as a high protein feed or base for processing into new protein foods may make it possible for the production of protein from green plants to compete with other sources of protein. This would markedly increase protein production per acre and allow the use of new plant species in our agriculture. The need for more research on protein production from different types of green plants and on ways to harvest, concentrate and process their proteins into edible forms is discussed.