Control of preharvest and postharvest fruit rot in Strawberry by Metschnikowia fructicola

The yeast Metschnikowia fructicola was tested as a preharvest treatment to control preharvest and postharvest rots of strawberry fruit in Turkey and Israel. In greenhouse trials, the efficacy of the yeast antagonist against preharvest rots was equal to that of a chemical control (fenhexamid) in two growing seasons. In an open-field experiment, the yeast reduced the incidence of rot to commercially acceptable levels. M. fructicola reduced the incidence of fruit rot by 56-69% in greenhouses, open-field culture, and in low plastic tunnels. The yeast suppressed postharvest incidence of fruit rot significantly better than fenhexamid. Among fruit from greenhouses, open-field culture, or tunnels, M. fructicola treatment reduced the incidence of fruit rot during postharvest storage by 70, 64, and 72%, respectively. When applied weekly in the greenhouse or in the field, the population density of M. fructicola was about 1×10⁵ cfu/fruit. Similar population density of the antagonist was also observed during storage of the fruit at 0° C.     

Effect of volume and concentration of conidial suspensions of Coniothyrium minitans on infection of Sclerotinia sclerotiorum sclerotia

White mould, caused by Sclerotinia sclerotiorum, is a serious disease affecting a wide range of agricultural and horticultural crops. Biological control is one option available to limit its damage. Field experiments to evaluate various concentrations and volumes of Coniothyrium minitans spore suspensions applied to S. sclerotiorum-infected bean crops were conducted in 1997 and 1998. Percentage sclerotia infected by C. minitans were scored. Three replicate experiments were performed in time in 1997 with 21 combinations of isolates, volumes and concentrations, including two controls. In 1998, 22 combinations of isolates, volumes and concentrations plus two controls were used, combined with the absence or presence of a maize buffer, with two replicates for each. Isolates as well as concentration and volume had no effect on infection by C. minitans, but there was a significant effect of total dose (volume×concentration) of inoculum applied over the full range from 100 L ha^-1 at 10⁴ conidia mL^-1 to 1000 L ha^-1 at 10⁷ conidia mL^-1. Percentage infected sclerotia increased linearly with log (dose) as well as from 1 to 4 weeks after application of C. minitans, and reached a level of about 100% at high doses under the humid conditions of 1998. Apothecia of S. sclerotiorum developing from sclerotia in collected soil samples from the 1997 experiment showed no significant effect of C. minitans inoculum dose, but there was a significant effect of the replicate experiments. The influence of weather conditions is highlighted, and the implications of the results for cost-effective biocontrol of S. sclerotiorum are discussed.     

Effect of Pathogen Isolate, Potato Cultivar, and Antagonist Strain on Potato Scab Severity and Biological Control

Antibiotic-producing Streptomyces spp. have shown potential in biocontrol of potato scab caused by Streptomyces scabies. However, results have been inconsistent among field trials. Pathogen isolate, antagonist strain and potato cultivar were investigated as potential sources of variation in the efficacy of potato scab biocontrol. Biocontrol success varied significantly among pathogen isolates and was not correlated with in vitro sensitivity to antibiotic inhibition. Antagonists also varied in their effectiveness as biocontrol agents, and the relative effectiveness of different antagonists varied among growing seasons. Finally, biocontrol varied among potato cultivars in the field. The diverse origins of significant variation in potato scab biocontrol suggest that consistent control in the field is likely to be difficult to achieve.     

Oviposition pattern of the predator Podisus nigrispinus (Heteroptera: Pentatomidae) under different temperatures

The daily reproductive rate of Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) fed with Alabama argillacea (Hübner) (Lepidoptera: Noctuidae) larvae was studied at constant temperatures of 20, 23, 25, 28, 30 and 33±0.2°C, relative humidity of 60±10% and photoperiod of L:D 14:10. Daily reproductive rate of P. nigripinus was affected by age of this predator. Each P. nigrispinus female laid 5.3 (20°C) to 19.9 eggs/day (28°C) which developed into 4.3–16.5 nymphs, respectively. Highest daily reproductive rate of P. nigrispinus was recorded at 28 and 30°C for 5–30-day-old females. This predator showed higher daily reproductive rate than its prey A. argillacea at 25°C. It was also able to reproduce at temperatures from 20 to 33°C with maximum daily reproductive rate between 25 and 30°C. These results are important for optimizing mass rearing of P. nigrispinus in the laboratory.     

白灵菇研究进展

白灵菇以其鲜美的味道、较好的口感和明显的保健作用成为我国近年来迅速发展的人工栽培珍稀食用菌。依据文献资料及研究工作综述了白灵菇的生物学特性、营养成分、药用价值、栽培研究的历史、现状 ,培养技术和遗传等方面的研究进展     

Functional Activity of Exoglycans from Rhizobium leguminosarum bv. viciae 250a and Its Nitrogen-Resistant Mutant M-71 during the Formation of Legume–Rhizobia Symbiosis against a High-Nitrogen Background

The functional activity of the exoglycan complex (EGC) polysaccharides from Rhizobium leguminosarum bv. viciae 250a and its nitrogen-resistant mutant M-71, capable of inducing the formation of nitrogen-fixing nodules on pea roots against a high-nitrogen background (4.8 mM NO₃ ^–), was studied in vegetation tests. For this purpose, the bacterial inoculum washed free of its own exoglycans was supplemented with EGC of the same or another strain grown in the presence of 6 or 20 mM nitrate. The best symbiotic characteristics (nodule number and nitrogenase activity, mass of the roots and aerial parts of plants) were recorded when the inoculum cells and exoglycans were obtained from strain M-71 grown in the presence of 20 mM nitrate. When the plants were inoculated with the cells (grown at 6 mM nitrate) + EGC (obtained at 6 mM nitrate) of this strain, the nodulation characteristics and the effectiveness of symbiosis decreased 1.5- to 2-fold. Partial recovery of the symbiotic potential of strain M-71 was observed when EGC (obtained at 20 mM nitrate) was substituted for its exoglycans (obtained at 6 mM nitrate). In the presence of exoglycans of the parent strain 250a (obtained at 6 or 20 mM nitrate), the mutant formed a substantially lesser number of nodules with a very low nitrogen-fixing activity. In turn, the mutant exoglycans synthesized in medium with either high or low nitrate nitrogen concentration did not recover the fix⁺ phenotype of strain 250a, capable of forming symbiosis with pea plants only against a low-nitrogen background. In study of the relative content of high-molecular-weight exopolysaccharide components and low-molecular-weight glycans in the exoglycan complex, it was established that, in strain 250a (grown at 6 and 20 mM nitrate), as well as in its mutant M-71 (grown at 6 mM nitrate), exopolysaccharides prevailed, accounting for 72–75% of the sum of both types of glycopolymers, while low-molecular-weight glycans accounted for 25–28%. In contrast, in the EGC of strain M-71 obtained at 20 mM nitrate, which was the most active inducer of the formation of the symbiotrophic system by strain M-71 in the presence of a high mineral nitrogen concentration, low-molecular-weight glycans were the main component, accounting for 61% of total glycopolymers, while the polysaccharide content was 39%. Low-molecular-weight exoglycans are supposed to be involved in maintaining the physiological activity and the symbiotic status of rhizobia under unfavorable environmental conditions.     

Aphid suppression by natural enemies in mulched cereals

Large populations of natural enemies are the basis for natural pest control. Effects of mulch on predator–prey interactions in arable fields are poorly known, despite its potential to enhance ground‐dwelling predators and thereby reduce pest infestations. We studied the densities of predators and parasitoids, and their impact on cereal aphids in the presence and absence of mulch. Released populations of the bird cherry aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), and two naturally occurring aphid species, were monitored under experimentally reduced densities of: (i) ground‐dwelling predators, (ii) flying predators and parasitoids, and (iii) with straw mulch. The three treatments were applied in a 2 × 2 × 2 factorial design in a field of spring wheat (Triticum aestivum L.). The exclusion of ground‐dwelling predators increased aphid populations by 55% in June and 40% in July, respectively. Mulched plots had 25% lower aphid densities in June. This was presumably due to enhanced densities of spiders (Araneida) in mulched plots. The exclusion of flying predators and parasitoids led to 94% higher aphid populations in late July (109 vs. 56 individuals per 100 shoots), irrespective of mulch or ground predator manipulation. This was attributed to the larvae of gall midges Aphidoletes cf. aphidimyza (Rondani) (Diptera: Cecidomyiidae) and hoverflies (Diptera: Syrphidae). The results indicate that a scarcity of predators and a bare soil surface renders crops more susceptible to arthropod pests. Farming schemes should aim at enhancing both ground‐dwelling and flying predators for elevated levels of natural pest control.     

虚拟生物实验室实例

虚拟生物实验室在生物课程资源中有巨大并且尚未开发的潜力。它对于不同级别学生的学习都是有利的。介绍了虚拟生物实验室的一些实例。并展望了其应用前景。