Effects of Folsomia candida (Collembola) on the microbial biomass in a grassland soil

Summary The effects of the presence of Folsomia candida on substrate-induced respiration, CO₂-C evolution, bacterial count and NH ₄ ⁺ -N were investigated in a grassland soil. Differences in these parameters, with the exception of NH ₄ ⁺ , were correlated with the age of the collembolan Folsomia candida. In the presence of juvenile animals total CO₂-C evolution was enhanced, but substrate-induced respiration and the bacterial count were unchanged. In fumigated soil with imagos, substrate-induced respiration and the number of bacteria were increased, but total CO₂-C evolution was unaltered. Different food selection strategies between adults and juvenile animals may explain the results.     

利用假丝酵母生产蛋白质饲料的研究

采用直接计数、快速酵母活菌计数(以下简称染色计数)、平板计数等方法研究比较假丝酵母在不同液体和固体培养基中的生长情况,明确了假丝酵母在固体培养基中生长发酵周期.     

The nonsusceptibility of soil Collembola to insect pathogens and their potential as scavengers of microbial pesticides

Collembola are very abundant soil insects which contribute to the decomposition of organic matter. This paper presents data on the interaction between Collembola and selected microbial agents being tested or used as biological pesticides. The Collembolan, Folsomia candida, was not susceptible to the entomopathogenic fungi Beauveria bassiana, Metarhizium anisopliae, Hirsutella spp., and Verticillium lecanii, or to the bacterium, Bacillus thuringiensis, and its endotoxins. F. candida consumed and inactivated the insect pathogens without suffering mortality, reproductive disturbance or any other harmful effects. Consumption of insect pathogens demonstrates the potential of the Collembola as scavengers of biological insecticides artificially introduced into the environment.     

Pathological and biochemical changes in Brassica juncea (mustard) infected with Albugo candida (white rust)

Components of disease reaction, including incubation period, pustule types, inoculum production and disease index (DI); and contents of protein, phenols, soluble sugars and reducing and non-reducing sugars were investigated in cotyledonary and true leaves of six genotypes of Brassica juncea : Varuna, Kranti, EC-399296, EC-399299, EC-399313 and EC-399301, inoculated with Albugo candida . Cotyledonary leaves were examined 14 days after inoculation (d.a.i.), whereas true leaves were scored 14 and 21 d.a.i. Disease indices were assessed on a 0% (resistant) to 100% (susceptible) scale. DIs at the cotyledonary leaf stage in the above six genotypes were 67, 65, 32, 31, 31 and 38%, respectively, whereas at the true-leaf stage they were 21, 28, 12, 17, 9 and 4%, respectively at 14 d.a.i., and 35, 45, 17, 19, 20 and 6%, respectively at 21 d.a.i. Protein contents were highest in the genotypes with the highest DIs, such as Varuna at the cotyledonary leaf stage and Kranti at the true-leaf stage, and lowest in the genotypes with the lowest DIs, such as EC-399299 at the cotyledonary stage and EC-399301 at the true-leaf stage. Total phenols, total sugars, reducing sugars and non-reducing sugars were generally negatively correlated with DI, but were not always consistent, particularly when differences in DI were small. The results indicated that factors conditioning the response of host genotypes to A. candida may differ or operate in different ways at different growth stages.     

Identification of sources and inheritance of resistance of Chinese Brassica vegetables to white blister

There is no information in the literature about the variability of resistance of Chinese Brassica vegetables, pak choi and Chinese cabbage, to the white blister disease caused by Albugo candida (Pers.) Kuntze. A collection of 43 accessions of pak choi and 19 accessions of Chinese cabbage was screened for resistance to the Portuguese A. candida isolate Ac 506 at the cotyledon stage. Different levels of resistance were found among the germplasm tested, ranging from complete resistance to full susceptibility. Most of the accessions were highly susceptible with less than 10% of resistant seedlings, and only four accessions of pak choi, presenting more than 50% resistant seedlings, were considered as new sources or resistance to white blister. Inheritance of resistance at the cotyledon stage was studied in two crosses between the most resistant pak choi accession, BRA 117, and the highly susceptible rapid cycling Brassica rapa line CrGC 1.19. It was proposed that resistance to white blister in pak choi BRA 117 is controlled by two nuclear genes with dominant recessive epistatic gene action.     

Epidemiological evidence that vegetatively propagated, solanaceous plant species act as sources of Potato spindle tuber viroid inoculum for tomato

In autumn 2006 in the Netherlands, Potato spindle tuber viroid (PSTVd) infections were detected in 42·3 and 71·9% of professionally grown lots of Brugmansia spp. and Solanum jasminoides respectively. The infected lots contained 73 985 and 431 374 plants, respectively, demonstrating the presence of many potential viroid sources for tomato ( Solanum lycopersicum ). PSTVd was identified in cultivars of Brugmansia × candida , B. × flava , B. sanguinea , B. suaveolens and unspecified Brugmansia species/cultivars. Most infected lots of Brugmansia spp. originated from a single Dutch nursery; most infected lots of S. jasminoides originated abroad. Sequence analysis revealed that the PSTVd genomes from Brugmansia spp. contained an average of 360 nt, whereas all genomes from S. jasminoides except one consisted of 357 nt. Furthermore, the collective PSTVd genotypes showed polymorphism at four or more positions, except for two cases in which genotypes from Brugmansia spp. and S. jasminoides were identical. Phylogenetic studies showed that PSTVd genotypes from Brugmansia spp. and S. jasminoides grouped apart from each other and from PSTVd isolates from potato ( Solanum tuberosum ) and Physalis peruviana . The PSTVd genotypes from tomato did not form a separate cluster, but were dispersed over clusters of vegetatively or partly vegetatively propagated plant species, i.e. potato, P. peruviana and S. jasminoides . Moreover, mechanical inoculation of the predominant PSTVd genotypes from S. jasminoides to tomato was successful. These results provide evidence that vegetatively propagated, solanaceous plant species have been sources of infection for tomato crops in the past.     

钙对葱兰花粉萌发和花粉管生长的影响

通过5种不同Ca2 浓度的培养基,研究了Ca2 对葱兰花粉萌发和花粉管生长的影响。结果表明,适当浓度的Ca2 能促进花粉萌发和花粉管的伸长,但对花粉萌发率的影响不显著。当培养基中的Ca2 浓度达到1.0×10-3mo·lL-1时,可抑制花粉的萌发和花粉管生长,并且与低浓度的Ca2 相比,对花粉管的破损显著。     

单波长太阳能灯诱杀杨毒蛾研究

为探索无公害防治杨毒蛾的方法,利用320~585 nm的单波长太阳能灯19盏开展林间诱杀研究。结果表明,365 nm太阳能灯对杨毒蛾总量和雄蛾诱杀量最大,368 nm太阳能灯对杨毒蛾雌蛾的诱杀量最大,以19:30-20:30时段诱杀效果最好。供试诱虫灯诱杀杨毒蛾总量的雌雄比2.1:1;18:30-19:30雌雄比最高,为7.5:1;21:30-22:30雌雄比最低,为0.7:1;4个时段诱杀杨毒蛾雌雄性比差异显著。蓝色容器的诱杀量较大,白色容器诱杀量较小;将装水容器放于距地面1.2 m高度比放在地面上对杨毒蛾有更好的诱杀效果。365 nm太阳能灯可作为诱杀杨毒蛾的最佳灯具,通过与筛选的最适时间、敏感容器颜色和容器高度组合,能够达到较好的诱杀效果。