Comparative analysis of Wanjincheng orange leaf and root responses to ‘Candidatus liberibacter asiaticus’ infection using leaf-disc grafting

Citrus Huanglongbing,associated with Candidatus Liberibacter asiaticus(Las),is the serious disease of citrus worldwide.Here,we compared differences between leaf and root responses in Wanjincheng Orange(Citrus sinensis Osbeck)to Las infection using leaf-disc grafting.Trees had no obvious symptoms in the first two months after grafting(MAG),but yellowing leaves,thickened midribs and decayed roots began to appear at 6 MAG.The Las growth rate in roots was greater than inmidribs from 2 to 6 MAG;however,by 10 MAG,it was significantly lower in roots than in midribs.Amicroscopic analysis revealed that starch accumulation,callose deposition,cellwall thickness and the number of cell layers increased in the phloem of infected trees.After Las infection,the starch content in the leaves was significantly higher than that in the roots,while the callose deposition in the midribs was 3–19 times that in the roots.A gene expression analysis showed that transcripts of callose-and starch metabolism-related genes were obviously affected by Las infection,and the pathogenesis-related genes PR1,PR2 and PR5 were significantly upregulated and downregulated in midrib and root,respectively.Our results indicated that the PR-mediated resistance response was repressed in root but activated in midrib,which may result in the more rapid Las growth in roots than in midribs during the early infection stage.

Effects of copper, lead and zinc in soil on egg development and hatching of Folsomia candida

Effects of CaCl2, CuCl2, ZnCl2 and PbCl2 on development and hatching success of eggs of Folsomia candida （Collembola） were studied under laboratory conditions. Thousands of healthy eggs from synchronized cultures were incubated in soils treated with different concentrations of the metals. Compared with the water control, egg hatch significantly decreased when concentrations of Cu, Pb and Zn reached 400, 1 600 and 800 mg/kg dry soil, respectively. Values of EC50（hatching）, calculated according to the exponential model （with 95% confidence limits in brackets）, were 625 （407-875）, 2 361 （2 064-2 687） and 1 763 （1 548-2 000） mg/kg dry soils for Cu, Pb and Zn, respectively. When Cu concentration reached 1 600 mg/kg dry soil, eggs became green and the percentage of green eggs changed from 5%-20% after incubation for 2 days to 15%- 30% after incubation for 4 days. At 3 200 mg Cu/kg dry soil, tissues inside eggs were black and shrunken.