Responses ofQuercus sapwood to infection with the pathogenic fungus of a new wilt disease vectored by the ambrosia beetlePlatypus quercivorus

Quercus serrata andQ. crispula wilt during the summer in wide areas along the Sea of Japan. Mass attacks of trees by an ambrosia beetle (Platypus quercivorus) are characteristic before appearance of the wilting symptoms. This study investigated the pathogenic effects of a fungus detected specifically in the wilting trees. This hyphomycete fungus,Raffaelea sp., has a distribution that correlates with the discolored xylem area called wound heartwood in which vessels are dysfunctional. Tylosis formation around the hyphae indicates vessel dysfunction. In areas with discoloration, the fungal hyphae were invading living ray parenchyma cells from the vessel lumen. As a protective reaction the ray cells exuded yellow substances into the vessels, but these substances seemed ineffective against the fungal activity, probably because the fungus disperses along the beetle's gallery before enough substance can accumulate. It should allow wide discoloration in sapwood. Cambium was not necrotic around the fungus. The cytological process in the host was as follows: (1) synthesis of secondary metabolites by the stimuli of oak fungus; (2) exudation of yellow substances into vessels; and (3) dysfunction of vessels and wound heartwood formation. In regard to wilting of trees, the pathogenicity of the fungus should be assessed by its ability to stop sap flow.     

胡杨茎木质部解剖结构与水力特性对干旱胁迫处理的响应

分析干旱胁迫下胡杨(Populus euphratica Oliv.)茎木质部解剖结构与水力特性的变化对解读其抗逆性机理具有重要意义.本文采用水分控制试验,分析胡杨幼株茎木质部解剖结构和水力特性对不同土壤干旱胁迫处理的响应.结果表明:在解剖结构方面,随着干旱胁迫的加剧,胡杨茎木质部导管密度呈极显著减小(P＜0.01)趋势,而导管内径、导管壁厚度、管壁机械强度呈极显著增大(P＜0.01)趋势,穿孔直径和纹孔直径显著增大(P＜0.05);但导管分子形态却没有发生显著变化,都具有孔纹式和螺纹式两种类型,其中纹孔多为具缘纹孔,呈互列式排列,端壁穿孔为单穿孔类型,并具有螺纹加厚现象;在水力特性方面,随着干旱胁迫的加剧,胡杨茎的木质部比导率(Ks)和自然栓塞程度(PLC)呈显著增加趋势(P＜0.05).为了适应干旱的环境,胡杨茎木质部结构和水力特性发生相应的变化,一定程度上弥补了干旱胁迫所带来的不利影响.     

Changes in water status in seedlings of six species in the Fagaceae after inoculation with Raffaelea quercivora Kubono et Shin-Ito

To clarify the differences in susceptibility of six species in the Fagaceae (Quercus crispula, Quercus serrata, Quercus acutissima, Quercus phillyraeoides, Quercus glauca, and Castanopsis cuspidata var. sieboldii) to Raffaelea quercivora, we inoculated this fungus on seven potted 5-year-old seedlings of each species, observed symptom development, and measured xylem pressure potential (XPP) after inoculation. The first death was observed on the 11th day in Q. crispula and on the 56th day in Q. serrata. The number of dead seedlings of Q. crispula and Q. serrata were five and one, respectively, whereas no mortality was observed in the other four species. The XPP of inoculated seedlings in both Q. crispula and Q. serrata decreased after inoculation. In contrast, the XPP of inoculated seedlings of the other four species remained almost the same as in the control seedlings. These results indicate that R. quercivora is pathogenic to Q. crispula and Q. serrata and that the susceptibility of the six Fagaceae species in our study differed among species.     

桐花树和海桑次生木质部的生态解剖

对紫金牛科 (Myrsinaceae)的桐花树 (Aegicerascorniculatum)和海桑科 (Sonneratiaceae)的海桑 (Son neratiacaseolaris)的次生木质部的组织结构和数量特征进行了研究 ;并讨论了桐花树和海桑的木材结构与环境关系 ;它们的导管直径小、导管数量多、导管分布频率高 ,是对海滨盐渍环境的适应 ,保证水分在植物体内运输的安全性。桐花树和海桑的纤维壁厚度 (W )与纤维腔宽度 (L)的比值 (2W /L)分别为 0 6 7和 0 4 5 ,均小于 1 ,从木纤维 2W /L <1的角度看 ,桐花树和海桑的木材可用作造纸原料     

Maturation property of fast-growing hardwood plantation species: A view of fiber length

The development of human civilization has caused many problems, among them increases in atmospheric CO₂ and shortage of fossil fuel resources. Fast-growing tree species can help solve these problems. Short rotations cause concern that fast-growing species contain a high proportion of juvenile wood, thus limiting their use. To use fast-growing species for timber, this concern must be addressed.     

玉米自交系木质部伤流液中氮素形态差异及其与氮效率的关系

研究了苗期玉米木质部伤流液中的氨基酸/硝态氮水平变异及其与田间产量的相互关系。在两个氮水平下,10个玉米自交系的田间产量变异分别达53.80%（不施氮）和59.89%(高氮),盆栽条件下苗期生物量变异为23.82%(不施氮)和26.37%(高氮),苗期生物量与田间产量间相关不显著。苗期木质部伤流液中不同形态氮的含量变化较大,低、高氮水平下,氨基酸浓度的变异系数分别为100.80%和60.45%,硝态氮分别为43.33%和16.82%,氨基酸/硝态氮的变异系数分别为118.39%和54.91%。在低氮条件下,伤流液中的氨基酸浓度、氨基酸/硝态氮与田间产量的相关达到极显著,这可能与氮在根中的还原及地上与地下部氮循环有密切关系,有可能作为低氮条件下氮高效品种筛选的指标之一。     

不同供水条件下田间冬小麦气栓塞发生基本特征

 应用超声波技术,在田间灌水及干旱条件下对冬小麦品种9195叶片木质部气栓塞发生特征进行了研究。结果表明,超声波(AE)信号发生的基本特征为1d内一般有3个活跃期,第一活跃期以上午10:00～11:00出现频率最多,第二、三活跃期多分别出现在18:00左右和0:00前后,一般夜间0:00～2:00后信号终止。3个活跃期的AE信号发生强度可随生育进程、土壤水分及气候状况等条件变化。土壤干旱时,第三活跃期减弱或消失。灌水当日第二活跃期有增强的趋势。拔节初期,干旱小麦的AE信号发生量高于灌水小麦的。抽穗后土壤过度干旱时,AE信号量却常低于灌水小麦,笔者称其为“AE信号衰减现象”。灌水后土壤水分充足时,气栓塞也有相当程度的发生。气栓塞是伴随气孔开启、光照增强和温度升高而出现的植株水势快速下降的一种生理性反映。     

Phenotyping vigour control capacity of new peach rootstocks by xylem vessel analysis

In peach, xylem anatomical characteristics have been shown to be related to vigour of selected rootstocks. The goal of this research was to determine if xylem characteristics of a new set of rootstocks that exhibit a range of size-controlling potential and have a different genetic background from previously examined material would also exhibit similar differences in xylem characteristics. If so, then anatomical analysis of xylem may be a useful means of predicting the vigour control capacity of selected peach rootstock genotypes. Samples of xylem tissue were taken from roots, trunks and shoots of four new rootstocks that were derived from a genetic cross between ‘Harrow Blood’ and ‘Okinawa’ peaches and compared with tissue from ‘Nemaguard’, a vigorous control. Xylem samples were sectioned and analysed by optical microscope. The number and dimensions of vessels in recently developed xylem of each rootstock were measured and compared. The more dwarfing rootstocks had fewer large vessels and more small vessels than the more vigorous rootstocks. Weighted mean vessel diameter (Wm) and calculated hydraulic conductance (K_h) differed among rootstocks: more vigorous rootstocks had higher K_h and Wm than dwarfing rootstocks. Rootstock xylem vessel dimensions varied in relation to the vigour they imparted to a common scion cultivar (‘O’Henry’). After the ‘Nemaguard’ control, ‘HBOK 50’ was the most vigorous rootstock followed by ‘HBOK 10’, ‘HBOK 32’ and ‘HBOK 27’, respectively. Thus, as was seen in previous research with a separate set of rootstocks, the vigour-control capacity of this new series of peach rootstocks was strongly related to their xylem hydraulic characteristics and it appears likely that it would be possible to use xylem anatomical characteristics of shoots or roots of young trees to pre-select for size-controlling potential in a rootstock development program.     

Decay development in living sapwood of coniferous and deciduous trees inoculated with six wood decay fungi

Development of decay and/or discoloration was assessed in the functional sapwood of one coniferous and three deciduous trees after wounding and artificial inoculation with six wood decay fungi. Living stems of mature Douglas fir, beech, oak, and sycamore trees were wounded in spring 2002 and immediately inoculated with brown, white, and soft rot fungi. Extent of discoloration and decay, wood weight loss, and total phenols in the reaction zone (zone of active response at a dynamic interface between living sapwood and wood colonized by decay fungi) were assessed 16 and 28 months after inoculation.     

Manipulating phenology and water relations in <Emphasis Type="Italic">Senna spectabilis</Emphasis> in a water limited environment in Kenya

The effect of shoot pruning on leaf phenology, stem wood anatomy and sap flow was investigated on Senna spectabilis (DC.) Irwin and Barneby in Machakos, Kenya. Unpruned trees (single stem) were compared to hedges (two to four stems), pruned 4 times a year during two rainy seasons (April–June, 1997 and November, 1997–January, 1998) separated by a dry season (July–October 1997). Trees attained peak leaf area of 55 m² plant⁻¹ during the rainy seasons, and shed all their leaves naturally during the dry season. Maximum hedge leaf area was 4 m² plant⁻¹ between pruning events and 5.2 m² plant⁻¹ during the dry season. Pruning induced multiple stems and narrow xylem vessels with low hydraulic conductivity. Average cross sectional area of conducting wood per plant was at least 1.8 times greater in trees than in hedges. Xylem lumen diameter at 5 mm depth below the cambium was significantly (P < 0.001) larger in trees (53.6 ± 6.21 μm) than that in hedges (36.2 ± 8.21 μm). Maximum sap flow occurred in the wet season for trees (4800 g d⁻¹ plant⁻¹) and in the dry season for hedges (1400 g d⁻¹ plant⁻¹). Wet season pruning suppressed crown expansion and modified the natural phenology of senna, reducing transpiration rate and therefore soil water depletion, causing crowns to grow. This enhanced the ecological combining ability of senna managed as hedges with annual crops.