Phytophthora citrophthora,a new pathogen causing decline on horse chestnut in Turkey

Dieback symptoms were observed on horse chestnut trees planted approximately 40 years ago in Ankara, Turkey. Lesions at the stem bases of the affected trees were similar to those of ink disease on sweet chestnut. A Phytophthora sp. was isolated from the fine roots and soil samples collected around the stem bases by baiting using chestnut leaves. The pathogen was identified as Phytophthora citrophthora based on several morphological features and DNA sequences of the ITS region. Pathogenicity of P. citrophthora was tested by stem inoculation on 3‐year‐old horse chestnut saplings. P. citrophthora produced large cankers in 20 days and killed 40% of the saplings. This is the first report of P. citrophthora causing dieback on horse chestnut.     

Diversity of Cryphonectria parasitica in callused chestnut blight cankers on European and American chestnut

Infection of American and European chestnuts with the chestnut blight fungus Cryphonectria parasitica results in the formation of cankers, lesions caused by the growth of mycelia within bark tissue of the host plant. Infection of the fungus with Cryphonectria hypovirus 1 (CHV‐1) results in conversion of the mycelial phenotype from virulent to hypovirulent, thus allowing production of callus around cankers as a reaction by infected trees, rendering active into inactive cankers. In this study, we sampled one USA and six European chestnut stands and assessed frequency of hypovirulent C. parasitica and diversity of vegetative compatibility (vc) types present in calluses and randomly sampled cankers. Callused cankers on C. dentata at West Salem in the USA yielded significantly more hypovirulent C. parasitica isolates compared with four sampled populations on C. sativa, while all six sampled European populations did not show any statistically significant differences among themselves. We observed no correlation between hypovirulence frequencies in randomly sampled cankers and calluses, as well as no correlation of C. parasitica vc type diversity in calluses and residential populations of the fungus. Furthermore, even though we have observed calluses with more than one vc type, they do not occur regularly. Even when present in C. parasitica populations with high vc type diversity, no more than three different vc types were observed in a single callus.     

The effects of logging and disease on American chestnut

Disturbance histories drive spatiotemporal patterns of species distributions, and multiple disturbances can have complex effects on these patterns of distribution. The introduction of the chestnut blight (Cryphonectria parasitica (Murril.) Barr.) to the eastern United States in the early 1900s coincided with an increase in logging, thus presenting an ideal situation for studying the effect of two disturbance events, logging and disease. The purpose of this study was to compare chestnut (Castanea dentata) abundance and the prevalence of chestnut blight among (1) sites that were and were not logged for chestnuts during the blight pandemic and (2) sites that varied in time since the last logging event. Current chestnut abundance and chestnut blight prevalence were assessed in areas where chestnut was known to occur before the blight. Elevation, soil pH, slope, aspect, age of canopy trees, and presence or absence of chestnut stumps indicating selective logging of chestnuts were recorded at each site. Chestnuts were more abundant on sites that had not been selectively logged for pre-blight chestnuts. Chestnut presence was more likely at high elevations (857 m ± 33 m). Chestnut abundance was greater at high elevations (>1000 m) and acidic soils (pH 4-5). Chestnut blight prevalence was not correlated with any measured environmental variable. Rather, 15.1% of all chestnut stems were infected with blight regardless of chestnut density. Thus, higher chestnut abundance is not due to lower mortality from the chestnut blight, although the temporal dynamics of blight infection and stem recovery were not within the scope of this study. This research shows that local rates of chestnut population decline differ between locations with different chestnut logging histories. Chestnut site preferences are better understood within the context of history, and thus teasing apart the effects of disease, logging, and environment will result in more successful chestnut restoration efforts.     

栗果霉烂机理及防治

为探讨栗果贮藏、运输期间的霉烂机理，通过大量调查研究，提出了影响栗果霉烂的主要原因及防治方法，为提高栗果的质量和保鲜度提供科学的理论依据。     

短枝型板栗的选育与推广前景

从20世纪80年代起，我国开始选育短枝型板栗，20年来取得了显著成效，如燕山早丰、燕魁、早熟大红等一批短枝型板栗新品种被选育出来，其单位面积产量远远超过优良乔化品种。作者就短枝型板栗的选育概况，植物学特征栽培性状和开发前景进行了详细论述，并对大面积推广这一新品系提出了建议性建议。     

Spread of white hypovirulent strains of Cryphonectria parasitica on grafted American chestnut trees exhibiting a high level of blight control

In 1982 and 1983, natural blight cankers, located in a zone extending from the ground to 183 cm on the main stem of grafted American chestnut trees, were inoculated with a mixture of dsRNA-containing, white (European) and pigmented hypovirulent strains of Cryphonectria parasitica (H-inoculated zone). In 1996, white isolates (34% of 156 C. parasitica isolates) were recovered from superficial cankers throughout the grafts and as far as 564 cm from the H-inoculated zone. Lloyd's index of patchiness value (1.36) indicated that white isolates were slightly aggregated in cankers on the grafts. Forty-five percent of 95 C. parasitica isolates, recovered 5–50 months after inoculating the grafts with pigmented virulent strain WK, were white and some converted strain WK to the white phenotype in vitro. All cankers and bark cores yielding only pigmented isolates, vegetatively compatible with virulent strain WK, had superficial necrosis 5 and 11 months after inoculation with strain WK. All white isolates of C. parasitica assayed contained a 12.7 kbp dsRNA in high concentrations, and were hypovirulent in pathogenicity trials. Twenty-eight vegetative compatibility groups were identified among 65 pigmented graft area isolates; none of 48 pigmented isolates contained dsRNA. In addition to host resistance factors, spread of white strains may be responsible for the unusually high level of blight control on the grafts.     

美洲栗抗疫病基因工程研究简介

该文介绍美国纽约州立大学环境科学院与林学院正在进行的美洲栗抗疫病基因工程研究 ,包括基因的选择、构建及初步结果     

Aboveground carbon biomass of plantation-grown American chestnut (Castanea dentata) in absence of blight

Forest management activities may help reduce global net CO₂ concentrations by capturing and storing atmospheric CO₂. Research related to carbon sequestration potential of plantations in North America has focused predominantly on conifers, with relatively little emphasis thus far on temperate deciduous forest tree species. American chestnut (Castanea dentata (Marsh.) Borkh.), a former dominant tree species in eastern North America until its demise associated with the introduced chestnut blight (Cryphonectria parasitica (Murr.) Barr.), is a temperate deciduous species that holds promise for future carbon sequestration programs with expected availability of blight-resistant backcross hybrids. We quantified aboveground biomass and bole carbon of American chestnut interplanted with black walnut (Juglans nirga L.) and northern red oak (Quercus rubra L.) across four blight-free experimental sites varying in site quality and/or age (8, 8, 12, and 19 years) isolated from the native American chestnut range in the Coulee Region of southwestern Wisconsin, USA. American chestnut exhibited more rapid growth and greater aboveground biomass and bole carbon than either of the other interplanted species. Aboveground biomass ranged from 46.9, 60.7, 55.0, and 179.9 Mg ha⁻¹ for the 8-, 8-, 12-, and 19-year-old sites, respectively, while bole carbon content ranged from 13.6, 18.6, 14.1, and 60.1 Mg ha⁻¹ for the 8-, 8-, 12-, and 19-year-old sites, respectively. Cross-referencing our data to studies conducted within this same physiographic region using other important forestry species (i.e., Populus tremuloides Michx., Pinus resinosa Ait., and Pinus strobus L.) showed that American chestnut compared favorably in growth and carbon uptake. Incorporating American chestnut into carbon sequestration plantations provides additional ecological and economic benefits associated with consistent production of quality nuts for wildlife, valuable timber, and contribution toward species restoration. Our data lend support to building evidence demonstrating rapid and sustained growth of American chestnut and the potential role of plantation-grown American chestnut in helping to mitigate climate change through carbon sequestration.     

Incomplete movement of Cryphonectria hypovirus 1 within a vegetative compatibility type of Cryphonectria parasitica in natural cankers on grafted American chestnut trees

American chestnut trees, grafted in 1980 from large survivors, were inoculated in 1982 and 1983 with four white (European) hypovirulent strains of Cryphonectria parasitica, infected with C. hypovirus 1 (CHV1); this hypovirus has been shown to be capable of moving rapidly within the mycelium of a vegetative compatibility (vc) type of C. parasitica in blight cankers. Using a 49‐cell lattice plot, 17.8×17.8 cm, the spatial patterns and frequencies of white and pigmented isolates and white and pigmented vc types were investigated within superficial cankers on the grafts located outside the hypovirulent‐strain‐inoculated zone. Four of six cankers assayed contained white isolates, and three of the four had random spatial patterns of white isolates, based on join‐count statistics. Vc tests, using pigmented isolates and pigmented single‐spore colonies of white isolates, indicated that the majority of white and pigmented isolates recovered from each of two cankers assayed were in one vc type. White and pigmented lattice‐plot cells of the same vc type were frequently in contact with each other, indicating incomplete movement of CHV1 within a vc type. Nine and 10 vc types were found in the two cankers; it is hypothesized that small, white vc type areas in each canker may be a source of CHV1 transmission to the major vc types. Based on join‐count statistics, the spatial pattern of the single, major vc type in one canker was non‐random (aggregated), whereas the other canker had a random major vc type pattern. White and pigmented in vitro variants (sectors) of C. parasitica, that resemble white and pigmented in vivo variants in spatial contact and vc compatibility, were intermediate hypovirulent and virulent on forest American chestnuts, and dsRNA positive and negative, respectively. Incomplete movement of CHV1 within a vc type could be a major cause of the prevalence of pigmented isolates in superficial cankers on chestnut trees.     

Spread of Cryphonectria hypovirus1 into 45 vegetative compatibility types of Cryphonectria parasitica on grafted American chestnut trees

A mixture of hypovirulent strains of Cryphonectria parasitica, including four white (European) strains infected with Cryphonectria hypovirus1 (CHV1), was used in 1982 and 1983 to inoculate natural blight cankers located within a zone ranging from the ground to 183 cm on grafted American chestnut trees. These four white strains belonged to three vegetative compatibility (vc) types. Using pigmented, single‐spore colonies from white isolates, 48 vc types were identified among 110 white isolates recovered in 1996, 1998, and 1999 from cankers located outside the inoculated zone. Twenty‐five of the 48 white vc types consisted of two or more isolates. The 25 major white vc types were vegetatively incompatible with all four of the original white hypovirulent strains, providing evidence for spread of CHV1 but not for spread of the original inoculated strains. Forty‐five vc types represent the minimum number of `new' vc types into which CHV1 had spread. The ratio of white vc types to white isolates tested (S/N) and Shannon diversity index were 0.436 and 3.64, respectively. The spatial pattern of white vc types on the grafts was found to be non‐random (p=0.019). White single‐spore colonies of white isolates were placed into four cultural morphology (CM) groups. The two largest groups contained 37 (CM group 3) and 33 (CM group 1) isolates. Single‐spore colonies from the original, white inoculated strain, Ep 49, were classified into CM groups 3 and 1, and colonies of Ep 51 W were classified into CM group 1.     

美国林产工业面临的挑战和对策

编者按:美国是全球最大的木材和木材产品市场.住房建造是美国木业的主要依托.Al Schuler等的论文分析了这个主要市场可能发生的变化和应对各种挑战的对策,并从中看到全球化进程的必然趋势和要求.这种对发展规律的思考对研讨我国木业的发展战略应有一定的参考价值.     

Genetic monitoring of traditional chestnut orchards reveals a complex genetic structure

Key message

This study presents the results of a systematic genetic analysis between wild and cultivated chestnuts in an orchard in southern Spain, highlighting a complex structure and considerable genetic diversity and opening the possibility to generalize this approach to other Mediterranean orchards.

Context

Tree genetic monitoring offers a good opportunity to evaluate populations and preserve their long-term adaptive evolutionary potential. Chestnut is a multipurpose species of high economic importance in the Mediterranean basin and considered an example of integration between natural and man-driven distribution of diversity under changing environmental and historical conditions. Due to its multipurpose characteristics, man influenced its populations (grafting/sexual propagation) and a complex genetic structure is expected.

Aims

We monitored the trees of a chestnut orchard for studying the genetic diversity and relationship in grafts and rootstocks and detecting possible response in its adaptive potential.

Methods

For this, morphological traits and genomic and genic microsatellite markers were used.

Results

Chestnut trees showed considerable genetic structure, with high level of clonality in the varieties and genetic diversity in rootstocks. The similarity analysis revealed a different clustering pattern for varieties, detecting higher variability for genomic microsatellite markers. Rootstocks harboured a high level of diversity, not previously described, and not contained in the genetic information from populations and varieties from the same region.

Conclusion

Results contribute to understanding the human role in the management of chestnut and demonstrate that rootstocks constitute an unexploited reservoir of variation valuable for conservation strategies against stress factors and future and unpredictable environmental changes.

     

Phytophthora species associated with dieback of sweet chestnut in Western Turkey

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey.     

核桃黑斑病病原研究与防治试验初报

研究了核桃黑斑病的病原及发生规律，进行了药剂防治试验。试验结果表明：锌铜波尔多液(0．3：0．5：1：200)防治效果为79．6％，95％细菌灵500倍液防治效果为64．9％，可在生产上推广应用。     

Reinvigoration of mature chestnut (Castanea sativa) by repeated graftings and micropropagation

Gradual reinvigoration of adult chestnut (Castanea sativa M. cv. Montemarano) shoots was obtained by serial grafting onto juvenile rootstocks. The phenomenon was evaluated on the basis of percentage of primary nodes regenerating axillary shoots and length and number of shoots (> 10 mm) per primary node. In vitro growth of explants from serially grafted shoots was significantly lower than that of explants from seedlings at the end of the establishment phase. Only microshoots from seedlings and plants that had been serially grafted four times could be subcultured on proliferation medium. Repeated subculture on medium containing a low cytokinin concentration induced progressive reinvigoration of microshoots derived from plants that had been serially grafted four times. The number of axillary shoots per explant increased significantly after six subcultures. After 12 subcultures, microshoots from serially grafted plants showed an increase in stem elongation, rooting and plantlet survival. After in vitro stabilization, there was no difference in in vitro performance between microshoots derived from seedlings and serially grafted plants. Microshoots multiplied from serially grafted plants displayed only a transitory appearance of juvenile traits.