Virulent Rhizoctonia spp. isolated from strawberry in Israel belonged to anastomosis groups (AG) of: binucleate Rhizoctonia (BNR) AG-A, AG-G, AG-K and AG-F, and to multinucleate Rhizoctonia (MNR) AG 4 subgroup HG-I. In addition, a soil isolate of AG 4 subgroup HG-III was also found to be virulent on strawberry.
None of the Israeli isolates obtained in the present study belonged to BNR AG-I, or other MNR AGs. In the cluster analysis
of rDNA-ITS sequences, all of the isolate sequences consistently clustered according to their known AGs and subgroups. One
AG-F cluster included sequences of 10 strawberry isolates, while another AG-F cluster included sequences of two isolates submitted
to GenBank. Additional work is needed to determine whether the isolates of these two clusters may belong to different AG-F
subgroups. The current virulence bioassay used for Rhizoctonia spp. isolates on strawberry is based on inoculation of stolon-derived daughter plants with the isolates and estimation of
the reduction in plant biomass, rather than on specific distinct disease severity symptoms. The duration of this test is relatively
long (ca. 5 weeks or more) and the availability of daughter plants from runners is naturally limited to a certain season.
Among the possible alternative methods evaluated in the present study (inoculation of fruits or seedlings developed from germinated
strawberry seeds), the method based on seedlings was best. This method has a potential to replace the currently used stolon-daughter
plant inoculation bioassay for testing virulence of strawberry root pathogens. This is the first report indicating that Rhizoctonia spp. isolates that belong to AG-F, AG-K, AG 4 HG-I and AG 4 HG-III are virulent to strawberry. 相似文献
The Lenglongling Mountains(LLM)located in northeastern part of the Tibet Plateau,belong to a marginal area of the East Asian summer monsoon(EASM)and are sensitive to monsoon dynamics.Two tree-ring width chronologies developed from six sites of Picea crassifolia in the LLM were employed to study the regional drought variability.Correlation and temporal correlation analyses showed that relationships between the two chronologies and self-calibrated Palmer Drought Severity Index(sc_PDSI)were significant and stable across time,demonstrating the strength of sc_PDSI in modeling drought conditions in this region.Based on the relationships,the mean sc_PDSI was reconstructed for the period from 1786 to 2013.Dry conditions prevailed during 1817–1819,1829–1831,1928–1931 and 1999–2001.Relatively wet periods were identified for 1792–1795 and 1954–1956.Spatial correlations with other fourteen precipitation/drought reconstructed series in previous studies revealed that in arid regions of Northwest China,long-term variability of moisture conditions was synchronous before the 1950 s at a decadal scale(1791–1954).In northwestern margin of the EASM,most of all selected reconstructions had better consistency in low-frequency variation,especially during dry periods,indicating similar regional moisture variations and analogous modes of climate forcing on tree growth in the region. 相似文献