The tea plant [Camellia sinensis (L.) O. Kuntze] is an industrial crop in China.  The Anhui Province has a long history of tea cultivation and has a large resource of tea germplasm with abundant genetic diversity.  To reduce the cost of conservation and utilization of germplasm resources, a core collection needs to be constructed.  To this end, 573 representative tea accessions were collected from six major tea-producing areas in Anhui Province.  Based on 60 pairs of simple sequence repeat (SSR) markers, phylogenetic relationships, population structure and principal coordinate analysis (PCoA) were conducted.  Phylogenetic analysis indicated that the 573 tea individuals clustered into five groups were related to geographical location and were consistent with the results of the PCoA.  Finally, we constructed a core collection consisting of 115 tea individuals, accounting for 20% of the whole collection.  The 115 core collections were considered to have a 90.9% retention rate for the observed number of alleles (Na), and Shannon’s information index (I) of the core and whole collections were highly consistent.  Of these, 39 individuals were preserved in the Huangshan area, accounting for 33.9% of the core collection, while only 10 individuals were reserved in the Jinzhai County, accounting for 8.9% of the core set.  PCoA of the accessions in the tea plant core collection exhibited a pattern nearly identical to that of the accessions in the entire collection, further supporting the broad representation of the core germplasm in Anhui Province.  The results demonstrated that the core collection could represent the genetic diversity of the original collection.  Our present work is valuable for the high-efficiency conservation and utilization of tea plant germplasms in Anhui Province

Radopholus similis (Cobb 1893) Thorne (1949) is a destructive migratory endoparasitic plant nematode.  In this study, the pathogenic process of R. similis infection in Nicotiana benthamiana (tobacco) was studied using quartz sand culture in laboratory.  The results showed that R. similis mainly parasitised the root cortex, leading to cortical cell decomposition and tissue decay.  We optimised the inoculation conditions to establish a method for determining the pathogenicity of R. similis as follows: (1) a glass culture tube was filled with quartz sand (about 1/3 of the height) and sterilised twice; (2) 20-day-old N. benthamiana seedlings were transplanted into test tubes and cultivated for 10 days at (25±1)°C; (3) R. similis female nematodes were inoculated in the root rhizosphere at a rate of 150 nematodes per plant; (4) the number of nematodes, disease severity, and growth of the plant at 30 days post-inoculation (dpi) were determined.  The pathogenicity of eight R. similis populations from different hosts was determined, which proved the feasibility of this method.

Plant structures and chemicals, which are developed from the shoot apical meristem (SAM), form the main barriers to insect feeding.  A plant chimera containing cells of different genetic origins in the SAM will be morphologically and chemically different compared with the parents and thus may result in differential resistance to herbivores.  In this study, we explore if particular elements of plant resistance are localized in one of the layers of SAM; the replacement of one cell layer in a chimera may be linked to change of a single resistance trait to herbivores.  The morphology and glucosinolate profiles of two periclinal chimeras (labeled as TTC and TCC, respectively) and grafted parents tuber mustard (labeled as TTT) and red cabbage (labeled as CCC) were compared and the performance of whitefly (Bemisia tabaci) in host selection, oviposition preference and development were assessed under controlled conditions.  Both chimeras possessed leaf trichomes as parent tuber mustard TTT, however, TTC had significantly more trichomes than TCC and parent TTT.  Leaf wax content of both chimeras was intermediate between the two parents.  Five aliphatic and two indole glucosinolates were detected in both chimeras, whereas three aliphatic glucosinolates (3-methyl-sulfinylpropyl, 4-methyl-sulfinylbutyl and 2-hydroxy-3-butenyl) were not detected in tuber mustard, and one aliphatic glucosinolate (3-butenyl) was not detected in red cabbage.  Unexpectedly for a chimera, the quantities of two aliphatic glucosinolates (3-methyl-sulfinylpropyl and 4-methyl-sulfinylbutyl) in both TTC and TCC were 3- to 5-fold higher than parents.  In olfactory preference assays, B. tabaci showed preference to CCC, followed by TCC, TTC and TTT, and number of eggs laid showed the same pattern: CCC>TCC>TTC>TTT.  Interestingly, more whiteflies landed on TTT plants than the other three types in a free choice experiment and the developmental duration from egg to adult was the shortest on TTT and increased in the order TTT<TTC<TCC<CCC.  Our results indicate plant defenses traits of leaf waxes, trichomes and glucosinolates are not controlled by one cell layer of SAM, but are influenced by interactions amongst cell layers.  The overall findings suggest that periclinal chimera systems can be a valuable approach for the study of plant-insect interactions and may also be useful for future resistance breeding. 

Ten populations of Radopholus similis from different ornamental hosts were tested for their parasitism and pathogenicity to water spinach (Ipomoea aquatic), malabar spinach (Basella rubra), and squash (Cucurbita moschata) in pots. The results showed all three plants were new hosts of R. similis. Growth parameters of plants inoculated with nematodes were significantly lower than those of healthy control plants. All R. similis populations were pathogenic to the three plants, but pathogenicity differed among populations from different hosts. The same R. similis populations also showed different pathogenic effects in the three different plants. RadN5 population from Anthurium andraeanum had the highest pathogenicity to the three studied plants. RadN1 from A. andraeanum had the lowest pathogenicity to squash and RadN7 from Chrysalidocarpus lutesens had the lowest pathogenicity to water spinach and malabar spinach. R. similis is usually associated with root tissues, but here we report that it could be found to move and feed in the stem bases of all three studied plants. Sequence and phylogenetic analyses of DNA markers of the 18S rRNA, 28S rRNA, ITS rRNA, and mitochondrial DNA gene sequences of ten R. similis populations revealed significant genetic diversity. RadN5 and RadN6 populations from anthurium showed a close genetic relationship and could be distinguished from other populations by PCR-RFLP. At the same time, RadN5 and RadN6 populations were the most pathogenic to three studied plants. These results confirm the existence of large biological variability and molecular diversity among R. similis populations from the same or different hosts, and these characteristics are related to pathogenic variability.