Thailand is one of the largest citrus producers in Southeast Asia. Pathogenic infection by Phytophthora, however, has become one of major impediments to production. This study identified a pathogenic oomycete isolated from rotted roots of pomelo (Citrus maxima) in Thailand as Phytophthora nicotianae by the internal transcribed spacer ribosomal DNA sequence analysis. Then, we examined the in vitro and in vivo effects of Chaetomium globosum, Chaetomium lucknowense, Chaetomium cupreum and their crude extracts as biological control agents in controlling this P. nicotianae strain. Represent as antagonists in biculture test, the tested Chaetomium species inhibited mycelial growth by 50~56% and parasitized the hyphae, resulting in degradation of P. nicotianae mycelia after 30 days. The crude extracts of these Chaetomium species exhibited antifungal activities against mycelial growth of P. nicotianae, with effective doses of 2.6~101.4 µg/mL. Under greenhouse conditions, application of spores and methanol extracts of these Chaetomium species to pomelo seedlings inoculated with P. nicotianae reduced root rot by 66~71% and increased plant weight by 72~85% compared to that in the control. The method of application of antagonistic spores to control the disease was simple and economical, and it may thus be applicable for large-scale, highly effective biological control of this pathogen.
Six iBPS primers and twenty-one morphological traits were used to assess the genetic diversity and relationships of 15 tea [Camellia sinensis (L.) O. Kuntze] accessions grown in Vietnam. The similarity index matrix generated from Dice coefficient (iPBS analysis) and the dissimilarity index matrix generated from Euclidian distance coefficient (morphological analysis) were used to build the respective un-weighted pair group method with arithmetic average (UPGMA) derived-dendrograms revealing the genetic relationships among the tested tea accessions. The iPBS analysis showed a slightly different result as compared to the result of morphological analysis which indicated that the group of Shan and Assam type were separate from the group of China type and the hybrids related to China type. Meanwhile, the iPBS analysis clustered 15 tea genotypes into two main groups; the tea genotypes of small leaved China, Assam-small leaved China hybrid and Shan-large leaved China hybrid type, with small leaf size, came together into one group; the other one was mainly nested by the tea genotypes of Shan, Assam and Shan-small leaved China type, with large leaf size. However, the iPBS analysis also shared the same basic agreements with the morphological analysis. All the tea genotypes, which originated from the same parents or the same type of crossing parental couple, revealed close relatedness. The results of morphological analysis are conformable with the conventional classification of tea taxa and give basic relative information among 15 tea genotypes to demonstrate particularly the result of molecular analysis. It could be concluded that iPBS is a useful DNA based-marker for evaluation of genetic diversity and relationships of tea.
Three new pyrrolobenzoxazine sesquiterpenoids, talatrachyoxazines A – C (1 – 3), together with fourteen known compounds (4 – 17), were isolated from the fungus Talaromyces trachyspermus EU23. Their structures were identified by spectroscopic evidence and mass spectrometry. The absolute configurations of 1 – 3 were determined by NOESY data and comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. Compound 1 showed cytotoxic activity against HelaS3, KB, HT-29, MCF-7, and HepG2 cell lines with IC50 values of 7, 11, 10, 12, and 10 µM, respectively. Compounds 1 and 14 showed weak antibacterial activity against the gram-positive bacteria Bacillus cereus and Bacillus subtilis, while 1 – 3 and 14 showed weak antibacterial activity against the gram-negative bacterium Pseudomonas aeruginosa. In addition, compound 1 showed weak antibacterial activity against Escherichia coli.
Bouea macrophylla Griff. is well-known as one of native typical fruits in Southeast Asia which needs to be preserved and continuously cultivated because of economical and ecological significances. More recently, sequence-related amplified polymorphism (SRAP) markers have been developed, which are used to amplify coding regions of DNA with primers targeting open reading frames. This technique has proven to be robust and highly variable and is attained through a significantly less technically demanding process. In this research, SRAP method was preliminary applied to assess genetic characterization of B. macrophylla. Genomic DNA was extracted from fresh leaf samples. The result clearly showed that at 100 ng template DNA and MgCl 2 5 mM concentration are suitable for further PCR analysis. Thirty SRAP primer combinations were initially screened for analysis and 26 primer combinations were chosen for further analysis. A total of 222 DNA fragments, varying from 90-2500 bp, were amplified. The produced band number for each optimal primer set ranged from 3 to 12 with a percentage of polymorphic bands spanning from 33.33 to 80.00%. Therefore, SRAP analysis is suitable for further analysis method on genetic study of Bouea species and related genera.
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