Bursaphelenchus xylophilus: An Important Pathogenic Factor of Pine Wilt Disease and Its Relationship with Bursaphelenchus mucronatus.

Pine wilt disease is the most devastating pine disease caused by Bursaphelenchus xylophilus. Bursaphelenchus mucronatus is morphologically similar to B. xylophilus and geographically overlaps in its distribution. Although interspecific hybridization of the two nematodes has been performed in vitro, the dynamic regularity of hybrid formation and its risk in forests has not been well evaluated. In this study, a hybrid of B. xylophilus and Bursaphelenchus mucronatus mucronatus was identified in the laboratory and fields by molecular markers. The heterozygosity of ITS-5.8S loci for identification was unstable in the hybrid population, and the allele inherited from B. m. mucronatus was lost over several generations. We also provided evidence that hybrids existed in some new epidemic areas, while old epidemic areas were usually dominated by B. xylophilus. Hybrids could be generated when B. m. mucronatus was invaded by B. xylophilus, and the pathogenicity of the hybrids was similar to that of B. xylophilus. These findings may improve the understanding of the natural hybridization between B. xylophilus and B. m. mucronatus and pathogenic variation in pine wilt disease, providing new insights for future studies on disease detection, transmission, and quarantine.

The composition of root exudates from two different resistant peanut cultivars and their effects on the growth of soil-borne pathogen.

The high incidence of various soil-borne diseases in the monoculture field of peanut is a major production constraint in the red soil regions of southern China. The peanut root exudates are generally thought to play an important role in regulating soil-borne pathogens. The responses of the soil-borne pathogens, Fusarium oxysporum and F. solani to the peanut root exudates were studied using one susceptible cultivar Ganhua-5 (GH) and one mid-resistant cultivar Quanhua-7 (QH) as the test materials. The components and contents of the amino acids, sugars and phenolic acids in the peanut root exudates were determined. The results demonstrated that the root exudates from both susceptible and mid-resistant cultivars significantly promoted the spore germination, sporulation and mycelial growth of soil-borne pathogens, F. oxysporum, F. solani compared with the control. The extent of the stimulation was depended on the strains of the Fusarium tested, and gradually increased with the increased concentrations of peanut root exudates. HPLC analysis showed that the contents of sugars, alanine, total amino acids in the root exudates of GH were significantly higher than that in QH, whereas the contents of p-hydroxybenzoic acid, benzoic acid, p-coumaric acid and total phenolic acids were significantly lower than that in QH. Results of the study suggested that the differences in the root exudates from the different peanut cultivars were considered to regulate the wilt-resistance mechanism in the rhizosphere of peanut. The results are therefore crucial important to illustrate the mechanism of peanut replanted obstacle, and to develop its control techniques in the red soil regions of southern China.

Root exudates of transgenic cotton and their effects on Fusarium oxysporum.

The components of the root exudates from two transgenic insect-resistant cotton lines and their parental cotton lines, and their effects on the growth of Fusarium oxysporum were investigated. The results demonstrated that the resistance of transgenic insect-resistant cotton to F. oxysporum was significantly reduced compared with their parental lines. Likewise, the root exudates from transgenic insect-resistant cotton significantly promoted the spore germination and mycelial growth of cotton F. oxysporum. The types of compounds found in the root exudates of transgenic insect-resistant cotton were similar to those of the parental cotton, but the composition and relative content of the compounds were different. The type and content of the fatty acids and esters were significantly reduced in the root exudates of the transgenic insect-resistant cotton, as were certain specific materials, whereas several alkanes were increased. The inhibition of the soil-borne pathogen F. oxysporum caused by the root exudates from the transgenic insect-resistant cotton was decreased compared with the parental cotton. This result provides a scientific basis for the decline in disease resistance in transgenic insect-resistant cotton.

[Effects of transgenic insect-resistant cotton root exudates on the growth of Verticillium dahliae Kleb].

The decline of disease resistance of transgenic insect-resistant cotton has become one of the important factors restricting China cotton production. With two transgenic insect-resistant cotton varieties and their parental conventional cotton lines as test materials, the effects of their root exudates on the spore germination and mycelial growth of Verticillium dahliae Kleb were studied, and the components and contents of the amino acids and sugars in the exudates were determined. Comparing with their parental lines, the two transgenic insect-resistant varieties had a declined resistance against V. dahliae, and their root exudates had promotion effects on V. dahliae spore germination and mycelial growth. The root exudates of transgenic cotton Zhong-41, compared with those of its parent line Zhong-23, contained two additional amino acids Met and Lys, and the contents of Asp, Glu, Ser, Ala, Val, Leu, and Tyr were significantly higher. Though the components of amino acids in the root exudates of Simian-3 and transgenic cotton GK-12 were the same, the Tyr, Val, and Leu contents in the root exudates of transgenic cotton GK-12 were significantly lower. Four kinds of sugar were detected in the root exudates of Zhong-41, while only glucose was detected in the root exudates of Zhong-23. These four kinds of sugar were also detected in the root exudates of Simian-3 and GK12, but their contents differed significantly.

The effect of root exudates from two transgenic insect-resistant cotton lines on the growth of Fusarium oxysporum.

The attenuation of disease resistance in transgenic insect-resistant cotton has become one of the important factors restricting cotton production in China. Two transgenic insect-resistant cotton lines and their parental conventional cotton lines were used as the testing materials. The effects of root exudates of these cotton lines on the spore germination and mycelial growth of Fusarium oxysporum were studied and the components, contents of amino acids and sugars were determined. The results showed that the resistance of the two insect-resistant cotton lines to F. oxysporum was inferior to the parental lines, and that their root exudates promoted fungal spore germination and mycelial growth. Considerable differences in the components and contents of both, amino acids and sugars were found between the root exudates of transgenic cotton lines and their parental lines, where the disease indices were highly correlated with the total amount of sugars in the root exudates.

[The localization of galanthamine in vegetative organ of Lycoris aurea Herb].

Using laser confocal microscopical techniques, we observed the anatomical structure of mature root, bulb, and leaf of Lycoris aurea Herb., and also did some research on the localization of galanthamine in the above-mentioned vegetative organ. The results are as follows: In the mature root, the galanthamine distributes mainly in cell wall, especially in cell wall of exodermis and endodermis and vessel wall. In the mature leaf, galanthamine exist in cell wall of vascular bundle, mesophyll cell between vascular bundles and epidermis cells. The scale leaf is the essential accumulational organ. Plenty of galanthamine distribute in the adaxial parenchyma cell, epidermis cell wall, and also in the clingy cell of abaxial epidermis cell.

[Identification of markers linked to resistance locus of Marssonina leaf spot in poplars by bulked segregant analysis(BSA)].

DNA markers linked to resistance locus of Marssonina leaf spot in poplars were found by bulked segregant analysis(BSA). The bulks consisted of individual with a extreme phenotype taken from a population of 91 F1 clones,which is a progeny of Populus deltoides Bartr.cv."Lux"(I-69/55)(Resistance) and P.euramericana cv.I-45(Susceptible). Out of 114 RAPD primers, four markers showed polymorphisms between the resistance-bulk and the susceptible-bulk.By using selective genotype linkage analysis,OPAI17-1550 and OPAI13-900 were found linked to the resistance locus. The genetic distances between the two markers and the resistance locus were 29.9cM and 37.4cM,respectively.