Molecular Tagging of a New Resistance Gene to Maize Dwarf Mosaic Virus Using Microsatellite Markers

With joint analysis based on the parents, F 1, F 2 and backcrosses, the authors found that the resistance of the maize inbred line Huangzaosi to the maize dwarf mosaic virus strain B was conditioned by a major gene and polygene, and identified a new major gene. Bulked segregate and microsatellite analysis of a F 2 progeny from the combination of Huangzaosi×Mo17 were used to identify the resistance gene, mdm1(t), on the long arm of chromosome 6. This new resistance gene is tightly linked to and located between the microsatellite markers loci, phi077 and bnlg391. The linkage distances between phi077-mdm1(t) and mdm1(t)-bnlg391 are 4.74 centiMorgan (cM) and 6.72 cM respectively.

Study on the Effective Prevention and Control of Maize Rough Dwarf Disease in Different Areas with Varying Epidemic Intensity in Shandong Province

[ Objective] This study aimed to investigate the effective prevention and control of maize rough dwarf disease in different areas with varying epidemic inten-sity in Shandong Province. [Method] Control effects of single application of virus in-hibitors and composite application of virus inhibitors with seed dressing agents and pesticides on maize rough dwarf disease in different areas with varying epidemic intensity were investigated. [Result] The same treatment possessed entirely different effects in severely affected areas and slightly affected areas. To be specific, single application of virus inhibitors in slightly affected areas exhibited good control effects, with a control efficiency of 76.59% and yield increment rate of 158.21%; in severely affected areas, single application of virus inhibitors led to low control efficiency and yield increment rate. The highest control efficiency of composite application of virus inhibitors with seed dressing agents and pesticides in severely affected areas was 71.38%, and experimental plots changed from total crop failure to have certain eco-nomic output. [Conclusion] ln different areas with varying epidemic intensity of maize rough dwarf disease, different application modes should be adopted according to lo-cal conditions, thereby saving cost and improving control efficiency.

The Application of Reverse Transcription-loop-mediated Isothermal Amplification for the Rapid Detection of Maize Chlorotic Dwarf Virus

Maize chlorotic dwarf virus （MCDV） is a quarantine pest as approved by Chinese government. A rapid, sensitive and specific MCDV detection method using reverse transcription-loop-mediated isothermal amplification （RT-LAMP） was estab- lished in this study. Based on the sequence of MCDV coat protein coding gene, specific primers were designed and similar sensitivities were observed between RT- LAMP and RT-PCR, except that RT-LAMP was quicker, and the reaction could be finished within 1 h. In addition, the presence or absence of the fluorescent display in daylight allows naked easy detection of the amplification of MCDV genomic RNA using calcein. The RT-LAMP assay was applied successfully to detect MCDV in maize seeds, and the result by the addition of calcein was consistent with the result detected by the real time turbidimeter.

Molecular Characterization of Segments S7 to S10 of a Southern Rice Black-streaked Dwarf Virus Isolate from Maize in Northern China

Southern rice black-streaked dwarf virus (SRBSDV) is a novel Fijivirus prevalent in rice in southern and central China,and northern Vietnam. Its genome has 10 segments of double-stranded RNA named S1 to S10 according to their size. An isolate of SRBSDV,JNi4,was obtained from naturally infected maize plants from Ji'ning,Shandong province,in the 2008 maize season. Segments S7 to S10 of JNi4 share nucleotide identities of 72.6%-73.1%,72.3%-73%,73.9%-74.5% and 77.3%-79%,respectively,with corresponding segments of Rice black-streaked dwarf virus isolates,and identities of 99.7%,99.1%-99.7%,98.9%-99.5%,and 98.6%-99.2% with those of SRBSDV isolates HN and GD. JNi4 forms a separate branch with GD and HN in the phylogenetic trees constructed with genomic sequences of S7 to S10. These results confirm the proposed taxonomic status of SRBSDV as a distinct species of the genus Fijivirus and indicate that JNi4 is an isolate of SRBSDV. Shandong is so far the northernmost region where SRBSDV is found in China.

Changes in Cell Ultrastructure in Maize Leaves Infected by Maize Dwarf Mosaic Virus

Ultrastructural alterations in foliar cells were studied in leaves of resistant maize variety Luyu16 and susceptible maize inbred line Luyuan92 infected by maize dwarf mosaic virus Shandong isolate (MDMV-SD), respectively. The results showed that marked cytopathological alterations were observed both in resistant plants and in susceptible plants, compared with that in healthy plants. However, some ultrastructural alterations, which observed in resistant plants, were different from those in susceptible plants. In resistant plants, which infected with the virus, the main organelles, including chloroplasts and mitochondria, were slightly destroyed, the amount of mitochondria and peroxisome were increased. A few or no plasmodesmata were observed. There were three kinds of inclusions including pinwheel, bundle and laminated aggregate, and the virus particles in the cytoplasm. In susceptible plants, which infected with the virus, the chloroplasts were heavily disrupted, including thylakoid swelling and envelope broking. The virus particles were more than those in the resistant variety. Four kinds of inclusions including pinwheel, bundle, laminated aggregate and high electon-dense body appeared in cytoplasm. Plasmodesmata and plasma membrane were abundant, and there were frequent invaginations of the plasma membrane that led to the formation of vesicles and myelin-like structures.

Disease Grading Criterion and Assessment of Yield Loss Caused by Maize Rough Dwarf Disease

[Objective] The paper was to study the disease grading criterion and assess the yield loss caused by maize rough dwarf disease. [Method] The ear lengths and yields of each healthy and infected plant of 5 cultivars were measured during 2009 and 2010. The severity grading criterion was deduced according to the ear length ratios. [Result]When the ratios were 0.92-1.00, 0.67-0.91, 0.41-0.66, 0.10-0.40 and 0, its corresponding disease grading criterions were 0, 1, 3, 5 and 7, respectively. The severity grading criterion was closely correlated to the yield loss. By analyzing the data of disease indexes and yield loss rates of 27 cultivars with DPS （Data Processing System）, the regression equations were established respectively. According to the comparison with each other, the Weibull Model was proved to have the highest fitting degree. Validating with the disease indexes of 27 cultivars in 2010, the equation supported the feasibility of the equation to predict the yield loss caused by maize rough dwarf disease. [Conclusion] The paper provided theoretical basis for further study on maize rough dwarf disease.

Ultrastructural Alteration of Maize Plants Infected with the Maize Rough Dwarf Virus

The ultrastructural alteration of maize plants infected with the maize rough dwarf virus (MRDV) was studied with transmission electron microscopy. The results revealed that aggregates of virus particles , with a diameter of 60nm, were found in the root cell, and always distributed near the vacuole membrane. However, no such particles were checked in leaf cells. Moreover, no virus was observed in choroplasts, mitochondria nuclei, plasmodesmata or intercellular canal of all kinds of infected cells of maize, either. Structures of various organelles changed in the infected leaf and root cells of maize. An inward collapse and localized splitting of the tonoplast were observed, the chloropoast structure was destroyed by MRDV, and the number of destroyed or dysplasia chloroplast in leaf cells with serious symptoms was more than that in leaves without symptoms. The matrix of mitochondria in cells infected by MRDV decreased and some of them expanded and destructed. Nuclei was abnormal and the nuclear membrane was broken. In addition, the infected cells were characterized by a voluminous cytoplasm containing hypertrophied endoplasmic reticulum, with rich ribosome content and lots of starch grain.