Brassinosteroids mediate susceptibility to brown planthopper by integrating with the salicylic acid and jasmonic acid pathways in rice.

Improved knowledge of the interactions between plants and insects will facilitate better insect control in crops. Brassinosteroids (BRs) play a vital role in plant growth, developmental processes, and responses to pathogen infection, but the role of BRs in interactions between plants and insects remain largely unknown. In this study, we characterized a negative role of BRs in rice defense against brown planthopper (BPH, Nilaparvata lugens) and examined its underlying mechanisms. We found that BPH infestation suppressed the BR pathway while successively activating the salicylic acid (SA) and jasmonic acid (JA) pathways. In addition, BR-overproducing mutants and plants treated with 24-epibrassinolide (BL) showed increased susceptibility to BPH, whereas BR-deficient mutants were more resistant than the wild-type. BRs down-regulated the expression of genes related to the SA pathway and reduced SA content while genes related to the JA pathway were up-regulated and JA content increased after BPH infestation. Furthermore, BR-mediated suppression of the SA pathway was impaired both in JA-deficient and JA-insensitive mutants. Our results demonstrate that BRs promote the susceptibility of rice plants to BPH by modulating the SA and JA pathways.

Detection of quantitative trait loci (QTLs) for resistances to small brown planthopper and rice stripe virus in rice using recombinant inbred lines.

Small brown planthopper (SBPH) and rice stripe virus (RSV) disease transmitted by SBPH cause serious damage to rice (Oryza sativa L.) in China. In the present study, we screened 312 rice accessions for resistance to SBPH. The indica variety, N22, is highly resistant to SBPH. One hundred and eighty two recombinant inbred lines (RILs) derived from a cross of N22 and the highly susceptible variety, USSR5, were used for quantitative trait locus (QTL) analysis of resistances to SBPH and RSV. In a modified seedbox screening test, three QTLs for SBPH resistance, qSBPH2, qSBPH3 and qSBPH7.1, were mapped on chromosomes 2, 3 and 7, a total explaining 35.1% of the phenotypic variance. qSBPH7.2 and qSBPH11.2, conferring antibiosis against SBPH, were detected on chromosomes 7 and 11 and accounted for 20.7% of the total phenotypic variance. In addition, qSBPH5 and qSBPH7.3, expressing antixenosis to SBPH, were detected on chromosomes 5 and 7, explaining 23.9% of the phenotypic variance. qSBPH7.1, qSBPH7.2 and qSBPH7.3, located in the same region between RM234 and RM429 on chromosome 7, using three different phenotyping methods indicate that the locus or region plays a major role in conferring resistance to SBPH in N22. Moreover, three QTLs, qSTV4, qSTV11.1 and qSTV11.2, for RSV resistance were detected on chromosomes 4 and 11. qSTV11.1 and qSTV11.2 are located in the same region between RM287 and RM209 on chromosome 11. Molecular markers spanning these QTLs should be useful in the development of varieties with resistance to SBPH and RSV.

Fine mapping of qSTV11(KAS), a major QTL for rice stripe disease resistance.

Rice stripe disease, caused by rice stripe virus (RSV), is one of the most serious diseases in temperate rice-growing areas. In the present study, we performed quantitative trait locus (QTL) analysis for RSV resistance using 98 backcross inbred lines derived from the cross between the highly resistant variety, Kasalath, and the highly susceptible variety, Nipponbare. Under artificial inoculation in the greenhouse, two QTLs for RSV resistance, designated qSTV7 and qSTV11(KAS), were detected on chromosomes 7 and 11 respectively, whereas only one QTL was detected in the same location of chromosome 11 under natural inoculation in the field. The stability of qSTV11(KAS) was validated using 39 established chromosome segment substitution lines. Fine mapping of qSTV11(KAS) was carried out using 372 BC(3)F(2:3) recombinants and 399 BC(3)F(3:4) lines selected from 7,018 BC(3)F(2) plants of the cross SL-234/Koshihikari. The qSTV11(KAS) was localized to a 39.2 kb region containing seven annotated genes. The most likely candidate gene, LOC_Os11g30910, is predicted to encode a sulfotransferase domain-containing protein. The predicted protein encoded by the Kasalath allele differs from Nipponbare by a single amino acid substitution and the deletion of two amino acids within the sulfotransferase domain. Marker-resistance association analysis revealed that the markers L104-155 bp and R48-194 bp were highly correlated with RSV resistance in the 148 landrace varieties. These results provide a basis for the cloning of qSTV11(KAS), and the markers may be used for molecular breeding of RSV resistant rice varieties.

Genetic dissection of the resistance to Rice stripe virus present in the indica rice cultivar 'IR24'.

Rice stripe disease, caused by Rice stripe virus (RSV) and transmitted by the small brown planthopper (Laodelphax striatellus Fallen), is one of the most serious viral diseases of rice in temperate East Asian production regions. Prior quantitative trait loci (QTL) mapping has established that Oryza sativa L. subsp. indica 'IR24' carries positive alleles at the three loci qSTV3, qSTV7, and qSTV11-i. Here, we report an advanced backcross analysis based on three selected chromosome segment substitution lines (CSSLs), each predicted to carry one of these three QTL. Three sets of BC(4)F(2:3) populations were bred from a cross between the critical CSSL and its recurrent parent Oryza sativa L. subsp. japonica 'Asominori'. Both qSTV3 and qSTV11-i were detected in their respective population, but qSTV7 was not. An allelic analysis based on a known carrier of the major RSV resistance gene Stvb-i, which is located on chromosome 11, showed that qSTV11-i was not allelic with Stvb-i. A large mapping population was used to delimit the location of qSTV11-i to a 73.6-kb region. The de novo markers developed for this purpose will be useful as marker-assisted selection tools in efforts to introduce qSTV11-i into breeding programmes aiming to improve the level of RSV resistance.

Long-term seasonal forecasting of a major migrant insect pest: the brown planthopper in the Lower Yangtze River Valley.

Rice planthoppers and associated virus diseases have become the most important pests threatening food security in China and other Asian countries, incurring costs of hundreds of millions of US dollars annually in rice losses, and in expensive, environmentally harmful, and often futile control efforts. The most economically damaging species, the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae), cannot overwinter in temperate East Asia, and infestations there are initiated by several waves of windborne spring or summer migrants originating from tropical areas in Indochina. The interaction of these waves of migrants and synoptic weather patterns, driven by the semi-permanent western Pacific subtropical high-pressure (WPSH) system, is of critical importance in forecasting the timing and intensity of immigration events and determining the seriousness of subsequent planthopper build-up in the rice crop. We analysed a 26-year data set from a standardised light trap network in Southern China, showing that planthopper aerial transport and concentration processes are associated with the characteristics (strength and position) of the WPSH in the year concerned. Then, using N. lugens abundance in source areas and indices of WPSH intensity or related sea surface temperature anomalies, we developed a model to predict planthopper numbers immigrating into the key rice-growing area of the Lower Yangtze Valley. We also demonstrate that these WPSH-related climatic indices combined with early-season planthopper catches can be used to forecast, several months in advance, the severity of that season's N. lugens infestations (the correlation between model predictions and outcomes was 0.59), thus allowing time for effective control measures to be implemented.

Marker assisted pyramiding of two brown planthopper resistance genes, Bph3 and Bph27 (t), into elite rice Cultivars.

BACKGROUND: Brown planthopper (BPH) is the most destructive insect in rice production. Breeding of resistant cultivars is the most cost-effective and environment-friendly strategy for BPH management; however, resistant cultivars are currently hampered by the rapid breakdown of BPH resistance. Thus, there is an urgent need to use more effective BPH resistance genes or pyramiding different resistance genes to develop more durable resistant rice cultivars. RESULTS: Here a dominant BPH resistance gene Bph27(t) were introgressed into a susceptible commercial japonica variety Ningjing3 (NJ3) and indica variety 93-11 using marker-assisted selection (MAS), respectively. Further, Bph27(t) and a durable BPH resistance gene Bph3 was pyramided by intercrossing single-gene introgressed lines through MAS. The introgression of BPH resistance genes significantly improved the BPH resistance and reduced the yield loss caused by BPH. CONCLUSION: The development of single and two genes pyramided lines in this study provides innovative resources for molecular breeding of durable BPH-resistant rice cultivars and BPH management through resistant cultivars.

[Detection and analysis of QTL for resistance to the brown planthopper, Nilaparvata lugens (Stål), in rice (Oryza sativa L.), using backcross inbred lines].

A mapping population of 98 BC1F9 lines (backcross inbred lines: BILs), derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare by the single-seed descent methods, was used to detect quantitative trait loci (QTL) for resistance to brown planthopper (BPH), Nilaparvata lugens (Stål). Seedbox Screening Technique (SST) was applied to evaluate the reactions of two parents and 98 BILs to BPH at the seedling stage, and the entries were graded on ratio of dead seedlings. A total of three QTL controlling BPH resistance were detected on chromosomes 2, 10 and 12, respectively. Individual QTL accounted for between 10.4% and 16.6% of the phenotypic variance, and the resistance of all the three QTL came from Kasalath, the moderate resistance parent. These QTL should be useful in breeding of varieties resistant to BPH in marker-assisted selection (MAS) program.

STV11 encodes a sulphotransferase and confers durable resistance to rice stripe virus.

Rice stripe virus (RSV) causes one of the most serious viral diseases of rice (Oryza sativa L.), but the molecular basis of RSV resistance has remained elusive. Here we show that the resistant allele of rice STV11 (STV11-R) encodes a sulfotransferase (OsSOT1) catalysing the conversion of salicylic acid (SA) into sulphonated SA (SSA), whereas the gene product encoded by the susceptible allele STV11-S loses this activity. Sequence analyses suggest that the STV11-R and STV11-S alleles were predifferentiated in different geographic populations of wild rice, Oryza rufipogon, and remained prevalent in cultivated indica and japonica rice varieties, respectively. Introgression of the STV11-R allele into susceptible cultivars or heterologous transfer of STV11-R into tobacco plants confers effective resistance against RSV. Our results shed new insights into plant viral defense mechanisms and suggest effective means of breeding RSV-resistant crops using molecular marker-assisted selection or genetic engineering.

[Community structure and its dynamics of predatory arthropod in different tobacco varieties fields].

With principal component analysis and using community structural characteristic indices, this paper studied the community structure and its dynamics of predatory arthropod in fields planted with tobacco varieties Nc89, Nc82 and K326. The results showed that in all test fields, spiders and predatory insects were the predominant components of the predatory arthropod community, and their relative abundances were 83.25%-86.87% and 13.13%-16.38%, respectively. There was a significant difference in the mean density (individuals per 8 plants) of the most common predatory arthropod groups between different tobacco varieties fields, which was the highest in K326 field, followed by Nc82, and Nc89 field. The individuals of both Linyphiidae and Coccinellidae played the dominant role in the community. There was a significant difference in the richness of predatory arthropod community between Nc89 and Nc82 fields, but the differences of other structural characteristic indices were not significant. The temporal dynamics of the richness and dominancy in all test fields had a trend of low-high-low, and those of the diversity and evenness index were high-low-high.

[Effects of imidacloprid on arthropod community structure in tobacco field].

The effects of imidacloprid on the structure of arthropod community and its sub-communities were analyzed. The results showed that after applied imidacloprid, the species number of arthropod community and its pest sub-community was influenced, but that of its natural insect enemy and spider sub-community was not influenced obviously. The individuals of arthropod community and its pest sub-community in both treatment plot (II) and control plot were decreased after the application of imidacloprid on May 23 to June 13, and the decline degree in treatment plot was larger than that in control plot. The individuals of arthropod community and its pest sub-community at treatment plots had a large decrease, and that in control plot had a large increase after imidacloprid application on June 14. Twice applications with imidacloprid did not reduce the number of the individuals of natural insect enemy and spider sub-community obviously. The individuals of tobacco aphids who were dominant in tobacco field decreased obviously within a period of time after application, and hence, the dominant concentration of arthropod community and its pest sub-community declined, and the diversity and stability increased.

[Chaotic diagnosis of Nilaparvata lugens occurrence system].

It is estimated that there are nearly 20 million hectares of rice crop being infested by Nilaparvata lugens, with an annual loss of some half a million tones of grain. In order to study the properties and laws of Nilaparvata lugens occurrence system further, the time series data of Nilaparvata lugens occurrence from 1986 to 1998 collected in Taihu Lake District were analyzed by using the methods of autocorrelation function, power spectrum figure, phase trajectory figure, poincare section, and return map of chaos theory. The results indicated that Nilaparvata lugens occurrence system in Yangtze River valley area in China had an obvious chaotic property, even though there was some interference of random noises.

[Spatial structure of populations Myzus persicae and its predatory natural enemy Erigonidium graminicola].

In this paper, the spatial construction models of populations M. persicae and its predatory natural enemy E. graminicola during different periods were simulated by geostatistics, and their spatial relationships were analyzed. The spatial structure of M. persicae population was described by spherical model, showing an aggregated spatial arrangement. Its spatial dependence was 2.0252-4.1495 m, heterogeneity degree was 10,281.36-300,216.30, and sample variance was 12,176.81-303,433.70. The spatial structure of E . graminicola population was also simulated by spherical model, showing an aggregated spatial arrangement. Its spatial dependence was 3.7328-4.8983 m, heterogeneity degree was 1.4482-4.4134, and sample variance was 1.6941-5.8167. The results and methods could be applied to monitor the temporal and spatial dynamics of target insect pest population in tobacco field, and provide scientific basis for ecological control.