High-resolution mapping of a gene conferring strong antibiosis to brown planthopper and developing resistant near-isogenic lines in 9311 background

The brown planthopper (BPH), Nilaparvata lugens Stål, is one of the most destructive pests to the rice production in the world. Thus, there is an urgency to identify new resistant genes for breeding. AC-1613 is an indica variety that has been reported to confer broad-spectrum resistance to BPH. In the present study, we found that AC-1613 exhibited strong antibiosis towards BPH insects. The body weight was significantly decreased when the insects fed on AC-1613 plants. By using BPH weight gain as an index of phenotyping, a novel dominant locus for resistance to BPH, designed as Bph30, was identified and its near-isogenic line (NIL) in 9311 background was developed. The F₂ population derived from a cross between AC-1613 and 9311 was used for mapping the gene. Through QTL scan, we located the gene on the short arm of chromosome 4 between RM16278 and RM16425, which explained 42.7% of the phenotypic variance (PEV) of BPH resistance in the F₂ population. The gene was finally located in a region flanking by simple sequence repeat (SSR) markers SSR-28 and SSR-69 through high-resolution mapping, the distance between the two markers in Nipponbare genome is 37.5 kb. In addition, SSR markers RM16294 and RM16299 tightly linked to Bph30 were applied effectively in introgressing Bph30 into elite rice cultivars. The developed NILs showed a strong antibiosis and high resistance to BPH.     

Mapping and pyramiding of two major genes for resistance to the brown planthopper (<Emphasis Type="Italic">Nilaparvata lugens</Emphasis> [Stål]) in the rice cultivar ADR52

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most serious and destructive pests of rice, and can be found throughout the rice-growing areas of Asia. To date, more than 24 major BPH-resistance genes have been reported in several Oryza sativa ssp. indica cultivars and wild relatives. Here, we report the genetic basis of the high level of BPH resistance derived from an Indian rice cultivar, ADR52, which was previously identified as resistant to the whitebacked planthopper (Sogatella furcifera [Horváth]). An F₂ population derived from a cross between ADR52 and a susceptible cultivar, Taichung 65 (T65), was used for quantitative trait locus (QTL) analysis. Antibiosis testing showed that multiple loci controlled the high level of BPH resistance in this F₂ population. Further linkage analysis using backcross populations resulted in the identification of BPH-resistance (antibiosis) gene loci from ADR52. BPH25 co-segregated with marker S00310 on the distal end of the short arm of chromosome 6, and BPH26 co-segregated with marker RM5479 on the long arm of chromosome 12. To characterize the virulence of the most recently migrated BPH strain in Japan, preliminary near-isogenic lines (pre-NILs) and a preliminary pyramided line (pre-PYL) carrying BPH25 and BPH26 were evaluated. Although both pre-NILs were susceptible to the virulent BPH strain, the pre-PYL exhibited a high level of resistance. The pyramiding of resistance genes is therefore likely to be effective for increasing the durability of resistance against the new virulent BPH strain in Japan.     

Development and characterization of <Emphasis Type="Italic">japonica</Emphasis> rice lines carrying the brown planthopper-resistance genes <Emphasis Type="Italic">BPH12</Emphasis> and <Emphasis Type="Italic">BPH6</Emphasis>

The brown planthopper (Nilaparvata lugens Stål; BPH) has become a severe constraint on rice production. Identification and pyramiding BPH-resistance genes is an economical and effective solution to increase the resistance level of rice varieties. All the BPH-resistance genes identified to date have been from indica rice or wild species. The BPH12 gene in the indica rice accession B14 is derived from the wild species Oryza latifolia. Using an F₂ population from a cross between the indica cultivar 93-11 and B14, we mapped the BPH12 gene to a 1.9-cM region on chromosome 4, flanked by the markers RM16459 and RM1305. In this population, BPH12 appeared to be partially dominant and explained 73.8% of the phenotypic variance in BPH resistance. A near-isogenic line (NIL) containing the BPH12 locus in the background of the susceptible japonica variety Nipponbare was developed and crossed with a NIL carrying BPH6 to generate a pyramid line (PYL) with both genes. BPH insects showed significant differences in non-preference in comparisons between the lines harboring resistance genes (NILs and PYL) and Nipponbare. BPH growth and development were inhibited and survival rates were lower on the NIL-BPH12 and NIL-BPH6 plants compared to the recurrent parent Nipponbare. PYL-BPH6 + BPH12 exhibited 46.4, 26.8 and 72.1% reductions in population growth rates (PGR) compared to NIL-BPH12, NIL-BPH6 and Nipponbare, respectively. Furthermore, insect survival rates were the lowest on the PYL-BPH6 + BPH12 plants. These results demonstrated that pyramiding different BPH-resistance genes resulted in stronger antixenotic and antibiotic effects on the BPH insects. This gene pyramiding strategy should be of great benefit for the breeding of BPH-resistant japonica rice varieties.     

Identification and fine mapping of <Emphasis Type="Italic">qWBPH11</Emphasis> conferring resistance to whitebacked planthopper (<Emphasis Type="Italic">Sogatella furcifera</Emphasis> Horvath) in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The whitebacked planthopper (WBPH), Sogatella furcifera Horvath, is one of the most destructive pests in rice (Oryza sativa L.) production. Host-plant resistance has been considered as an efficient and eco-friendly strategy to reduce yield losses caused by WBPH. In this study, we found that an indica rice cultivar IR54751-2-44-15-24-2 (IR54751) displayed high resistance to WBPH at both seedling and tillering stages. The resistance of IR54751 was mainly contributed by antixenosis and tolerance rather than antibiosis. An F₂ population derived from a cross between IR54751 and a susceptible japonica cultivar 02428 was constructed to detect the quantitative trait loci (QTLs) conferring the resistance to WBPH. In total, four QTLs including qWBPH3.1, qWBPH3.2, qWBPH11, and qWBPH12 were identified and distributed on three different chromosomes. The four QTLs had LOD scores of 3.8, 8.2, 5.8, and 3.9, accounting for 8.2, 21.5, 13.9, and 10.4% of the phenotypic variation, respectively. Except for qWBPH3.1, the resistance alleles of the other three QTLs were all from IR54751. Further, a secondary population harboring only single qWBPH11 locus was developed from the F₂ population by marker-assisted selection. Finally, qWBPH11 was delimited in a 450-kb region between markers DJ53973 and SNP56. The identification of WBPH resistance QTLs and the fine mapping of qWBPH11 will be helpful for cloning resistance genes and breeding resistant rice cultivars.     

Genetic and biochemical mechanisms of rice resistance to planthopper

Key message

This article presents a comprehensive review on the genetic and biochemicalmechanisms governing rice-planthopper interactions, aiming to contribute substantialplanthopper control and facilitate breeding for resistance to planthoppers in rice.

Abstract

The rice planthopper is the most destructive pest of rice and a substantial threat to rice production. The brown planthopper (BPH), white-backed planthopper (WBPH) and small brown planthopper (SBPH) are three species of delphacid planthoppers and important piercing-sucking pests of rice. Host-plant resistance has been recognized as the most practical, economical and environmentally friendly strategy to control planthoppers. Until now, at least 30, 14 and 34 major genes/quantitative trait loci for resistance to BPH, WBPH and SBPH have been identified, respectively. Recent inheritance and molecular mapping of gene analysis showed that some planthopper-resistance genes in rice derived from different donors aggregate in clusters, while resistance to these three species of planthoppers in a single donor is governed not by any one dominant gene but by multiple genes. Notably, Bph14, Bph26, Bph3 and Bph29 were successfully identified as BPH-resistance genes in rice. Biological and chemical studies on the feeding of planthoppers indicate that rice plants have acquired various forms of defence against planthoppers. Between the rice-planthopper interactions, rice plants defend against planthoppers through activation the salicylic acid-dependent systemic acquired resistance but not jasmonate-dependent hormone response pathways. Transgenic rice for the planthopper-resistance mechanism shows that jasmonate and its metabolites function diversely in rice’s resistance to planthopper. Understanding the genetic and biochemical mechanisms underlying resistance in rice will contribute to the substantial control of such pests and facilitate breeding for rice’s resistance to planthopper more efficiently.

     

Lipid profiles reveal different responses to brown planthopper infestation for pest susceptible and resistant rice plants

Introduction

Brown planthopper (BPH) is the most destructive insect pest for rice, causing major reductions in rice yield and large economic losses. More than 31 BPH-resistance genes have been located, and several of them have been isolated. Nevertheless, the metabolic mechanism related to BPH-resistance genes remain uncharacterized.

Objectives

To elucidate the resistance mechanism of the BPH-resistance gene Bph6 at the metabolic level, a Bph6-transgenic line R6 (BPH-resistant) and the wild-type Nipponbare (BPH-susceptible) were used to investigate their lipid profiles under control and BPH treatments.

Methods

In conjunction with multivariate statistical analysis and quantitative real-time PCR, BPH-induced lipid changes in leaf blade and leaf sheath were investigated by GC–MS-based lipidomics.

Results

Forty-five lipids were identified in leaf sheath extracts. Leaf sheath lipidomics analysis results show that BPH infestation induces significant differences in the lipid profiles of Nipponbare and R6. The levels of hexadecanoic acid, methyl ester, linoleic acid, methyl ester, linolenic acid, methyl ester, glycidyl palmitate, eicosanoic acid, methyl ester, docosanoic acid, methyl ester, beta-monolinolein, campesterol, beta-sitosterol, cycloartenol, phytol and phytyl acetate had undergone enormous changes after BPH feeding. These results illustrate that BPH feeding enhances sterol biosynthetic pathway in Nipponbare plants, and strengthens wax biosynthesis and phytol metabolism in R6 plants. The results of quantitative real-time PCR of 5 relevant genes were consistent with the changes in metabolic level. Forty-five lipids were identified in the leaf blade extracts. BPH infestation induces distinct changes in the lipid profiles of the leaf blade samples of Nipponbare and R6. Although the lipid changes in Nipponbare are more drastic, the changes within the two varieties are similar. Lipid profiles in leaf sheath brought out significant differences than in leaf blade within Nipponbare and R6. We propose that Bph6 mainly affects the levels of lipids in leaf sheath, and mediates resistance by deploying metabolic re-programming during BPH feeding.

Conclusion

The results indicate that wax biosynthesis, sterol biosynthetic pathway and phytol metabolism play vital roles in rice response to BPH infestation. This finding demonstrated that the combination of lipidomics and quantitative real-time PCR is an effective approach to elucidating the interactions between brown planthopper and rice mediated by resistance genes.

     

Characterization and genetics of multiple soybean aphid biotype resistance in five soybean plant introductions

Key message

Five soybean plant introductions expressed antibiosis resistance to multiple soybean aphid biotypes. Two introductions had resistance genes located in the Rag1, Rag2, and Rag3 regions; one introduction had resistance genes located in the Rag1, Rag2, and rag4 regions; one introduction had resistance genes located in the Rag1 and Rag2 regions; and one introduction had a resistance gene located in the Rag2 region.

Abstract

Soybean aphid (Aphis glycines Matsumura) is the most important soybean [Glycine max (L.) Merr.] insect pest in the USA. The objectives of this study were to characterize the resistance expressed in five plant introductions (PIs) to four soybean aphid biotypes, determine the mode of resistance inheritance, and identify markers associated with genes controlling resistance in these accessions. Five soybean PIs, from an initial set of 3000 PIs, were tested for resistance against soybean aphid biotypes 1, 2, 3, and 4 in choice and no-choice tests. Of these five PIs, PI 587663, PI 587677, and PI 587685 expressed antibiosis against all four biotypes, while PI 587972 and PI 594592 expressed antibiosis against biotypes 1, 2, and 3. F₂ populations derived from PI 587663 and PI 587972 were evaluated for resistance against soybean aphid biotype 1, and populations derived from PIs 587677, 587685, and 594592 were tested against biotype 3. In addition, F_2:3 plants were tested against biotypes 2 and 3. Genomic DNA from F₂ plants was screened with markers linked to Rag1, Rag2, Rag3, and rag4 soybean aphid-resistance genes. Results showed that PI 587663 and PI 594592 each had three genes with variable gene action located in the Rag1, Rag2, and Rag3 regions. PI 587677 had three genes with variable gene action located in the Rag1, Rag2 and rag4 regions. PI 587685 had one dominant gene located in the Rag1 region and an additive gene in the Rag2 region. PI 587972 had one dominant gene located in the Rag2 region controlling antixenosis- or antibiosis-type resistance to soybean aphid biotypes 1, 2, or 3. PIs 587663, 587677, and 587685 also showed antibiosis-type resistance against biotype 4. Information on multi-biotype aphid resistance and resistance gene markers will be useful for improving soybean aphid resistance in commercial soybean cultivars.

     

RFLP-facilitated investigation of the quantitative resistance of rice to brown planthopper ( Nilaparvata lugens)

Quantitative trait loci (QTLs), conferring quantitative resistance to rice brown planthopper (BPH), were investigated using 160 F₁₁ recombinant inbred lines (RILs) from the Lemont/Teqing cross, a complete RFLP map, and replicated phenotyping of seedbox inoculation. The paternal indica parent, Teqing, was more-resistant to BPH than the maternal japonica parent, Lemont. The RILs showed transgressive segregation for resistance to BPH. Seven main-effect QTLs and many epistatic QTL pairs were identified and mapped on the 12 rice chromosomes. Collectively, the main-effect and epistatic QTLs accounted for over 70% of the total variation in damage scores. Teqing has the resistance allele at four main-effect QTLs, and the Lemont allele resulted in resistance at the other three. Of the main-effect QTLs identified, QBphr5b was mapped to the vicinity of gl1, a major gene controlling leaf and stem pubescence. The Teqing allele controlling leaf and stem pubescence was associated with resistance, while the Lemont allele for glabrous stem and leaves was associated with susceptibility, indicating that this gene may have contributed to resistance through antixenosis. Similar to the reported BPH resistance genes, the other six detected main-effect QTLs were all mapped to regions where major disease resistance genes locate, suggesting they might have contributed either to antibiosis or tolerance. Our results indicated that marker-aided pyramiding of major resistance genes and QTLs should provide effective and stable control over this devastating pest. Received: 10 December 2000 / Accepted: 7 May 2001     

Marker-assisted pyramiding of <Emphasis Type="BoldItalic">Thinopyrum-</Emphasis>derived leaf rust resistance genes <Emphasis Type="BoldItalic">Lr19</Emphasis> and <Emphasis Type="BoldItalic">Lr24</Emphasis> in bread wheat variety HD2733

This study was undertaken to pyramid two effective leaf rust resistance genes (Lr19 and Lr24) derived from Thinopyrum (syn. Agropyron), in the susceptible, but agronomically superior wheat cultivar HD2733 using marker-assisted selection. In the year 2001, HD2733 was released for irrigated timely sown conditions of the north eastern plains zone (NEPZ) of India became susceptible to leaf rust, a major disease of the region. Background selection helped in developing near-isogenic lines (NILs) of HD2733 with Lr19 and Lr24 with 97.27 and \(98.94\%\), respectively, of genomic similarity with the parent cultivar, after two backcrossing and one generation of selfing. NILs were intercrossed to combine the genes Lr19 and Lr24. The combination of these two genes in the cultivar HD2733 is expected to provide durable leaf rust resistance in farmers’ fields.     

Differential expression of vitellogenin mRNA and protein in response to rice resistance genes in two strains of <Emphasis Type="Italic">Nilaparvata</Emphasis><Emphasis Type="Italic">lugens</Emphasis> (Hemiptera: Delphacidae) with different levels of virulence

Controlling the brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a difficult task in rice (Oryza sativa L.) production. We focused on vitellogenins (Vg), which are the major yolk protein precursors of vitellins and play an important role in the reproduction of oviparous species, including insects. We studied the accumulation of Vg mRNA and protein in a virulent BPH strain, Nagasaki-03, and a nonvirulent strain, Hatano-66, after rearing them on four rice lines. The rice lines used were two single resistance gene introgression lines, Norin-PL3 (Bph1 carrier) and Norin-PL4 (bph2 carrier), a pyramided line in which both genes were combined, and a susceptible japonica recurrent parent Tsukushibare. RT-PCR and quantitative RT-PCR analyses showed that the Vg mRNA level decreased greatly in Hatano-66 on the resistant lines. In contrast, the level of reduction on the resistant lines was much less in Nagasaki-03. Immunoblot analysis showed that Nagasaki-03 retained comparable levels of 175 kDa Vg protein on both the susceptible and resistant lines, whereas in Hatano-66, no Vg protein was detected on the resistant lines. Our results showed that BPH resistance genes caused differential reduction in the accumulation of Vg mRNA and protein, leading to the retardation of BPH reproduction on the resistant host rice plants.     

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F₃ wheat hybrid families to the bird cherry-oat aphid.     

Identification of antibiosis and tolerance in rice varieties carrying brown planthopper resistance genes

Brown planthopper (BPH) [Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)] is a major pest in rice [Oryza sativa L. (Poaceae)] production. Identification of resistance genes and development of BPH‐resistant varieties is an economical and effective way to control this pest. In this study, BPH honeydew excretion, survival rate, and emergence rate were used as indicators to detect the antibiotic level, whereas the relative growth rates of plant height (R_H) and fresh weight (R_W), and the number of days until yellowing were used to identify the level of tolerance to BPH in rice varieties. Rice varieties Swarnalata and B5, which showed high levels of antibiosis and tolerance to BPH, thus were highly resistant in the seedling bulk test; Mudgo and T12, which showed moderate resistance to the insects, had a high level of tolerance and moderate antibiosis to BPH. Varieties Rathu Heenati, ARC 10550, and Chin Saba were identified to be susceptible to BPH, showing a moderate level of tolerance and no antibiosis. In comparison to the evaluation methods of BPH resistance, the honeydew excretion and survival rate could be used to detect the antibiotic level, and the R_H, R_W, or leaf yellowing days could be employed as indicators to evaluate the rice varieties’ tolerance. Overall, a combined application of these indicators can effectively identify the levels of antibiosis and tolerance to BPH in rice varieties, and BPH‐resistance levels of the varieties were mainly determined by the antibiosis level. The results should help in understanding BPH‐resistance categories of rice varieties and for resistance breeding.     

Mapping novel aphid resistance QTL from wild soybean, <Emphasis Type="Italic">Glycine soja</Emphasis> 85-32

Key message

Two novel QTLs conferring aphid resistance were mapped and validated on soybean chromosomes 8 and 16, respectively. Closely linked markers were developed to assist breeding for aphid resistance.

Abstract

Soybean aphid, Aphis glycines Matsumura, is a highly destructive pest for soybean production. E08934, a soybean advanced breeding line derived from the wild soybean Glycine soja 85-32, has shown strong resistance to aphids. To dissect the genetic basis of aphid resistance in E08934, a mapping population (070020) consisting of 140 F₃-derived lines was developed by crossing E08934 with an aphid-susceptible line E00003. This mapping population was evaluated for aphid resistance in a greenhouse trial in 2010 and three field trials in 2009, 2010, and 2011, respectively. The broad-sense heritability across the field trials was 0.84. In the mapping population 070020, two major quantitative trait loci (QTL) were detected as significantly associated with aphid resistance, and designated as Rag6 and Rag3c, respectively. Rag6 was mapped to a 10.5 centiMorgan (cM) interval between markers MSUSNP08-2 and Satt209 on chromosome 8, explaining 19.5–46.4% of the phenotypic variance in different trials. Rag3c was located at a 7.5 cM interval between markers MSUSNP16-10 and Sat_370 on chromosome 16, explaining 12.5–22.9% of the phenotypic variance in different trials. Rag3c had less resistance effect than Rag6 across all the trials. Furthermore, Rag6 and Rag3c were confirmed in two validation populations with different genetic backgrounds. No significant interaction was detected between Rag6 and Rag3c in either the mapping population or the validation populations. Both Rag6 and Rag3c were indicated as conferring antibiosis resistance to aphids by a no-choice test. The new aphid-resistance gene(s) derived from the wild germplasm G. soja 85-32 are valuable in improving soybeans for aphid resistance.

     

Genetic analyses of resistance to the peach root-knot nematode (<Emphasis Type="Italic">Meloidogyne floridensis</Emphasis>) using microsatellite markers

Most commercially important rootstocks for peach [Prunus persica (L.) Batsch] had been selected for resistance to one or more of the root-knot nematode (RKN) species: Meloidogyne incognita, M. arenaria, and M. javanica. The peach root-knot nematode, M. floridensis (MF), is a relatively newly discovered threat to peach and is not controlled by resistance genes in “Nemared,” “Nemaguard,” and “Okinawa.” The “Flordaguard” peach seedling rootstock, conventionally bred to provide resistance to MF, has solely been used for low-chill peach production in Florida for over 20 years and has already shown signs of resistance breakdown. A source of high resistance to the pathogenic MF isolate (“MFGnv14”) was identified from wild peach Prunus kansuensis Rehder (Kansu peach), thereby suggesting the potential for broadening spectrum and increasing durability of resistance in peach rootstocks through interspecific hybridization with P. kansuensis. Using 12 F₂ and BC₁F₁ populations derived from crosses between Okinawa or Flordaguard peach and P. kansuensis populations, we examined the genetic control for MF resistance by identifying associated microsatellite markers and determining genomic location of the resistance locus. One microsatellite marker (UDP98-025) showed strong and consistent association with resistance based on root-galling index. The resistance locus was mapped on the subtelomeric region of linkage group 2, co-localizing with other previously reported RKN resistance genes in Prunus. Segregation of gall-index-based resistance observed in F₂ and BC₁F₁ populations is compatible with the involvement of a multiallelic locus wherein a dominant (Mf₁) or recessive (mf₃) resistance allele is inherited from P. kansuensis, and susceptibility alleles (mf₂) from peach.     

Brown planthopper, Nilaparvata lugens, resistance in rice cultivar IR64: mechanism and role in successful N. lugens management in Central Luzon, Philippines

We investigated the mechanism of brown planthopper, Nilaparvata lugens (Stål), resistance in the popular rice cultivar IR64, and the current level of resistance of IR64 to N. lugens in a large rice growing area with low brown planthopper populations (Central Luzon, Philippines). In greenhouse experiments with N. lugens populations collected from Central Luzon, IR64 showed slight to moderate levels of antibiosis, antixenosis, and tolerance relative to the cultivars IR22 and Azucena, which contain no major genes for N. lugens resistance. IR64 was also more resistant than IR26 in most experiments, despite the fact that both varieties have the same major gene for N. lugens resistance, Bph1. This confirms that IR64 contains one or more additional, apparently minor, genes for brown planthopper resistance. Our findings also demonstrate that, in an area with low insecticide use, it is not necessary to have high levels of N. lugens resistance, even in a rice cultivar grown by the majority of farmers, to maintain low and stable N. lugens populations.     

<Emphasis Type="Italic">STAYGREEN</Emphasis> (<Emphasis Type="Italic">CsSGR</Emphasis>) is a candidate for the anthracnose (<Emphasis Type="Italic">Colletotrichum orbiculare</Emphasis>) resistance locus <Emphasis Type="Italic">cla</Emphasis> in Gy14 cucumber

Key message

Map-based cloning identified a candidate gene for resistance to the anthracnose fungal pathogen Colletotrichum orbiculare in cucumber, which reveals a novel function for the highly conserved STAYGREEN family genes for host disease resistance in plants.

Abstract

Colletotrichum orbiculare is a hemibiotrophic fungal pathogen that causes anthracnose disease in cucumber and other cucurbit crops. No host resistance genes against the anthracnose pathogens have been cloned in crop plants. Here, we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Phenotypic and QTL analysis in multiple populations revealed that a single recessive gene, cla, was underlying anthracnose resistance in both lines, but WI2757 carried an additional minor-effect QTL. Fine mapping using 150 Gy14?×?9930 recombinant inbred lines and 1043 F₂ individuals delimited the cla locus into a 32 kb region in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested that the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance locus. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Quantitative real-time PCR analysis indicated that CsSGR was significantly upregulated upon anthracnose pathogen inoculation in the susceptible 9930, while its expression was much lower in the resistant Gy14. Investigation of allelic diversities in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.

     

Characterization of aphid resistance loci in black raspberry (<Emphasis Type="Italic">Rubus occidentalis</Emphasis> L.)

Viruses vectored by the aphid Amphorophora agathonica cause decline in black raspberry plant health resulting in a shortened life and poor fruit quality of the infected plantings. New aphid resistant cultivars could increase the longevity of plantings providing growers and processors with consistent fruit production. Recent exploration of the native range of black raspberry identified three sources of aphid resistance: Ag₄ from Ontario (ON), Canada, Ag₅ from Maine (ME), and a third source from Michigan (MI) with no formal designation. The objectives of this study were to assess segregation of these three sources of aphid resistance in populations with single and combined sources and develop markers that can identify each source of resistance. A genetic linkage map constructed for ORUS 4305 placed the ON aphid resistance locus on Rubus linkage group (RLG) 6. Segregation ratios in populations with single and combined sources, and linkage mapping in two populations (ORUS 4304 and ORUS 4812) segregating for the Ag₅ and MI sources, respectively, indicated that these three sources of resistance are each conferred by single dominant genes/alleles that are linked on RLG6. Confirmation of marker association in 16 validation populations identified four markers that could be used to predict resistance; however, none could distinguish between the ON and MI sources. These four markers may be useful for screening populations to enrich the field-planted progeny for aphid resistance. Fine mapping of the resistance loci is needed to develop functional markers at each of the resistance loci to enable pyramiding and durable aphid resistance.     

High-resolution mapping of the brown planthopper resistance gene Bph6 in rice and characterizing its resistance in the 9311 and Nipponbare near isogenic backgrounds

Brown planthopper (Nilaparvata lugens Stål, BPH) is one of the most destructive insect pests of rice. Exploring resistance genes from diverse germplasms and incorporating them into cultivated varieties are critical for controlling this insect. The rice variety Swarnalata was reported to carry a resistance gene (designated Bph6), which has not yet been assigned to a chromosome location and the resistance mechanism is still unknown. In this study, we identified and mapped this gene using the F₂ and backcrossing populations and characterized its resistance in indica 9311 and japonica Nipponbare using near isogenic lines (NILs). In analysis of 9311/Swarnalata F₂ population, the Bph6 gene was located on the long arm of chromosome 4 between the SSR markers RM6997 and RM5742. The gene was further mapped precisely to a 25-kb region delimited between the STS markers Y19 and Y9; and the distance between these markers is 25-kb in Nipponbare genome. The Bph6 explained 77.5% of the phenotypic variance of BPH resistance in F₂ population and 84.9% in BC₂F₂ population. Allele from Swarnalata significantly increased resistance to the BPH, resulted in a reduced damage score. In characterization of Bph6-mediated resistance, the BPH insects showed significant preference between NIL-9311 and 9311 in 3 h and between NIL-NIP and Nipponbare in 120 h after release. BPH growth and development were inhibited, and the insect’s survival rates were lower on Bph6-NIL plants, compared with the parents 9311 and Nipponbare. The results indicate that the Bph6 exerted prolonged antixenotic and antibiotic effects in Bph6-NIL plants, and NIL-9311 plants showed a quicker and stronger effect toward BPH than NIL-NIP plants.