Bt Gene Research Articles

Susceptibility of Louisiana and Florida Populations ofSpodoptera frugiperda(Lepidoptera: Noctuidae) to Pyramided Bt Corn Containing Genuity®Vt Double Pro™and Smartstax™Traits

ABSTRACT The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a target species of transgenic corn containing pyramided Bt genes in the United States. During 2011, a total of 149 F2 two-parental family lines were established using single-pairing of S. frugiperda collected from 3 locations in Louisiana and Florida. This study examined the susceptibility of these F2 two-parental family lines to 2 commonly used pyramided Bt corn traits, Genuity®VT Double Pro™ and Genuity®SmartStax™. Nine out of the 149 family lines showed less susceptibility to the leaf tissue of Genuity®VT Double Pro™ or Genuity®SmartStax plants. Larvae of these 9 family lines exhibited significant survivorship and growth on leaf tissue of the Bt corn plants. Two laboratory colonies were established from the F2 survivors of 2 of the 9 family lines. However, larvae from both colonies could not survive on whole plants of their corresponding Bt corn products in the greenhouse, suggesting these families were not resistant to the pyramided ...

Development of elite rice restorer lines in the genetic background of R022 possessing tolerance to brown planthopper, stem borer, leaf folder and herbicide through marker-assisted breeding

Rice leaf folder, stem borer and brown planthopper (BPH) are the most devastating rice insect pests. Developing and planting insect-resistant rice varieties is the most economical and effective measure for controlling these pests. BPH can be controlled with native BPH-resistance genes in rice, while at present rice leaf folder and stem borer can only be controlled through planting transgenic Bt rice. In this study, the breeding of a new restorer line KR022 possessing stacked BPH-resistance genes Bph14 and Bph15, Bt gene cry1C and glufosinate-resistance gene bar, is reported for the first time. A rice restorer line R022 with BPH-resistance genes Bph14 and Bph15 was used as a recurrent parent to cross with the transgenic rice T1C-19 of cry1C and bar genes during the breeding process. The restorer line KR022 was developed from the backcross populations of R022 and T1C-19 through molecular marker-assisted selection and glufosinate-resistance selection. The cry1C and bar genes were found to integrate on chromosome 11 of KR022, and the genome recovery of KR022 was up to 95.8 % of the R022 genome. The quantification of Cry1C protein expression showed that it was expressed at different levels in the leaf, stem, panicle, endosperm, and root of KR022 and its hybrid rice. The insect-resistance evaluation indicated that KR022 and its hybrid rice had good resistance to rice leaf folder and stem borer, both in laboratory settings and in the field. Furthermore, they exhibited increased resistance to BPH at both the seedling and mature stage. The field trial showed there was no significant difference in key agronomic traits between KR022 and its recurrent parent R022, and four hybrids from KR022 yield much higher than the control II-You 838. Moreover, KR022 and its hybrid rice were found to have resistance to the herbicide glufosinate. These results demonstrate that KR022 is effective as a rice restorer line for the breeding of “green super rice”, possessing multiple tolerances to rice BPH, stem borer, leaf folder and glufosinate.

Chloroplast-targeted expression of recombinant crystal-protein gene in cotton: An unconventional combat with resistant pests

Plants transformed with single Bt gene are liable to develop insect resistance and this has already been reported in a number of studies carried out around the world where Bt cotton was cultivated on commercial scale. Later, it was envisaged to transform plants with more than one Bt genes in order to combat with resistant larvae. This approach seems valid as various Bt genes possess different binding domains which could delay the likely hazards of insect resistance against a particular Bt toxin. But it is difficult under field conditions to develop homozygous plants expressing all Bt genes equally after many generations without undergoing recombination effects. A number of researches claiming to transform plants from three to seven transgenes in a single plant were reported during the last decade but none has yet applied for patent of homozygous transgenic lines. A better strategy might be to use hybrid-Bt gene(s) modified for improved lectin-binding domains to boost Bt receptor sites in insect midgut. These recombinant-Bt gene(s) would express different lectin domains in a single polypeptide and it is relatively easy to develop homozygous transgenic lines under field conditions. Enhanced chloroplast-localized expression of hybrid-Bt gene would leave no room for insects to develop resistance. We devised and successfully applied this strategy in cotton (Gossypium hirsutum) and data up to T3 generation showed that our transgenic cotton plants were displaying enhanced chloroplast-targeted Cry1Ac-RB expression. Laboratory and field bioassays gave promising results against American bollworm (Heliothis armigera), pink bollworm (Pictinophora scutigera) and fall armyworm (Spodoptera frugiperda) that otherwise, were reported to have evolved resistance against Cry1Ac toxin. Elevated levels of hybrid-Bt toxin were confirmed by ELISA of chloroplast-enriched protein samples extracted from leaves of transgenic cotton lines. While, localization of recombinant Cry1Ac-RB protein in chloroplast was established through confocal laser scanning microscopy.

High incidence of partial biotinidase deficiency cases in newborns of Greek origin

Biotinidase deficiency (BTD) is an inherited disorder with severe clinical manifestations if not treated early. 63,119 neonates were tested for BTD according to a 3-step protocol. Biotinidase activity was initially estimated through standard colorimetric method on dried blood spots, then the suspected samples were subjected to molecular analysis of the BT gene and determination of BT activity in serum through an HPLC method. 14 infants with partial BTD (incidence 1:4508) were detected. Nine of them were homozygotes (D444H/D444H), and 4 compound heterozygotes carrying D444H combined with Q456H, T532M, C186Y and R157H, respectively. All were asymptomatic and supplemented with 10mg biotin. Although the number of screened neonates is rather small, it may be suggested that the incidence of the partial BTD infants is the highest ever reported. Detection of BTD should be added to the Greek national neonatal screening program.

Transgenic Bt corn varietal resistance against the Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae) and implications to sugarcane

The Mexican rice borer, Eoreuma loftini (Dyar), attacks crops including corn, Zea mays L., rice, Oryza sativa L., sorghum, Sorghum bicolor (L.) Moench, and sugarcane, Saccharum spp. Strongly resistant varieties of any kind, native or otherwise, have not been identified. A field plot corn variety test using two transgenic Bt varieties, Pioneer 31G71, expressing the Cry1F insecticidal protein, and Golden Acres 28V81, expressing the Cry1A.105, Cry2Ab2, and Cry3Bb1 insecticidal proteins, and two non-Bt controls, Dekalb DKC 69-72 and BH Genetics 9050, all four commonly grown in the Lower Rio Grande Valley of Texas, showed that, although oviposition preference was not affected, 28V81 resisted larval stalk boring to the extent that Mexican rice borer injury was almost non-existent. Pioneer 31G71 was infested nearly as much as the controls, but larval development to adulthood was reduced by ≈70%. Rearing larvae on 5, 50, 500, and 5000 μg of corn leaf tissue per ml of artificial diet showed that, while the three lowest concentrations did not affect larval growth and development, the high concentration of 28V81 reduced survivorship to the pupal stage, decreased weight of 4-wk-old larvae, and prolonged development to pupation. Lower numbers of pheromone trap-captured adults at the edges of commercial Bt and non-Bt corn fields showed that populations were lower at the Bt cornfields, suggesting a lesser rate of adult production. Because corn is a preferred host plant over sugarcane, sorghum or rice, use of resistant transgenic Bt corn varieties will likely protect the crop from the substantial injury that can be caused by the pest. This study also suggests that Bt genes might result in similarly strong resistance when inserted in other vulnerable crops such as sugarcane.

Field and laboratory studies on the impact of two Bt rice lines expressing a fusion protein Cry1Ab/1Ac on aquatic organisms

Genetically modified (GM) rice expressing Bt toxins is at the edge of commercial release in China. However, little information is available concerning the impact of Bt rice on aquatic organisms which are abundant in paddy field. A two-year study was conducted to assess the effects of two GM rice lines expressing a fusion protein Cry1Ab/1Ac (Bt rice) on three groups of zooplankton, rotifers, cladocerans and copepods in field conditions. Multi-factor ANOVA revealed that the population densities of rotifers, cladocerans and copepods in paddy field varied significantly between years and rice developmental stages, but did not differ significantly between Bt and non-Bt rice treatments. In all the field investigations, only one significant difference was found on copepods in the tillering stage of 2009, but the difference was not related to the presence of the Cry toxin. Under open-air conditions, we simulated the farming practice of straw mulch, using Bt rice straw as a food source for the water flea Daphnia hyalina. After one and two months of culture, the density of D. hyalina did not differ between Bt rice treatments and non-Bt rice treatments. A laboratory experiment found that purified Bt toxins Cry1Ab and Cry1Ac had no toxic effect on D. hyalina even in the treatment in which the Bt toxin concentration was as high as 2500ng/ml. Those above results indicate that the two Bt rice lines have no negative effect on the three groups of zooplankton. However, further studies are needed to compare the effects of Bt rice and non-Bt rice on the paddy zooplankton community in the context of integrated pest management which includes the use of pesticides.

Molecular characterization of a new synthetic cry2ab gene in Nicotiana tabacum

A newly-synthesized cry2Ab gene was characterized in Nicotiana tabacum, before its further transformation in cotton. Synthetic cry2Ab gene was cloned in pGreen0029 and its expression was transiently analyzed at mRNA level through agroinfiltration in tobacco. The mRNA of cry2Ab was detected after 72h agroinfiltration through PCR using total plant RNA. This construct was then transformed into N. tabacum through Agrobacterium. Insect bioassays were conducted on detached leaves using first instar Spodoptera exigua larvae; after 96h significant insect mortality was recorded. This newly synthesized gene was effective in controlling S. exigua first instar larvae. It can be used in combinations with other Bt genes like cry1Ac for developing resistance against major insect pests of cotton and further widening the insect control spectrum.

Breeding and Identification of Insect-Resistant Rice by Transferring Two Insecticidal Genes, sbk and sck

The plasmid of pCDMARUBA-Hyg, which contained two insect-resistance genes, sbk (modified from Cry1A(c)) and sck (modified from CpTI), was transformed into an Agrobacterium EHA105 for infection of the calli of a super japonica rice Nanjing 45. Primarily, using polymerase chain reaction (PCR) detection with the primers of sbk and sck genes, 42 positive transgenic plants that were marker-free and contained the two target genes were selected from 97 regenerated plants. Results of southern-blotting indicated that 23, 11, 5, 2 and 1 plants had one, two, three, four and five copies of the transformed genes, respectively. Analysis of reverse transcription PCR (RT-PCR) and Bt gene testing paper showed that 28 T3 generation plants derived from four transgenic plants having a single copy were insect-resistant. Feeding experiment with rice stem borer revealed that the insect resistance was greatly increased with the larva mortality ranging from 94% to 100%. In addition, among the transgenic plants, three T3 transgenic plants possessed some desirable characteristics for breeding and production, such as plant height, seed-setting rate, 1000-grain weight and larva mortality. The mechanism of insect resistance of Bt gene and its application in rice transgenic research were also briefly discussed.

Mismatch in Source and Sink as a Reason Determining Realized Potentiality of Bt Cotton Hybrids

The onset of Bt era has lead to increase in productivity of cotton in Indian scenario. Many of the hybrids commercialized in the initial phase were those hybrids which were popular in non Bt era and some of them have failed to give same high productivity in their Bt form. A comparison of Bt cotton hybrids for productivity, plant type features has revealed that though Bt cotton hybrids revealed increased productivity some hybrids reveal early scenecense leading to a more determinate habit. The increase in yield in these hybrids mostly comes from the bolls borne on the lower half of the plant than the upper half of the plant. There is a mismatch between the source and sink especially in the upper half of the plant. These hybrids reveal visibly weakened leaves at a later stage as a result of which they show reduced photosynthetic activity. As compared to this, some of the most potential hybrids remained green and photosynthetically active enough to support the increased reproductive load. There is a fairly comparable harvest index in both upper and lower halves. Thus these hybrids reveal higher productivity in both lower and upper halves of the plant canopy. This observation has an important implication in plant breeding that the parents(at least one of them) chosen for developing Bt hybrids should have strong photosynthetic system and stay green nature so that the hybrid is capable of withstand enhanced Bt gene induced reproductive load. Keywords Bt gene; Cotton; Source and sink

Development of transgenic cotton lines harboring a pesticidal gene (cry1Ab)

Each transgenic plant has its unique genetic architecture and level of expression. The present study was conducted to study each transgenic plant separately in order to develop pure transgenic lines to be further used in efficient cotton breeding programme. Earlier MNH-93 cultivar was transformed with the Bacillus thuringiensis (Bt) gene cry1Ab through Agrobacterium-mediated transformation method using mature cotton embryos as explants. Transformed plants obtained out of this transformation event were used to develop pure lines for five consecutive generations. The selection criteria contained confirmation of transgene through PCR and western dot blot, boll damage percentage, insect mortality percentage in lab bioassay with heliothis larvae, seed cotton yield (g), plant height (cm), number of monopodial branches per plant and number of sympodial branches per plant. All the characters were stably inherited in further generations. The expression of introduced genes was found to be variable; however it conferred protection against targeted insect pests. It was concluded that the transgenic pure lines are an excellent source of germplasm to be used in conventional breeding programme.

Larval survival and plant injury of Cry1Ab-susceptible, -resistant, and -heterozygous genotypes of the sugarcane borer on transgenic corn containing single or pyramided Bt genes

Transgenic corn (Zea mays L.) products expressing multiple Bt proteins targeting a same group of insect pests have become commercially available in the U.S. The first commercialized pyramided Bt corn technologies for managing lepidopteran pests include Genuity® VT Triple Pro™ and Genuity® SmartStax™. In this study, larval survival and plant injury of Cry1Ab-susceptible (Cry1Ab-SS), -resistant (Cry1Ab-RR), and -heterozygous (Cry1Ab-RS) genotypes of the sugarcane borer, Diatraea saccharalis F., on five commercial corn hybrids were evaluated in a leaf tissue bioassay and two greenhouse trials during 2010–2011. The five hybrids included two non-Bt corn and three Bt corn hybrids representing three transgenic technologies: YieldGard® Corn Borer, Genuity® VT Triple Pro™, and Genuity® SmartStax™. YieldGard® Corn Borer corn contains a single Bt protein (Cry1Ab), while Genuity® VT Triple Pro™ and SmartStax™ contain two and three pyramided Cry genes targeting above-ground lepidopteran pests, respectively. An average of 75.5% of larvae survived after 6 d on non-Bt corn leaf tissue. The 6-d survivorship on Cry1Ab corn leaf tissue was 3% for Cry1Ab-SS, 19% for Cry1Ab-RS, and 35% for Cry1Ab-RR larvae, while none of the three insect genotypes survived for 6-d on the leaf tissue of the two pyramided Bt corn hybrids. After 21 d on whole plants in the greenhouse, 42.6–62.5% of larvae survived on non-Bt corn plants. Larval survivorship rates on YieldGard® Corn Borer plants after 21 d in the greenhouse were 4.7–5.6% for Cry1Ab-SS, 29.4–32.5 % for Cry1Ab-RS, and 36.6–45.6% for Cry1Ab-RR. Both pyramided Bt corn hybrids were very effective against D. saccharalis regardless of the insect genotype with 21-d survivorship of <2% for Cry1Ab-SS and Cry1Ab-RS, and <5% for Cry1Ab-RR. Cry1Ab-RS and –RR caused significant entry/exit holes and tunneling inside the plant stalks of non-Bt and YieldGard® corn plants, while they caused little injury on the two pyramided Bt corn hybrids. The data generated from both the leaf tissue and whole plant tests showed that the Cry1Ab-resistant D. saccharalis was susceptible to the pyramided Bt corn hybrids. The results suggest that the pyramided Bt corn containing Genuity® VT Triple Pro™ or SmartStax™ traits should offer a means for Cry1Ab resistance management in D. saccharalis.

Maize–planting date interaction and effect of Bt maize on European corn borer (Ostrinia nubilalis (Hubner) (Coleoptera: Crambidae) damage

A study was conducted to determine the influence of planting date and transgenic maize on maize yield following stalk injury by European corn borer, Ostrinia nubilalis (Hubner). Transgenic and non-transgenic maize hybrids with short- and full-season maturity were planted in late April, mid-May and early June from 2006 to 2008 in Ohio, USA. Maize stem tunnelling was significantly higher on non-transgenic maize and increased with delayed planting. Significantly higher yields were obtained from full-season than short-season hybrids when maize was planted early. The results suggest that when planting is delayed and an European corn borer population is known to cause economic damage in an area, selection of short-season hybrids with the Bt gene can be beneficial in controlling damage and improving yield.

Gene technology in agriculture, environment and biopharming: beyond Bt-rice and building better breeding budgets for crops

Applications of gene technology in agriculture, the environment and human health fields are reviewed. This case study of the intricate historical details of the development of Bt crops like cotton and rice unveils essential elements of productive funding schemes and effective multinational collaborations. Gene technology applied to pest resistance traits in global cotton is analyzed using nation-specific data from India to demonstrate ‘ricochet’ results: Regulatory approval for one crop catalyzes an ‘Enhancer Effect’ for promoting more research funding and more competitive results for other crops-in-waiting, namely rice. Just as cotton commerce promoted philanthropy in unpredictable situations like the Kreenholm dynasty of Ludwig Knoop, research budgets for pesticide and biocide technology have yielded intended effects, but several surprising unintended effects as well. Finally, the case is made for greater control of gene flow and identity preserve issues in plant biotechnology research by invoking Appellation d’Origine Controlee for Bt genes.

Preliminary transformation of Saccharum officinarum L. with Bt gene

Preliminary transformation of Saccharum officinarum L. with Bt gene

Extended monitoring of resistance to Bacillus thuringiensis Cry1Ab maize in Diatraea saccharalis (Lepidoptera

The sugarcane borer, Diatraea saccharalis (F.), is a major target of transgenic maize expressing Bacillus thuringiensis (Bt) proteins in South America and the mid-Southern region of the United States. During 2007–2009, a total of 986 feral individuals of D. saccharalis were collected from maize fields in six locations of Louisiana and Mississippi and examined for resistance to Cry1Ab maize using F1/F2 screens. Major resistance alleles to Cry1Ab maize in the populations sampled from non-Bt maize plants during 2007 and 2008 in Louisiana and 2009 in Mississippi were rare. From a total of 487 individuals collected from three locations in Louisiana in 2007 and 2008, only one individual was identified with major resistance alleles. In addition, no major resistance alleles were detected in 242 individuals collected from three locations in Mississippi in 2009. The frequency of major resistance alleles was estimated to be 0.002 with a 95% CI of 0.00025–0.0057 for the Louisiana populations and < 0.0061, with 95% probability, for the Mississippi populations. The resistance frequency estimated for the Louisiana populations in 2007 and 2008 was not significantly different from those reported previously for populations sampled in 2004–2006. However, among 200 individuals sampled from non-Bt maize plants in 2009 in Louisiana, six individuals were identified to possess major resistance alleles. The estimated major resistance allele frequency for the populations sampled from non-Bt maize plants in 2009 in Louisiana was 0.0176 with a 95% CI of 0.0072 to 0.0328, which was significantly greater than those estimated for the populations collected in 2004–2008. Similarly, the frequency of minor resistance alleles to Cry1Ab maize for the Louisiana populations collected in 2009 was also significantly greater than those estimated for the populations sampled before. In addition, two out of 57 feral individuals collected from Bt maize plants in Louisiana in 2009 were identified to carry major resistance alleles to Cry1Ab maize. Since 2010, transgenic maize expressing pyramided Bt genes has been planted in the US mid-Southern region and by 2011, pyramided Bt maize has replaced Cry1Ab maize as the dominant Bt maize for managing lepidopteran pests including D. saccharalis. The timely switching from single-gene Cry1Ab maize to the pyramided Bt maize should prevent further increases in Cry1Ab resistance allele frequency and thus ensure the continued success of Bt maize for managing D. saccharalis in the region.

Phytophthora bilorbang sp. nov., a new species associated with the decline of Rubus anglocandicans (European blackberry) in Western Australia

A new homothallic Phytophthora species, isolated from rhizosphere soil and roots of declining or dead Rubus anglocandicans (European blackberry) in south-west Western Australia, is described as Phytophthora bilorbang sp. nov. It produces non-papillate sporangia, smooth-walled oogonia containing thick-walled oospores, and paragynous antheridia. Although morphologically similar to several species within ITS Clade 6 and sub-clade II, namely P. gibbosa, P. gregata and P. megasperma, phylogenetic analyses of the ITS, cox1, HSP90, BT and NADH gene regions demonstrate that P. bilorbang sp. nov. is a distinct species. Additionally, P. bilorbang differs from these species in its growth and colony morphology on several media. Pathogenicity tests indicate that P. bilorbang could be responsible for the decline syndrome of blackberry within the Warren and Donnelly River catchments in the south-west of Western Australia.

Inheritance of an insecticidal gene (cry1Ab) in genetically modified cotton

The present study was conducted to evaluate inheritance pattern of insecticidal gene (Cry1Ab) in F1 and F2 generations derived from six combinations of crosses made between two transgenic lines (CEMB-3 and CEMB-11) and two non transgenic lines (MNH-93 and CIM-482). PCR, southern blot, western dot blot assay and lab biotoxicity assay were used to confirm the gene integration and expression of insecticidal gene in successive generations. The insecticidal gene was stably integrated in the genome of all F1 plants showing the dominant nature of introduced gene (cry1Ab). Furthermore, heterosis, heterobeltiosis, heritability and genetic advance studies of Bt gene were also conducted. Heterosis and heterobeltiosis were estimated for five characters i.e. cotton yield per plant, no. of bolls per plant, boll weight, ginning out turn % age and laboratory bioassay results. The heterosis and heterobeltiosis ranged from—15.19 to 107.07% and 18.58 to 98.79%, respectively for yield per plant; from −20.34 to 81.36% and −20.34 to 81.36%, respectively for number of bolls per plant; from -6.96 to 21.38% and −9.30 to 9.99%, respectively for boll weight; from 13.02 to 26.44% and −0.52 to 26.17%, respectively for ginning outturn; and from −8.11 to 36.23% and −5.56 to 23.68%, respectively for mortality % age of Heliothis larvae in laboratory bioassays. The Broad Sense Heritability and Genetic Advance for insect resistance in Bt versus non-Bt crosses were calculated. Both of these were high in four out of six hybrids. Our data recorded showed that these transgenic lines are an excellent source of germplasm to be used in conventional breeding programme.

Bt-Cotton in India: The Technology Wins as the Controversy Wanes India Approves Bt-Cotton – The First Agribiotech Product

Bt-cotton developed by Mahyco (Maharashtra Hybrid Seed Company) containing the Bollgard Bt gene, cry 1Ac, licensed from Monsanto, was approved by Government of India for commercial cultivation in March 2002. This approval was preceded by a large number of laboratory studies and about 500 field trials carried out during 1996-2001 to demonstrate the safety and benefits of Bt-cotton as per regulatory requirements. The area planted with Bt-cotton in 2002, the first year of introduction, was 29,415 ha (72,685 acres). It increased to 86,240 ha in 2003 and to 530,800 ha in 2004. A nationwide survey carried out in 2003 indicated that the Bt-cotton growers in India were able to obtain , on an average, a yield increase by about 29% due to effective control of bollworms, a reduction in chemical sprays by 60% and an increase in net profit by 78% as compared to their non-Bt counterparts. The indications are that the demand for Bt-cotton will grow significantly in the coming years. Realizing its potential, 19 other seed companies have already joined Mahyco-Monsanto as their sub-licensees for Bt-cotton. The details of the development of Bt-cotton, safety studies, field performance, opposition it faced, problem of illegal Bt-cotton and the prospects of this technology in India are outlined in this article.

Segregation and expression of transgenes in the progenies of Bt transgenic rice crossed to conventional rice varieties

β -Glucuronidase (GUS) activity bioassay, western blotting and polymerase chain reaction (PCR) analysis demonstrated that the cry1Ab gene was closely inherited and expressed with reporter gene gus in the progenies of Bacillus thuringiensis ( Bt ) transgenic rice ( Oryza sativa L.) crossed to conventional rice varieties. Therefore, it is feasible using GUS-assisted-selection to preliminarily identify the Bt gene and study the inheritance of transgenes in breeding program. Mendelian segregation was observed in BC1F1, BC1F2 and F2 populations derived from Bt rice crossed to japonica rice respectively which indicated that the cry1Ab gene was inherited as a single dominant locus. PCR, Southern blotting and Western dot blotting analysis confirmed that cry1Ab gene was transferred to the genome of conventional rice varieties and it was highly expressed in the different progenies of Bt rice crossed to conventional rice varieties. Among these lines, the highest Bt toxin protein content reached 2.88% of total soluble proteins, even though the amount of Bt toxin protein in leaves of some GUS positive plants was higher than that detected in the original Bt rice. Meanwhile, the variances in Bt toxin protein between crosses and its parents were significant at 0.05 or 0.01 levels, respectively. Therefore, foreign cry1Ab gene with native insect resistant trait can be easily transferred to other rice varieties with higher yield potential and good quality through classical breeding. Keywords: Oryza sativa L., transgenes, inheritance, expression

Effects of N treatments on the yield advantage of Bt-SY63 over SY63 (Oryza sativa) and the concentration of Bt protein

It has been widely demonstrated that insect-resistant rice containing various Bt genes can provide an effective control of lepidopteron pests. It is well known, however, that rice plants will suffer more pressure from pests when high nitrogen fertilizer is applied. Therefore, how is the efficacy of Bt transgenic rice against lepidopteron pests in response to N application? In this study, we try to study the effect of nitrogen treatments on the yield advantage of Bt transgenic SY63 (1C*) and SY63 (2A*) [SY63 (1C*) and SY63 (2A*) represent the hybrid variety Shanyou63 contain a Bt gene of cry1C* and cry2A*, respectively.] over its non-Bt Shanyou63 (SY63) and disclose the relationship between N concentration and Bt protein in rice leaves. Field experiment was conducted in 2010 and 2011 at Zhangbang village, Wuxue city (29°51′N 115°33′E), Hubei Province, China from May to October. Treatments were arranged in a split-plot design with three replications, and nitrogen treatments were the main plots and genotypes were the subplots. No pesticides against lepidopteron pests were applied in the whole growth season. It was found that both SY63 (1C*) and SY63 (2A*) exhibited effective resistance to leaffolders, although SY63 (1C*) was more efficient than SY63 (2A*). There were significant correlations between the yield advantages of SY63 (1C*) and SY63 (2A*) over SY63 and their grain yield, respectively. The maximum yield advantages of SY63 (1C*) and SY63 (2A*) over SY63 were both near 20%, however, no significant yield advantages for Bt rice were observed when their grain yield was below 6.5tha−1. There was a significant correlation between N and Bt protein concentrations. Bt protein concentrations at 210kgNha−1 were significantly higher than those at zero N treatment, but there were no significant differences among 90, 150 and 210kgNha−1. In addition, the concentration of Cry2A* was several times higher than that of Cry1C*. Therefore, it is meaningful to incorporate the Bt genes into varieties with high yield potential and adopt appropriate N management practice to ensure high grain yield, so that its insect-resistance advantage could be fulfilled.