Philippine Journal of Crop Science December 2004, 29(3): 53-60 Copyright 2005, Crop Science Society of the Philippines Released 11 April 2005 EFFICACY OF INSECT-PROTECTED MAIZE (BT-11) AGAINST ASIATIC CORN BORER (OSTRINIA FURNACALIS) EUFEMIO T RASCO JR1, JHOANAVI MANGUBAT1, ARISTOTLE BURGONIO2, MANUEL LOGRONO2, VIOLETA VILLEGAS2 & EDUARDO °C FERNANDEZ2 1 University of the Philippines in Mindanao, 2 Syngenta Philippines Inc. [email protected] Three experimental hybrid versions of NK5445 Bt, a hybrid maize developed by Syngenta Seed Company, along with 3 checks were subjected to repeated artificial infestation with Asiatic corn borer (ACB) egg masses and neonate larvae in a screenhouse study to test the efficacy of Bt-11 containing the truncated gene cry1Ab. Results show that all the 3 experimental hybrids were consistently highly resistant to ACB across 3 assessment periods during the vegetative stage. In contrast, the 3 check entries (non-Bt isogenic hybrid of NK5445, sweet corn hybrid Sugar 73, and NK5468, a commercial non-Bt hybrid), showed several elongated feeding holes on as much as two-thirds of the leaves. At harvest, the checks showed severe damage to the stalks, ears, ear shanks and tassels, and relatively minor damage to the kernel. Pupae of ACB were observed inside the stalks. The NK5445 Bt entries showed little or no damage to the stalk, ear shanks, ears, tassels, and kernels. The data clearly demonstrated the efficacy of Bt-11 in controlling the ACB under screenhouse conditions. The presence of 4 other insect species in both checks and NK5445 Bt plants, possibly introduced through the field-collected egg masses used for infestation, is an indication of the safety of the use of Bt-11 concerning non-target insects. Asiatic corn borer, Bt-11, Bt maize, cry1Ab, genetically modified organism, NK5445, Ostrinia furnacalis, transgenic crop INTRODUCTION increase due to the use of Bt maize. With a 60% reduction in pesticide use, Bt maize gave an Insect-protected maize hybrids (Bt maize) are incremental profit of P10,132 per hectare. among the products of modern biotechnology that Monsanto is not the only maize seed company have proven to be effective in controlling insect pests that is developing Bt maize technology. Syngenta’s Bt and consequently, reducing pesticide usage, increasing maize, using a similar gene (cry1Ab) that Monsanto yield, and reducing mycotoxin contamination of corn uses in its hybrid, is now increasingly being used by kernels (Phipps & Park 2002, Fernandez et al 1997). maize farmers to control European corn borer in the In 2004, Bt maize was planted in 11.2 million hectares USA and Canada. Syngenta aims to introduce its own worldwide, representing 14% of hectarage of all Bt maize in the Philippines. Towards this objective, transgenic crops (James 2005). Syngenta signed a Memorandum of Agreement with The Department of Agriculture of the Philippines the University of the Philippines in Mindanao to test recognized the importance of Bt maize when it gave the efficacy of its Bt maize (Bt-11) against the ACB. approval for commercial planting of Monsanto’s Bt Considering available information about Bt-11, maize in December 2002. Aside from other data, the including the results of various tests that it has been basis of this approval was the demonstrated efficacy of previously subjected to (Essential Biosafety 2002), a this material against the Asiatic corn borer (ACB) screenhouse study on the Syngenta Bt maize was under Philippine conditions. In a study covering conducted by UP Mindanao in Bago-Oshiro, Davao 10,000 hectares of Bt maize in the Philippines during City, Philippines during the period 15 December 2002 the years 2003 and 2004, Yorobe reported a 37% yield to 28 March 2003. The objective of this study was to test the efficacy of Bt-11 maize containing the Artificial infestation truncated gene cry1Ab against the ACB under The experimental plants were artificially infested screenhouse conditions, the results of which would with egg masses of ACB at 27 DAP. This was repeated become the basis for recommendation of further steps at 41 DAP. One egg mass attached to a 1 x 1 cm leaf to take. piece was dropped on the whorl of the corn plant on the first day. Additional egg masses were applied on MATERIALS & METHODS the second and third days; thus a total of 3 egg masses (approximately 100 eggs) were applied per plant Test materials during each infestation during the vegetative stage. Three experimental hybrid versions of Bt-11 were The egg masses were collected from cornfields in used in this study. These were NK5445Bt (A), General Santos City 1 to 2 days before infestation. NK5445Bt (B), and NK5445Bt (C). For comparison, the When they reached blackhead stage, they were kept in following checks were used: NK5445 non-Bt (isogenic a refrigerator until they were used. hybrid of NK5445), sweet corn hybrid Sugar 73, and Starting at early reproductive stage (55 DAP) to 69 NK 5468. Seeds of the 6 entries were planted in 10 clay DAP, tassels and silks were artificially infested with Table 1. Guthrie et al (1960) feeding damage scale Score Resistance Description Rating 1 HR No visible injury or a small amount of pin or fine shot-hole type of injury on a few leaves 2 Small amount of shot-hole type lesions on a few leaves 3 R Shot-hole injury common on several leaves 4 Several leaves with shot-hole and elongated lesions 5 I Several leaves with elongated lesions 6 S Several leaves with elongated lesions about 2.5 cm 7 Long lesions common on about one half of the leaves 8 HS Long lesions common on about 2/3 of the leaves 9 Most leaves with long lesions pots (12-inch diameter) per entry, each pot neonate larvae (total of 15 neonate larvae per silk and representing a replicate in a completely randomized tassel) using camel hairbrush. Most of the tassels were experimental design. Initially, 4 seeds were planted infested at 55 DAP, while silk infestation was more per pot; the plants were subsequently thinned to 2 per diffused over time, with most of the infestation carried pot 12 days after planting (DAP), and finally to 1 plant out at 58 and 62 DAP. The neonate larvae were per pot after the first damage rating. The least produced from egg masses laid on wax paper in the damaged plants were retained during thinning. screen cages in the laboratory by adults derived from Seeds of NK5445 Bt experimental hybrids were field-collected pupae. imported from Syngenta (Hawaii), while seeds of NK5445 non-Bt were imported from Thailand. Evaluation Syngenta (Philippines) supplied the seeds of Sugar 73 Leaf-feeding damage was evaluated using the and NK5468. Plant Quarantine Officers, following Guthrie et al (1960) 1-9 leaf-feeding damage scale as established protocol, supervised importation and shown in Table 1. Individual plants were evaluated 14 subsequent handling of the imported seeds. days after the first infestation, and 11 days and 14 days after the second infestation. 54 Bt Maize Against Asiatic Corn Borer At harvest, damage to the stalks and ear shanks (Figure 1). An ante-room and disinfectant (Lysol) foot- was evaluated by splitting these along the length, and dip were provided. To avoid heat buildup during warm counting the holes and measuring the total length of days, the concrete floor of the plastic house was tunneling by ACB. Damage to the tassel was covered with coco-coir matting that was kept wet by determined by counting the number of cut tassel and drip irrigation. A 50-cm fan aided in air circulation. number of holes in each tassel. Damage to the ear was The prevailing air temperature inside the greenhouse determined by counting the number of holes and was 30-33°C at mid-day. Prevailing soil temperature percent of kernel damaged. at 15 cm depth during mid-day was in the range of 22- 24°C. The entire floor of the plastic house, including Trial facility and plant care the immediate perimeter area were cleaned with The study was conducted under the supervision of pressurized water and subsequently sanitized with the National Committee on Biosafety of the chlorox everyday throughout the study. Philippines (NCBP), the Institutional Biosafety The plastic house was secured by a perimeter Committee of the University of the Philippines in fence of interlinked wire with 3 strands of barbed wire Figure 1. View of the plastic house at 40 days after planting Mindanao and the Plant Quarantine Office of the on top. To prevent rodent invasion, the perimeter at Bureau of Plant Industry. The study was conducted in the bottom of the fence down to the soil level was a 15 x 6 x 4 meters (length x width x height) insect- covered with a strip of galvanized metal sheet 50 cm proof screenhouse specially built for the purpose wide. Entrance to the enclosed facility was restricted Eufemio T Rasco Jr et al 55 to the project personnel and others authorized by the RESULTS Plant Quarantine Service. Steam-sterilized garden soil was used as growing Leaf/plant feeding damage rating medium for the maize. Watering was done daily to Table 2 shows that the 3 experimental hybrids of keep the soil moisture near field capacity. Pots were NK5445 Bt were uniformly rated HR (highly resistant; sited on plastic shallow pails to catch excess water. 1 in a scale of 1-9), showing no visible injury or only a At planting, 45 grams of 14-14-14 granular small amount of pin-hole or fine shot-hole type of fertilizer was applied per pot. Fertilizer application feeding injury on a few leaves.