Materials and Methods

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1 International journal of Agronomy and Plant Production. Vol., 3 (8), , 2012 Available online at ISSN VictorQuest Publications Management of aromatic rice (Oryza sativa L.) genotypes using varietal resistance against the prevalence of rice stems borers Muhammad Sarwar Nuclear Institute of Agriculture, Tandojam-70060, Pakistan *Corresponding Author drmsarwar64@yahoo.com Abstract Growing of resistant cultivars against insects infestation has received much consideration due to increasing problems of environmental pollution and health hazards. Systematic screening of 42 aromatic rice genotypes was initiated for testing their resistance to the rice stem borers (Lepidoptera) under field conditions. By choosing pest damage and seed yield parameters, the tolerance and susceptibility of rice genotypes were determined. The obtained results showed prominent differences between the genotypes due to variability in the degree of all parameters studied. Out of screened aromatic rice selections, the variety Khushboo-95 followed by Basmati-15-14/93 and Basmati-20-1/93 showed the least deadhearts and whiteheads causing maximum yield as compared to the remaining genotypes identified for tolerance. Owing to the occurrence of highest seed yield and least borer s invasions these varieties expressed resistance to pest. High densities of borers (deadhearts and whiteheads) and lower yield were associated with SG-15-7/97, Jajai-77 (P) and Basmati-370 (P) which were susceptible for the parameters under observations. These resistant sources found in the trial can further be exploited in breeding program for the development of borer s resistant commercial rice cultivars by determining their genetics. Keywords: rice, steme, resistance, borer's infestation and yield. Introduction The rice stem borers (Lepidoptera) are serious pests and of regular occurrence to infest the rice (Oryza sativa L.) crop at all stages of growth. The yellow stem borer Scirpophaga incertulas (Walker) (Pyralidae) had emerged as the dominant pest of rice. The major factors regulating its populations were; the incidence of weather extremes (temperatures> 34 0 C with relative humidity< 70%) before flooding which are lethal to eggs and 1 st instars; the presence of succulent and elongating stems which are favourable for larval penetration and development; the occurrence of rapid water rises (6-8 cm day -1 ) which drown the immature stages; the activity of natural enemies particularly the complex of egg parasitoids, spider and orthopteran predators; and the harvesting and threshing operations which kill many diapausing larvae in the stems ( Catling & Islam, 1995). Observations carried out by Catling et al., (1984}.showed that S. incertulas usually comprised more than 90%, Chilo polychrysus 11% and Sesamia inferens 6% of the population in the pre-flood and ripening stages. Tripathy et al., (1999) in a field study examined the population dynamics of different rice borers species. The yellow stem borer ( S. incertulas) produced two broods, with the first peaking during the last week of September and the second peaking during the second week of November which coincided with the dough stage of rice. Egg masses were more abundant in the second brood than the first. The S. incertulas was dominant species until the first week of October when the stripe stem borer (C. suppressalis) and pink stem borer (S. inferens) contributed to the total larval population, which were greatest during the second and third week of December (Sarwar, 2011; 2012 a).

2 The fine grain basmati varieties of rice are considered high quality rice and fetch a high price in national and international trade. However, yield per unit area of basmati rice is very low due to tall plant habit and late maturity (Rashid et al., 2003). Flowering behaviour is also an important character which distinguishes basmati rice from non basmati rice. All traditional basmati varieties are highly photoperiod sensitive with respect to flowering. These are tall stature having weak culm, low yield and prone to lodging. At the time of selection of a basmati variety, special attention should be given to those varieties which show photosensitivity ( Rafiq et al., 2005). The appearance of a novel, resistant plant genotype in the environment presents a challenge to its herbivores insect populations utilizing that host ( Thompson, 1996; Hawthorne, 1998). On account of new developments in rice genetics, the need for examining host plant resistance to insect pests has been progressively intensified. As a result, growers and other members of the rice industry would be benefited tremendously from the information on resistance of rice germplasm resources that is the cornerstone of crop breeding and protection. Therefore, this work aims to elucidate the larval or adult preference of stem borers for susceptible and a resistant rice plant genotypes. Materials and Methods Forty two aromatic rice genotypes/ lines representing distinct parentages were used in this field study and compared for pest damage and seed yield parameters to determine their tolerance and susceptibility. Early in July 2004 seeds of each genotype/ were sown at Nuclear Institute of Agriculture, Tandojam, for use in the field assays. All seeds were obtained from Rice Genetics Laboratory of the Institute. After 7 week, nursery seedlings of each variety/ genotype were transplanted for use in the trial. Trial was arranged in a Randomized Complete Block Design replicated thrice. For each genotype and replicate an area of 3 m 2 was specified.the fertilizer granules N: P: K were applied as broadcast, and especially in the vicinity of the roots at a dose of 60:30:30 kg/ ha. Total Phosphorus and Potash and 1/3 nitrogen granules were applied at the time of land preparation, whereas, left over 2/3 N was applied at 25 and 45 days after nursery transplanting in two equal doses. ZnSO 4 (35%) was 12.5 kg/ ha, 15 days after nursery transplanting. The weeds in rice field were controlled manually. No pesticide was used throughout the experimental period. The differences in genotypic resistance of rice were identified by taking the criterions; (a) the percentage of deadhearts, (b) the percentage of whiteheads, and (c) grain yield. Yield parameter was recorded at crop maturity stage after harvesting. Total numbers of plants in 1 m 2 selected area were counted and then total numbers of damaged tillers hill -1 were recorded to calculate percentage deadhearts. At the later stage for borers infestation data were recorded on whiteheads basis by counting numbers of damaged panicles and then percent whiteheads were calculated. Pooled and average data calculated were analyzed statistically and treatment means were compared with each other by using Duncan s Multiple Range (DMR) Test. Then differences were considered only when significant at p< Results and Discussion In the present study, different rice germplasm accessions were screened against stem borers under field conditions, but no one of these were absolutely resistant or even extremely resistant to pest. This shows a high level of aggressiveness of the pest or comparatively constricted diversification of genetic material under study. In the area of the present study, stem borers infestation in various germplasm after transplantation was at variable levels. The infestation levels on Khushboo-95, Basmati-15-14/93 and Basmati-20-1/93 genotypes (2.51, 3.65 and 3.72% deadhearts, and 4.09, 4.55 and 4.87% whiteheads, respectively) were significantly different from that of S.G-15-7/95, Jajai-77 (P) and Basmati-370 (P) (18.41, and 13.58% deadhearts, and whiteheads 14.80, and 16.50%, respectively). Owing to the occurrence of highest seed yield and least borers invasions on Khushboo-95, Basmati-15-14/93 and Basmati-20-1/93, these varieties/ genotypes expressed resistance to pest. High densities of borers (deadhearts and whiteheads) and yield were associated with S.G-15-7/95, Jajai-77 (P) and Basmati-370 (P) which were susceptible for both the parameters under observations (Table 1). The mainly imperative parameter and critical task of farming community is paddy yield which differed significantly with various genotypes. It can be visualized from data in Table 1 that genotype Khushboo-95 produced maximum paddy yield of 1803 gm per 3 m 2 area and it remained statistically more yielder than with Basmati-15-14/93 and Basmati-20-1/93 genotypes with 1763 and 1707 gm paddy yields. The genotypes S.G-15-7/95, Jajai-77 (P) and Basmati-370 (P) gave minimum paddy yield (610.0, and mg/ 3 m 2 ). Similar results were reported by Ahmad et al., (2006), Safdar et al., (2008) who claimed that among various basmati strains tested paddy yield varied. Yield losses caused by borers were mainly due to increases in the number of 296

3 empty panicles and a reduction in grain weight. The relationship between yield components and resistance to striped rice borer (C. suppressalis) was investigated by Kang (1997) in rice cultivars differing in resistance level to pest. Yield losses caused by borers were mainly due to increases in the number of empty panicles and a reduction in 1000-grain weight. Our research findings are also in the same direction. The specific mechanism of resistance responsible for the differences between tolerant Khushboo-95 and susceptible SG-15-7/95 germplasms is unknown; however, the evidence suggests that resistance in rice may be primarily due to involvement of some kind of secondary compounds to which the feeding larvae is forced to respond. In other words, neonates feeding on the resistant host Khushboo-95 faced with secondary compounds and responded negatively, while neonates on S.G-15-7/95 which is the more palatable host would not have such compounds. Further studies are necessary to determine the secondary compounds responsible for resistance in Khushboo-95 and the mechanisms of resistance used by borers in response to these compounds in the host plant. There may be adult moth s oviposition preference or non preference for the susceptible or resistant rice germplasms. It may be possible that the females moth were able to discriminate between the tolerant or susceptible varieties of rice. Both tolerant and susceptible lines did not appear to be identical due to differences in secondary compounds between the lines, and these may be detectable prior to adult s oviposition or ingestion by neonates. As such, there may be chemical cues available to the female to indicate that one line is less suitable for its offspring than another. Such type of genetic correlation between oviposition preference and offspring performance has also been pointed out by Nylin & Janz (1996). Previous studies have suggested that adult host preference is strongly influenced by factors such as plant abundance and experience with a particular host ( Cunningham & West, 2001). Whether the preference or non preference for either genotype of rice found here is due to the ability to discriminate between the two resistant or susceptible hosts or due to a of experience with either host, it seems likely that females encountering a large patch of host plants, as would occur in an agricultural situation, would oviposit in regard of the genotype present. Under these circumstances, it seems likely that there would be strong selection acting on neonates for improved performance and that the response to such selection would be rapid. Future studies should be focused on the strength of selection at each life stage to further examine the potential for insect adaptation to resistant or susceptible hosts in the field environment. Host plant resistance, an important component of integrated pest management, which can be triggered by biotic (pathogen, non-pathogen) or abiotic elicitors (like simple chemicals), can be used very effectively when combined with selective pesticides and induced resistance technique (Inbar et al., 1998). Induced resistance has been considered a potential strategy for disease/ insect pest control in plants. Inducible defenses play a major role in conferring resistance against plant pests and their effects on phytophagous insects can include increased toxicity, delay of larval development or increased attack by insect parasitoids (Baldwin & Prest on, 1999). Chandramani et al., (2010) carried out experiments in field conditions to analyze the effects of induced resistance on certain major pests of rice. It was concluded that application of organic sources of nutrition reduced the incidence of pests and increased the yield in rice. These observations led to investigate that induction of resistance in rice is possible by treating the plants with chemicals. In the current research it is hoped that resistant genotypes showing tolerant reaction to stem borer would also be fatal to other rice pests. This statement is endorsed by Chandramohan & Chelliah (1984) that rice accessions with resistance or moderate resistance to the yellow stem-borer was also resistant to brown planthopper [Nilaparvata lugens], the whitebacked planthopper [Sogatella furcifera] and the green leafhopper [Nephotettix sp]. According to Pathak (1990) the resistance in rice to stem borer, Chilo suppressalis is low to moderate and appears to be under polygenic control. A recurrent selection programme using male sterile lines could be effective in improving resistance. Identification of genes and their manipulation in rice cultivars and elite breeding lines characterized by resistance to insect pests, may present a major breakthrough in rice genetics and breeding. It is mainly the genetic variability available in O. sativa germplasm which can be exploited for resistance breeding. Genetic variability for agronomic traits is the key component of breeding programmes for broadening the gene pool of rice crop. However, the genetic variability for many traits, such as tolerance to stem borer might be given due importance in cultivated germplasm. Breeders therefore should search for genetic variability in other gene pools involving wild relatives of Oryza (Sarwar et al., 2010; Sarwar, 2012 b). Hence, all these attributes and aspects pointed by the previous researchers should be considered as important factors in breeding rice varieties for stem borers resistance. Host plant tolerance should be reckoned as an important factor in breeding and implications of these results for rice pest management including evolving of cultivars tolerant to stem borer s injury is essential 297

4 Table 1. Appraisals of different aromatic rice genotypes against rice stem borers populations. S. No. Rice genotypes Borers infestation (%) Yield/ plot (3 m 2 ) Dead hearts Whiteheads (gm) 1. Basmati-370 (P) c c x 2. Basmati ghij jkl r 3. Basmati-1.5-3/ cd e u 4. Basmati-2.0-1/ jk jklm q 5. Basmati cde f t 6. Basmati s 6.63 r d 7. Basmati-15-2/ no 9.73 lmn j 8. Basmati lmno 9.91 lm l 9. Basmati-15-5/ op hijk n 10. Basmati ghi f t 11. Basmati-15-13/ lmn hijkl n 12. Basmati-15-14/ s 4.55 tu b 13. Basmati l lmn m 14. Basmati op 9.94 lm jk 15. Basmati ef cd w 16. Basmati-20-1/ s 4.87 stu c 17. Basmati-30-2/ ghi hi s 18. Basmati-30-4/ lmn 8.95 no m 19. Basmati de f t 20. Super Basmati fg gh t 21. Jajai-77 (P) b b y 22. Khushboo t 4.09 u a 23. Jajai-LG l jkl n 24. Jajai-15A/ pqr 6.48 r h 25. Jajai-15-1/ qr 6.37 r e 26. Jajai-15-2/ opq 7.80 pq i 27. Jajai-15-4/ l ijkl no 28. Jajai lm klm o 29. Jajai fg fg s 30. Jajai cd de v 31. Sada Gulab (P) 9.11 k ijkl o 32. S.G-15-3/ ijk ijkl p 33. S.G-15-7/ a a z 34. Sonehri Sugdasi (P) gh hij s 35. S.S pqr hij g 36. Basmati hijk 6.48 r qr 37. M.S. Line No mno 8.53 op k 38. M.S. Line No op 7.21 qr j 39. M.S. Line No r 5.28 st e 40. M.S. Line No op 9.28 mno l 41. M.S. Line No.22/A 5.07 pqr 4.98 st h 42. M.S. Line No.22/B 4.73 r s f LSD value Means under each variety sharing the same letter in a column are not significantly different at P<0.05. References Ahmad M, Ashraf MM, Safdar ME, Ali L and Akhtar MS, Role of transplanting times on yield and quality of basmati rice. Proc. Inter. Sympo. on Sustainable Crop Impr. and Integ. Manag., Sep , 2006, Univ. of Agric., Faisalabad, Pakistan. pp Baldwin IT and Preston CA, The eco-physiological complexity of plant responses to insect herbivores. Planta, 208:

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