Studies on the tolerance mechanism in selected rice accession against yellow stem borer, Scirpophaga incertulas (Walker)

Introduction

Insect pests are considered to be major limiting factors in achieving the targeted yield in rice and their attack cause annual loss of about 20 per cent. Among these insects, YSB is the most important and destructive pest of rice throughout the tropical South and South East Asia including India and attacks both in the Kharif and Rabi seasons. Yield losses to the tune of 25-30% have been reported due to its attack both at vegetative and reproductive stages in different parts of India Pasalu et al. (2002) [1] . It is the most abundant stem borer in tropical low land (Catling and Islam 1995) [2] due to its close association, profound preference and adaptablility to aquatic environment. Although various efforts are being made to manage this pest, but the use of resistant varieties is the most appropriate tool to manage this pest because it is basically free to farmers and judicially fit in IPM schedules. But the progress in developing stable resistant varieties against this pest is very limited because of nonavailability of good donors and polygenic nature of resistance (Panigrahi and Rajamani, 2008) [3] . Therefore, emphasis is now given on identifying YSB tolerant varieties which can effectively be incorporated in to the integrated management schedule and increase in yield of this ideal eco-system. Also tolerant varieties does not exert selection pressure on insect population for development of new bio-types, favours natural enemy population build up and minimize the frequency of insecticide application. In the light of this, the present study was undertaken to measure the tolerance level of selected rice accessions against YSB.

Materials and Methods

The experiment was conducted during 2015 at Insectary, Department of Agricultural Entomology, Agricultural College and Research Institute, Madurai with selected rice accessions obtained by screening of twenty two rice accessions under green house and sixteen accessions under field conditions. Among twenty two accessions screened for YSB resistance, four accessions viz., IET 23272, IET 23673, IET 23694 and IET 23715 exhibited good tolerance mechanism through high tillering ability. Tolerance mechanisms for four accessions along with TN 1 were studied under screen house condition. The experiment was replicated three times with five To compare the yield loss due to YSB, the ability of the accessions to recover was assessed by comparing infested plants over the healthy plants. The number of tillers/hill, percentage of productive tillers, plant height, no. of grains/panicle, panicle length, percentage of chaffy grains, 1000 grain weight and yield per plant were recorded from both healthy and infested plants from all the selected accessions. The mean per cent reductions were worked out for all the characters except chaffy grains. For the chaffy grains, per cent increase was worked out by infested plants over healthy plants (Chandra Mohan, 1987) [5] during harvesting stage.

Results and Discussions

The evaluation of selected rice accessions against YSB along with biometric variation in YSB infested plants in comparison with healthy plants are presented in table 1 1).

From the selected accessions, IET 23694 in spite of supporting high larval population and exhibiting more dead heart incidence and also recorded higher percentage of surviving hill with minimum reduction in grain yield/panicle, grains/panicle and per cent increase in chaffy grains compared to the moderately resistant accessions. This was attributed to the stimulation of crop growth leading to production of more tillers which compensated the damage caused by the stem borer. This possibly supported that tolerance ability of the accessions, since the modality of tolerance mechanism operated upon the capacity of plants to repair injury or grow to produce an adequate yield despite supporting an insect population at a level capable of causing more damage to a susceptible host. Similar findings were reported by Panigrahi and Rajamani (2010) [6] reported that early medium varieties like Konark, Kumar, Ananga, Amaravati and Vikash indicated compensatory mechanism when infestation took place at vegetative stage. Ratna showed tolerance both at vegetative and reproductive stages. Panigrahi and Rajmani (2010) [7]; Panigrahi (2011) [8] were reported that infestation at reproductive stage indicated that the reduction in EBT (Earhead Bearing Tillers) was at a lower range in the resistant varieties and lowest in TKM-6 and in the higher range in the moderately resistant varieties and the highest in ADT-32. Bandang and Litsinger (2005) [9] reported that rice plants were able to tolerate infestation by producing more compensatory tillers and suffered more yield losses when damage occurred at the reproductive stage than at the vegetative stage Earlier worker also reported that rice genotypes showed tolerance reactions to Basmati-15-15, Jajai-25/A, Basmati-15-13 and CR-33 (Sarwar, 2013d) [10] . Khan et al. (2010) [11] reported that IRRI-6 was found tolerant to rice stem borer attack and also showed maximum number of tillers, spike length, grains spike, 1000 grains weight and grain yield/ha.

Conclusion

After completion of this present investigation it is concluded that IET 23715 showed moderately resistant, IET 23694 and IET 23272 showed moderately susceptible, whereas IET 23673 and IET 23681 showed susceptible as against TN 1. Among the accessions, per cent yield reduction was lowest in IET 23694 followed by IET 23715, IET 23272, IET 23681 and IET 23673 in contrary to IET 23673.

References

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