Susceptibility of Milled Rice Varieties to the Lesser Grain Borer ( Rhyzopertha dominica , F )

The susceptibility of six milled rice varieties (IR-64, Ciherang, Membramo, Cibogo, Sembada, and Intani-2) to the Lesser Grain Borer (Rhyzopertha dominica, F) was studied by No Choice Test Method under laboratory condition (27 ± 2°Cand 65 ± 5% RH). The Susceptibility was assessed on the basis of eggs number laid by female insects, the number of F1 progeny emerged, the weight loss of infested samples and also the Dobie’s Index of susceptibility. The results revealed that the number of eggs laid by female insects, the number of F1 progeny emerged and weight loss of infested samples were significantly low in Membramo variety followed by Ciherang, IR-64, Cibogo, Sembada and Intani-2. Based on the index of susceptibility, the milled rice variety of Membramo had the lowest susceptibility index and was regarded as resistant. While the milled rice varieties of Ciherang, IR-64, Cibogo and Sembada were considered as moderately resistant, Intani-2 seen as the most highly susceptible. These results imply that the milled rice variety with high phenolic content and hardness potentialy revealed resistant to the R. dominica infestation.


Introduction
Rice (Oryza sativa L.) is playing an important role in Indonesian livelihood.It is a staple for all classes in Indonesia and also holds the central place in Indonesian culture and cuisine.Government program for increasing rice production, both through extensification and intensification had yielded some success.Unfortunately, the quantity and quality of rice can be easily dropped and damaged by several species of insects during storage.Hence, in addition to agronomic obstacles, storage insect is the major problems to attain rice self sufficiency.Head of East Java Indonesian Logistic Bureau (BULOG) stated that every year the lost due to insect storage in average of 10 -25%.In India, the quantitative losses caused by storage insects are in the range of 5-25% per year (Prakash & Rao, 1995).
There are many kind of insects that reduce the quality of rice in storage.Some of them are Lesser Grain Borer (Rhyzopertha dominica (F)), Rice Weevil (Sitophilus oryzae (L)), Red Flour Beetle (Tribolium castaneum (H)), Rusty Grain Beetle (Cryptolestes ferrugeneus (S)) and also Saw-toothed Grain Beetle (Oryzaephilus surinamensis (L)) (Prakash & Rao, 1995).At the end of 2008, there was a serious damage in the Indonesia government storage (BULOG) caused by R. dominica (Susanto, 2010: Personal communication).This insect infestation has made rice broken into dust (Emery & Nayak, 2007).Sittisuang and Imura (1987) stated that brown rice lost 40% of initial weight over the 14 weeks through infestation of R. dominica.
The common treatment to minimize insect infestation in rice storage is the ecosystem approach.Ecosystem approach was done by altering both the rice and environment so that the insect cannot develop.These include alterations of the abiotic components of storage such as grain moisture content, temperature, condition and type of storage structure and additional components include the use of synthetic and botanical grain protectants and other nonconventional methods such as grain resistance (Prakash & Rao, 1995).According to Cogburn et al. (1983), McGaughey et al. (1990); Arnason et al. (1992) and Chanbang et al. (2008), grain characteristics such as grain grade, silica content, thickness of husk, relative hardness of grain kernel, phenolic, protein and amylase content were associated with different responses to the attack of stored products insects.
Recently, many rice cultivars are developed to increase its productivity, but there have been few assessment of varietal susceptibility to R. dominica (Chanbang et al., 2008).Therefore, the objestives of this research were to: (1) assess varieties of milled rice for susceptibility to R. dominica and (2) determine if there will be any specific characteristics of milled rice variety confer susceptibility to R. dominica.

Materials and Methods
The research was conducted from November 2010 to July 2011.The experiment was conducted by No Choice Test method at Pest Laboratory, Department of Plant Protection, Agriculture Faculty of Brawijaya University, Malang, Indonesia.During the study, the laboratory condition was kept at a temperature of 27 ± 2℃ and 60 ± 5% relative humidity.The hardness of milled rice variety were analyzed at the Laboratory of Food Quality and Food Safety, Faculty of Agriculture Technology.The phenolic content analysis was done at the Environmental Laboratory, Faculty of Mathematic and Life Sciences and the other chemicals content were analized at Central Laboratory of Life Sciences, Brawijaya University, Malang, Indonesia.
Six rice varieties; namely IR 64, Ciherang, Membramo, Cibogo, Sembada, and Intani-2 were tested for their susceptibility to R.dominica.These six rice varieties were arranged in Completely Randomized Design with five replications.
The rice sample used was obtained from the local farmers at Malang district.These farmers obtained their seeds from local Agriculture Services of Malang, Indonesia.The milled rice sample was sterilized at -15℃ for a week and then removed to 5℃ for another week.Before used in the study, the samples were preconditioned at room temperature (27 ± 2℃) for two weeks.R. dominica adult was obtained from the farmer's storage which has been infested by R. dominica at Rejoso vilage, Junrejo, Batu, East Java, Indonesia.These insects were then reared in the pest laboratory as the stock culture.
Thirty g of each sterilized milled rice variety was put in glass vials (7 x 4.5 cm).Then, the 15 pairs of 2 to 3 weeks old adults R. Dominica was transfered from stock culture and covered with muslin cloth on top.The adult of R. dominica allowed to infest for seven days.At the end of seven days oviposition period, the adult of R. dominica were discharded and the number of egg was recorded.Afterwhich, the rice samples with eggs of R. dominica were kept under the experiment conditions to assessed the emergence of F 1 progeny.Emerging progeny was counted in each vial on each assessement day.This observation continued until all F 1 progeny was expected to have emerged before the F 2 generation starts (Bashir, 2002).
The hardness of milled rice variety was determined using digital force gauge zp 200 N.The phenolic content was determined using spectrofotometric apparatus (ASTM, 1976), fat was determined by the method by Pendl et al. (1998) and protein content were analyzed by Kjeldahl Method.The moisture content was determined using method of SNI 01-2891-1992 point 5. 1 and ash content was determined by the method of SNI 01-2891-1992 point 6. 1.The carbohydrate content was calculated by different ( i.e 100% -protein content (%) -fat content (%) -ash content (%) -moisture content (%)).
The data were analized by analysis of variance (ANOVA), while the significant means were determined by using Least Significant Difference (LSD) at 5% level of significance.The correlation analysis was used to determine the relation among the physico-chemicals of milled rice varieties with the eggs number of R. dominica, the number of F 1 progeny emerged, the median developmental time and the index of susceptibility.
The index of susceptibility was calculated using the method of Dobie and Kilminster (1977) which given by │(log e F)/D x 100│ where F is the number of F 1 insects developing from eggs laid by 15 pairs of adult R. dominica during seven days and D is the median development period, estimated as the time (days) from the middle of the oviposition period to the emergence of 50% of the F 1 generation.The susceptibility index ranging from 0 to 11, was used to categorized the milled rice varieties, where: 0 -3 = resistant, 4 -7 = moderately resistant, 8 -10 = susceptible and ≤ 11 = highly susceptible (Dobie, 1974).

Results and Discussion
The experimental result shows that there was a significant different in the number of eggs between rice varieties (Table 1).The highest egg number (263.6) was observed on Intani-2 milled rice variety, whereas the lowest egg number (52.2) was observed on Membramo variety.Furthermore, Table 1 also show that Membramo variety had the lowest F 1 progeny emerged (16.4), which is significantly different with the other varieties.The highest F 1 progeny emerged (36.6) was observed on Intani-2 variety.By this result it could be said that the Membramo variety is more resistant than the other rice variety.One of the reasons for this phenomenon it might be due to the different of physical characteristics and chemical content of milled rice variety.Noris and Kogan (1980) said that plant defense to the insect attack by it's physical characteristics and chemical content such as the phenolic compounds.
If the number of eggs and F 1 progeny emerged could be regarded as the infestation intensity, then it could be suggested that the weight loss due to the infestation of R. dominica corresponds with the infestation intensity.This suggestion was supported by the data presented in Table 1 which show that the lowest weight loss (0.43%) occurred on Membramo variety, although it did not significantly different with IR-64 and Ciherang, but significantly different with the other three varieties.The highest weight loss (12.06%) occurred on Intani-2 variety.This is significantly higher than that of Cibogo and Sembada varieties.Following the criteria developed by Dobie (1974), the rice varieties tested in this study could be catagorized into: (a) resistance variety which consists of Membramo, (b) moderately resistance which consists of Ciherang, IR-64, Cibogo, and Sembada, and (c) high susceptible which consist of Intani-2 variety (Table 3).
The characteristics of grain resistance to stored insects, is still debatable (Dobie, 1974;Safique & Chaudry, 2007a;Abebe et al., 2009;& Nadeem et al., 2011).As Arnason et al. (1992) stated that high phenolic content of maize grain was strongly and negatively correlated with resistance to Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae).There was also evidence that the larval development of T.castaneum and Trogoderma granarium (Everts.) was inhibited by the thought siliceous hull of paddy (Shafique & Chaudry, 2007b).Hull morphology was thus considered an unreliable base of resistance as the effectiveness varied with species of insects.Cogburn et al. (1983) and Ahmad et al. (1998) stated that varietals resistance to stored rice insects is related to grain hardness, amylase content, non-chalkiness and phenolic content in the rice kernels.The research on grain hardness in its relation with index susceptibility has been conducted by McGaughey et al. (1990) on wheat grain.He stated that the hardness characteristics of wheat will strongly affect the attack of S. oryzae.
In this study, it was suggested that protein, fat, ash, carbohydrate, phenolic content and the hardness characteristics would be the important characteristics that determined the resistance to stored insect.To test this hypothesis was conducted by calculating the correlation coefficient between protein, fat, ash, carbohydrate, phenolic content and milled rice hardness with the number of eggs, F 1 progeny emerged, median developmental time of R. dominica and the susceptibility index.The result of this analysis can be seen at Furthermore, the result in Table 3 show that ash content negatively correlated with the median developmental time.It means that the milled rice varieties with the high ash content would effect the high number of eggs, high number of F 1 progeny emerged of R. dominica and faster development and consequently would be susceptible to the R. dominica attacks.On the other hand, variable of phenolic content and the hardness characteristics of milled rice have significantly negative correlation with the number of eggs, F 1 progeny emerged, and the susceptibility index.Furthermore, those two variables, that are phenolic content and hardness, have positively correlated with the median developmental time.By this result appear that high phenolic content and hardness characteristics attributed low number of eggs, low number of F 1 progeny emerged, and the slow development of R. dominica.As a result, the milled rice variety, with the high phenolic content and hardness characteristics appear to be resistant to the R. dominica attacks.

Conclusions
The study reported here show that Membramo milled rice variety is the resistance variety to R. dominica.The milled rice varieties with higher phenolic content and hardness would be more resistant to R. dominica.The milled rice variety with higher ash content would be more susceptible to R. dominica infestation.Protein, fat, and carbohydrate content do not correlate with the susceptibility to the R. dominica.
This research showed that it was also important to breed of paddy rice considered on the low ash content and high phenolic content and also the hardness characteristics in order to get milled rice variety which is resistant to R. dominica infestation.
the same letters in the same column are non-significant (α < 0.05).

Table 1 .
The Means Number of Eggs (from 15 Females which were Infested), the Number of F 1 Progeny Emerged of R. dominica and Weight Loss on Six Milled Rice Varieties The range of median developmental time of R. dominica on the six milled rice varieties are 32.1 days to 83.1 days.From Table2., it also showed that the Intani-2 variety has the shortest median developmental time (32.1 days), while Membramo has the longest median developmental time (83.1 days).By the variable of median developmental time shows that R. dominica rapidly develops on the Intani-2 variety, while the slowest development is on the Membramo variety.Based on the median developmental time variable and the numbers of F 1 progeny emerged were created the susceptibility index.By that catagorization it can be said that the lowest susceptibility index is shown by the Membramo variety (3.355), while the highest one is on the Intani-2 variety (11.213).
Abebe et al. (2009)me letters in the same column are non-significant (α<0.05)Shafique and Chaudry (2007)suggested that the low insect population and low weight loss of grain can be used as one of the attribute of the grain resistance to insects.Hence, based on the data presented in Table2, it could be concluded that Membrano variety was the most resistant variety, and Intani-2 was the most susceptible variety to R. dominica.In addition to weight loss and number of F 1 progeny,Abebe et al. (2009)used median developmental time, and percentage of seed damage as indicators of the susceptibility of maize varieties to the attack of S. zeamais (Motsch).The mean of median developmental time of R. dominica, susceptibility index of six milled rice varieties, and resistance category can be seen in Table2.

Table 2 .
Median Developmental Time of R. dominica, Susceptibility Index of Six Milled Rice Varieties and

Table 3 .
The variables of protein, fat and carbohydrate content are not significantly correlated with variables of eggs number, F 1 progeny emerged, median developmental time, and the susceptibility index.On the other hand, variable of ash content positively correlated with the variable of eggs number, F 1 progeny emerged of R. dominica, and the susceptibility index.Tabel 3. The Matrix Correlation Coefficient (r) between Physico-Chemical Characteristics of Milled Rice Varieties and Eggs Number, F 1 Progeny Emerged, Median Developmental Time of R. dominica and the * Significant at α < 0.05.