Establishment of the efficient evaluation methods for breeding of rice variety for processing food and its application to practical breeding programs

In order to effectively develop a superior rice variety suitable for the changes in the social and the agricultural situation as well as the diversified consumer's demands, conducting precise and rapid evaluation of characteristics from earlier generations of breeding on the basis of using the excellent breeding materials is extremely important. However, in the breeding of rice varieties for processing food, examination of appearance grain quality or ingredient analyses such as protein contents, etc. have been mainly used for the earlier generations of breeding, accordingly research and development of effectively evaluation methods for processing characteristics are extremely behind those of rice varieties of non-processing, namely eating for cooked rice as a staple food. In this study, a simple, rapid, easy and a small amount of samples evaluation method for the processing characteristics have newly been developed and validated its usefulness. Moreover, this evaluation method has also been applied to the practical breeding. As a result, individual and line selection of breeding programs will be advanced efficiently, and the development of an excellent rice variety for processing food, which is suitable for the cultivation in Niigata prefecture, will be promoted successfully. Development of an efficient evaluation method for rice*cake processing characteristics in breeding of waxy rice variety The hardening rate of waxy (or glutinous) rice-cake is one of the important processing characteristic related with the manufacturing cost of rice-cakes (mochi) and rice-crackers (Arare and Okaki), because whether or not the hardening rate of rice-cake is slow or fast affects the length of refrigeration period required before cutting (Yanase 1982b). However, the waxy rice strain has been selected chiefly on the basis of appearance grain qualities of brown rice kernels. The processing characteristics such as the hardening rate of rice-cake has been evaluated in the advanced generations of breeding, because sample amounts of more than 1 kg was needed in the evaluation. Also, there was no standard investigation method for palatability of rice-cakes, and accuracy and repeatability of the testing palatability method have not been clarified at all. Therefore, a simple, rapid, easy and a small amount of samples evaluation methods for the processing characteristics applicable in the early stage of waxy rice breeding have newly been developed, and a precise method of testing palatability has also been developed. 1. Investigation and evaluation of parameters related with the hardening rate of rice-cake "Koganemochi" and "Wataboushi" with different hardening rate of rice-cake were used, in order to investigate the relationship between hardening rate of rice-cake and contents of water soluble sugar in rice grains, spectrophotometric analytical values of alkali-pasted starch and heat gelatinization properties. As a result, the possibility that the contents of water soluble sugar in rice grains affected to the hardness of rice-cake was inferred. Moreover, obvious varietal differences were observed in the max absorbance wave length and the pasting temperature measured by the Micro Tm analysis system. 2. Evaluation method of hardening rate of rice-cake by the contents of water soluble sugar in rice grains and the max absorbance wave length of alkali-pasted starch Twenty eight waxy rice varieties and strains with different hardening rate of rice-cake were used for investigations. In order to investigate in detail relationship of the contents of water soluble sugar and max absorbance wave length between the hardening rate of rice-cake, and examined the applicability of both methods for evaluation of the rice-cake hardening property. As a result, a significant negative correlation was observed between hardening rate of rice-cake and contents of water soluble sugar in rice grains, whereas a significant positive correlation was observed between the former and max absorbance wave length of alkali-pasted starch. The multiple regression analysis was conducted by hardening rate of rice-cake as the dependent variables, and contents of water soluble sugar and max absorbance wave length as independent variables, the multiple correlation coefficient of 0.850 was obtained. It was suggested, the hardening rate of rice-cake could be evaluated by using of these Two parameters. 3. Evaluation method of hardening rate of rice-cake by the Micro Tm analysis system (MTAS Method) Eighty two varieties and strains of waxy rice were investigated of heat gelatinization properties of waxy starch by the Micro Tm analysis system {MTAS method) comparing with generally used RVA method. As a result, "Initial pasting temperature" and "Final pasting temperature" determined by the MTAS method showed a significant correlation with the "Pasting temperature" and "Peak temperature" measured by the RVA method, and exhibited a positive correlation with the hardening rate of rice-cake. The MTAS method is considered to be able to evaluate the hardening rate of rice-cake efficiently as compared with RVA method, and an efficient individual selection of early stage of breeding programs seemed to be possible by applying this method to the screening of hybrid population. 4. Development of rapid measuring method on hardening rate of rice-cake in waxy rice and evaluation of its characteristics In order to evaluate efficiently and correctly the hardening rate of rice-cake on the early generation single pedigrees selected by the method mentioned above, preparing methods of rice-cake from small amount of rice-flour sample and a simple, rapid and easy method for measuring of hardening rate of rice-cake were developed. By these methods, over 60 samples (40g for each) per day can be measured, and the results tended to show the same traits as that of rice-cakes prepared by the conventional method. Thus, these developed methods were proved to be applicable to the selection of pedigrees and to the test of specific character in the yield trial. 5. Development of method for testing palatability of rice-cakes and evaluation of its palatability Method of testing palatability of rice-cakes was developed by using of the samples prepared from yield trials in Niigata Crop Research Center. From the evaluation results of palatability of breeding strains yielded in different years and "Koganemochi" used for comparison, this newly developed method was proved to be effective. Thus, a model by which the palatability of rice-cakes precisely reflecting with the consumer's demands can be established. 6. Establishment of a new breeding program of waxy rice varieties A program for breeding of waxy rice varieties by combining the newly developed evaluation methods for processing characteristics of rice-cake and the improvement of standard agronomic characters such as rice blast disease resistance or lodging resistance, etc. have been established. In the 1st stage of breeding, individual selection in the fields by stand observations are eased sharply, because of the analytical efficiency of MTAS method is remarkably high, and rice-cake hardening property by the MTAS method for numbers of samples in the primary screening will be conducted, Subsequently, the appearance rate of pedigrees with excellent rice-cake hardening property will be increased in the early generation single pedigree by discarding those with property below the standard level, such as "Wataboushi". Next year, in the early generation single pedigree, the rice-cake hardening property will be reconfirmed by the developed rapid measuring method in hardening rate of rice-cake, and the testing palatability of rice-cake will be evaluated at the same time. Also, standard agronomic characters such as the rice blast disease resistance were examined. By these programs will be realized earlier breeding of the strains with "excellent rice-cake processing and cultivation characteristics", both. These programs were applied to the practical breeding of waxy rice varieties partially or totally, and its application effectiveness was verified. Application of new breeding program to the practical breeding of waxy rice varieties and its effect 1. Application of the measuring method of hardening rate of rice-cake to waxy rice breeding Summarizing the results of selection by the hardening rate of rice-cake carried out since 1993, applicability to the practical breeding and precision in measurement by the difference cultivation conditions were clarified. As a result, it was concluded, selection by the hardening rate of rice-cake was extremely effective in the individual selection at the hybrid population, and its effect was exhibited also in the advanced generations. Moreover, the inbreeding coefficient to "Koganemochi" in hybrid combinations became higher, the hardening rate of rice-cake became higher, and distinct relationship was not recognized between agronomic characters and hardening rate of rice-cake. Then, the hybrid population for which "Koganemochi" or the other varieties/strains with the close relation to "Koganemochi" were used for parent, and the selection by the hardening rate of rice-cake was carried out repeatedly from earlier stage of breeding, it was concluded that the strains with outstanding hardening rate of rice-cake and excellent cultivation characteristics could be efficiently selected by this method. 2. Breeding of a elite line "Niigatamochi 61" with outstanding hardening rate of rice-cake "Niigatamochi 61", an early-maturing elite line with excellent hardening rate of rice-cake compatible with "Koganemochi", has been succeeded in breeding only seven years after crossing, by choosing a hybrid combination of "Koganemochi/Niigatamochi 31 (later Wataboushi} and by conducting with the rice-cake hardness selection from individual selection. "Niigatamochi 61", of which heading and maturing date are earlier than "Wataboushi" about 2 days, hardening rate of rice-cake was markedly improved as well as "Koganemochi" and its hardening rate of rice-cake showed higher than that of ordinary early-maturing waxy rice varieties in Niigata prefecture. However, "Niigatamochi 61" seemed to be needed along with more improvement of agronomic characters such as rice blast disease resistance, lodging resistance and further enhancement of palatability of rice-cakes. 3. Development of the elite waxy rice strains with "excellent processing characteristics and the rice blast disease resistance" As the hybrid combination between "Koganemochi" with excellent rice-cake processing characteristics and early-maturing strain of "Tohokumochi 161" with strong rice blast disease resistance in fields, the multiple selection of those two important characteristics based on the 1st screening by the MTAS method were conducted. As a result, the elite lines with "excellent processing characteristics and strong rice blast disease resistance" could be selected efficiently, and carried out the preliminary yield trial and specific character test only two years later from the individual selection. Thus, development period could be also shorten by about a half of the ordinary breeding programs. 4. Investigation of the practicability on the processing properties of rice-cake in induced waxy mutants of rice In order to efficiently breed of waxy rice varieties with various characteristics of rice-cake processing and properties suitable for the development of new processed rice-cake foods, induced waxy mutants of rice, expectable for rice-cake processing characteristics previously unknown and a variety of variation in waxy starch, were explored for new breeding materials. Their processing suitability for rice-cake and processing characteristics in response to the ripening temperature were also investigated. As a result, waxy mutants of rice have been succeeded in finding marked processing properties previously unknown in the commercial waxy rice varieties in Japan. It is considered that the induced waxy mutants with distinguishing traits could become useful breeding materials for the manufacture of new rice processing foods and would be suitable for various processed products required by the rice processing industries. Development of an efficient evaluation method of brewing properties in breeding of the brewer's rice varieties In the breeding of rice varieties suitable for sake (or rice wine) brewing in Niigata prefecture, the examination of appearance of brown rice kernels such as grain size and white core, and analysis of the protein contents have been mainly conducted. However, investigations on other important brewing properties such as rice polishing characteristics, water absorption properties, digestibility, etc. have never been conducted at all in earlier generations of breeding programs. In order to effectively develop a superior brewer's rice variety with endurable to high polishing rate over 40%, suitable for brewing of "Daiginjyo-shu (the highest class of sake)", evaluation of brewing properties in individual plants is extremely important in earlier generations of breeding. For this purpose, it is necessary to polish samples with a minimum amount up to the standard rice polishing ratio (apparent polishing ratio of 70%) in conformity with the National Standard Analysis Method (Research Association on Brewer's Rice, 1996) as simply, easily and rapidly as possible. However, even by the ordinary method developed by Aramaki et al. (1993) which require the smallest amount of samples and is the most rapid, rice polishing time of more than 30 min for one sample and nearly one hour for cooling of the role are necessary. Thus, this ordinary method was unsuitable for treating several hundred samples in individual selection on the earlier generations of breeding programs. Therefore, simpler and more rapid polishing method by which rice polishing ratio of 70% was developed and its applicability was verified. 1. Development of rapid polishing method for brewer's rice breeding By mounting barley polishing parts on a small-type rice miller Pearlest (Kett Electric Laboratory, Tokyo) in which rice can usually be polished only to an apparent polishing ratio of 90%, it was found that the polishing of brown rice could be conveniently and rapidly performed up to the apparent polishing ratio of 70%. And it became possible to evaluate the water absorption properties, which are closely related to the brewing suitability, in earlier generations. 2. Applicability of the rapid polishing method Brown rice was polished using Pearlest equipped with barley polishing parts for the rapid method, and the performance of rice polishing was compared with the method using a compact testing mill HS-4 developed by Aramaki et al. (1993) for the control method. As a result, brown rice could be simply and rapidly polished up to the targeted polishing ratio of 70% comparing with the control method. Rapid polishing method was characterized by a low ratio of broken rice, reduction of the loss of moisture content of the samples, and more spherical polishing of rice kernels. Twenty-minute water absorption ratio was clearly enhanced in varieties such as Ipponjime with kernels showing a low hardness, and the nitrogen content was lower compared with the control method. But these tendencies were not considered to hinder the evaluation of relative varietal differences. because it was found that the nitrogen content and 20-minute water absorption ratio of polished rice by this method could be utilized as stable evaluation parameters revealing the intrinsic characteristics of the varieties. Development of this rapid polishing method is considered to be extremely important for efficient selection in breeding programs for brewer's rice, because it may be possible to evaluate the nitrogen content of 70%-polished rice and water absorption properties which had not been examined so far in earlier generations. 3. Validity of evaluation of brewing properties of rice polished by the rapid polishing method When more than 30 varieties/strains were investigated for their brewing characteristics in 1996 and 1997 by using the rapid polishing method, significant annual fluctuations were observed in the polishing time and the ratio of broken rice. The maturity in 1997 was earlier by about 4 days on the average, due to the higher temperature and longer duration of sunshine, and differences in the quality and physical properties of rice could be anticipated. It is possible to predict the polishing characteristics of harvested rice to some extent by applying the rapid polishing method. By comparing the results of evaluation of the characteristics of tested varieties based on the Standard Analysis Method and the rapid polishing method, a significant correlation was observed for the rice polishing time and the nitrogen content, but not for the ratio of broken rice. However, it was considered that the possibility of increasing the varietal differences that already existed was limited. It was assumed that the inconsistency in the results of the ratio of broken rice between the two methods was due to the comparison of characteristics with a larger variance, 4. Establishment of a new program for the evaluation of brewing properties In order to find out individuals and lines with excellent characteristics for sake brewing, promote the selection efficiency drastically and fix the characteristics for sake brewing precisely, a new program for the evaluation of properties for sake brewing was established. By the program for the evaluation of sake brewing properties based on the rapid polishing method, it became possible to incorporate polishing, water absorption and viscosity of starch properties, which are important parameters practically into the new selection items of characteristics, in addition to the appearance of brown rice kernels such as grain size, white core, nitrogen contents, etc. This program was applied to each stage in the breeding of brewer's rice partially or totally, and its effectiveness was verified. Application of the new evaluation programs to the practical breeding of brewer's rice varieties and its effect 1. Application of the new evaluation programs to the individual and line selection Evaluation of sake brewing properties based on the rapid polishing method to the individual and line selection in the practical brewer's rice breeding programs, and verified its effect. As a result, the effects of selecting individuals by 20-minute water absorption ratio and the nitrogen contents in the polished rice were confirmed, but the ratio of broken rice was variable considerably in years. Thus, the polishing properties such as ratio of broken rice were confirmed to be inadequate only in the selection of the single year. However, the selection by the polishing properties were repeated, the appearance frequency of lines with high ratio of broken rice tended to decrease every years. Accordingly, it was speculated that lines with excellent brewing characteristics could be bred efficiently by evaluating them in successive years. 2. Application of the new evaluation program to the selection by the multiple brewing properties based on the values of "Yamadanishiki" By using the new evaluation program, the precise selection of individuals and lines were attempted in progeny generations of hybrid combination of "Yamadanishiki/Bio-43", evaluated by the brewing properties newly used for the apparent amylose content and heat geratinization properties of starch in addition to other brewing properties. These selection effects were summarized by the principal component analysis, it proved that individuals and lines characterized "Yamadanishiki" type with excellent brewing characteristics was confirmed to be selected precisely. 3. Application of the new evaluation program to the test of specific character in yield trial The new evaluation programs of brewing characteristics was applied to the test of specific character in yield trial, and the brewing characteristics of testing lines were actually evaluated. The sake brewing characteristics of tested lines in yield trial, which applied before and after the new selection program were compared to summarizing by the PCA. As a result, many lines in accordance with the new selection program were proved to be shifted to "Ymadanishiki" type in brewing characteristics, therefore effects of the new evaluation program of brewing properties to breed of brewer's rice varieties were confirmed. Moreover, brewer's rice strains with newly type of brewing characteristics in Niigata prefecture were also raised. Thus, this program produced satisfactory results in raising varieties demanded with the demands of consumers. 4. Application of the new evaluation program to the cultivation trial Samples obtained in the fertilizing reaction trials in cultivation fields. The elite brewer's rice strain of "Niigatasake 72" was examined in accordance with the developed new evaluation program of brewing properties. As a result, this program was proved to be applicable to the evaluation of brewing properties in the cultivation trial, and it was proved very important method for preparing the cultivation manual for the stable production of "Niigatasake 72" grain with keeping high brewing properties. On the other hand, the brewing properties were evaluated for samples obtained from commercial scale cultivation fields over 1 ha. As a result, water absorption ratio, nitrogen contents, amylose contents and heat geratinization properties seemed hardly to reflect the difference in cultivation conditions, whereas the ratio of broken rice was proved to be a parameter being liable to be affected by it. This evaluation method will be simply and rapidly, so it may be introduced into Agricultural Extension Center. By applying this method to check of the brewing properties of rice produced in various districts, the possibility that it will become an effective procedure for keeping the quality of brewer's rice yielded in Niigata prefecture at a highly averaged level has been recognized