DEVELOPMENT OF POSTHARVEST TECHNOLOGIES FOR Fi OF PSB Rc72H HYBRID RICE: THRESHING, DRYING & STORING

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1 Philippine Journal of Crop Science 2003, 28(1): Copyright 2005, Crop Science Society of the Philippines Released January 2005 DEVELOPMENT OF POSTHARVEST TECHNOLOGIES FOR Fi OF PSB Rc72H HYBRID RICE: THRESHING, DRYING & STORING ERNESTO D GUZMAN, GENEROSO M OLI, LITO M CARANGUIAN, MICHAEL L CALIMAG, GENEBIB G DANTE, EDWIN S EGIPTO, RIZALINA T MANUEL & LORENZO M CARANGUIAN National Postharvest Institute for Research and Extension, Science City of Mt' loz, Nueva Ecija Based on data obtained from the study, the postharvest technologies developed for the Fl of hybrid rice PSB Rc72H are threshing, drying and storing for optimum seed quality. A mechanical thresher should have a cylinder speed of 600 to 750 revolutions per minute (rpm). Increasing the rpm to the speed for inbred rice results in increased loss of half-filled seeds via the blower. Viability of seeds is not affected by method of threshing. Seeds from the mechanical thresher show 94.3% viability and those from the traditional hand-thrashing (hampas) show 95%. A moisture content (mc) of 9-11% can be attained after 5 hours of sundrying with stirring every hour under a heat intensity range of cal / cm2/ hour. This mc level is safe for storing Fl seeds and does not cause thermal injury. In cold storage and tin cans, seeds maintain at least 85% viability after 6 months; in vinyl sack, vinyl sack lined with plastic, cloth bag, and vinyl sack with monthly re-drying, there is significant decline in viability. Regardless of packing material, if seeds are stored at 9-11% mc, there is no significant reduction in viability of seeds stored for a maximum of 4 months. Keywords drying, Fi, germination percentage, hampas, hybrid rice, postharvest technologies, rice, storing, threshing, viability RATIONALE The program for the wider cultivation of hybrid rice in the country is considered a positive response to the call for food security due to the high yield potential. However, most seed growers are reluctant to produce the Fi seeds due to some technological difficulties in crop management and postharvest operations. PSB Rc72H is the first Philippine hybrid rice, and is the most preferred variety of hybrid rice in Region 2. A major problem is that the Fi seed is susceptible to rapid deterioration before it reaches commercial growers. Deterioration starts immediately at harvesting and continues to the threshing, drying and storage stages. Unlike inbred seeds, hybrid seeds are more sensitive to the different postharvest operations and during storage due to their peculiar grain structure. Andales (1992) reported that improper postharvest operations on rice can result in a total loss ranging from 9 to 23%. This study was conducted to determine the conditions ideal for postharvest handling of Fi grains and, based on these, to set standard procedures to be followed by seed growers in order that seed quality can be preserved until the seeds reach the commercial growers. In a study conducted by PhilRice San Mateo on the storability of hybrid rice, results showed that with any application rate from 60 to 125 g/ha of gibberellic acid, there is no decrease in the germinability of A-line seeds even after 6 months of storage under ambient conditions. The best packaging material is vinyl sack. However, results of the preliminary assessment on the storability of hybrid rice parental conducted by CVLMROS in Cagayan Valley showed that the best packaging material is vinyl sack lined with plastic. Seeds stored in vinyl sack alone show low viability after 6 months of storage. The National Postharvest Institute for

2 Research and Extension (NAPHIRE) reported that high temperature (as high as 100 C) at high airflow rate can be used for first-stage drying without significantly affecting the head rice yield. However, at this temperature, grains should not be dried below 18% me to avoid heat stress which leads to grain-fissuring. Virmani & Sharma (1993) recommended that hybrid rice seeds not be dried abruptly to 13% moisture content if the beginning of seed moisture is higher than 20%. It was also recommended by the CVLMROS researchers (Guzman et al 2001) that other postharvest operations be monitored to establish correlation with seed viability. The general objective of the study was to develop appropriate postharvest technologies for the Fi rice grains. The specific objectives were: 1. To determine the appropriate cylinder speed of the existing commercial rice thresher for the Fi seeds of PSB Rc72H, with resulting minimal loss and less damage to grains, and with higher seed viability. 2. To determine the optimum duration of sun-drying the Fi seeds to attain the safe moisture content for storage. 3. To determine the best packaging material for maintaining high viability of Fi seeds up to 6 months of storage. MATERIALS & METHODS Following the objectives, this project was implemented with 3 studies namely: a) Study 1: Evaluation on the Effects of Different Cylinder Speeds in Threshing Efficiency and Viability of Fi Hybrid Rice. b) Study 2: Evaluation of the Appropriate Duration of Sun-drying Fi Hybrid Rice Seeds for Safe Storage c) Study 3: Evaluation on the Storability of Fi Hybrid Rice Using Different Storage Materials and Duration Study 1: Threshing A mechanical reaper designed for inbred rice was utilized in harvesting the samples to attain a uniform length of straw and for easy handling/picking. The commercial mini-thresher for rice used was a Lakas Kuliglig, LK-300, capacity-30 to 40 kg/hour, with a recovery of %, and powered by HP gasoline engine. The harvested samples were threshed using the thresher with different cylinder speeds, as well as manually threshed (hampas). This was to assess the efficiency of the thresher in terms of the resulting viability of the grains from the threshed batch. The treatments were as follows: T1-600 rpm (13 m/s, peripheral speed) T2-650 rpm (14 m/s, peripheral speed) T3-700 rpm (15 m/s, peripheral speed) T4-750 rpm (16 m/s, peripheral speed) T5 - Manual threshing (hampas) (check) The cylinder speeds of the thresher were tested and checked by the use of a hand tachometer. The primary consideration in choosing the most appropriate speed was the resulting high seed viability. Secondary considerations were minimal damage to the grains, minimal number of blown grains, high purity, and high capacity of the thresher. Three samples were collected for 15 sec at equal intervals in all outlets for each treatment. From the samples, the weights of the following were recorded: clean seeds, damaged seeds, blown seeds and impurities. The viability of the clean seeds was evaluated using standard procedures for a germination test. The performance of the thresher was evaluated using the recorded data and the following formulas: a. Output Capacity (kg /hour), B B = weight of seeds collected at all outlets per unit time b. Cleaning Efficiency (%), CE CE = (CB) x 100 C = weight of clean seeds collected at all outlets per unit time c. Damaged Grain (%), DG DG = (D/B) x 100 D = weight of damage grains collected per unit time d. Blown Grains (%), BG BG = (E/B) x 100 E = weight of blown grains collected per unit time Study 2: Sun-drying The seeds obtained from Study 1 were the subject of Study 2. Sun-drying was undertaken immediately after threshing. In this method, the grains were spread uniformly on concrete pavement lined with a drying net with a thickness of 2.5 cm. The grains were manually stirred twice and dried depending on the

3 duration of the treatment from 8:00 am to 11:00 am where the heat intensity is appropriately within cal/cm2/hour. The drying period was in the morning only to avoid exposure of the grains to excessive heat in the afternoon, which might result in thermal injury to the Fi seeds due to their very peculiar structure, compared to inbred rice (Figure 1), and considering the high me after harvest. Moisture content was taken one day after each drying treatments. The treatments were as follows: T1-2 hours T2-3 hours T3-5 hours Study 3. Storage Materials The F1 seeds (PSB Rc72H) were stored under ambient conditions at the DA-CVLMROS from April to October 2001 using different storage containers. The initial moisture content was recorded. Each treatment contained 1 kg of seeds. A 50-g sample for each of the parameters (moisture content, viability, and weevil damage) was taken from each treatment after 2 months of storage and every month thereafter until the 6th month. Room temperature and relative assessment of moisture content, weevil damage and seed viability. The viability of the seeds was evaluated using the Accelerated Aging Test (AAT). In this method, the seeds were subjected to high temperature (40-45 C) and high relative humidity (100%) for 48 hours inside the oven. This was followed by a germination test. The moisture content was assessed using the primary method (air-oven method). A 50-g per treatment replicate was placed in an oven set at C for 72 hours. This was placed in a desiccator and weighed after 30 min of cooling. RESULTS & DISCUSSION Threshing The results of the assessment on the viability of the Fi seeds threshed manually (hampas method) and mechanically with a commercial rice thresher are shown in Table 1. Statistical analysis showed less than 1% difference between the viability of the seeds threshed mechanically and manually, and this was not significant. Results on the evaluation on the performance of the commercial rice thresher Table 1. Comparative viability of manually threshed hybrid rice and using the commercial rice thresher. Treatment Replication I II III Mean 1. Rice thresher Manual threshing Level of Significance cv = 1.5% humidity were recorded daily for the duration of the study. The treatments were: T1 - seeds stored in tin cans T2 - seeds stored in vinyl sack T3 - seeds stored in cloth bag T4 - seeds stored in vinyl sack lined with plastic T5 - seeds stored in vinyl sack with monthly re- drying T6 - seeds stored in cold storage (control) The study was laid out in Randomized Complete Block Design (RCBD) with 3 replications. Destructive sampling was employed in the using different cylinder speeds showed no significant differences in terms of output capacity, percent purity, percent damaged and percent blown grains. This indicates that the commercial rice thresher can be used to thresh hybrid rice with a threshing drum speed ranging from 600 to 750 rpm (13 to 16 mps). Increasing the threshing drum speed increases the machine efficiency in terms of output capacity and purity. However, it also increases the percentage losses, those of the blown and damaged grains (Table 2). ns

4 Pal a Awn Sterile Lemma Le ma Opening Endosperm (a) Hybrid Rice Grain Implications of the peculiar structure of the hybrid rice grain to postharvest operations: 1) Traditional method of threshing is not recommended, because of the lightness of the grains. 2) Grains can easily be blown by thresher with the rpm set for inbred rice. 3) Grains are easily damaged by mechanical shock and oven-drying. 4) Grains easily absorb moisture and is easily damaged by weevil. 5) Grains cannot be milled for human consumption. For seed purposes only. Pa lea Awn Sterile Lemma Lemma (b) Inbred Rice Grain Endosperm Figure 1. Comparative structures of (a) Fi hybrid and (b) inbred Rice Grain and implications of the peculiar hybrid rice grain structure to postharvest operations 30 Ernesto de Guzman et al

5 Drying A moisture content of 9 to 11% could be attained in sun-drying hybrid rice seeds in 5 hours starting from 8:00 to 11:00 in the morning under average light intensity of cal/cm2/hour (Table 3). The seeds were uniformly spread with a thickness of 2.5 cm on the concrete pavement lined with a net (canvas or lona). The seeds were dried for 2 consecutive days and turned twice per drying period. Storage The initial viability of the hybrid rice seeds was 94.50% (Figure 2). Viability declined with a longer storage duration in the different storage maintained their moisture content (Figure 3). Statistical analysis showed highly significant differences in mc among the storage materials and storage duration (2 months to 6 months). However, comparison among treatments revealed that the mc of the seeds stored in tin cans was comparable with that of the seeds in cold storage at the end of storage period. The mc of seeds stored in tin cans had increased by only 0.53% from the initial mc (Table 5). There was no weevil damage on the stored seeds up to the third month of storage. On the fourth month, insects started to attack the seeds in three packaging materials, namely cloth, Table 2. Performance of commercial rice thresher at different cylinder speeds. Particular Cylinder Speed (rpm) Level of Significance 1. Output Capacity ns (kg/hour) 2. Purity (%) ns 3. Damaged grain (%) ns 4. Blown grain (%) ns ns = not significant packaging materials, but there were no significant differences in the viability of the seeds stored in the different storage materials after 5 months. However, at 6 months of storage, results showed highly significant differences in viability of seeds with the storage materials tested. Seeds in tin cans and cold storage showed statistically higher viability at 94%. The lowest percentage of viability was obtained from seeds stored in vinyl sack lined with plastic with only 74% but was comparable with seeds stored in vinyl sack, cloth and redried monthly (Table 4). The low viability of seeds stored in vinyl sack lined with plastic may be attributed to moisture absorption of seeds and weevil infestation. Generally, the seeds stored in vinyl sack, cloth bag, vinyl sack with monthly re-drying, and vinyl sack lined with plastic, increased moisture during the storage duration of 6 months, while those in tin cans and under cold vinyl sack, and vinyl sack lined with plastic. These results may be explained by the increase in relative humidity of the storage structure at the fourth month (Figure 4). There was no significant damage up to the fifth month of storage. However, on the sixth month, significant damage was observed on the seeds stored in vinyl lined with plastic. It had the most damage at 17.99%, followed by the seeds stored in vinyl sack at 2.44%. There was no weevil damage on the seeds stored in tin cans and those re-dried monthly during the entire duration of storage. CONCLUSIONS & RECOMMENDATIONS Conclusions Hybrid rice seeds (Fi) require technologies in harvesting and postharvest handling different from those for inbred rice. The most important consideration in postharvest handling

6 of Fi seed is the unique physical structure of the seed that has direct relation to seed viability. Using the conventional mini-rice thresher (Lakas Kuliglig, LK 300, capacity of 30 to 40 kg/hour, recovery of 99 to 100%, and powered by 12-16HP gasoline engine), requires a reduced threshing speed of 600 to 750 rpm. This is just above the idle speed of a 16 HP gasoline engine. Increasing the rpm to the ideal rpm for inbred rice increases blower loss including the halffilled Fi quality seeds. A shorter drying time of about 5 hours under a heat intensity of cal/cm2/hour in a initial 9-11% moisture content. Recommendations Based on the results of the study, the following can be recommended: 1. The conventional or mechanical thresher could be used for threshing Fi seeds but threshing speed should be adjusted to rpm to minimize blower loss. 2. Drying of F1 hybrid seeds (PSB Rc72H) should be done using nylon canvas in 2 successive days with heat intensity range of approximately cal/cm2i/hour. Five Table 3. Moisture content (%) of Fl hybrid rice sun-dried at different durations. TREATMENTS REPLICATION MEAN I II II 1. Two (2) hours a 2. Three (3) hours b 3. Five (5) hours c Level of Significance ** cu= 7.5%. Means followed by the same letters are not significantly different from each other. nylon canvas is sufficient to attain 9 to 11% mc. This is within the recommended moisture for storage of Fi hybrid seeds. Drying is attained within 2 consecutive days from 8:00-11:00 am with turning at 1 hour interval. Generally, the viability of stored Fi hybrid seeds declined after 6 months storage under ambient conditions. A significant decline in viability of seeds was apparent using the different packaging materials tested after 6 months except seeds stored in tin cans, whose viability was comparable to that of the seeds put under cold storage. There was no significant change in viability, however, if the seeds were stored for 4 months, regardless of packaging material. This result indicates that a farmer can store his seeds in any packaging material if he intends to keep his seeds for only 4 months. The seeds must be dried, however, to 9-11% mc before storage. Longer storage period requires storing in tin cans or cold storage to attain viability or germination of at least 90% with an hours cumulative drying period with a turning interval of 1 hour is required to lower the mc to 9-11%, which is the recommended moisture content for storage. Abrupt drying and/or lowering of mc is not recommended for Fi seeds of PSB Rc72H due to its unique grain structure, unlike that of other hybrid rice varieties. 3. To attain 90% germination of stored seed after 4 months, the following conditions are required: a) Moisture content of the seeds should not be higher than 11% but not lower than 9% at storage. b) Seeds should be free from weevils. c) Room temperature should not be higher than 30 C and the relative humidity should be within 60-80%. d) Tin cans or cold storage should be used. 4. The use of tin can as a storage container is recommended to store Fi seeds for 6 months in the absence of cold storage.

7 REFERENCES Andales SC An Overview of Postharvest in the Philippines. Technical Paper Report, NAPHIRE Gayanilo VG Paddy Sundrying Studies. Unpublished report. IRRI Guzman ED et at Hybrid Seed Production. Cagayan Valley Technoguide Guzman ED et at Preliminary Assessment on the Storability of Hybrid Rice Parentals Under Ambient Condition. Unpublished technical paper NAPHIRE NAPHIRE annual report Virmani SS & Sharma HL Manual For Hybrid Rice Seed Production. IRRI > E Initial 2 months 3 months 4 months 5 months 6 months DURATION + Tin can Vinyl sack Cloth bag Vinyl sack lined w/ plastic -x-vinyl sack w/ monthly re-drying +Cold storage (control) Figure 2. Viability of Fl hybrid seeds stored in different packaging materials

8 Table 4. Viability of hybrid rice (PSB Re 72H) stored at different duration and storage materials. Treatment Initial 2 months Duration 3 months 4 months 5 months 6 months Tin can a a b a b Vinyl sack a a a a a Cloth bag a a ab a a Vinyl sack lined with plastic Vinyl sack with monthly re-drying a a b a a a a ab a a Cold Storage (Control) a a ab a b Level of Significance ns ns ns ns ** CV (%) In a column, means followed by a common letter are not significantly different at the 5% level by DMRT

9 Initial 2 months 3 months 4 months DURATION 5 months 6 months -0-Tin can -0-Vinyl sack Cloth bag Vinyl sack lined w/ plastic -X-Vinyl sack w/ monthly re-drying -0-Cold Storage (control) Figure 3. Moisture content of hybrid rice seed stored in different storage materials Postharvest Technologies For Hybrid Rice 35

10 Table 5. Change in Moisture content of hybrid rice seed stored at different duration and storage materials. Treatment Initial 2 months Duration 3 Months 4 Months 5 Months 6 Months Tin can b 9.63 a 9.07 a 9.53 b 9.53 a Vinyl sack d 11.27b c d c Cloth bag d 11.53b c d c Vinyl sack lined with plastic a 7.87a b c d Vinyl sack with monthly d 12.40b c d b Re-drying Cold Storage (Control) c 8.27a b 8.67 a 9.20 a Level of Significance ** ** ** ** ** CV (%) In a column, means followed by a common letter are not significantly different at the 5% level by DMRT Table 6. Percent Weevil damaged of seeds stored at different duration and storage materials. Treatment Duration 4 Months 5 Months 6 Months Cloth bag 2.56 a 1.11 a 0.88 b Vinyl sack 0.44 a 1.33 a 2.44 b Vinyl sack lined with plastic 1.44 a 0.66 a a Level of Significance ns ns * In a column, means followed by a common letter are not significantly different at the 5% level by DMRT

11 May June July August September October Temperature ( C) -0-Relative Humidity(%) Figure 4. Average Relative Humidity and Ambient Temperature in the Storage Structure