Relationship between Grain Shedding and Abscission Layer in Pedicel of Japonica-Indica Hybrid Rices in Korea

Abstract

In general, Japonica-Indica hybrid rices in Korea exhibit easy shedding compared with the Japonica type. To obtain detailed information on the grain shedding of Japonica-Indica hybrid rices, thc tensile breaking strength required to detach rice grain from its pedicel was examined by using unbonded gauge type transducer and automatic null balancing recorder. The abscission layer between pedicel and spikelet was investigated anatomically. Varieties Yushin and Milyang 21 of Japonica-Indica hybrid, and Jojeongjo and Akibare of Japonica type rices were used. Yushin and Jojeongjo belong to easily shedding group and other two varieties belong to medium or persistent one. The results obtained are as follows: 1. In both Yushin and Milyang 21 of Japonica-Indica hybrid, tensile breaking strength decreased with time from 1 week after heading, reached the minimum after 3 weeks, and then did not vary until the harvest time. In Japonica type rices, on the other hand, the strength of Jojeongjo decreased slightly with time after heading, while that of Akibare increased gradually with time after heading (Fig. 1). 2. Grain ripening of Japonica-Indica hybrid rice was earlier than that of Japonica type rices. In the former, grain on the upper portion of the ear became to bc almost fully ripe at 3 weeks after heading (Fig. 2). From this result and Fig. 1, it appears that in the Japonica-Indica hybrid rice the decrease in tensile breaking strength is related with its ripening. 3. In the varieties Yushin, Milyang 21 and Jojeongjo, number of grains detached from the abscission region of the pedicel gradually increased with time after heading, while in variety Akibare, number of grains detached from the bent portion of the pedicel increased (Fig. 3 and Table 1). 4. The abscission layers of Yushin and Milyang 21, Japonica-Indica hybrid rice, appear to have one to two layers of large parenchymatous cells, while that of Jojeongjo, Japonica type rice, consists of one layer of somewhat smaller parenchymatous cells with some sclerenchymatous cells. In the former, the splitting in the abscission layer was observed at three weeks after heading, but no such splitting in the abscission layer was observed in Jojeongjo even at harvest time. Furthermore, no abscission layer was observed in the Japanese cultivar, Akibare (Fig. 4). 5. From the above results, it appears that the tensile breaking strength is closely related to the width of supporting zone which is composed of central vascular tissue and sclerenchyma tissue. The occurrence of splitting in the abscission layer probably has no relationship to tensile breaking strength. 6. Based on the abscission layer characteristics, the rice varieties used in this experiment could be classified into three types; i) abscission layer exists and splitting occurs at maturity (Yushin and Milyang 21), ii) abscission layer exists but no splitting occurs until harvest time (Jojeongjo), and iii) abscission layer is absent (Akibare).