Studies on Structure and Function of the Rice Ear : V. Changes in ear type as influenced by fertilizer level and planting density

Abstract

Eight varieties differed in ear type were used in this study: Stirpe 136 and Anthocyane (javanica) (ear type I: Number of grains on the secondary rachis-branch was abundant in the basal position of ear), Jaekeon (japonica) and Milyang No. 23 (japonica-indica hybrid) (ear type II: number or grains on the secondary rachis-branch was less near panicle base than in ear type: I), Norin No. 8(japonica) and Josaeng Tongil(japonica-indica hybrid) (ear type III: number of grains on the secondary rachis-branch was abundant in the middle position of ear) and Dojinkyo and Panbila (indica) (ear type V: number of grains on the secondary rachis-branch was abundant in thc upper position of ear). After harvesting, number of the primary rachis-branches per ear, and number of grains on the primary rachis-branch, and number or the secondary rachis-branches and their grains at each node of rachis were determined for the ear of the longest stem in the hill in twenty replicates. Under the same level of fertilizer, increase in planting density decreases number of the primary rachis-branches per ear, and the secondary rachis-branches and their grains at all the nodes of rachis, especially, at the basal position of ear. These trends seemed to be intensified by increase in fertilizer level in almost all the varieties (Fig. 2 A-H). Because of the extreme decrease of number of the secondary rachis-branches and their grains at the basal position of ear as mentioned above, Stirpe 136, Anthocyane and Milyang No. 23 changed their ear type, II to III in high fertilizer and dense planting plot (Fig. 2 A, B and C). In the previous experiment which was undertaken under favourable climates for the rice cultivation, Stirpe 136 and Anthocyane, Jaekeon and Panbila showed ear type I, II and V, respectively. However, there existed no those ear types in the present experiment. These may be due to decrease of number of grains on the secondary rachis-branch at the basal (Stirp 136, Anthocyane and Jaekeon) and upper (Panbila) positions, which appeared to have been caused by the low temperature during the present study (Fig. 1). Anthocyane and Panbila were used for determination of ear type in all the tillers of four hills as influenced by fertilizer level and planting density. Number of the primary rachis-branches per ear, number of the secondary rachis-branches and their grains at each node of rachis were determined as for the ear having every different number of the primary rachis-branches per ear in four hills in four replicates. Number of the secondary rachis-branches and their gains decreased at all the nodes of rachis, especially, at the basal position of ear, with reduction of number of the primary rachis-branches per ear. This caused changes in ear type of cars having reduced number of the primary rachis-branches per ear, viz. ear type II to III and further, in some cases, to ear type IV in the hill of Anthocyane (Fig. 3A), but ears of Panbila showed ear type IV or V in all the plots differing in fertilizer level and planting density (Fig. 3B). Increase in fertilizer level and planting density decreases number of the secondary rachis-branches and their grains at all the nodes of rachis, especially at the basal position of ear. For this reason, number of secondary rachis-branches and their grains was almost zero at the panicle base in the plots of high fertilizer level and dense planting density, regardless of number of the primary rachis-branches per ear. Anthocyane and Panbila showed ear type II and IV in the ears with the largest number of the primary rachis-branches, respectively. Number of grains on the primary rachis-branch at almost all the nodes of rachis was about 6 in all the plots, varieties and tillers.