VARIETAL DIFFERENCE OF PHYSICAL CHARACTERISTICS OF THE CULM RELATED TO LODGING RESISTANCE IN PADDY RICE

Varietal difference of lodging resistance in paddy rice was studied using nine Japanese cultivars and thirteen foreign cultivars (cv. Kamenoo : KA, Aikoku : AK, Koshihikari : KO, Dobashi 1 : DO, Fujiminori : FU, Reimei : PE, Nipponbare : NI, Musashikogane : MU, Akenohoshi : AK, Chugoku 117 : Cl 17, Taichung 189 : T189, Tainung 67 : T67, Bahia: BAH, Ballila : BAL, M-302: M302, Lemont : LE, Blue Bonnet : BB, Zenith: ZE, Jaguary : JA, Arborio : AR, Milyang 23 : M23, Nanjing 11 : N11). Japanese long culm cultivars were more susceptible to lodging compared with foreign cultivars, because the breaking strength which indicated the minimum force required to break the basal (the 5th from the top) internode of the main culm with leaf sheaths was much smaller, ranging from 1000 to 1200 g. On the contrary, some long and short culm cultivars did not lodge until the harvest, because these cultivars maintained the large breaking strength of the basal internode with leaf sheaths during grain filling period, ranging from 2100 to 2600 g. The reasons why the breaking strength of the culm with leaf sheaths was different among the cultivars were as follows. In Japanese cultivars, as leaf sheath died down earlier, the degree to which the culm was reinforced by leaf sheath covering was smaller, and the breaking strength of the basal internode was also smaller compared with those of foreign cultivars. Taichung 189, Tainung 67, Chugoku 117, Akenohoshi and Milyang 23 showed the high breaking strength of the basal internode which was mainly based on reinforcement due to leaf sheath covering, the large area of the basal internode cross section and the large bending stress in the basal internode. Approximately, the increase of the breaking strengh of the basal internode was doubled due to leaf sheath covering in Akenohoshi, and was tripled due to the larger area of the basal internode cross section in Milyang 23, as compared with that of Koshihikari, respectively.