Recovery Processes after Leaf Cuttng in Cereals and Forage Grasses : 1. Activation of growth hy defoliation at several growth stage in rice plant.

Abstract

Leaf-blade cuttings at several growth stages were conducted on rice plants grown under paddy field conditions in 1957 and under pot cultures filled with river sand in 1958, and the subsequent growth processes were observed mainly morphologically and the starch content in the shoot was measured. Two cutting treatments were conducted; all the expanded blades in every culm except the newly appearing leaf were clipped (old-leaf cut), or, on the contrary, only newly expanding blades were clipped every day as they appeared above the top of the leaf-sheaths which enclosed them (new-leaf cut). Some results obtained are outlined as follows: 1. Tillering and rooting stopped for a while after the both treatments, and growth in terms of dry matter production was heavily checked. However, the leaf formation in already established tillers were rather accelerated and the area of newly formed blades became gradually larger, and the dry-weight percentage of green leaves in the whole plant was maintained higher compared with those of undefoliated plants. On the contrary, the starch amount in stem and leaf-sheath was very much decreased as a result of defoliation, since most of the reserved carbohydrates might be consumed to make up for compensatory growth of new leaf. 2. Shortly after the treatments, both tillering and rooting were activated even during ear developlment, while the undefoliated plants tended to stop tillering and to decrease root formation during the same period. At the later stages of growth, the relative growth rate in dry matter production was much accelerated in the treated plants probably due to intensified respiration, photosynthesis and other life processes by enlarged blades. Under these situations, the amount of starch in the shoot was always less than that of the untreated plants, indicating the greater consumption of carbohydrates for the stimulated growth with much nitrogen absorbed by newly formed vigorous roots. 3. Defoliation might have lead the rice plant to rejuvenescent state, resulting in higher growth rate, larger panicle and greater number of kernels per plant, if there was enough time to recover from the clipping damage untill the flower initiation began. In the two experiments, the cutting of newly expanding leaves did not promote heading, but delayed it much more than the cutting of old leaves. 4. The clipping of the leaf-blades some days before ear formation retarded the elongation of the lower internodes, hence the resistance to lodging of rice plant might sometimes become stronger by defoliation treatments.