Time Of Occurrence Of Hopperburn Symptom And Effect On Allocation Of Different Parts On Rice Following Root And Leaf Cutting Under Brown Planthopper, Nilaparvata Lugens (St(?)l) Infestation

This study investigated effects of removal of rice leaves and roots, foliar spray of P and K fertilizers and double P and K in hydroponic culture on the time(days) before hopperburn symptoms(DHS), and effects of leaves and roots cutting under brown planthopper, Nilaparvata lugens infestation on the allocation of dry weight of different parts of rice plants. Experimental results are as follows:1.Time of occurrence of hopperburn symptom on rice following root and leaf cutting and fertilizer application with brown planthopper, Nilaparvata lugens (St?l) infestationThe manifestation of brown planthopper Nilaparvata lugens (St?l) hopperburn damage was investigated by leaves cutting and roots cutting. Plants were grown under hydroponic culture, with a nutrient solution (P,K) foliar applied to assess the effect on the onset of the damage symptoms. The effect of both roots and leaves removal on the time (days) before hopperburn symptoms (DHS) depended on the rice variety. Results are as follows:DHS was significantly shortened with TN1 variety(BPH susceptible), but not with root cutting. Removal of both leaves and roots from Xieyou 63 variety (BPH tolerant), did not affect DHS. However, multiple comparisons of means of combined treatments for leaf and root cutting showed that removal of two thirds of roots and leaves significantly shortened DHS. Foliar P sprays with root cutting had no impact of DHS on TN1 compared to no spray, but with leaf cutting DHS of TN1 was shortened significantly. In contrast to TN1, foliar P sprays significantly prolonged DHS of Xieyou 63. For the two rice varieties, foliar K sprays did not affect DHS, nor did doubling P and K concentrations in hydroponics solutions with TN1 under root removal. There was a significant interaction between leaf removal and doubling P and K with leaf cutting, the DHS being shortest for the combined treatment of two thirds of leaf cut and double K. Doubling P and K concentrations did not affect DHS of Xieyou 63 with both root and leaf removal. The understanding of the relationship between DHS and root/leaf cutting, and application of P and K fertilizer for two rice varieties can provide valuable information for determining a control threshold of BPH when two pests coexist and for rational application of fertilizers. A high damage rate of rice leaves by C. medinalis can enhance the damage inflicted by BPH due to an interaction effect. The variety that delays DHS indicates that it has some tolerance to BPH infestation, thus control threshold should be increased or pesticide application be reduced.2.Effect of removal of leaves and roots on allocation of different parts in rice under N. lugens infestationEffect of rice leaves and roots cutting on allocation of different parts of rice varied with rice varieties. ANOVA showed that ratio of dry root weight to leaf weight (R:L) for TN1 under N. lugens infestation was significantly higher than for Xieyou 963, but R:L of control plants did not show significant difference between two varieties. Ratio of root weight to total plant weight at the tillering stage for TN1 was significantly smaller than that for Xieyou 963, but that at the heading stage was significantly higher than that for Xieyou 963. R:L at the tillering and heading stages for TN1 under N. lugens infestation was significantly higher than control (Non- infestation); and that for Xieyou 963 was also such difference except for one third of leaves cut treatment. Among three ratios of TN1, i.e., root , leaf and leaf sheath ratios, root ratio both at the tillering and at heading stages for N. lugens infestation showed significant difference compared to control; while leaf and leaf sheath ratios only at the tillering stage showed that significant difference compared to control. For Xieyou 963, however, changes of three ratios at the tillering stage were variety. For example, root ratio for root cutting and root non-cutting under N. lugens infestation was lower than control (non-infestation), but leaf ratio under the same condition was higher than control; root ratio at the heading stage for one third and two thirds of leaf cutting under N. lugens infestation was significantly higher control; spike ratio for one third of leaf cutting under N. lugens infestation was significantly lower than control; allocation indices of plant parts for other treatments did not show significant differences. ANOVA of effect of N. lugens infestation duration allocation indices showed that R:L at 3, 6 and 9days after N. lugens infestation at the tillering stage of TN1 did not show significant difference, while R:L of control plants for one third and two thirds of roots increased with increase of infestation durations. R:L for two thirds of leaves cutting under N. lugens infestation at the heading stage of TN1 decreased with increase of infestation durations; that of other treatments showed an increase trend; but that of control plants decreased with increase of time. For Xieyou 963, R:L at the tillering stage did not show obvious trend, while R:L of all treatments at the heading stage significantly declined. For TN1, ANOVA of allocation indices of dry substances of different parts showed that in leaf-cut treatments, leaf weight ratios of two thirds of leaf cutting and root ratio of one third and two thirds of root cutting at the tillering stage increased with increase of infestation durations; in root-cut treatments, root ratios of one third and two thirds of roots cutting increased with increase of infestation durations, in contrast, leaf ratios decreased with increase of infestation durations. However, those at the heading stage were changeable. For Xieyou, allocation indices of different parts under both root-cut and leaf-cut at the tillering stage were changeable, but root weight ratio control plants under leaf-cut increased with increase of infestation durations. Spikes weight ratio under leaf-cut at the heading stage increased with increase of infestation durations but root weight ratio showed a decline trend, and leaf sheath and stem weight ratios were changeable; leaf weight ratio for non-removal of leaf treatment showed a decline trend.