Damage Mechanism Of Small Brown Planthopper To The Rice Seedling And Its Effect On Growth Of Rice Later Stages

Resent years, the small brown planthopper (Laodelphax striatellus Fallen,SBPH) has become one of the important pests on rice in Jiangsu province. It can do great harm to rice not only as vector in spread of rice stripe virus (RSV), but also by sucking directly which caused serious threaten to the rice production. For proving up the mechanism of the small brown planthopper which damaged straightly to the rice, the paper studied the small brown planthopper attacked straightly to the seedlings at the different leaf-age and its effect on the growth at the later stage, the main results were as follows:1 Through resistance identification of the different rice varieties to the small brown planthopper at seedling stage, the damage grade of 11 cultivated varieties was primarily clarified. Mass seedling screening and individual seedling were tested, the results indicated that damage grade of wuyujing 3 and wuyujing 21 was 9 damage, yangdao 4038 and wuyunjing 7 was 7grade, yangjing 9538 was 5grade, huaidao 11, ningjing 1 and zhendao 2 was 3 grade,xieyou 136 was 1 grade and huaidao 9,shanyou 136 and xudao 3 was 0 grade. Basis on the damage grades, different rice varieties were clarified into different resistant levels to the small brown planthopper. Huaidao9,shanyou136 and xudao3 reached immunity level; xieyou136 reached highly resistant level; wuyujing2 and wuyunjing21 reached highly susceptible level; the other tested varieties were resistant to moderately resistant level.2 Effect of L. striatellus with different densities on damage index of leaves at different leaf ages of rice seedling was investigated. The results showed that the damage index of the three tested rice varieties decreased with leaf-age and attacked day when damaged by the same density of L. striatellus. When damaged after same day, damage index increased with densities of L. striatellus. When the density of L. striatellus was 7 nymphs per plant, and damaged for 7 days, the different leaf-age of the three tested rice were: wuyujing3ï¹¥yangjing9538ï¹¥xudao3. When the same density of L. striatellus, same damage days,same leaf-age, the different instars and stages of L. striatellus damage grade to the rice: high instar nymphsï¹¥adultsï¹¥low instar nymphs.3 Physiological indexes of rice seedlings which have been damaged by the small brown planthopper were tested. The results indicated that with the density of L. striatellus increased, the gross content of chlorophyll and content of soluble sugar declined and there were significant difference(P<0.01), when the insect density was 9 nymphs per plant, the content of gross chlorophyll was1.32mg/L , while the control was 20.01 mg/L. The declined rate of soluble sugar was 60.45% compared with the control. When the density of L. striatellus was 9 nymphs per plant, the content of soluble proteins decreased obviously and there was significant difference(P<0.01); With the density of L. striatellus increased, the content of MDA and free proline tend to improve, but it did not reach significant level; With the density of L. striatellus increased, the root activity and POD decreased obviously, the declined rate of root activity and POD was 24.25% and 40.15% respectively.4 The effects of L. striatellus at seedling stage on growth of rice pant at later stage were studied. The results indicated that the height and leaf area of damaged seedlings decreased at the transplanted stage, the plant height of tested rice varieties were significant difference(P<0.01), and the leaf area of four rice varieties were significant difference compared with the control; At the tillering stage, the effect on damaged plant height became lighten, wuyujing21 and yangdao4038 were significant difference (P<0.01)compared with control, the effect on leaf area was notable difference, the effect on tiller number was light, only the tiller number of yangdao4038 was siganificant difference (P<0.05)compared with control; At rice adult stage, the effect on the thousand-grains weight was most significant, the thousand-grains weight of wuyunjing21,yangdao4038 and yangjing 9538 were significant difference(P<0.01), the other three rice varieties were significant difference(P<0.05) compared with control.