Role Of Plant Nutrients,Nitrogen,Phosphofus,Potassium And Silicon On Resistance To Brown Planthopper(Nilaparvata Lugens Stal),in Rice(Dryza Sativa L.)

Rice (Oryza sativa L.), one of the world’s most important grain crops, has been grown in different agroecological zones, mainly in the special type of artificial wetland with summer rainfall. The macronutrients, Nitrogen (N), phosphorus (P), potassium (K), and silicon (Si) are the important components of agricultural systems, and their effects on insect pests would influence rice growth and production. The brown planthopper (BPH), Nilaparvata lugens Stal,(Homoptera:Delphacidae), which is one of the serious insect pests of cultivated rice, has become a major threat after farmers widely adopted green revolution technologies including hybrid rice, fertilizers and insecticides. However, it’s still not entirely clear the effect of fertilizers application on the survival, growth, host-plant choice and honeydew excretion of BPH feeding on rice plants.The experiments were conducted in the greenhouse using hydroponic culture at Guangxi University. Two rice lines9311(BPH-susceptible) and BPHR96(BPH-resistant) were used. Brown planthoppers were collected from rice fields in Nanning, where BPH populations of biotype2dominated. Second instars and adult insects were collected and used for experiments. Ten-day old seedlings were planted under hydroponic culture and treated with different levels of nutrient solution. By the thirtieth day after treatment, five traits of phenotypic performance, tiller number (TN), plant height (PH), root length (RL), aboveground fresh weight (AFW), and root fresh weight (RFW) were measured to determine plant response to nutrient treatment. Ten days after the application of the treatments, survival rate, growth rate, host-plant choice and honeydew excretion were measured to quantify the effects of rice plants treated with nutrient solution on BPH. The main results were summarized as follows:(1) The data showed that low nitrogen (4mg/L N) significantly decreased seedling phenotypic values of the rice lines9311and BPHR96in TN, PH, AFW and RFW, but increased the values in RL. As for low phosphorus (1mg/L P) and low potassium (4mg/L K), the nutrient stress caused a significant decrease in all measured traits including TN, PH, RL, AFW and RFW. However, high silicon (240mg/L SiO2) had no significant effects on the phenotypic performance of two rice lines.(2) The results indicated that low nitrogen and low phosphorus caused a significant decrease on the BPH growth rate in the rice line9311(F=6.292, P=0.036under low nitrogen; F=5.598, P=0.046under low phosphorus), whereas no significant differences were found on BPHR96. Potassium and silicon application had no significant effects on BPH growth rate on9311and BPHR96.(3) There were significant differences in BPH survival rate on9311with nutrient stress at several time points (F=7.05,P=0.024at216h under low nitrogen; F=5.13, P=0.047at192h and F=9.63, P=0.011at216h under low phosphorus; F=6.68, P=0.03at192h and F=5.11, P=0.05at216h under high silicon). In contrast to the BPH survival rate on9311plants, the BPH survival rate on BPHR96treated with low nitrogen, low phosphorus, or high silicon remained constant up to216h after infestation. In addition, potassium application had no significant effects on BPH survival rate on9311and BPHR96.(4) In the host choice test, the BPH settling on9311and BPHR96plants under low nitrogen and low phosphorus significantly reduced over the120h observation period compared to the control. High silicon caused a significant decrease on the settled BPH in the rice line9311from the96th hour, but only a trend downward on BPHR96. No significant differences were found on the settling BPH on9311and BPHR96treated with three levels of potassium.(5) The scores of honeydew excretion were significantly low in the rice lines9311and BPHR96under low nitrogen, low phosphorus or high silicon. However, no significant differences were observed in honeydew scores on9311and BPHR96under potassium stress. The results indicated that low nitrogen, low phosphorus and high silicon had an antibiotic effect on BPH in the susceptible rice line9311compared to the control, whereas the effect was weak in the resistant rice line BPHR96. Low nitrogen and low phosphorus had a quick and strong antixenotic effect on the BPH in rice line9311and BPHR96, and the effect was weak under high silicon. Potassium had no effect on the performance of BPH on9311and BPHR96. As the plant macronutrients, nitrogen, phosphorus and potassium were the key restrictive factors in rice growth and development, while the main factors to limit the BPH development were nitrogen, phosphorus and silicon, but no potassium in rice-BPH bitrophic interactions.