The Resistance Response Of Rice Against White-backed Planthopper And Its Inoculation Manipulated By SRBSDV Infection

Rice (Oryza sativa, L.) is one of the most important food crops worldwide. Improving the rice production is the first business of food safety. Rice planthoppers are typical r-strategy pests of rice. They have a strong ability of migration, most likely lead to outbreaks, and threaten the safety of rice production. Over rely on insecticidal treatments lead to "3R" problems which become more and more serious nowadays. Of the various strategies, host-plant resistance is the most practical and economical approach to control insect pests. More importantly, white-backed planthopper is the vector of Southern rice black-streaked dwarf virus.1EPG analysis of feeding behavior of Sogatella furcifera (Hemiptera:Delphacidae) on different rice varietiesTo elucidate the resistance mechanisms of different rice varieties (i.e., Fengyuanyou272, R9810-T, Huahuiyihao, Minghui63, Manuogu and Rathu Heenati) against the white-backed planthopper, Sogatella furcifera. Electronic penetration graph (EPG) was used to record the feeding behavior of S. furcifera on the seedlings of these six rice varieties at the3rd leaf stage. Nine non-phloem variables and22phloem variables based on typical EPG waveforms were considered in the analysis. During8h recordings, the total time of non-penetration waveform (np) on Rathu Heenati was the longest, followed by that on Manuogu, their total time of np had significant difference, and both of them were significantly longer than that on the other four varieties. The total time of pathway waveform (Nc)(8523.41s) on Rathu Heenati was1.24times longer than that on susceptible variety Minghui63. S. furcifera spent significantly less time on Rathu Heenati for phloem sap ingestion (N4-b) than other varieties. All the EPG variables on Huahuiyihao or R9810-T had no significant difference from those of susceptible variety Minghui63. Longer average duration of watery salivation (N4-a) followed by long time of sap ingestion was recorded on Fengyuanyou272. It was inferred that antixenosis components and resistance factors out of or in the phloem region might prevent this insect pest from feeding on Rathu Heenati. Only antixenosis components might restrict S. furcifera to feed on Manuogu. However, Huahuiyihao and R9810-T might not possess obvious resistance to S. furcifera, and Fengyuanyou272might be a more susceptible variety than Minghui63. Combined with the correlation between feeding behavior of insect vector and transmission of persistent plant viruses, these results also provide some information for control of Southern rice black-streaked dwarf virus (SRBSDV) by using S. furcifera-resistant rice varieties.2The activity dynamics of protective enzymes in different rice varieties under the feeding stress of Sogatella furciferaTo elucidate the physiological basis of rice plant under the feeding stress of S. furcifera, some physiological indices of three rice varieties (i.e. Rathu Heenati, R9810-T and Fengyuanyou272) infested by S. furcifera for0,3,6,12,18,24,30and36h were detected. The results showed that the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) had no significant change in Rathu Heenati under the stress of S. furcifera, meanwhile, both of them tended to increase in R9810-T and Fengyuanyou272. The activities of superoxide dismutase (SOD, EC1.15.1.1) and peroxidase (POD, EC1.11.1.7) in all the three varieties tended to increase, however, the activities of catalase (CAT, EC1.11.1.6) had no significant change in Rathu Heenati, they had the tendency to decline in R9810-T, while slightly increased after declining in Fengyuanyou272. The activities of glutathione peroxidase (GPX, EC1.11.1.9) were not changed significantly in three rice varieties. These indicate that oxidative damage is less in Rathu Heenati than in R9810-T and Fengyuanyou272under the feeding stress of S. furcifera. SOD, POD and CAT coordinately participate in the response of the stress, resistant and susceptible varieties show different response pattern to the feeding stress of the planthopper, however, GPX do not participate in the defending.3Manipulated the feeding behavior of Sogatella furcifera by SRBSDV and the key to inoculationTo better understand the virus-vector-host plant relationship and the virus inoculation mechanism of S. furcifera, this chapter evaluated the direct effects of SRBSDV on S. furcifera feeding behavior and determined the viruliferous S. furcifera feeding behavior related to SRBSDV inoculation. The third to fifth-instar nymphs of the insect were allowed to feed for2days on infected plants, and then reared for8-15days on healthy rice seedlings. Electronic penetration graph was used to record the feeding behavior of both the nonviruliferous and viruliferous planthoppers for12h. The rice plant was detected by RT-PCR in15-22days after the recording. The transmission experiments showed that ca.72.0%of planthoppers became viruliferous and ca.26.0%of them could actually transmit the virus. The EPG recording revealed that the duration of1st phloem contact (N4) was15times longer in viruliferous insect than in nonviruliferous ones; the mean duration of watery salivation (N4-a) of viruliferous panthoppers were significantly longer than the nonviruliferous. However, a lower significant number of the viruliferous were able to produce sustained phloem ingestions (N4-b>10min) than the nonviruliferous. The stepwise-backward logistic regression model showed that number of N4-a (>10min) followed by N4-b (P=0.034) and total duration of N4(P=0.019) were the most significant variables with positive relationship for SRBSDV inoculation. These results revealed that SRBSDV modified the feeding behavior of S. furcifera in a direct way and enhanced transmission efficiency. Salivation into phloem region might be the most important stylet activity for inoculation of SRBSDV.