Description

[Synopsis]

Despite its significant contribution to the rice production increase in 1980's in China, Chinese hybrid rice has caused great changes in insect pest status in the paddy fields, because of its high vulnerability to insect infestations. Among the insect pests, the whitebacked planthopper, Sogatella furcifera , has dramatically emerged as a key pest of the hybrid rice. S. furcifera infests not only the hybrid rice, but also the japonica rice in Middle China by massive immigrations from the hybrid rice-prone area in South China. There is a growing fear of deterioration of sustainable rice production ecosystem under the increasing insecticide treatments. Insect resistance in rice varieties is an alternative tool to cope with the pest threats, which is compatible with biological and ecological approaches of pest management.
A Chinese japonica rice, Chenjiang 06 (CJ-06), expressed a strong field resistance to S. furcifera infestations. The immigrants of S. furcifera did not prefer to settle on CJ-06, and failed to establish populations on the variety. Significantly less honeydew excretion by female adults of S. furcifera indicated their reluctant sucking on CJ-06 sap. Adult fecundity was reduced to about one third on CJ-06 as compared with susceptible varieties, because of suppressed sap ingestion on CJ-06. Besides, S. furcifera eggs suffered from a high mortality in the watery lesions induced at oviposition sites of CJ-06.
From these results, field resistance in CJ-06 to S. furcifera was explained by two distinct mechanisms, namely the sucking suppression and the ovicidal function. The sucking suppression was the primary cause of the antixenosis of CJ-06 against S. furcifera immigrants as well as the antibiosis to reduce fecundity of the inhabitants. The ovicidal function is another antibiotic resistance induced by a specific interaction between CJ-06 and S. furcifera eggs.
The sucking suppression and ovicidal function were inherited independently. The F2 populations from the crosses between CJ-06 and the susceptible TN1 variety were segregated into 4 phenotypes with different combinations of sucking suppression and ovicidal function. The segregation rations fitted statistically to the theoretically expected ratio of 45:15:3:1, where 2 dominant and 1 recessive genes presumably controlled sucking suppression and ovicidal function, respectively.
Preliminary genealogical analysis indicated that the both resistance traits to S. furcifera in CJ-06 were derived conjointly from a single parental line, Xiushui 620. The other parental line, C81-40, had only the ovicidal activity. Sucking suppression and ovicidal resistance in Xiushui 620 were independently inherited from Xiushui 04 and Xianghu 24, respectively.